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Caldwell HG, Hoiland RL, Bain AR, Howe CA, Carr JMJR, Gibbons TD, Durrer CG, Tymko MM, Stacey BS, Bailey DM, Sekhon MS, MacLeod DB, Ainslie PN. Evidence for direct CO 2-mediated alterations in cerebral oxidative metabolism in humans. Acta Physiol (Oxf) 2024:e14197. [PMID: 38958262 DOI: 10.1111/apha.14197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 06/18/2024] [Accepted: 06/20/2024] [Indexed: 07/04/2024]
Abstract
AIM How the cerebral metabolic rates of oxygen and glucose utilization (CMRO2 and CMRGlc, respectively) are affected by alterations in arterial PCO2 (PaCO2) is equivocal and therefore was the primary question of this study. METHODS This retrospective analysis involved pooled data from four separate studies, involving 41 healthy adults (35 males/6 females). Participants completed stepwise steady-state alterations in PaCO2 ranging between 30 and 60 mmHg. The CMRO2 and CMRGlc were assessed via the Fick approach (CBF × arterial-internal jugular venous difference of oxygen or glucose content, respectively) utilizing duplex ultrasound of the internal carotid artery and vertebral artery to calculate cerebral blood flow (CBF). RESULTS The CMRO2 was altered by 0.5 mL × min-1 (95% CI: -0.6 to -0.3) per mmHg change in PaCO2 (p < 0.001) which corresponded to a 9.8% (95% CI: -13.2 to -6.5) change in CMRO2 with a 9 mmHg change in PaCO2 (inclusive of hypo- and hypercapnia). The CMRGlc was reduced by 7.7% (95% CI: -15.4 to -0.08, p = 0.045; i.e., reduction in net glucose uptake) and the oxidative glucose index (ratio of oxygen to glucose uptake) was reduced by 5.6% (95% CI: -11.2 to 0.06, p = 0.049) with a + 9 mmHg increase in PaCO2. CONCLUSION Collectively, the CMRO2 is altered by approximately 1% per mmHg change in PaCO2. Further, glucose is incompletely oxidized during hypercapnia, indicating reductions in CMRO2 are either met by compensatory increases in nonoxidative glucose metabolism or explained by a reduction in total energy production.
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Affiliation(s)
- Hannah G Caldwell
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Ryan L Hoiland
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
- Department of Anesthesiology, Pharmacology and Therapeutics, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
- Collaborative Entity for REsearching Brain Ischemia (CEREBRI), University of British Columbia, Vancouver, British Columbia, Canada
| | - Anthony R Bain
- Department of Kinesiology, Faculty of Human Kinetics, University of Windsor, Windsor, Ontario, Canada
| | - Connor A Howe
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Jay M J R Carr
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Travis D Gibbons
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Cody G Durrer
- Centre for Physical Activity Research, Rigshospitalet, Copenhagen, Denmark
| | - Michael M Tymko
- Division of Critical Care Medicine, Department of Medicine, Faculty of Medicine, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
- Human Cerebrovascular Physiology Laboratory, Department of Human Health and Nutritional Sciences, College of Biological Science, University of Guelph, Guelph, Ontario, Canada
| | - Benjamin S Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Mypinder S Sekhon
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, British Columbia, Canada
- Collaborative Entity for REsearching Brain Ischemia (CEREBRI), University of British Columbia, Vancouver, British Columbia, Canada
- Division of Critical Care Medicine, Department of Medicine, Faculty of Medicine, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
- Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, British Columbia, Canada
| | - David B MacLeod
- Human Pharmacology and Physiology Lab, Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina, USA
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
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O'Croinin BR, Young DA, Maier LE, van Diepen S, Day TA, Steinback CD. Influence of hypercapnia and hypercapnic hypoxia on the heart rate response to apnea. Physiol Rep 2024; 12:e16054. [PMID: 38872580 PMCID: PMC11176737 DOI: 10.14814/phy2.16054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2024] [Revised: 04/30/2024] [Accepted: 04/30/2024] [Indexed: 06/15/2024] Open
Abstract
We aimed to determine the relative contribution of hypercapnia and hypoxia to the bradycardic response to apneas. We hypothesized that apneas with hypercapnia would cause greater bradycardia than normoxia, similar to the response seen with hypoxia, and that apneas with hypercapnic hypoxia would induce greater bradycardia than hypoxia or hypercapnia alone. Twenty-six healthy participants (12 females; 23 ± 2 years; BMI 24 ± 3 kg/m2) underwent three gas challenges: hypercapnia (+5 torr end tidal partial pressure of CO2 [PETCO2]), hypoxia (50 torr end tidal partial pressure of O2 [PETO2]), and hypercapnic hypoxia (combined hypercapnia and hypoxia), with each condition interspersed with normocapnic normoxia. Heart rate and rhythm, blood pressure, PETCO2, PETO2, and oxygen saturation were measured continuously. Hypercapnic hypoxic apneas induced larger bradycardia (-19 ± 16 bpm) than normocapnic normoxic apneas (-11 ± 15 bpm; p = 0.002), but had a comparable response to hypoxic (-19 ± 15 bpm; p = 0.999) and hypercapnic apneas (-14 ± 14 bpm; p = 0.059). Hypercapnic apneas were not different from normocapnic normoxic apneas (p = 0.134). After removal of the normocapnic normoxic heart rate response, the change in heart rate during hypercapnic hypoxia (-11 ± 16 bpm) was similar to the summed change during hypercapnia+hypoxia (-9 ± 10 bpm; p = 0.485). Only hypoxia contributed to this bradycardic response. Under apneic conditions, the cardiac response is driven by hypoxia.
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Affiliation(s)
- Benjamin R O'Croinin
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Desmond A Young
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Lauren E Maier
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Sean van Diepen
- Department of Critical Care Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Division of Cardiology, Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Trevor A Day
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Craig D Steinback
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada
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Tymko MM, Drapeau A, Vieira-Coelho MA, Labrecque L, Imhoff S, Coombs GB, Langevin S, Fortin M, Châteauvert N, Ainslie PN, Brassard P. Acute isometric and dynamic exercise do not alter cerebral sympathetic nerve activity in healthy humans. J Cereb Blood Flow Metab 2024:271678X241248228. [PMID: 38613232 DOI: 10.1177/0271678x241248228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 04/14/2024]
Abstract
The impact of physiological stressors on cerebral sympathetic nervous activity (SNA) remains controversial. We hypothesized that cerebral noradrenaline (NA) spillover, an index of cerebral SNA, would not change during both submaximal isometric handgrip (HG) exercise followed by a post-exercise circulatory occlusion (PECO), and supine dynamic cycling exercise. Twelve healthy participants (5 females) underwent simultaneous blood sampling from the right radial artery and right internal jugular vein. Right internal jugular vein blood flow was measured using Duplex ultrasound, and tritiated NA was infused through the participants' right superficial forearm vein. Heart rate was recorded via electrocardiogram and blood pressure was monitored using the right radial artery. Total NA spillover increased during HG (P = 0.049), PECO (P = 0.006), and moderate cycling exercise (P = 0.03) compared to rest. Cerebral NA spillover remained unchanged during isometric HG exercise (P = 0.36), PECO after the isometric HG exercise (P = 0.45), and during moderate cycling exercise (P = 0.94) compared to rest. These results indicate that transient increases in blood pressure during acute exercise involving both small and large muscle mass do not engage cerebral SNA in healthy humans. Our findings suggest that cerebral SNA may be non-obligatory for exercise-related cerebrovascular adjustments.
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Affiliation(s)
- Michael M Tymko
- Integrative Cerebrovascular and Environmental Physiology SB Laboratory, Department of Human Health and Nutritional Sciences, College of Biological Science, University of Guelph, Guelph, Canada
- Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, Canada
| | - Audrey Drapeau
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada
- Institut universitaire de cardiologie et de pneumologie de Québec-Université Laval, Québec, Canada
| | - Maria Augusta Vieira-Coelho
- Department of Biomedicine, Pharmacology and Therapeutics Unit, Faculty of Medicine, University of Porto, Portugal
- Department of Psychiatry and Mental Health, University Hospital Center of São João, Porto, Portugal
| | - Lawrence Labrecque
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada
- Institut universitaire de cardiologie et de pneumologie de Québec-Université Laval, Québec, Canada
| | - Sarah Imhoff
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada
- Institut universitaire de cardiologie et de pneumologie de Québec-Université Laval, Québec, Canada
| | - Geoff B Coombs
- Department of Kinesiology, Faculty of Science, McMaster University, Hamilton, Canada
| | - Stephan Langevin
- Institut universitaire de cardiologie et de pneumologie de Québec-Université Laval, Québec, Canada
| | - Marc Fortin
- Institut universitaire de cardiologie et de pneumologie de Québec-Université Laval, Québec, Canada
| | - Nathalie Châteauvert
- Institut universitaire de cardiologie et de pneumologie de Québec-Université Laval, Québec, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, Canada
| | - Patrice Brassard
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada
- Institut universitaire de cardiologie et de pneumologie de Québec-Université Laval, Québec, Canada
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Steele AR, Howe CA, Gibbons TD, Foster K, Williams AM, Caldwell HG, Brewster LM, Duffy J, Monteleone JA, Subedi P, Anholm JD, Stembridge M, Ainslie PN, Tremblay JC. Hemorheological, cardiorespiratory, and cerebrovascular effects of pentoxifylline following acclimatization to 3,800 m. Am J Physiol Heart Circ Physiol 2024; 326:H705-H714. [PMID: 38241007 PMCID: PMC11221811 DOI: 10.1152/ajpheart.00783.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/18/2023] [Revised: 01/16/2024] [Accepted: 01/17/2024] [Indexed: 02/23/2024]
Abstract
Pentoxifylline is a nonselective phosphodiesterase inhibitor used for the treatment of peripheral artery disease. Pentoxifylline acts through cyclic adenosine monophosphate, thereby enhancing red blood cell deformability, causing vasodilation and decreasing inflammation, and potentially stimulating ventilation. We conducted a double-blind, placebo-controlled, crossover, counter-balanced study to test the hypothesis that pentoxifylline could lower blood viscosity, enhance cerebral blood flow, and decrease pulmonary artery pressure in lowlanders following 11-14 days at 3,800 m. Participants (6 males/10 females; age, 27 ± 4 yr old) received either a placebo or 400 mg of pentoxifylline orally the night before and again 2 h before testing. We assessed arterial blood gases, venous hemorheology (blood viscosity, red blood cell deformability, and aggregation), and inflammation (TNF-α) in room air (end-tidal oxygen partial pressure, ∼52 mmHg). Global cerebral blood flow (gCBF), ventilation, and pulmonary artery systolic pressure (PASP) were measured in room air and again after 8-10 min of isocapnic hypoxia (end-tidal oxygen partial pressure, 40 mmHg). Pentoxifylline did not alter arterial blood gases, TNF-α, or hemorheology compared with placebo. Pentoxifylline did not affect gCBF or ventilation during room air or isocapnic hypoxia compared with placebo. However, in females, PASP was reduced with pentoxifylline during room air (placebo, 19 ± 3; pentoxifylline, 16 ± 3 mmHg; P = 0.021) and isocapnic hypoxia (placebo, 22 ± 5; pentoxifylline, 20 ± 4 mmHg; P = 0.029), but not in males. Acute pentoxifylline administration in lowlanders at 3,800 m had no impact on arterial blood gases, hemorheology, inflammation, gCBF, or ventilation. Unexpectedly, however, pentoxifylline reduced PASP in female participants, indicating a potential effect of sex on the pulmonary vascular responses to pentoxifylline.NEW & NOTEWORTHY We conducted a double-blind, placebo-controlled study on the rheological, cardiorespiratory and cerebrovascular effects of acute pentoxifylline in healthy lowlanders after 11-14 days at 3,800 m. Although red blood cell deformability was reduced and blood viscosity increased compared with low altitude, acute pentoxifylline administration had no impact on arterial blood gases, hemorheology, inflammation, cerebral blood flow, or ventilation. Pentoxifylline decreased pulmonary artery systolic pressure in female, but not male, participants.
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Affiliation(s)
- Andrew R Steele
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada
| | - Connor A Howe
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada
| | - Travis D Gibbons
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada
- Department of Biological Sciences, Northern Arizona University, Flagstaff, Arizona, United States
| | - Katharine Foster
- Pulmonary and Critical Care, Veterans Affairs Loma Linda Healthcare System, Loma Linda, California, United States
- Department of Medicine, Loma Linda University School of Medicine, Loma Linda, California, United States
| | - Alexandra M Williams
- Department of Cellular & Physiological Sciences, Faculty of Medicine, University of British Columbia, Kelowna, British Columbia, Canada
| | - Hannah G Caldwell
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada
| | - L Madden Brewster
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada
| | - Jennifer Duffy
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada
| | - Justin A Monteleone
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada
| | - Prajan Subedi
- Pulmonary and Critical Care, Veterans Affairs Loma Linda Healthcare System, Loma Linda, California, United States
- Department of Medicine, Loma Linda University School of Medicine, Loma Linda, California, United States
| | - James D Anholm
- Pulmonary and Critical Care, Veterans Affairs Loma Linda Healthcare System, Loma Linda, California, United States
- Department of Medicine, Loma Linda University School of Medicine, Loma Linda, California, United States
| | - Mike Stembridge
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, United Kingdom
| | - Philip N Ainslie
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, Canada
| | - Joshua C Tremblay
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, United Kingdom
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Anderson GK, Davis KA, Bhuiyan N, Rusy R, Rosenberg AJ, Rickards CA. The effect of oscillatory hemodynamics on the cardiovascular responses to simulated hemorrhage during isocapnia. J Appl Physiol (1985) 2023; 135:1312-1322. [PMID: 37881852 PMCID: PMC10911761 DOI: 10.1152/japplphysiol.00241.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Revised: 10/17/2023] [Accepted: 10/20/2023] [Indexed: 10/27/2023] Open
Abstract
During cerebral hypoperfusion induced by lower body negative pressure (LBNP), cerebral tissue oxygenation is protected with oscillatory arterial pressure and cerebral blood flow at low frequencies (0.1 Hz and 0.05 Hz), despite no protection of cerebral blood flow or oxygen delivery. However, hypocapnia induced by LBNP contributes to cerebral blood flow reductions, and may mask potential protective effects of hemodynamic oscillations on cerebral blood flow. We hypothesized that under isocapnic conditions, forced oscillations of arterial pressure and blood flow at 0.1 Hz and 0.05 Hz would attenuate reductions in extra- and intracranial blood flow during simulated hemorrhage using LBNP. Eleven human participants underwent three LBNP profiles: a nonoscillatory condition (0 Hz) and two oscillatory conditions (0.1 Hz and 0.05 Hz). End-tidal (et) CO2 and etO2 were clamped at baseline values using dynamic end-tidal forcing. Cerebral tissue oxygenation (ScO2), internal carotid artery (ICA) blood flow, and middle cerebral artery velocity (MCAv) were measured. With clamped etCO2, neither ICA blood flow (ANOVA P = 0.93) nor MCAv (ANOVA P = 0.36) decreased with LBNP, and these responses did not differ between the three profiles (ICA blood flow: 0 Hz: 2.2 ± 5.4%, 0.1 Hz: -0.4 ± 6.6%, 0.05 Hz: 0.2 ± 4.8%; P = 0.56; MCAv: 0 Hz: -2.3 ± 7.8%, 0.1 Hz: -1.3 ± 6.1%, 0.05 Hz: -3.1 ± 5.0%; P = 0.87). Similarly, ScO2 did not decrease with LBNP (ANOVA P = 0.21) nor differ between the three profiles (0 Hz: -2.6 ± 3.3%, 0.1 Hz: -1.6 ± 1.5%, 0.05 Hz: -0.2 ± 2.8%; P = 0.13). Contrary to our hypothesis, cerebral blood flow and tissue oxygenation were protected during LBNP with isocapnia, regardless of whether hemodynamic oscillations were induced.NEW & NOTEWORTHY We examined the role of forcing oscillations in arterial pressure and blood flow at 0.1 Hz and 0.05 Hz on extra- and intracranial blood flow and cerebral tissue oxygenation during simulated hemorrhage (using lower body negative pressure, LBNP) under isocapnic conditions. Contrary to our hypothesis, both cerebral blood flow and cerebral tissue oxygenation were completely protected during simulated hemorrhage with isocapnia, regardless of whether oscillations in arterial pressure and cerebral blood flow were induced. These findings highlight the protective effect of preventing hypocapnia on cerebral blood flow under simulated hemorrhage conditions.
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Affiliation(s)
- Garen K Anderson
- Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - K Austin Davis
- Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Nasrul Bhuiyan
- Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Ryan Rusy
- Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Alexander J Rosenberg
- Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
- Physiology Department, Midwestern University, Downers Grove, Illinois, United States
- Integrative Physiology Laboratory, Department of Kinesiology and Nutrition, University of Illinois at Chicago, Chicago, Illinois, United States
| | - Caroline A Rickards
- Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
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Pruter WW, Klassen SA, Dominelli PB, Wiggins CC, Senefeld JW, Roy TK, Joyner MJ, Baker SE. Attenuated cardiac autonomic function in humans with high-affinity hemoglobin and compensatory polycythemia. Am J Physiol Regul Integr Comp Physiol 2023; 324:R625-R634. [PMID: 36878486 PMCID: PMC10085552 DOI: 10.1152/ajpregu.00113.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 02/28/2023] [Accepted: 03/01/2023] [Indexed: 03/08/2023]
Abstract
During hypoxic exposure, humans with high-affinity hemoglobin (and compensatory polycythemia) have blunted increases in heart rate compared with healthy humans with typical oxyhemoglobin dissociation curves. This response may be associated with altered autonomic control of heart rate. Our hypothesis-generating study aimed to investigate cardiac baroreflex sensitivity and heart rate variability among nine humans with high-affinity hemoglobin [6 females, O2 partial pressure at 50% [Formula: see text] (P50) = 16 ± 1 mmHg] compared with 12 humans with typical affinity hemoglobin (6 F, P50 = 26 ± 1 mmHg). Participants breathed normal room air for a 10-min baseline, followed by 20 min of isocapnic hypoxic exposure, designed to lower the arterial partial pressure O2 ([Formula: see text]) to ∼50 mmHg. Beat-by-beat heart rate and arterial blood pressure were recorded. Data were averaged in 5-min periods throughout the hypoxia exposure, beginning with the last 5 min of baseline in normoxia. Spontaneous cardiac baroreflex sensitivity and heart rate variability were determined using the sequence method and the time and frequency domain analyses, respectively. Cardiac baroreflex sensitivity was lower in humans with high-affinity hemoglobin than controls at baseline and during isocapnic hypoxic exposure (normoxia: 7 ± 4 vs. 16 ± 10 ms/mmHg, hypoxia minutes 15-20: 4 ± 3 vs. 14 ± 11 ms/mmHg; group effect: P = 0.02, high-affinity hemoglobin vs. control, respectively). Heart rate variability calculated in both the time (standard deviation of the N-N interval) and frequency (low frequency) domains was lower in humans with high-affinity hemoglobin than in controls (all P < 0.05). Our data suggest that humans with high-affinity hemoglobin may have attenuated cardiac autonomic function.
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Affiliation(s)
- Wyatt W Pruter
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Stephen A Klassen
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
- Department of Kinesiology, Brock University, St. Catharines, Ontario, Canada
| | - Paolo B Dominelli
- Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada
| | - Chad C Wiggins
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Jonathon W Senefeld
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Tuhin K Roy
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Michael J Joyner
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Sarah E Baker
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota, United States
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7
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Stacey BS, Hoiland RL, Caldwell HG, Howe CA, Vermeulen T, Tymko MM, Vizcardo‐Galindo GA, Bermudez D, Figueroa‐Mujíica RJ, Gasho C, Tuaillon E, Hirtz C, Lehmann S, Marchi N, Tsukamoto H, Villafuerte FC, Ainslie PN, Bailey DM. Lifelong exposure to high-altitude hypoxia in humans is associated with improved redox homeostasis and structural-functional adaptations of the neurovascular unit. J Physiol 2023; 601:1095-1120. [PMID: 36633375 PMCID: PMC10952731 DOI: 10.1113/jp283362] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Accepted: 12/20/2022] [Indexed: 01/13/2023] Open
Abstract
High-altitude (HA) hypoxia may alter the structural-functional integrity of the neurovascular unit (NVU). Herein, we compared male lowlanders (n = 9) at sea level (SL) and after 14 days acclimatization to 4300 m (chronic HA) in Cerro de Pasco (CdP), Péru (HA), against sex-, age- and body mass index-matched healthy highlanders (n = 9) native to CdP (lifelong HA). Venous blood was assayed for serum proteins reflecting NVU integrity, in addition to free radicals and nitric oxide (NO). Regional cerebral blood flow (CBF) was examined in conjunction with cerebral substrate delivery, dynamic cerebral autoregulation (dCA), cerebrovascular reactivity to carbon dioxide (CVRCO2 ) and neurovascular coupling (NVC). Psychomotor tests were employed to examine cognitive function. Compared to lowlanders at SL, highlanders exhibited elevated basal plasma and red blood cell NO bioavailability, improved anterior and posterior dCA, elevated anterior CVRCO2 and preserved cerebral substrate delivery, NVC and cognition. In highlanders, S100B, neurofilament light-chain (NF-L) and T-tau were consistently lower and cognition comparable to lowlanders following chronic-HA. These findings highlight novel integrated adaptations towards regulation of the NVU in highlanders that may represent a neuroprotective phenotype underpinning successful adaptation to the lifelong stress of HA hypoxia. KEY POINTS: High-altitude (HA) hypoxia has the potential to alter the structural-functional integrity of the neurovascular unit (NVU) in humans. For the first time, we examined to what extent chronic and lifelong hypoxia impacts multimodal biomarkers reflecting NVU structure and function in lowlanders and native Andean highlanders. Despite lowlanders presenting with a reduction in systemic oxidative-nitrosative stress and maintained cerebral bioenergetics and cerebrovascular function during chronic hypoxia, there was evidence for increased axonal injury and cognitive impairment. Compared to lowlanders at sea level, highlanders exhibited elevated vascular NO bioavailability, improved dynamic regulatory capacity and cerebrovascular reactivity, comparable cerebral substrate delivery and neurovascular coupling, and maintained cognition. Unlike lowlanders following chronic HA, highlanders presented with lower concentrations of S100B, neurofilament light chain and total tau. These findings highlight novel integrated adaptations towards the regulation of the NVU in highlanders that may represent a neuroprotective phenotype underpinning successful adaptation to the lifelong stress of HA hypoxia.
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Affiliation(s)
- Benjamin S. Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and EducationUniversity of South WalesPontypriddUK
| | - Ryan L. Hoiland
- Department of Anaesthesiology, Pharmacology and Therapeutics, Vancouver General HospitalUniversity of British ColumbiaVancouverBritish ColumbiaCanada
- Department of Cellular and Physiological Sciences, Faculty of MedicineUniversity of British ColumbiaVancouverBritish ColumbiaCanada
| | - Hannah G. Caldwell
- Centre for Heart, Lung and Vascular HealthUniversity of British Columbia‐Okanagan CampusKelownaBritish ColumbiaCanada
| | - Connor A. Howe
- Centre for Heart, Lung and Vascular HealthUniversity of British Columbia‐Okanagan CampusKelownaBritish ColumbiaCanada
| | - Tyler Vermeulen
- Centre for Heart, Lung and Vascular HealthUniversity of British Columbia‐Okanagan CampusKelownaBritish ColumbiaCanada
| | - Michael M. Tymko
- Centre for Heart, Lung and Vascular HealthUniversity of British Columbia‐Okanagan CampusKelownaBritish ColumbiaCanada
- Faculty of Kinesiology, Sport, and RecreationUniversity of AlbertaEdmontonAlbertaCanada
- Department of Medicine, Faculty of MedicineUniversity of British ColumbiaVancouverBritish ColumbiaCanada
| | - Gustavo A. Vizcardo‐Galindo
- Laboratorio de Fisiología Comparada, Departamento de Ciencias Biológicas y Fisiológicas, Facultad de Ciencias y FilosofíaUniversidad Peruana Cayetano HerediaLima 31Peru
| | - Daniella Bermudez
- Laboratorio de Fisiología Comparada, Departamento de Ciencias Biológicas y Fisiológicas, Facultad de Ciencias y FilosofíaUniversidad Peruana Cayetano HerediaLima 31Peru
| | - Rómulo J. Figueroa‐Mujíica
- Laboratorio de Fisiología Comparada, Departamento de Ciencias Biológicas y Fisiológicas, Facultad de Ciencias y FilosofíaUniversidad Peruana Cayetano HerediaLima 31Peru
| | - Christopher Gasho
- Division of Pulmonary and Critical CareLoma Linda University School of MedicineLoma LindaCAUSA
| | - Edouard Tuaillon
- Department of Infectious DiseasesUniversity of MontpellierMontpellierFrance
| | - Christophe Hirtz
- LBPC‐PPCUniversité de Montpellier, IRMB CHU de Montpellier, INM INSERMMontpellierFrance
| | - Sylvain Lehmann
- LBPC‐PPCUniversité de Montpellier, IRMB CHU de Montpellier, INM INSERMMontpellierFrance
| | - Nicola Marchi
- Laboratory of Cerebrovascular and Glia Research, Department of Neuroscience, Institute of Functional GenomicsUniversity of MontpellierMontpellierFrance
| | - Hayato Tsukamoto
- Faculty of Sport and Health ScienceRitsumeikan UniversityKusatsuShigaJapan
| | - Francisco C. Villafuerte
- Laboratorio de Fisiología Comparada, Departamento de Ciencias Biológicas y Fisiológicas, Facultad de Ciencias y FilosofíaUniversidad Peruana Cayetano HerediaLima 31Peru
| | - Philip N. Ainslie
- Neurovascular Research Laboratory, Faculty of Life Sciences and EducationUniversity of South WalesPontypriddUK
- Centre for Heart, Lung and Vascular HealthUniversity of British Columbia‐Okanagan CampusKelownaBritish ColumbiaCanada
| | - Damian M. Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and EducationUniversity of South WalesPontypriddUK
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8
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Carr JMJR, Howe CA, Gibbons TD, Tymko MM, Steele AR, Vizcardo-Galindo GA, Tremblay JC, Ainslie PN. Cerebral endothelium-dependent function and reactivity to hypercapnia: the role of α 1-adrenoreceptors. J Appl Physiol (1985) 2022; 133:1356-1367. [PMID: 36326471 DOI: 10.1152/japplphysiol.00400.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
We assessed hypercapnic cerebrovascular reactivity (CVR) and endothelium-dependent function [cerebral shear-mediated dilation (cSMD)] in the internal carotid artery (ICA) with and without systemic α1-adrenoreceptor blockade via Prazosin. We hypothesized that CVR would be reduced, whereas cSMD would remain unchanged, after Prazosin administration when compared with placebo. In 15 healthy adults (3 female, 26 ± 4 years), we conducted ICA duplex ultrasound during CVR [target +10 mmHg partial pressure of end-tidal carbon dioxide ([Formula: see text]) above baseline, 5 min] and cSMD (+9 mmHg [Formula: see text] above baseline, 30 s) using dynamic end-tidal forcing with and without α1-adrenergic blockade (Prazosin; 0.05 mg/kg) in a placebo-controlled, double-blind, and randomized design. The CVR in the ICA was not different between placebo and Prazosin (P = 0.578). During CVR, the reactivities of mean arterial pressure and cerebrovascular conductance to hypercapnia were also not different between conditions (P = 0.921 and P = 0.664, respectively). During Prazosin, cSMD was lower (1.1 ± 2.0% vs 3.8 ± 3.0%; P = 0.032); however, these data should be interpreted with caution due to the elevated baseline diameter (+1.3 ± 3.6%; condition: P = 0.0498) and lower shear rate (-14.5 ± 23.0%; condition: P < 0.001). Therefore, lower cSMD post α1-adrenoreceptor blockade might not indicate a reduction in cerebral endothelial function per se, but rather, that α1-adrenoreceptors contribute to resting cerebral vascular restraint at the level of the ICA.NEW & NOTEWORTHY We assessed steady-state hypercapnic cerebrovascular reactivity and cerebral endothelium-dependent function, with and without α1-adrenergic blockade (Prazosin), in a placebo-controlled, double-blind, and randomized study, to assess the contribution of α1-adrenergic receptors to cerebrovascular CO2 regulation. After administration of Prazosin, cerebrovascular reactivity to CO2 was not different compared with placebo despite lower blood flow, whereas cerebral endothelium-dependent function was reduced, likely due to elevated baseline internal carotid arterial diameter. These findings suggest that α1-adrenoreceptor activity does not influence cerebral blood flow regulation to CO2 and cerebral endothelial function.
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Affiliation(s)
- Jay M J R Carr
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, British Columbia, Canada
| | - Connor A Howe
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, British Columbia, Canada
| | - Travis D Gibbons
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, British Columbia, Canada
| | - Michael M Tymko
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, British Columbia, Canada.,Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada.,Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
| | - Andrew R Steele
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, British Columbia, Canada
| | - Gustavo A Vizcardo-Galindo
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, British Columbia, Canada
| | - Joshua C Tremblay
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, British Columbia, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, British Columbia, Canada
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9
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Carr JMJR, Ainslie PN, Howe CA, Gibbons TD, Tymko MM, Steele AR, Hoiland RL, Vizcardo-Galindo GA, Patrician A, Brown CV, Caldwell HG, Tremblay JC. Brachial artery responses to acute hypercapnia: The roles of shear stress and adrenergic tone. Exp Physiol 2022; 107:1440-1453. [PMID: 36114662 DOI: 10.1113/ep090690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2022] [Accepted: 09/12/2022] [Indexed: 12/14/2022]
Abstract
NEW FINDINGS What is the central question of this study? What are the contributions of shear stress and adrenergic tone to brachial artery vasodilatation during hypercapnia? What is the main finding and its importance? In healthy young adults, shear-mediated vasodilatation does not occur in the brachial artery during hypercapnia, as elevated α₁-adrenergic activity typically maintains vascular tone and offsets distal vasodilatation controlling flow. ABSTRACT We aimed to assess the shear stress dependency of brachial artery (BA) responses to hypercapnia, and the α₁-adrenergic restraint of these responses. We hypothesized that elevated shear stress during hypercapnia would cause BA vasodilatation, but where shear stress was prohibited (via arterial compression), the BA would not vasodilate (study 1); and, in the absence of α₁-adrenergic activity, blood flow, shear stress and BA vasodilatation would increase (study 2). In study 1, 14 healthy adults (7/7 male/female, 27 ± 4 years) underwent bilateral BA duplex ultrasound during hypercapnia (partial pressure of end-tidal carbon dioxide, +10.2 ± 0.3 mmHg above baseline, 12 min) via dynamic end-tidal forcing, and shear stress was reduced in one BA using manual compression (compression vs. control arm). Neither diameter nor blood flow was different between baseline and the last minute of hypercapnia (P = 0.423, P = 0.363, respectively) in either arm. The change values from baseline to the last minute, in diameter (%; P = 0.201), flow (ml/min; P = 0.234) and conductance (ml/min/mmHg; P = 0.503) were not different between arms. In study 2, 12 healthy adults (9/3 male/female, 26 ± 4 years) underwent the same design with and without α₁-adrenergic receptor blockade (prazosin; 0.05 mg/kg) in a placebo-controlled, double-blind and randomized design. BA flow, conductance and shear rate increased during hypercapnia in the prazosin control arm (interaction, P < 0.001), but in neither arm during placebo. Even in the absence of α₁-adrenergic restraint, downstream vasodilatation in the microvasculature during hypercapnia is insufficient to cause shear-mediated vasodilatation in the BA.
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Affiliation(s)
- Jay M J R Carr
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
| | - Connor A Howe
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
| | - Travis D Gibbons
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
| | - Michael M Tymko
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada.,Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Canada.,Faculty of Medicine, Department of Medicine, University of British Columbia, Vancouver, BC, Canada
| | - Andrew R Steele
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
| | - Ryan L Hoiland
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
| | - Gustavo A Vizcardo-Galindo
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
| | - Alex Patrician
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
| | - Courtney V Brown
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
| | - Hannah G Caldwell
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
| | - Joshua C Tremblay
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
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10
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Rieger MG, Tallon CM, Perkins DR, Smith KJ, Stembridge M, Piombo S, Radom-Aizik S, Cooper DM, Ainslie PN, McManus AM. Cardiopulmonary and cerebrovascular acclimatization in children and adults at 3800 m. J Physiol 2022; 600:4849-4863. [PMID: 36165275 DOI: 10.1113/jp283419] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Accepted: 09/20/2022] [Indexed: 12/24/2022] Open
Abstract
Maturational differences exist in cardiopulmonary and cerebrovascular function at sea-level, but the impact of maturation on acclimatization responses to high altitude is unknown. Ten children (9.8 ± 2.5 years) and 10 adults (34.7 ± 7.1 years) were assessed at sea-level (BL), 3000 m and twice over 4 days at 3800 m (B1, B4). Measurements included minute ventilation ( V ̇ E ${\dot{V}}_{\rm{E}}$ ), end-tidal partial pressures of oxygen ( P ETO 2 ${P}_{{\rm{ETO}}_{\rm{2}}}$ ) and carbon dioxide, echocardiographic assessment of pulmonary artery systolic pressure (PASP) and stroke volume (SV) and ultrasound assessment of blood flow through the internal carotid and vertebral arteries was performed to calculate global cerebral blood flow (gCBF). At 3000 m, V ̇ E ${\dot{V}}_{\rm{E}}$ was increased from BL by 19.6 ± 19.1% (P = 0.031) in children, but not in adults (P = 0.835); SV was reduced in children (-11 ± 13%, P = 0.020) but not adults (P = 0.827), which was compensated for by a larger increase in heart rate in children (+26 beats min-1 vs. +13 beats min-1 , P = 0.019). Between B1 and B4, adults increased V ̇ E ${\dot{V}}_{\rm{E}}$ by 38.5 ± 34.7% (P = 0.006), while V ̇ E ${\dot{V}}_{\rm{E}}$ did not increase further in children. The rise in PASP was not different between groups; however, ∆PASP from BL was related to ∆ P ETO 2 ${P}_{{\rm{ETO}}_{\rm{2}}}$ in adults (R2 = 0.288, P = 0.022), but not children. At BL, gCBF was 43% higher in children than adults (P = 0.017), and this difference was maintained at high altitude, with a similar pattern and magnitude of change in gCBF between groups (P = 0.845). Despite V ̇ E ${\dot{V}}_{\rm{E}}$ increasing in children but not adults at a lower altitude, the pulmonary vascular and cerebrovascular responses to prolonged hypoxia are similar between children and adults. KEY POINTS: Children have different ventilatory and metabolic requirements from adults, which may present differently in the pulmonary and cerebral vasculature upon ascent to high altitude. Children (ages 7-14) and adults (ages 23-44) were brought from sea level to high altitude (3000 to 3800 m) and changes in ventilation, pulmonary artery systolic pressure (PASP) and cerebral blood flow (CBF) were assessed over 1 week. Significant increases in ventilation and decreases in left ventricle stroke volume were observed at a lower altitude in children than adults. PASP and CBF increased by a similar relative amount between children and adults at 3800 m. These results help us better understand age-related differences in compensatory responses to prolonged hypoxia in children, despite similar changes in pulmonary artery pressure and CBF between children and adults.
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Affiliation(s)
- M G Rieger
- Centre for Heart, Lung & Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
| | - C M Tallon
- Centre for Heart, Lung & Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
| | - D R Perkins
- Cardiff School of Sport & Health Sciences, Cardiff Metropolitan University, Cardiff, UK.,Youth Physical Development Centre, Cardiff School of Sport & Health Sciences, Cardiff Metropolitan University, Cardiff, UK
| | - K J Smith
- Cerebrovascular Health, Exercise, and Environmental Research Sciences, University of Victoria, Victoria, British Columbia, Canada
| | - M Stembridge
- Cardiff School of Sport & Health Sciences, Cardiff Metropolitan University, Cardiff, UK.,Youth Physical Development Centre, Cardiff School of Sport & Health Sciences, Cardiff Metropolitan University, Cardiff, UK
| | - S Piombo
- Pediatric Exercise and Genomics Research Center, University of California Irvine School of Medicine, Irvine, CA, USA
| | - S Radom-Aizik
- Pediatric Exercise and Genomics Research Center, University of California Irvine School of Medicine, Irvine, CA, USA
| | - D M Cooper
- Pediatric Exercise and Genomics Research Center, University of California Irvine School of Medicine, Irvine, CA, USA
| | - P N Ainslie
- Centre for Heart, Lung & Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
| | - A M McManus
- Centre for Heart, Lung & Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
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11
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Kelly T, Brown C, Bryant-Ekstrand M, Lord R, Dawkins T, Drane A, Futral JE, Barak O, Dragun T, Stembridge M, Spajić B, Drviš I, Duke JW, Ainslie PN, Foster GE, Dujic Z, Lovering AT. Blunted hypoxic pulmonary vasoconstriction in apnoea divers. Exp Physiol 2022; 107:1225-1240. [PMID: 35993480 DOI: 10.1113/ep090326] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Accepted: 08/11/2022] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is new and noteworthy? What is the central question of this study? Does the hyperbaric, hypercapnic, acidotic, hypoxic stress of apnoea diving lead to greater pulmonary vasoreactivity and increased right-heart work in apnoea divers? What is the main finding and its importance? Compared to sex- and age-matched controls, Divers had a significantly lower change in total pulmonary resistance in response to short duration isocapnic hypoxia. With oral sildenafil (50 mg), there were no differences in total pulmonary resistance between groups, suggesting Divers can maintain normal pulmonary artery tone in hypoxic conditions. Blunted hypoxic pulmonary vasoconstriction may be beneficial during apnoea diving. ABSTRACT Competitive apnoea divers repetitively dive to depths beyond 50 m. During the final portions of ascent, Divers experience significant hypoxaemia. Additionally, hyperbaria during diving increases thoracic blood volume while simultaneously reducing lung volume, increasing pulmonary artery pressure. We hypothesized that Divers would have exaggerated hypoxic pulmonary vasoconstriction leading to increased right-heart work due to their repetitive hypoxaemia and hyperbaria, and that the administration of sildenafil would have a greater effect in reducing pulmonary resistance in Divers. We recruited 16 Divers and 16 age and sex matched non-diving controls (Controls). Using a double-blinded, placebo-controlled, cross-over design, participants were evaluated for normal cardiac and lung function, then their cardiopulmonary responses to 20-30 minutes of isocapnic hypoxia (end-tidal PO2 = 50 mm Hg) were measured one hour following ingestion of 50 mg sildenafil or placebo. Cardiac structure and cardiopulmonary function were similar at baseline. With placebo, Divers had a significantly smaller increase in total pulmonary resistance than controls after 20-30 minutes isocapnic hypoxia (Δ -3.85 ± 72.85 vs 73.74 ± 91.06 dynes/sec/cm-5 , p = .0222). With sildenafil, Divers and Controls had similarly blunted increases in total pulmonary resistance after 20-30 minutes of hypoxia. Divers also had a significantly lower systemic vascular resistance following sildenafil in normoxia. These data indicate that repetitive apnoea diving leads to a blunted hypoxic pulmonary vasoconstriction. We suggest this is a beneficial adaption allowing for increased cardiac output with reduced right heart work and thus reducing cardiac oxygen utilization under hypoxemic conditions. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Tyler Kelly
- Department of Human Physiology, University of Oregon, Eugene, Oregon, USA
| | - Courtney Brown
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | | | - Rachel Lord
- School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, Wales, UK
| | - Tony Dawkins
- School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, Wales, UK
| | - Aimee Drane
- School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, Wales, UK
| | - Joel E Futral
- Department of Human Physiology, University of Oregon, Eugene, Oregon, USA
| | - Otto Barak
- Department of Physiology, University of Novi Sad, Novi Sad, Serbia
| | - Tanja Dragun
- Department of Integrative Physiology, University of Split School of Medicine, Split, Croatia
| | - Michael Stembridge
- School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, Wales, UK
| | - Boris Spajić
- Faculty of Kinesiology, University of Zagreb, Zagreb, Croatia
| | - Ivan Drviš
- Faculty of Kinesiology, University of Zagreb, Zagreb, Croatia
| | - Joseph W Duke
- Department of Biological Sciences, Northern Arizona University, Flagstaff, Arizona, USA
| | - Philip N Ainslie
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | - Zeljko Dujic
- Department of Integrative Physiology, University of Split School of Medicine, Split, Croatia
| | - Andrew T Lovering
- Department of Human Physiology, University of Oregon, Eugene, Oregon, USA
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12
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Caldwell HG, Hoiland RL, Smith KJ, Brassard P, Bain AR, Tymko MM, Howe CA, Carr JM, Stacey BS, Bailey DM, Drapeau A, Sekhon MS, MacLeod DB, Ainslie PN. Trans-cerebral HCO 3- and PCO 2 exchange during acute respiratory acidosis and exercise-induced metabolic acidosis in humans. J Cereb Blood Flow Metab 2022; 42:559-571. [PMID: 34904461 PMCID: PMC8943603 DOI: 10.1177/0271678x211065924] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
This study investigated trans-cerebral internal jugular venous-arterial bicarbonate ([HCO3-]) and carbon dioxide tension (PCO2) exchange utilizing two separate interventions to induce acidosis: 1) acute respiratory acidosis via elevations in arterial PCO2 (PaCO2) (n = 39); and 2) metabolic acidosis via incremental cycling exercise to exhaustion (n = 24). During respiratory acidosis, arterial [HCO3-] increased by 0.15 ± 0.05 mmol ⋅ l-1 per mmHg elevation in PaCO2 across a wide physiological range (35 to 60 mmHg PaCO2; P < 0.001). The narrowing of the venous-arterial [HCO3-] and PCO2 differences with respiratory acidosis were both related to the hypercapnia-induced elevations in cerebral blood flow (CBF) (both P < 0.001; subset n = 27); thus, trans-cerebral [HCO3-] exchange (CBF × venous-arterial [HCO3-] difference) was reduced indicating a shift from net release toward net uptake of [HCO3-] (P = 0.004). Arterial [HCO3-] was reduced by -0.48 ± 0.15 mmol ⋅ l-1 per nmol ⋅ l-1 increase in arterial [H+] with exercise-induced acidosis (P < 0.001). There was no relationship between the venous-arterial [HCO3-] difference and arterial [H+] with exercise-induced acidosis or CBF; therefore, trans-cerebral [HCO3-] exchange was unaltered throughout exercise when indexed against arterial [H+] or pH (P = 0.933 and P = 0.896, respectively). These results indicate that increases and decreases in systemic [HCO3-] - during acute respiratory/exercise-induced metabolic acidosis, respectively - differentially affect cerebrovascular acid-base balance (via trans-cerebral [HCO3-] exchange).
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Affiliation(s)
- Hannah G Caldwell
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Ryan L Hoiland
- Department of Anesthesiology, Pharmacology and Therapeutics, Vancouver General Hospital, University of British Columbia, Vancouver, BC, Canada.,Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Kurt J Smith
- Department of Exercise Science, Physical and Health Education, Faculty of Education, University of Victoria, Victoria, British Columbia, Canada
| | - Patrice Brassard
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada.,Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, QC, Canada
| | - Anthony R Bain
- Faculty of Human Kinetics, Department of Kinesiology, University of Windsor, Windsor, ON, Canada
| | - Michael M Tymko
- Neurovascular Health Laboratory, Faculty of Kinesiology, Sport and Recreation, University of Alberta, Edmonton, AB, Canada
| | - Connor A Howe
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Jay Mjr Carr
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Benjamin S Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Audrey Drapeau
- Department of Kinesiology, Faculty of Medicine, Université Laval, Québec, Canada.,Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Québec, QC, Canada
| | - Mypinder S Sekhon
- Division of Critical Care Medicine, Department of Medicine, 8167Vancouver General Hospital, Vancouver General Hospital, University of British Columbia, Vancouver, BC, Canada
| | - David B MacLeod
- Human Pharmacology and Physiology Lab, Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, Canada
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13
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Hoiland RL, Caldwell HG, Carr JMJR, Howe CA, Stacey BS, Dawkins T, Wakeham DJ, Tremblay JC, Tymko MM, Patrician A, Smith KJ, Sekhon MS, MacLeod DB, Green DJ, Bailey DM, Ainslie PN. Nitric oxide contributes to cerebrovascular shear-mediated dilatation but not steady-state cerebrovascular reactivity to carbon dioxide. J Physiol 2021; 600:1385-1403. [PMID: 34904229 DOI: 10.1113/jp282427] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 12/07/2021] [Indexed: 12/15/2022] Open
Abstract
Cerebrovascular CO2 reactivity (CVR) is often considered a bioassay of cerebrovascular endothelial function. We recently introduced a test of cerebral shear-mediated dilatation (cSMD) that may better reflect endothelial function. We aimed to determine the nitric oxide (NO)-dependency of CVR and cSMD. Eleven volunteers underwent a steady-state CVR test and transient CO2 test of cSMD during intravenous infusion of the NO synthase inhibitor NG -monomethyl-l-arginine (l-NMMA) or volume-matched saline (placebo; single-blinded and counter-balanced). We measured cerebral blood flow (CBF; duplex ultrasound), intra-arterial blood pressure and P aC O 2 . Paired arterial and jugular venous blood sampling allowed for the determination of trans-cerebral NO2 - exchange (ozone-based chemiluminescence). l-NMMA reduced arterial NO2 - by ∼25% versus saline (74.3 ± 39.9 vs. 98.1 ± 34.2 nM; P = 0.03). The steady-state CVR (20.1 ± 11.6 nM/min at baseline vs. 3.2 ± 16.7 nM/min at +9 mmHg P aC O 2 ; P = 0.017) and transient cSMD tests (3.4 ± 5.9 nM/min at baseline vs. -1.8 ± 8.2 nM/min at 120 s post-CO2 ; P = 0.044) shifted trans-cerebral NO2 - exchange towards a greater net release (a negative value indicates release). Although this trans-cerebral NO2 - release was abolished by l-NMMA, CVR did not differ between the saline and l-NMMA trials (57.2 ± 14.6 vs. 54.1 ± 12.1 ml/min/mmHg; P = 0.49), nor did l-NMMA impact peak internal carotid artery dilatation during the steady-state CVR test (6.2 ± 4.5 vs. 6.2 ± 5.0% dilatation; P = 0.960). However, l-NMMA reduced cSMD by ∼37% compared to saline (2.91 ± 1.38 vs. 4.65 ± 2.50%; P = 0.009). Our findings indicate that NO is not an obligatory regulator of steady-state CVR. Further, our novel transient CO2 test of cSMD is largely NO-dependent and provides an in vivo bioassay of NO-mediated cerebrovascular function in humans. KEY POINTS: Emerging evidence indicates that a transient CO2 stimulus elicits shear-mediated dilatation of the internal carotid artery, termed cerebral shear-mediated dilatation. Whether or not cerebrovascular reactivity to a steady-state CO2 stimulus is NO-dependent remains unclear in humans. During both a steady-state cerebrovascular reactivity test and a transient CO2 test of cerebral shear-mediated dilatation, trans-cerebral nitrite exchange shifted towards a net release indicating cerebrovascular NO production; this response was not evident following intravenous infusion of the non-selective NO synthase inhibitor NG -monomethyl-l-arginine. NO synthase blockade did not alter cerebrovascular reactivity in the steady-state CO2 test; however, cerebral shear-mediated dilatation following a transient CO2 stimulus was reduced by ∼37% following intravenous infusion of NG -monomethyl-l-arginine. NO is not obligatory for cerebrovascular reactivity to CO2 , but is a key contributor to cerebral shear-mediated dilatation.
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Affiliation(s)
- Ryan L Hoiland
- Department of Anesthesiology, Pharmacology and Therapeutics, Faculty of Medicine, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada.,Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada.,Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.,International Collaboration on Repair Discoveries (ICORD), University of British Columbia, Vancouver, British Columbia, Canada
| | - Hannah G Caldwell
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Jay M J R Carr
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Connor A Howe
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Benjamin S Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Tony Dawkins
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, UK
| | - Denis J Wakeham
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, UK
| | - Joshua C Tremblay
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Michael M Tymko
- Neurovascular Health Laboratory, University of Alberta, Edmonton, Alberta, Canada
| | - Alexander Patrician
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Kurt J Smith
- Integrative Physiology Laboratory, Department of Kinesiology and Nutrition, College of Applied Health Sciences, University of Illinois, Chicago, IL, USA.,Cerebrovascular Health, Exercise, and Environmental Research Science (CHEERS) Laboratory, School of Exercise Science, Physical and Health Education, Faculty of Education, University of Victoria, Victoria, British Columbia, Canada
| | - Mypinder S Sekhon
- Division of Critical Care Medicine, Department of Medicine, Faculty of Medicine, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada
| | - David B MacLeod
- Human Pharmacology and Physiology Lab, Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - Daniel J Green
- School of Human Sciences (Exercise and Sport Sciences), University of Western Australia, Nedlands, Western Australia, Australia
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Philip N Ainslie
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
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14
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Boulet LM, Atwater TL, Brown CV, Shafer BM, Vermeulen TD, Cotton PC, Day TA, Foster GE. Sex differences in the coronary vascular response to combined chemoreflex and metaboreflex stimulation in healthy humans. Exp Physiol 2021; 107:16-28. [PMID: 34788486 DOI: 10.1113/ep090034] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Accepted: 11/08/2021] [Indexed: 12/18/2022]
Abstract
NEW FINDINGS What is the central question of this study? Coronary blood flow in healthy humans is controlled by both local metabolic signalling and adrenergic activity: does the integration of these signals during acute hypoxia and adrenergic activation differ between sexes? What are the main findings and its importance? Both males and females exhibit an increase in coronary blood velocity in response to acute hypoxia, a response that is constrained by adrenergic stimulation in males but not females. These findings suggest that coronary blood flow control differs between males and females. ABSTRACT Coronary hyperaemia is mediated through multiple signalling pathways, including local metabolic messengers and adrenergic stimulation. This study aimed to determine whether the coronary vascular response to adrenergic stressors is different between sexes in normoxia and hypoxia. Young, healthy participants (n = 32; 16F) underwent three randomized trials of isometric handgrip exercise followed by post-exercise circulatory occlusion (PECO) to activate the muscle metaboreflex. End-tidal P O 2 was controlled at (1) normoxic levels throughout the trial, (2) 50 mmHg for the duration of the trial (hypoxia trial), or (3) 50 mmHg only during PECO (mixed trial). Mean left anterior descending coronary artery velocity (LADVmean ; transthoracic Doppler echocardiography), heart rate and blood pressure were assessed at baseline and during PECO. In normoxia, there was no change in LADVmean or cardiac workload induced by PECO in males and females. Acute hypoxia increased baseline LADVmean to a greater extent in males compared with females (P < 0.05), despite a similar increase in cardiac workload. The change in LADVmean induced by PECO was similar between sexes in normoxia (P = 0.31), greater in males during the mixed trial (male: 12.8 (7.7) cm/s vs. female: 8.1 (6.3) cm/s; P = 0.02) and reduced in males but not females in acute hypoxia (male: -4.8 (4.5) cm/s vs. female: 0.8 (6.2) cm/s; P = 0.006). In summary, sex differences in the coronary vasodilatory response to hypoxia were observed, and metaboreflex activation during hypoxia caused a paradoxical reduction in coronary blood velocity in males but not females.
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Affiliation(s)
- Lindsey M Boulet
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Taylor L Atwater
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Courtney V Brown
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Brooke M Shafer
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Tyler D Vermeulen
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Paul C Cotton
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
| | - Trevor A Day
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, British Columbia, Kelowna, Canada
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15
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Carr JMJR, Caldwell HG, Carter H, Smith K, Tymko MM, Green DJ, Ainslie PN, Hoiland RL. The stability of cerebrovascular CO 2 reactivity following attainment of physiological steady-state. Exp Physiol 2021; 106:2542-2555. [PMID: 34730862 DOI: 10.1113/ep089982] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2021] [Accepted: 10/14/2021] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? During a steady-state cerebrovascular CO2 reactivity test, do different data extraction time points change the outcome for cerebrovascular CO2 reactivity? What is the main finding and its importance? Once steady-state end-tidal pressure of CO2 and haemodynamics were achieved, cerebral blood flow was stable, and so cerebrovascular CO2 reactivity values remained unchanged regardless of data extraction length (30 vs. 60 s) and time point (at 2-5 min). ABSTRACT This study assessed cerebrovascular CO2 reactivity (CVR) and examined data extraction time points and durations with the hypotheses that: (1) there would be no difference in CVR values when calculated with cerebral blood flow (CBF) measures at different time points following the attainment of physiological steady-state, (2) once steady-state was achieved there would be no difference in CVR values derived from 60 to 30 s extracted means, and (3) that changes in V ̇ E would not be associated with any changes in CVR. We conducted a single step iso-oxic hypercapnic CVR test using dynamic end-tidal forcing (end-tidal P C O 2 , +9.4 ± 0.7 mmHg), and transcranial Doppler and Duplex ultrasound of middle cerebral artery (MCA) and internal carotid artery (ICA), respectively. From the second minute of hypercapnia onwards, physiological steady-state was apparent, with no subsequent changes in end-tidal P C O 2 , P O 2 or mean arterial pressure. Therefore, CVR measured in the ICA and MCA was stable following the second minute of hypercapnia onwards. Data extraction durations of 30 or 60 s did not give statistically different CVR values. No differences in CVR were detected following the second minute of hypercapnia after accounting for mean arterial pressure via calculated conductance or covariation of mean arterial pressure. These findings demonstrate that, provided the P C O 2 stimulus remains in a steady-state, data extracted from any minute of a CVR test during physiological steady-state conditions produce equivalent CVR values; any change in the CVR value would represent a failure of CVR mechanisms, a change in the magnitude of the stimulus, or measurement error.
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Affiliation(s)
- Jay M J R Carr
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, British Columbia, Canada
| | - Hannah G Caldwell
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, British Columbia, Canada
| | - Howard Carter
- Cardiovascular Research Group, School of Human Sciences (Exercise and Sport Science), University of Western Australia, Perth, Australia
| | - Kurt Smith
- Cerebrovascular Health, Exercise, and Environmental Research Sciences Laboratory (CHEERS), School of Exercise Science and Physical Health Education, Faculty of Education, University of Victoria, Victoria, British Columbia, Canada
| | - Michael M Tymko
- Neurovascular Health Laboratory, Faculty of Kinesiology, Sport, & Recreation, University of Alberta, Edmonton, Canada
| | - Daniel J Green
- Cardiovascular Research Group, School of Human Sciences (Exercise and Sport Science), University of Western Australia, Perth, Australia
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, British Columbia, Canada
| | - Ryan L Hoiland
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, British Columbia, Canada.,Department of Anesthesiology, Pharmacology and Therapeutics, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada.,Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.,International Collaborations on Repair Discoveries (ICORD), University of British Columbia, Vancouver, British Columbia, Canada
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16
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Bader TJ, Leacy JK, Keough JRG, Ciorogariu‐Ivan A, Donald JR, Marullo AL, O’Halloran KD, Jendzjowsky NG, Wilson RJA, Day TA. The effects of acute incremental hypocapnia on the magnitude of neurovascular coupling in healthy participants. Physiol Rep 2021; 9:e14952. [PMID: 34350726 PMCID: PMC8339533 DOI: 10.14814/phy2.14952] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2021] [Accepted: 04/17/2021] [Indexed: 12/03/2022] Open
Abstract
The high metabolic demand of cerebral tissue requires that local perfusion is tightly coupled with local metabolic rate (neurovascular coupling; NVC). During chronic altitude exposure, where individuals are exposed to the antagonistic cerebrovascular effects of hypoxia and hypocapnia, pH is maintained through renal compensation and NVC remains stable. However, the potential independent effect of acute hypocapnia and respiratory alkalosis on NVC remains to be determined. We hypothesized that acute steady-state hypocapnia via voluntary hyperventilation would attenuate the magnitude of NVC. We recruited 17 healthy participants and insonated the posterior cerebral artery (PCA) with transcranial Doppler ultrasound. NVC was elicited using a standardized strobe light stimulus (6 Hz; 5 × 30 s on/off) where absolute delta responses from baseline (BL) in peak, mean, and total area under the curve (tAUC) were quantified. From a BL end-tidal (PET )CO2 level of 36.7 ± 3.2 Torr, participants were coached to hyperventilate to reach steady-state hypocapnic steps of Δ-5 Torr (31.6 ± 3.9) and Δ-10 Torr (26.0 ± 4.0; p < 0.001), which were maintained during the presentation of the visual stimuli. We observed a small but significant reduction in NVC peak (ΔPCAv) from BL during controlled hypocapnia at both Δ-5 (-1.58 cm/s) and Δ-10 (-1.37 cm/s), but no significant decrease in mean or tAUC NVC response was observed. These data demonstrate that acute respiratory alkalosis attenuates peak NVC magnitude at Δ-5 and Δ-10 Torr PET CO2 , equally. Although peak NVC magnitude was mildly attenuated, our data illustrate that mean and tAUC NVC are remarkably stable during acute respiratory alkalosis, suggesting multiple mechanisms underlying NVC.
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Affiliation(s)
- Taylor J. Bader
- Department of BiologyFaculty of Science and TechnologyMount Royal UniversityCalgaryABCanada
| | - Jack K. Leacy
- Department of PhysiologySchool of MedicineCollege of Medicine and HealthUniversity College CorkCorkIreland
| | - Joanna R. G. Keough
- Department of BiologyFaculty of Science and TechnologyMount Royal UniversityCalgaryABCanada
| | | | - Joshua R. Donald
- Department of BiologyFaculty of Science and TechnologyMount Royal UniversityCalgaryABCanada
| | - Anthony L. Marullo
- Department of BiologyFaculty of Science and TechnologyMount Royal UniversityCalgaryABCanada
| | - Ken D. O’Halloran
- Department of PhysiologySchool of MedicineCollege of Medicine and HealthUniversity College CorkCorkIreland
| | - Nicholas G. Jendzjowsky
- Division of Respiratory and Critical Care Physiology and MedicineThe Lundquist Institute for Biomedical Innovation at Harbor‐UCLA Medical CenterTorranceCAUSA
| | - Richard J. A. Wilson
- Department of Physiology and PharmacologyHotchkiss Brain InstituteCumming School of MedicineUniversity of CalgaryCalgaryABCanada
| | - Trevor A. Day
- Department of BiologyFaculty of Science and TechnologyMount Royal UniversityCalgaryABCanada
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17
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Keough JRG, Cates VC, Tymko MM, Boulet LM, Jamieson AN, Foster GE, Day TA. Regional differences in cerebrovascular reactivity in response to acute isocapnic hypoxia in healthy humans: Methodological considerations. Respir Physiol Neurobiol 2021; 294:103770. [PMID: 34343693 DOI: 10.1016/j.resp.2021.103770] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Revised: 07/15/2021] [Accepted: 07/29/2021] [Indexed: 11/30/2022]
Abstract
The cerebrovasculature responds to blood gas challenges. Regional differences (anterior vs. posterior) in cerebrovascular responses to increases in CO2 have been extensively studied. However, regional cerebrovascular reactivity (CVR) responses to low O2 (hypoxia) are equivocal, likely due to differences in analysis. We assessed the effects of acute isocapnic hypoxia on regional CVR comparing absolute and relative (%-change) responses in the middle cerebral artery (MCA) and posterior cerebral artery (PCA). We instrumented 14 healthy participants with a transcranial Doppler ultrasound (cerebral blood velocity), finometer (beat-by-beat blood pressure), dual gas analyzer (end-tidal CO2 and O2), and utilized a dynamic end-tidal forcing system to elicit a single 5-min bout of isocapnic hypoxia (∼45 Torr PETO2, ∼80 % SpO2). During exposure to acute hypoxia, absolute responses were larger in the anterior compared to posterior cerebral circulation (P < 0.001), but were not different when comparing relative responses (P = 0.45). Consistent reporting of CVR to hypoxia will aid understanding normative responses, particularly in assessing populations with impaired cerebrovascular function.
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Affiliation(s)
- Joanna R G Keough
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Valerie C Cates
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Michael M Tymko
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada; Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada; Faculty of Kinesiology, Sport and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Lindsey M Boulet
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada; Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Alenna N Jamieson
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Glen E Foster
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Trevor A Day
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada.
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18
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Caldwell HG, Howe CA, Hoiland RL, Carr JMJR, Chalifoux CJ, Brown CV, Patrician A, Tremblay JC, Panerai RB, Robinson TG, Minhas JS, Ainslie PN. Alterations in arterial CO 2 rather than pH affect the kinetics of neurovascular coupling in humans. J Physiol 2021; 599:3663-3676. [PMID: 34107079 DOI: 10.1113/jp281615] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Accepted: 06/08/2021] [Indexed: 12/11/2022] Open
Abstract
KEY POINTS We investigated the influence of arterial P C O 2 ( P aC O 2 ) with and without acute experimental metabolic alkalosis on neurovascular coupling (NVC). We assessed stepwise iso-oxic alterations in P aC O 2 prior to and following intravenous NaHCO3 to acutely elevate arterial pH and [HCO3 - ]. The NVC response was not altered following NaHCO3 between stepwise P aC O 2 stages; therefore, NVC is acutely mediated by P aC O 2 rather than the prevailing arterial [H+ ]/pH. The NVC response was attenuated by 27-38% with -10 mmHg P aC O 2 and the absolute peak change was reduced by -19% with +10 mmHg P aC O 2 irrespective of acutely elevated arterial pH/[HCO3 - ]. The NVC kinetics (i.e. time to peak) were markedly slower with hypercapnia versus hypocapnia (24 ± 5 vs. 7 ± 5 s, respectively) likely indicating an influence of resting cerebrovascular tone on NVC responsiveness. ABSTRACT Elevations in cerebral metabolism necessitate appropriate coordinated and localized increases in cerebral blood flow (i.e. neurovascular coupling; NVC). Recent pre-clinical work indicates that arterial P C O 2 ( P aC O 2 ) mediates NVC independently of arterial/extracellular pH; this has yet to be experimentally tested in humans. The goal of this study was to investigate the hypotheses that: (1) the NVC response would be unaffected by acute experimentally elevated arterial pH; rather, P aC O 2 would regulate any changes in NVC; and (2) stepwise respiratory alkalosis and acidosis would each progressively reduce the NVC response. Ten healthy males completed a standardized visual stimulus-evoked NVC test during matched stepwise iso-oxic alterations in P aC O 2 (hypocapnia: -5, -10 mmHg; hypercapnia: +5, +10 mmHg) prior to and following intravenous NaHCO3 (8.4%, 50 mEq/50 ml) that elevated arterial pH (7.406 ± 0.019 vs. 7.457 ± 0.029; P < 0.001) and [HCO3 - ] (26.2 ± 1.5 vs. 29.3 ± 0.9 mEq/l; P < 0.001). Although the NVC response was collectively attenuated by 27-38% with -10 mmHg P aC O 2 (stage post hoc: all P < 0.05), this response was unaltered following NaHCO3 (all P > 0.05) irrespective of the higher pH (P = 0.002) at each matched stage of P aC O 2 (P = 0.417). The absolute peak change was reduced by -19 ± 41% with +10 mmHg P aC O 2 irrespective of acutely elevated arterial pH/[HCO3 - ] (stage post hoc: P = 0.022). The NVC kinetics (i.e. time to peak) were markedly slower with hypercapnia versus hypocapnia (24 ± 5 vs. 7 ± 5 s, respectively; stage effect: P < 0.001). Overall, these findings indicate that temporal patterns in NVC are acutely regulated by P aC O 2 rather than arterial pH per se in the setting of acute metabolic alkalosis in humans.
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Affiliation(s)
- Hannah G Caldwell
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Connor A Howe
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Ryan L Hoiland
- Department of Anesthesiology, Pharmacology, and Therapeutics, Vancouver General Hospital, West 12th Avenue, University of British Columbia, Vancouver, BC, V5Z 1M9, Canada.,Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Jay M J R Carr
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Carter J Chalifoux
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Courtney V Brown
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Alexander Patrician
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Joshua C Tremblay
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
| | - Ronney B Panerai
- Cerebral Haemodynamics in Ageing and Stroke Medicine (CHiASM) Research Group, Leicester Biomedical Research Centre, University of Leicester, Leicester, UK
| | - Thompson G Robinson
- Cerebral Haemodynamics in Ageing and Stroke Medicine (CHiASM) Research Group, Leicester Biomedical Research Centre, University of Leicester, Leicester, UK
| | - Jatinder S Minhas
- Cerebral Haemodynamics in Ageing and Stroke Medicine (CHiASM) Research Group, Leicester Biomedical Research Centre, University of Leicester, Leicester, UK
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, V1V 1V7, Canada
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19
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Caldwell HG, Smith KJ, Lewis NCS, Hoiland RL, Willie CK, Lucas SJE, Stembridge M, Burgess KR, MacLeod DB, Ainslie PN. Regulation of cerebral blood flow by arterial PCO 2 independent of metabolic acidosis at 5050 m. J Physiol 2021; 599:3513-3530. [PMID: 34047356 DOI: 10.1113/jp281446] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2021] [Accepted: 05/21/2021] [Indexed: 12/23/2022] Open
Abstract
KEY POINTS We investigated the influence of arterial PCO2 (PaCO2 ) with and without experimentally altered pH on cerebral blood flow (CBF) regulation at sea level and with acclimatization to 5050 m. At sea level and high altitude, we assessed stepwise alterations in PaCO2 following metabolic acidosis (via 2 days of oral acetazolamide; ACZ) with and without acute restoration of pH (via intravenous sodium bicarbonate; ACZ+HCO3 - ). Total resting CBF was unchanged between trials at each altitude even though arterial pH and [HCO3 - ] (i.e. buffering capacity) were effectively altered. The cerebrovascular responses to changes in arterial [H+ ]/pH were consistent with the altered relationship between PaCO2 and [H+ ]/pH following ACZ at high altitude (i.e. leftward x-intercept shifts). Absolute cerebral blood velocity (CBV) and the sensitivity of CBV to PaCO2 was unchanged between trials at high altitude, indicating that CBF is acutely regulated by PaCO2 rather than arterial pH. ABSTRACT Alterations in acid-base balance with progressive acclimatization to high altitude have been well-established. However, how respiratory alkalosis and the resultant metabolic compensation interact to regulate cerebral blood flow (CBF) is uncertain. We addressed this via three separate experimental trials at sea level and following partial acclimatization (14 to 20 days) at 5050 m; involving: (1) resting acid-base balance (control); (2) following metabolic acidosis via 2 days of oral acetazolamide at 250 mg every 8 h (ACZ; pH: Δ -0.07 ± 0.04 and base excess: Δ -5.7 ± 1.9 mEq⋅l-1 , trial effects: P < 0.001 and P < 0.001, respectively); and (3) after acute normalization of arterial acidosis via intravenous sodium bicarbonate (ACZ + HCO3 - ; pH: Δ -0.01 ± 0.04 and base excess: Δ -1.5 ± 2.1 mEq⋅l-1 , trial effects: P = 1.000 and P = 0.052, respectively). Within each trial, we utilized transcranial Doppler ultrasound to assess the cerebral blood velocity (CBV) response to stepwise alterations in arterial PCO2 (PaCO2 ), i.e. cerebrovascular CO2 reactivity. Resting CBF (via Duplex ultrasound) was unaltered between trials within each altitude, indicating that respiratory compensation (i.e. Δ -3.4 ± 2.3 mmHg PaCO2 , trial effect: P < 0.001) was sufficient to offset any elevations in CBF induced via the ACZ-mediated metabolic acidosis. Between trials at high altitude, we observed consistent leftward shifts in both the PaCO2 -pH and CBV-pH responses across the CO2 reactivity tests with experimentally reduced arterial pH via ACZ. When indexed against PaCO2 - rather than pH - the absolute CBV and sensitivity of CBV-PaCO2 was unchanged between trials at high altitude. Taken together, following acclimatization, CO2 -mediated changes in cerebrovascular tone rather than arterial [H+ ]/pH is integral to CBF regulation at high altitude.
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Affiliation(s)
- Hannah G Caldwell
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Kurt J Smith
- Integrative Physiology Laboratory, Department of Kinesiology and Nutrition, University of Illinois Chicago, Chicago, Illinois, USA
| | - Nia C S Lewis
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Ryan L Hoiland
- Department of Anesthesiology, Pharmacology and Therapeutics, Vancouver General Hospital, West 12th Avenue, University of British Columbia, Vancouver, British Columbia, Canada.,Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Christopher K Willie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Samuel J E Lucas
- Department of Physiology, University of Otago, Dunedin, New Zealand.,School of Sport, Exercise and Rehabilitation Sciences & Centre for Human Brain Health, University of Birmingham, Birmingham, UK
| | - Michael Stembridge
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, UK
| | - Keith R Burgess
- Peninsula Sleep Clinic, Sydney, New South Wales, Australia.,Department of Medicine, University of Sydney, Sydney, New South Wales, Australia
| | - David B MacLeod
- Human Pharmacology and Physiology Lab, Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina, USA
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
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20
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Incognito AV, Teixeira AL, Shafer BM, Nardone M, Vermeulen TD, Foster GE, Millar PJ. Muscle sympathetic single-unit responses during rhythmic handgrip exercise and isocapnic hypoxia in males: the role of sympathoexcitation magnitude. J Neurophysiol 2021; 126:170-180. [PMID: 34133241 DOI: 10.1152/jn.00678.2020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A small proportion of postganglionic muscle sympathetic single units can be inhibited during sympathoexcitatory stressors in humans. However, whether these responses are dependent on the specific stressor or the level of sympathoexcitation remains unclear. We hypothesize that, when matched by sympathoexcitatory magnitude, different stressors can evoke similar proportions of inhibited single units. Multiunit and single-unit muscle sympathetic nerve activity (MSNA) were recorded in seven healthy young males at baseline and during 1) rhythmic handgrip exercise (40% of maximum voluntary contraction) and 2) acute isocapnic hypoxia (partial pressure of end-tidal O2 47 ± 3 mmHg). Single units were classified as activated, nonresponsive, or inhibited if the spike frequency was above, within, or below the baseline variability, respectively. By design, rhythmic handgrip and isocapnic hypoxia similarly increased multiunit total MSNA [Δ273 ± 208 vs. Δ254 ± 193 arbitrary units (AU), P = 0.84] and single-unit spike frequency (Δ8 ± 10 vs. Δ12 ± 13 spikes/min, P = 0.12). Among 19 identified single units, the proportions of activated (47% vs. 68%), nonresponsive (32% vs. 16%), and inhibited (21% vs. 16%) single units were not different between rhythmic handgrip and isocapnic hypoxia (P = 0.42). However, only 9 (47%) single units behaved with concordant response patterns across both stressors (7 activated, 1 nonresponsive, and 1 inhibited during both stressors). During the 1-min epoch with the highest increase in total MSNA during hypoxia (Δ595 ± 282 AU, P < 0.01) only one single unit was inhibited. These findings suggest that the proportions of muscle sympathetic single units inhibited during stress are associated with the level of sympathoexcitation and not the stressor per se in healthy young males.NEW & NOTEWORTHY Subpopulations of muscle sympathetic single units can be inhibited during mild sympathoexcitatory stress. We demonstrate that rhythmic handgrip exercise and isocapnic hypoxia, when matched by multiunit sympathoexcitation, induce similar proportions of single-unit inhibition, highlighting that heterogeneous single-unit response patterns are related to the level of sympathoexcitation independent of the stressor type. Interestingly, only 47% of single units behaved with concordant response patterns between stressors, suggesting the potential for functional specificity within the postganglionic neuronal pool.
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Affiliation(s)
- Anthony V Incognito
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - André L Teixeira
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Brooke M Shafer
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Massimo Nardone
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Tyler D Vermeulen
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Philip J Millar
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.,Toronto General Research Institute, Toronto General Hospital, Toronto, Ontario, Canada
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21
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Caldwell HG, Howe CA, Chalifoux CJ, Hoiland RL, Carr JMJR, Brown CV, Patrician A, Tremblay JC, Panerai RB, Robinson TG, Minhas JS, Ainslie PN. Arterial carbon dioxide and bicarbonate rather than pH regulate cerebral blood flow in the setting of acute experimental metabolic alkalosis. J Physiol 2021; 599:1439-1457. [DOI: 10.1113/jp280682] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Accepted: 12/14/2020] [Indexed: 12/11/2022] Open
Affiliation(s)
- Hannah G. Caldwell
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Connor A. Howe
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Carter J. Chalifoux
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Ryan L. Hoiland
- Department of Anesthesiology Pharmacology and Therapeutics Vancouver General Hospital University of British Columbia Vancouver BC Canada
- Department of Cellular and Physiological Sciences University of British Columbia Vancouver BC Canada
| | - Jay M. J. R. Carr
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Courtney V. Brown
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Alexander Patrician
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Joshua C. Tremblay
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Ronney B. Panerai
- Cerebral Haemodynamics in Ageing and Stroke Medicine (CHIASM) Research Group Leicester Biomedical Research Centre University of Leicester Leicester UK
| | - Thompson G. Robinson
- Cerebral Haemodynamics in Ageing and Stroke Medicine (CHIASM) Research Group Leicester Biomedical Research Centre University of Leicester Leicester UK
| | - Jatinder S. Minhas
- Cerebral Haemodynamics in Ageing and Stroke Medicine (CHIASM) Research Group Leicester Biomedical Research Centre University of Leicester Leicester UK
| | - Philip N. Ainslie
- Centre for Heart, Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
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22
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The effect of hypercapnia on regional cerebral blood flow regulation during progressive lower-body negative pressure. Eur J Appl Physiol 2020; 121:339-349. [PMID: 33089364 DOI: 10.1007/s00421-020-04506-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 09/19/2020] [Indexed: 10/23/2022]
Abstract
PURPOSE Previous work indicates that dynamic cerebral blood flow (CBF) regulation is impaired during hypercapnia; however, less is known about the impact of resting hypercapnia on regional CBF regulation during hypovolemia. Furthermore, there is disparity within the literature on whether differences between anterior and posterior CBF regulation exist during physiological stressors. We hypothesized: (a) lower-body negative pressure (LBNP)-induced reductions in cerebral blood velocity (surrogate for CBF) would be more pronounced during hypercapnia, indicating impaired CBF regulation; and (b) the anterior and posterior cerebral circulations will exhibit similar responses to LBNP. METHODS In 12 healthy participants (6 females), heart rate (electrocardiogram), mean arterial pressure (MAP; finger photoplethosmography), partial pressure of end-tidal carbon dioxide (PETCO2), middle cerebral artery blood velocity (MCAv) and posterior cerebral artery blood velocity (PCAv; transcranial Doppler ultrasound) were measured. Cerebrovascular conductance (CVC) was calculated as MCAv or PCAv indexed to MAP. Two randomized incremental LBNP protocols were conducted (- 20, - 40, - 60 and - 80 mmHg; three-minute stages), during coached normocapnia (i.e., room air), and inspired 5% hypercapnia (~ + 7 mmHg PETCO2 in normoxia). RESULTS The main findings were: (a) static CBF regulation in the MCA and PCA was similar during normocapnic and hypercapnic LBNP trials, (b) MCA and PCA CBV and CVC responded similarly to LBNP during normocapnia, but (c) PCAv and PCA CVC were reduced to a greater extent at - 60 mmHg LBNP (P = 0.029; P < 0.001) during hypercapnia. CONCLUSION CBF regulation during hypovolemia was preserved in hypercapnia, and regional differences in cerebrovascular control may exist during superimposed hypovolemia and hypercapnia.
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23
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Carr JMJR, Hoiland RL, Caldwell HG, Coombs GB, Howe CA, Tremblay JC, Green DJ, Ainslie PN. Internal carotid and brachial artery shear‐dependent vasodilator function in young healthy humans. J Physiol 2020; 598:5333-5350. [DOI: 10.1113/jp280369] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Accepted: 09/07/2020] [Indexed: 12/12/2022] Open
Affiliation(s)
- Jay M. J. R. Carr
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
| | - Ryan L. Hoiland
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
- Department of Anesthesiology Pharmacology and Therapeutics Vancouver General Hospital University of British Columbia Vancouver British Columbia Canada
| | - Hannah G. Caldwell
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
| | - Geoff B. Coombs
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
| | - Connor A. Howe
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
| | - Joshua C. Tremblay
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
| | - Daniel J. Green
- School of Human Sciences (Sport and Exercise Sciences) The University of Western Australia Crawley Western Australia Australia
| | - Philip N. Ainslie
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia – Okanagan Campus Kelowna British Columbia Canada
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24
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Tymko MM, Hoiland RL, Vermeulen TD, Howe CA, Tymko C, Stone RM, Steinback CD, Steele AR, Villafuerte F, Vizcardo-Galindo G, Mujica RJF, Ainslie PN. Global REACH 2018: The carotid artery diameter response to the cold pressor test is governed by arterial blood pressure during normoxic but not hypoxic conditions in healthy lowlanders and Andean highlanders. Exp Physiol 2020; 105:1742-1757. [PMID: 32829509 DOI: 10.1113/ep088898] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Accepted: 08/18/2020] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? What is the impact of oxygen on the circulatory responses to an isocapnic cold pressor test (CPT) in lowlanders and Andean highlanders? What is the main finding and its importance? Overall, the circulatory responses to an isocapnic CPT were largely unaltered with acute normobaric hypoxia and chronic hypobaric hypoxia exposure in lowlanders. However, the relationship between mean arterial pressure and common carotid artery diameter was dampened in hypoxic conditions. Furthermore, there were no differences in the circulatory responses to the CPT between lowlanders and Andean highlanders with lifelong exposure to high altitude. ABSTRACT The impact of oxygen on the circulatory responses to a cold pressor test (CPT) in lowlanders and Andean highlanders remains unknown. Our hypotheses were as follows: (i) in lowlanders, acute normobaric and hypobaric hypoxia would attenuate the common carotid artery (CCA) diameter response to the CPT compared with normobaric normoxia; (ii) Andean highlanders would exhibit a greater CCA diameter response compared with lowlanders; and (iii) a positive relationship between CCA diameter and blood pressure in response to the CPT would be present in both lowlanders and highlanders. Healthy lowlanders (n = 13) and Andean highlanders (n = 8) were recruited and conducted an isocapnic CPT, which consisted of a 3 min foot immersion into water at 0-1°C. Blood pressure (finger photoplethysmography) and CCA diameter and blood flow (Duplex ultrasound) were recorded continuously. The CPT was conducted in lowlanders at sea level in isocapnic normoxic and hypoxic conditions and after 10 days of acclimatization to 4300 m (Cerro de Pasco, Peru) in hypoxic and hyperoxic conditions. Andean highlanders were tested at rest at high altitude. The main findings were as follows: (i) in lowlanders, normobaric but not hypobaric hypoxia elevated CCA reactivity to the CPT; (ii) no differences in response to the CPT were observed between lowlanders and highlanders; and (iii) although hypobaric hypoxaemia reduced the relationship between CCA diameter and blood pressure compared with normobaric normoxia (P = 0.132), hypobaric hyperoxia improved this relationship (P = 0.012), and no relationship was observed in Andean highlanders (P = 0.261). These data demonstrate that the circulatory responses to a CPT were modified by oxygen in lowlanders, but were unaltered with lifelong hypoxic exposure.
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Affiliation(s)
- Michael M Tymko
- Faculty of Kinesiology, Sport and Recreation, University of Alberta, Edmonton, Alberta, Canada.,Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Ryan L Hoiland
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada.,Department of Anesthesiology, Pharmacology, and Therapeutics, Vancouver General Hospital, Vancouver, British Columbia, Canada
| | - Tyler D Vermeulen
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada.,Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada
| | - Connor A Howe
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Courtney Tymko
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Rachel M Stone
- Faculty of Human Kinetics, University of Windsor, Windsor, Ontario, Canada
| | - Craig D Steinback
- Faculty of Kinesiology, Sport and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Andrew R Steele
- Faculty of Kinesiology, Sport and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Francisco Villafuerte
- Laboratorio de Fisiología Comparada/Fisiología del Transporte de Oxígeno, Facultad de Ciencias y Filosofía, Universidad Peruana Cayetano Heredia, Lima, Perú
| | - Gustavo Vizcardo-Galindo
- Laboratorio de Fisiología Comparada/Fisiología del Transporte de Oxígeno, Facultad de Ciencias y Filosofía, Universidad Peruana Cayetano Heredia, Lima, Perú
| | - Romulo Joseph Figueroa Mujica
- Laboratorio de Fisiología Comparada/Fisiología del Transporte de Oxígeno, Facultad de Ciencias y Filosofía, Universidad Peruana Cayetano Heredia, Lima, Perú
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
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25
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Vermeulen TD, Benbaruj J, Brown CV, Shafer BM, Floras JS, Foster GE. Peripheral chemoreflex contribution to ventilatory long-term facilitation induced by acute intermittent hypercapnic hypoxia in males and females. J Physiol 2020; 598:4713-4730. [PMID: 32744340 DOI: 10.1113/jp280458] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Accepted: 07/30/2020] [Indexed: 01/30/2023] Open
Abstract
KEY POINTS Ventilatory long-term facilitation (vLTF) refers to respiratory neuroplasticity that develops following intermittent hypoxia in both healthy and clinical populations. A sustained hypercapnic background is argued to be required for full vLTF expression in humans. We determined whether acute intermittent hypercapnic hypoxia elicits vLTF during isocapnic-normoxic recovery in healthy males and females. We further assessed whether tonic peripheral chemoreflex drive is necessary and contributes to the expression of vLTF. Following 40 min of intermittent hypercapnic hypoxia, minute ventilation was increased throughout 50 min of isocapnic-normoxic recovery. Inhibition of peripheral chemoreflex drive with hyperoxia attenuated the magnitude of vLTF. Males and females achieve vLTF through different respiratory recruitment patterns. ABSTRACT Ventilatory long-term facilitation (vLTF) refers to respiratory neuroplasticity that manifests as increased minute ventilation ( V ̇ I ) following intermittent hypoxia. In humans, hypercapnia sustained throughout intermittent hypoxia and recovery is considered necessary for vLTF expression. We examined whether acute intermittent hypercapnic hypoxia (IHH) induces vLTF, and if peripheral chemoreflex drive contributes to vLTF throughout isocapnic-normoxic recovery. In 19 individuals (9 females, age: 22 ± 3 years; mean ± SD), measurements of tidal volume (VT ), breathing frequency (fB ), V ̇ I , and end-tidal gases ( P ET O 2 and P ETC O 2 ), were made at baseline, during IHH and 50 min of recovery. Totalling 40 min, IHH included 1 min intervals of 40 s hypercapnic hypoxia (target P ET O 2 = 50 mmHg and P ETC O 2 = +4 mmHg above baseline) and 20 s normoxia. During baseline and recovery, dynamic end-tidal forcing maintained resting P ET O 2 and P ETC O 2 and delivered 1 min of hyperoxia ( P ET O 2 = 355 ± 7 mmHg) every 5 min. The depression in V ̇ I during hyperoxia was considered an index of peripheral chemoreflex drive. Throughout recovery V ̇ I was increased 4.6 ± 3.7 l min-1 from baseline (P < 0.01). Hyperoxia depressed V ̇ I at baseline, and augmented depression was evident following IHH (Δ V ̇ I = -0.8 ± 0.9 vs. -1.7 ± 1.3 l min-1 , respectively, P < 0.01). The vLTF was similar between sexes (P = 0.15), but males had larger increases in VT than females (sex-by-time interaction, P = 0.03), and females tended to increase fB (P = 0.09). During isocapnic-normoxic recovery following IHH: (1) vLTF is expressed in healthy humans; (2) vLTF expression is attenuated but not abolished with peripheral chemoreflex inhibition by hyperoxia, suggesting a contribution from central nervous pathways in vLTF expression; and (3) males and females develop similar vLTF through different ventilatory recruitment strategies.
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Affiliation(s)
- Tyler D Vermeulen
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada.,Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Canada
| | - Jenna Benbaruj
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada
| | - Courtney V Brown
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada
| | - Brooke M Shafer
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada
| | - John S Floras
- University Health Network and Mount Sinai Hospital Division of Cardiology, Department of Medicine, University of Toronto, Toronto, Canada
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada
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26
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Kato T, Matsumoto T, Yamashiro SM. Effect of 3% CO2 inhalation on respiratory exchange ratio and cardiac output during constant work-rate exercise. J Sports Med Phys Fitness 2020; 61:175-182. [PMID: 32734753 DOI: 10.23736/s0022-4707.20.11012-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
BACKGROUND The aim of this study was to examine whether the decrease in respiratory exchange ratio (RER) during constant work-rate exercise (CWE) with 3% carbon dioxide (CO<inf>2</inf>) inhalation could be caused by the combination of the decrease in CO<inf>2</inf> output (V̇CO<inf>2</inf>) and the increase in oxygen uptake (V̇O<inf>2</inf>). In addition, we investigated the effect of 3% CO<inf>2</inf> inhalation on cardiac output (Q̇) during CWE. METHODS Seven males (V̇O<inf>2max</inf>: 44.1±6.4 mL/min/kg) carried out transitions from low-load cycling (baseline; 40w) to light intensity exercise (45% V̇O<inf>2 max</inf>; 89.3±12.5 W) and heavy intensity exercise (80% V̇O<inf>2max</inf>; 186.5±20.2 W) while inhaling normal air (Air) or an enriched CO<inf>2</inf> gas (3% CO<inf>2</inf>, 21% O<inf>2</inf>, balance N<inf>2</inf>). Each exercise session was 6 min, and respiratory responses by Douglas bag technique and cardiac responses by thoracic bio-impedance method were measured during the experiment. RESULTS Ventilation for 3% CO<inf>2</inf> was higher than for air through the experiment (P<0.05). Steady and non-steady state RER and V̇CO<inf>2</inf> for 3% CO<inf>2</inf> were less than for air in both light and heavy intensities (P<0.05), but V̇O<inf>2</inf> and Q̇ did not differ between the two conditions. CONCLUSIONS 3% CO<inf>2</inf> inhalation induced the decrease in RER during CWE at light and heavy intensities, which was due to the decrease in V̇CO<inf>2</inf>. The promoted ventilation with 3% CO<inf>2</inf> did not lead to the increase in V̇O<inf>2</inf>. Moreover, 3% CO<inf>2</inf> inhalation did not affect Q̇ during CWE at light and heavy intensities.
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Affiliation(s)
- Takahide Kato
- Department of General Education, National Institute of Technology, Toyota College, Toyota, Japan -
| | - Takaaki Matsumoto
- Laboratory for Exercise Physiology and Biomechanics, School of Health and Sport Sciences, Chukyo University, Toyota, Japan
| | - Stanley M Yamashiro
- Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, CA, USA
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27
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Leacy JK, Linares AM, Zouboules SM, Rampuri ZH, Bird JD, Herrington BA, Mann LM, Soriano JE, Thrall SF, Kalker A, Brutsaert TD, O'Halloran KD, Sherpa MT, Day TA. Cardiorespiratory hysteresis during incremental high‐altitude ascent–descent quantifies the magnitude of ventilatory acclimatization. Exp Physiol 2020; 106:139-150. [DOI: 10.1113/ep088488] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Accepted: 05/13/2020] [Indexed: 11/08/2022]
Affiliation(s)
- Jack K. Leacy
- Department of Biology Faculty of Science and Technology Mount Royal University Calgary Alberta Canada
- Department of Physiology School of Medicine College of Medicine & Health University College Cork Cork Ireland
| | - Andrea M. Linares
- Department of Biology Faculty of Science and Technology Mount Royal University Calgary Alberta Canada
| | - Shaelynn M. Zouboules
- Department of Biology Faculty of Science and Technology Mount Royal University Calgary Alberta Canada
| | - Zahrah H. Rampuri
- Department of Biology Faculty of Science and Technology Mount Royal University Calgary Alberta Canada
| | - Jordan D. Bird
- Department of Biology Faculty of Science and Technology Mount Royal University Calgary Alberta Canada
| | - Brittney A. Herrington
- Department of Biology Faculty of Science and Technology Mount Royal University Calgary Alberta Canada
| | - Leah M. Mann
- Department of Biology Faculty of Science and Technology Mount Royal University Calgary Alberta Canada
| | - Jan E. Soriano
- Department of Biology Faculty of Science and Technology Mount Royal University Calgary Alberta Canada
| | - Scott F. Thrall
- Department of Biology Faculty of Science and Technology Mount Royal University Calgary Alberta Canada
| | - Anne Kalker
- Department of Biology Faculty of Science and Technology Mount Royal University Calgary Alberta Canada
- Radboud University Nijmegen The Netherlands
| | | | - Ken D. O'Halloran
- Department of Physiology School of Medicine College of Medicine & Health University College Cork Cork Ireland
| | | | - Trevor A. Day
- Department of Biology Faculty of Science and Technology Mount Royal University Calgary Alberta Canada
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28
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Tymko MM, Hoiland RL, Tremblay JC, Stembridge M, Dawkins TG, Coombs GB, Patrician A, Howe CA, Gibbons TD, Moore JP, Simpson LL, Steinback CD, Meah VL, Stacey BS, Bailey DM, MacLeod DB, Gasho C, Anholm JD, Bain AR, Lawley JS, Villafuerte FC, Vizcardo-Galindo G, Ainslie PN. The 2018 Global Research Expedition on Altitude Related Chronic Health (Global REACH) to Cerro de Pasco, Peru: an Experimental Overview. Exp Physiol 2020; 106:86-103. [PMID: 32237245 DOI: 10.1113/ep088350] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Accepted: 03/26/2020] [Indexed: 12/18/2022]
Abstract
NEW FINDINGS What is the central question of this study? Herein, a methodological overview of our research team's (Global REACH) latest high altitude research expedition to Peru is provided. What is the main finding and its importance? The experimental objectives, expedition organization, measurements and key cohort data are discussed. The select data presented in this manuscript demonstrate the haematological differences between lowlanders and Andeans with and without excessive erythrocytosis. The data also demonstrate that exercise capacity was similar between study groups at high altitude. The forthcoming findings from our research expedition will contribute to our understanding of lowlander and indigenous highlander high altitude adaptation. ABSTRACT In 2016, the international research team Global Research Expedition on Altitude Related Chronic Health (Global REACH) was established and executed a high altitude research expedition to Nepal. The team consists of ∼45 students, principal investigators and physicians with the common objective of conducting experiments focused on high altitude adaptation in lowlanders and in highlanders with lifelong exposure to high altitude. In 2018, Global REACH travelled to Peru, where we performed a series of experiments in the Andean highlanders. The experimental objectives, organization and characteristics, and key cohort data from Global REACH's latest research expedition are outlined herein. Fifteen major studies are described that aimed to elucidate the physiological differences in high altitude acclimatization between lowlanders (n = 30) and Andean-born highlanders with (n = 22) and without (n = 45) excessive erythrocytosis. After baseline testing in Kelowna, BC, Canada (344 m), Global REACH travelled to Lima, Peru (∼80 m) and then ascended by automobile to Cerro de Pasco, Peru (∼4300 m), where experiments were conducted over 25 days. The core studies focused on elucidating the mechanism(s) governing cerebral and peripheral vascular function, cardiopulmonary regulation, exercise performance and autonomic control. Despite encountering serious logistical challenges, each of the proposed studies was completed at both sea level and high altitude, amounting to ∼780 study sessions and >3000 h of experimental testing. Participant demographics and data relating to acid-base balance and exercise capacity are presented. The collective findings will contribute to our understanding of how lowlanders and Andean highlanders have adapted under high altitude stress.
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Affiliation(s)
- Michael M Tymko
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada.,Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Ryan L Hoiland
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada.,Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, BC, Canada
| | - Joshua C Tremblay
- Cardiovascular Stress Response Laboratory, School of Kinesiology and Health Studies, Queen's University, Kingston, Ontario, Canada
| | - Mike Stembridge
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, UK
| | - Tony G Dawkins
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, UK
| | - Geoff B Coombs
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Alexander Patrician
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Connor A Howe
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Travis D Gibbons
- School of Physical Education, Sport & Exercise Science, University of Otago, Dunedin, New Zealand
| | - Jonathan P Moore
- School of Sport, Health and Exercise Sciences, Bangor University, Bangor, UK
| | - Lydia L Simpson
- School of Sport, Health and Exercise Sciences, Bangor University, Bangor, UK
| | - Craig D Steinback
- Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Victoria L Meah
- Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Benjamin S Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Glamorgan, UK
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Glamorgan, UK
| | - David B MacLeod
- Human Pharmacology & Physiology Lab, Duke University Medical Center, Durham, NC, USA
| | - Christopher Gasho
- Department of Medicine, Division of Pulmonary and Critical Care, Loma Linda University School of Medicine, Loma Linda, CA, USA
| | - James D Anholm
- Department of Medicine, Division of Pulmonary and Critical Care, Loma Linda University School of Medicine, Loma Linda, CA, USA
| | - Anthony R Bain
- Department of Integrative Physiology, University of Colorado, Boulder, NC, USA.,Faculty of Human Kinetics, University of Windsor, Windsor, Ontario, Canada
| | - Justin S Lawley
- Department of Sport Science, University of Innsbruck, Innsbruck, Austria
| | - Francisco C Villafuerte
- Laboratorio de Fisiología Comparada/Fisiología del Transporte de Oxígeno, Facultad de Ciencias y Filosofía, Universidad Peruana Cayetano Heredia, Lima, Perú
| | - Gustavo Vizcardo-Galindo
- Laboratorio de Fisiología Comparada/Fisiología del Transporte de Oxígeno, Facultad de Ciencias y Filosofía, Universidad Peruana Cayetano Heredia, Lima, Perú
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
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29
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Brown CV, Boulet LM, Vermeulen TD, Sands SA, Wilson RJA, Ayas NT, Floras JS, Foster GE. Angiotensin II-Type I Receptor Antagonism Does Not Influence the Chemoreceptor Reflex or Hypoxia-Induced Central Sleep Apnea in Men. Front Neurosci 2020; 14:382. [PMID: 32410951 PMCID: PMC7198907 DOI: 10.3389/fnins.2020.00382] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 03/27/2020] [Indexed: 12/15/2022] Open
Abstract
Components of the renin-angiotensin system (RAS) situated within the carotid body or central nervous system may promote hypoxia-induced chemoreceptor reflex sensitization or central sleep apnea (CSA). We determined if losartan, an angiotensin-II type-I receptor (AT1R) antagonist, would attenuate chemoreceptor reflex sensitivity before or after 8 h of nocturnal hypoxia, and consequently CSA severity. In a double-blind, randomized, placebo-controlled, crossover protocol, 14 men (age: 25 ± 2 years; BMI: 24.6 ± 1.1 kg/m2; means ± SEM) ingested 3 doses of either losartan (50 mg) or placebo every 8 h. Chemoreceptor reflex sensitivity was assessed during hypoxic and hyperoxic hypercapnic ventilatory response (HCVR) tests and during six-20s hypoxic apneas before and after 8 h of sleep in normobaric hypoxia (FIO2 = 0.135). Loop gain was assessed from a ventilatory control model fitted to the ventilatory pattern of CSA recorded during polysomnography. Prior to nocturnal hypoxia, losartan had no effect on either the hyperoxic (losartan: 3.6 ± 1.1, placebo: 4.0 ± 0.6 l/min/mmHg; P = 0.9) or hypoxic HCVR (losartan: 5.3 ± 1.4, placebo: 5.7 ± 0.68 l/min/mmHg; P = 1.0). Likewise, losartan did not influence either the hyperoxic (losartan: 4.2 ± 1.3, placebo: 3.8 ± 1.1 l/min/mmHg; P = 0.5) or hypoxic HCVR (losartan: 6.6 ± 1.8, placebo: 6.3 ± 1.5 l/min/mmHg; P = 0.9) after nocturnal hypoxia. Cardiorespiratory responses to apnea and participants’ apnea hypopnea indexes during placebo and losartan were similar (73 ± 15 vs. 75 ± 14 events/h; P = 0.9). Loop gain, which correlated with CSA severity (r = 0.94, P < 0.001), was similar between treatments. In summary, in young healthy men, hypoxia-induced CSA severity is strongly associated with loop gain, but the AT1R does not modulate chemoreceptor reflex sensitivity before or after 8 h of nocturnal hypoxia.
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Affiliation(s)
- Courtney V Brown
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia - Okanagan, Kelowna, BC, Canada
| | - Lindsey M Boulet
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia - Okanagan, Kelowna, BC, Canada
| | - Tyler D Vermeulen
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia - Okanagan, Kelowna, BC, Canada
| | - Scott A Sands
- Division of Sleep and Circadian Disorders, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, United States
| | - Richard J A Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
| | - Najib T Ayas
- Sleep Disorders Program, University of British Columbia, Vancouver, BC, Canada.,Respiratory and Critical Care Divisions, University of British Columbia, Vancouver, BC, Canada
| | - John S Floras
- University Health Network and Sinai Health System Division of Cardiology, Department of Medicine, University of Toronto, Toronto, ON, Canada
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia - Okanagan, Kelowna, BC, Canada
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Williams AM, Ainslie PN, Anholm JD, Gasho C, Subedi P, Stembridge M. Left Ventricular Twist Is Augmented in Hypoxia by β 1-Adrenergic-Dependent and β 1-Adrenergic-Independent Factors, Without Evidence of Endocardial Dysfunction. Circ Cardiovasc Imaging 2020; 12:e008455. [PMID: 31060374 DOI: 10.1161/circimaging.118.008455] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Left ventricular (LV) twist mechanics are augmented with both acute and chronic hypoxemia. Although the underlying mechanisms remain unknown, sympathetic activation and a direct effect of hypoxemia on the myocardium have been proposed, the latter of which may produce subendocardial dysfunction that is masked by larger subepicardial torque. This study therefore sought to (1) determine the individual and combined influences of β1-AR (β1-adrenergic receptor) stimulation and peripheral O2 saturation (Spo2) on LV twist in acute and chronic hypoxia and (2) elucidate whether endocardial versus epicardial mechanics respond differently to hypoxia. METHODS Twelve males (27±4 years) were tested near sea level in acute hypoxia (Spo2=82±4%) and following 3 to 6 days at 5050 m (high altitude; Spo2=83±3%). In both settings, participants received infusions of β1-AR blocker esmolol and volume-matched saline (double-blind, randomized). LV mechanics were assessed with 2-dimensional speckle-tracking echocardiography, and region-specific analysis to compare subendocardial and subepicardial mechanics. RESULTS At sea level, compared with baseline (14.8±3.0°) LV twist was reduced with esmolol (11.2±3.3°; P=0.007) and augmented during hypoxia (19.6±4.9°; P<0.001), whereas esmolol+hypoxia augmented twist compared with esmolol alone (16.5±3.3°; P<0.001). At 5050 m, LV twist was increased compared with sea level (19.5±5.4°; P=0.004), and reduced with esmolol (13.0±3.8°; P<0.001) and Spo2 normalization (12.8±3.4°; P<0.001). Moreover, esmolol+normalized Spo2 lowered twist further than esmolol alone (10.5±3.1°; P=0.036). There was no mechanics-derived evidence of endocardial dysfunction with hypoxia at sea level or high altitude. CONCLUSIONS These findings suggest LV twist is augmented in hypoxia via β1-AR-dependent and β1-AR-independent mechanisms (eg, α1-AR stimulation), but does not appear to reflect endocardial dysfunction.
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Affiliation(s)
- Alexandra M Williams
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, The University of British Columbia, Kelowna, Canada (A.M.W., P.N.A.).,Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, Canada (A.M.W.)
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, The University of British Columbia, Kelowna, Canada (A.M.W., P.N.A.)
| | - James D Anholm
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, Canada (A.M.W.)
| | - Chris Gasho
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, Canada (A.M.W.)
| | - Prajan Subedi
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, Canada (A.M.W.)
| | - Mike Stembridge
- Pulmonary and Critical Care Section, VA Loma Linda Healthcare System, Loma Linda, CA (J.D.A., C.G., P.S.)
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31
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Caldwell HG, Coombs GB, Howe CA, Hoiland RL, Patrician A, Lucas SJ, Ainslie PN. Evidence for temperature‐mediated regional increases in cerebral blood flow during exercise. J Physiol 2020; 598:1459-1473. [DOI: 10.1113/jp278827] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Accepted: 12/20/2019] [Indexed: 12/18/2022] Open
Affiliation(s)
- Hannah G. Caldwell
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Geoff B. Coombs
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Connor A. Howe
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Ryan L. Hoiland
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Alexander Patrician
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
| | - Samuel J.E. Lucas
- School of Sport Exercise and Rehabilitation Sciences & Centre for Human Brain Health University of Birmingham Birmingham UK
| | - Philip N. Ainslie
- Centre for Heart Lung and Vascular Health School of Health and Exercise Sciences University of British Columbia Okanagan Kelowna BC Canada
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32
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Kuenzel A, Marshall B, Verges S, Anholm JD. Positional Changes in Arterial Oxygen Saturation and End-Tidal Carbon Dioxide at High Altitude: Medex 2015. High Alt Med Biol 2020; 21:144-151. [PMID: 31985275 DOI: 10.1089/ham.2019.0066] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Background: Body position alters aspects of pulmonary function in health and disease. Although studies have assessed positional effects on the heart and lungs, little is known about positional changes in gas exchange parameters at high altitude. We hypothesized that following ascent, supine positioning would cause lower oxygen saturation than sitting, partially due to decreased ventilation and increased partial pressure of end-tidal carbon dioxide (Petco2). Materials and Methods: Twenty-eight healthy subjects were studied at sea level and following gradual ascent to 5150 m. After 10 minutes of sitting rest, subjects were studied for 5 minutes each in the sitting, supine, and prone positions with the order randomly assigned. Pulse oximeter oxygen saturation (SpO2), minute ventilation (VE), end-tidal O2 (Peto2) and Petco2, oxygen consumption, and CO2 production were continuously measured. Alveolar ventilation (VA) was calculated from the measured parameters. Results: At high altitude, VE was not affected by body position (12.96 ± 3.09 and 11.54 ± 3.45 L/min in the sitting and supine positions, respectively, p = 0.255). Petco2 increased from sitting to supine (22.8 ± 3.1 to 23.5 ± 3.3 mm Hg, p < 0.005), but VE and Petco2 were not different between the supine and prone positions. Calculated VA was not significantly affected by body position at either sea level or high altitude. SpO2 decreased from 81.3% ± 4.4% sitting to 78.8% ± 6.0% supine (p = 0.025), with a mean positional SpO2 difference of 2.5% ± 4.9% (95% confidence interval 0.6%-4.4%). SpO2 was not different between the supine and prone positions. Twenty-two of 28 subjects had lower SpO2 supine compared with sitting. Conclusions: These results extend earlier low-altitude studies and demonstrate the importance of postural regulation in different environments. As 79% of subjects had lower SpO2 while supine than sitting, control of body position is necessary for SpO2 comparisons at altitude to be meaningful.
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Affiliation(s)
- Arlena Kuenzel
- Department of Anaesthesia, Royal Infirmary of Edinburgh, NHS Lothian, Edinburgh, Scotland
| | - Ben Marshall
- Sheffield Teaching Hospitals, NHS Foundation Trust, Sheffield, United Kingdom
| | - Samuel Verges
- INSERM U1042 and HP2 Laboratory, Grenoble Alpes University, Grenoble, France
| | - James D Anholm
- Division of Pulmonary, Critical Care, Hyperbaric and Sleep Medicine, Department of Medicine, Loma Linda University School of Medicine, Loma Linda, California, USA
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Gibbons TD, Tymko MM, Thomas KN, Wilson LC, Stembridge M, Caldwell HG, Howe CA, Hoiland RL, Akerman AP, Dawkins TG, Patrician A, Coombs GB, Gasho C, Stacey BS, Ainslie PN, Cotter JD. Global REACH 2018: The influence of acute and chronic hypoxia on cerebral haemodynamics and related functional outcomes during cold and heat stress. J Physiol 2020; 598:265-284. [PMID: 31696936 DOI: 10.1113/jp278917] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2019] [Accepted: 10/28/2019] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Thermal and hypoxic stress commonly coexist in environmental, occupational and clinical settings, yet how the brain tolerates these multi-stressor environments is unknown Core cooling by 1.0°C reduced cerebral blood flow (CBF) by 20-30% and cerebral oxygen delivery (CDO2 ) by 12-19% at sea level and high altitude, whereas core heating by 1.5°C did not reliably reduce CBF or CDO2 Oxygen content in arterial blood was fully restored with acclimatisation to 4330 m, but concurrent cold stress reduced CBF and CDO2 Gross indices of cognition were not impaired by any combination of thermal and hypoxic stress despite large reductions in CDO2 Chronic hypoxia renders the brain susceptible to large reductions in oxygen delivery with concurrent cold stress, which might make monitoring core temperature more important in this context ABSTRACT: Real-world settings are composed of multiple environmental stressors, yet the majority of research in environmental physiology investigates these stressors in isolation. The brain is central in both behavioural and physiological responses to threatening stimuli and, given its tight metabolic and haemodynamic requirements, is particularly susceptible to environmental stress. We measured cerebral blood flow (CBF, duplex ultrasound), cerebral oxygen delivery (CDO2 ), oesophageal temperature, and arterial blood gases during exposure to three commonly experienced environmental stressors - heat, cold and hypoxia - in isolation, and in combination. Twelve healthy male subjects (27 ± 11 years) underwent core cooling by 1.0°C and core heating by 1.5°C in randomised order at sea level; acute hypoxia ( P ET , O 2 = 50 mm Hg) was imposed at baseline and at each thermal extreme. Core cooling and heating protocols were repeated after 16 ± 4 days residing at 4330 m to investigate any interactions with high altitude acclimatisation. Cold stress decreased CBF by 20-30% and CDO2 by 12-19% (both P < 0.01) irrespective of altitude, whereas heating did not reliably change either CBF or CDO2 (both P > 0.08). The increases in CBF with acute hypoxia during thermal stress were appropriate to maintain CDO2 at normothermic, normoxic values. Reaction time was faster and slower by 6-9% with heating and cooling, respectively (both P < 0.01), but central (brain) processes were not impaired by any combination of environmental stressors. These findings highlight the powerful influence of core cooling in reducing CDO2 . Despite these large reductions in CDO2 with cold stress, gross indices of cognition remained stable.
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Affiliation(s)
- T D Gibbons
- School of Physical Education, Sport & Exercise Science, University of Otago, 55/47 Union St W, Dunedin, 9016, New Zealand
| | - M M Tymko
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - K N Thomas
- Department of Surgical Sciences, University of Otago, 201 Great King St, Dunedin, 9016, New Zealand
| | - L C Wilson
- Department of Medicine, University of Otago, 201 Great King St, Dunedin, 9016, New Zealand
| | - M Stembridge
- Cardiff Centre for Exercise and Health, Cardiff Metropolitan University, Cyncoed Road, Cardiff, CF23 6XD, UK
| | - H G Caldwell
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - C A Howe
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - R L Hoiland
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - A P Akerman
- Faculty of Health Sciences, University of Ottawa, 125 University St, Ottawa, Ontario, Canada, K1N 6N5
| | - T G Dawkins
- Cardiff Centre for Exercise and Health, Cardiff Metropolitan University, Cyncoed Road, Cardiff, CF23 6XD, UK
| | - A Patrician
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - G B Coombs
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - C Gasho
- Division of Pulmonary, Critical Care, Hyperbaric and Sleep Medicine, Loma Linda University School of Medicine, Loma Linda, CA, USA
| | - B S Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, UK
| | - P N Ainslie
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - J D Cotter
- School of Physical Education, Sport & Exercise Science, University of Otago, 55/47 Union St W, Dunedin, 9016, New Zealand
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Dominelli PB, Baker SE, Wiggins CC, Stewart GM, Sajgalik P, Shepherd JRA, Roberts SK, Roy TK, Curry TB, Hoyer JD, Oliveira JL, Foster GE, Joyner MJ. Dissociating the effects of oxygen pressure and content on the control of breathing and acute hypoxic response. J Appl Physiol (1985) 2019; 127:1622-1631. [PMID: 31647724 PMCID: PMC6962610 DOI: 10.1152/japplphysiol.00569.2019] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Revised: 10/18/2019] [Accepted: 10/20/2019] [Indexed: 11/22/2022] Open
Abstract
Arterial oxygen tension and oxyhemoglobin saturation (S a O 2 ) decrease in parallel during hypoxia. Distinguishing between changes in oxygen tension and oxygen content as the relevant physiological stimulus for cardiorespiratory alterations remains challenging. To overcome this, we recruited nine individuals with hemoglobinopathy manifesting as high-affinity hemoglobin [HAH; partial pressure at 50% S a O 2 (P50) = 16 ± 0.4 mmHg] causing greater S a O 2 at a given oxygen partial pressure compared with control subjects (n = 12, P50 = 26 ± 0.4 mmHg). We assessed ventilatory and cardiovascular responses to acute isocapnic hypoxia, iso-oxic hypercapnia, and 20 min of isocapnic hypoxia (arterial Po2 = 50 mmHg). Blood gas alterations were achieved with dynamic end-tidal forcing. When expressed as a function of the logarithm of oxygen partial pressure, ventilatory sensitivity to hypoxia was not different between groups. However, there was a significant difference when expressed as a function of S a O 2 . Conversely, the rise in heart rate was blunted in HAH subjects when expressed as a function of partial pressure but similar when expressed as a function of S a O 2 . Ventilatory sensitivity to hypercapnia was not different between groups. During sustained isocapnic hypoxia, the rise in minute ventilation was similar between groups; however, heart rate was significantly greater in the controls during 3 to 9 min of exposure. Our results support the notion that oxygen tension, not content, alters cellular Po2 in the chemosensors and drives the hypoxic ventilatory response. Our study suggests that in addition to oxygen partial pressure, oxygen content may also influence the heart rate response to hypoxia.NEW & NOTEWORTHY We dissociated the effects of oxygen content and pressure of cardiorespiratory regulation studying individuals with high-affinity hemoglobin (HAH). During hypoxia, the ventilatory response, expressed as a function of oxygen tension, was similar between HAH variants and controls; however, the rise in heart rate was blunted in the variants. Our work supports the notion that the hypoxic ventilatory response is regulated by oxygen tension, whereas cardiovascular regulation may be influenced by arterial oxygen content and tension.
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Affiliation(s)
- Paolo B Dominelli
- Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | - Sarah E Baker
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | - Chad C Wiggins
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | - Glenn M Stewart
- Department of Cardiovascular Disease, Mayo Clinic, Rochester, Minnesota
| | - Pavol Sajgalik
- Department of Cardiovascular Disease, Mayo Clinic, Rochester, Minnesota
| | - John R A Shepherd
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | - Shelly K Roberts
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | - Tuhin K Roy
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | - Timothy B Curry
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | - James D Hoyer
- Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota
| | - Jennifer L Oliveira
- Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota
| | - Glen E Foster
- School of Health and Exercise Science, University of British Columbia, Kelowna, British Columbia, Canada
| | - Michael J Joyner
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
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Hansen RK, Nielsen PS, Schelske MW, Secher NH, Volianitis S. CO 2 supplementation dissociates cerebral oxygenation and middle cerebral artery blood velocity during maximal cycling. Scand J Med Sci Sports 2019; 30:399-407. [PMID: 31650627 DOI: 10.1111/sms.13582] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Revised: 09/28/2019] [Accepted: 10/21/2019] [Indexed: 12/15/2022]
Abstract
This study evaluated whether the reduction of prefrontal cortex oxygenation (ScO2 ) during maximal exercise depends on the hyperventilation-induced hypocapnic attenuation of middle cerebral artery blood velocity (MCA Vmean ). Twelve endurance-trained males (age: 25 ± 3 years, height: 183 ± 8 cm, weight: 75 ± 9 kg; mean ± SD) performed in three separate laboratory visits, a maximal oxygen uptake (VO2 max) test, an isocapnic (end-tidal CO2 tension (PetCO2 ) clamped at 40 ± 1 mmHg), and an ambient air controlled-pace constant load high-intensity ergometer cycling to exhaustion, while MCA Vmean (transcranial Doppler ultrasound) and ScO2 (near-infrared spectroscopy) were determined. Duration of exercise (12 min 25 s ± 1 min 18 s) was matched by performing the isocapnic trial first. Pulmonary VO2 was 90 ± 6% versus 93 ± 5% of the maximal value (P = .012) and PetCO2 40 ± 1 versus 34 ± 4 mmHg (P < .05) during the isocapnic and control trials, respectively. During the isocapnic trial MCA Vmean increased by 16 ± 13% until clamping was applied and continued to increase (by 14 ± 28%; P = .017) until the end of exercise, while there was no significant change during the control trial (P = .071). In contrast, ScO2 decreased similarly in both trials (-3.2 ± 5.1% and -4.1 ± 9.6%; P < .001, isocapnic and control, respectively) at exhaustion. The reduction in prefrontal cortex oxygenation during maximal exercise does not depend solely on lowered cerebral blood flow as indicated by middle cerebral blood velocity.
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Affiliation(s)
- Rasmus K Hansen
- Sport Sciences, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
| | - Peter S Nielsen
- Sport Sciences, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
| | - Markus W Schelske
- Sport Sciences, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
| | - Niels H Secher
- Department of Anaesthesia, The Copenhagen Muscle Research Centre, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | - Stefanos Volianitis
- Sport Sciences, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark.,Department of Anaesthesia, The Copenhagen Muscle Research Centre, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
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Teppema LJ, Boulet LM, Hackett HK, Dominelli PB, Cheyne WS, Dominelli GS, Swenson ER, Foster GE. Influence of methazolamide on the human control of breathing: A comparison to acetazolamide. Exp Physiol 2019; 105:293-301. [PMID: 31595565 DOI: 10.1113/ep088058] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Accepted: 10/04/2019] [Indexed: 01/15/2023]
Abstract
NEW FINDINGS What is the central question of this study? Acetazolamide and methazolamide both reduce hypoxic pulmonary vasoconstriction equally, but methazolamide does not impair skeletal muscle function. The effect of methazolamide on respiratory control in humans is not yet known. What is the main finding and its importance? Similar to acetazolamide after chronic oral administration, methazolamide causes a metabolic acidosis and shifts the ventilatory CO2 response curve leftwards without reducing O2 sensitivity. The change in ventilation over the change in log P O 2 provides a more accurate measure of hypoxic sensitivity than the change in ventilation over the change in arterial oxyhaemoglobin saturation. ABSTRACT Acetazolamide is used to prevent/treat acute mountain sickness and both central and obstructive sleep apnoea. Methazolamide, like acetazolamide, reduces hypoxic pulmonary vasoconstriction, but has fewer side-effects, including less impairment of skeletal muscle function. Given that the effects of methazolamide on respiratory control in humans are unknown, we compared the effects of oral methazolamide and acetazolamide on ventilatory control and determined the ventilation-log P O 2 relationship in humans. In a double-blind, placebo-controlled, randomized cross-over design, we studied the effects of acetazolamide (250 mg three times daily), methazolamide (100 mg twice daily) and placebo in 14 young male subjects who were exposed to 7 min of normoxic hypercapnia and to three levels of eucapnia and hypercapnic hypoxia. With placebo, methazolamide and acetazolamide, the CO2 sensitivities were 2.39 ± 1.29, 3.27 ± 1.82 and 2.62 ± 1.79 l min-1 mmHg-1 (n.s.) and estimated apnoeic thresholds 32 ± 3, 28 ± 3 and 26 ± 3 mmHg, respectively (P < 0.001, placebo versus methazolamide and acetazolamide). The relationship between ventilation ( V ̇ I ) and log P O 2 (using arterialized venous P O 2 in hypoxia) was linear, and neither agent influenced the relationship between hypoxic sensitivity ( Δ V ̇ I / Δ log P O 2 ) and arterial [H+ ]. Using Δ V ̇ I / Δ log P O 2 rather than Δ V ̇ I /Δ arterial oxyhaemoglobin saturation enables a more accurate estimation of oxygenation and ventilatory control in metabolic acidosis/alkalosis when right- or leftward shifts of the oxyhaemoglobin saturation curve occur. Given that acetazolamide and methazolamide have similar effects on ventilatory control, methazolamide might be preferred for indications requiring the use of a carbonic anhydrase inhibitor, avoiding some of the negative side-effects of acetazolamide.
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Affiliation(s)
- Luc J Teppema
- Department of Anesthesiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Lindsey M Boulet
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Heather K Hackett
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Paolo B Dominelli
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada.,Department of Kinesiology, University of Waterloo, Waterloo, ON, Canada
| | - William S Cheyne
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Giulio S Dominelli
- Southern Medical Program, University of British Columbia, Kelowna, BC, Canada
| | - Erik R Swenson
- Division of Pulmonary & Critical Care Medicine, VA Puget Sound Health Care System, University of Washington, Seattle, WA, USA
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
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Hoiland RL, Fisher JA, Ainslie PN. Regulation of the Cerebral Circulation by Arterial Carbon Dioxide. Compr Physiol 2019; 9:1101-1154. [DOI: 10.1002/cphy.c180021] [Citation(s) in RCA: 101] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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38
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Patrician A, Tymko MM, Caldwell HG, Howe CA, Coombs GB, Stone R, Hamilton A, Hoiland RL, Ainslie PN. The Effect of an Expiratory Resistance Mask with Dead Space on Sleep, Acute Mountain Sickness, Cognition, and Ventilatory Acclimatization in Normobaric Hypoxia. High Alt Med Biol 2019; 20:61-70. [PMID: 30720346 DOI: 10.1089/ham.2018.0074] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
We examined the hypothesis that an expiratory resistance mask containing a small amount of dead space (ER/DS) would reduce the apnea-hypopnea index (AHI) during sleep, attenuate the severity of acute mountain sickness (AMS), and offset decrements in cognitive function compared with a sham mask. In a double-blinded, randomized, sham-controlled, crossover design, 19 volunteers were exposed to two nights of normobaric hypoxia (FIO2 = 0.125), using a ER/DS mask (3.5 mm restrictive expiratory orifice; 125 mL DS volume) and sham mask (zero-flow resistance; 50 mL DS volume). Cognitive function, AMS, and ventilatory acclimatization were assessed before and after the 12-hour normobaric hypoxia exposure. Polysomnography was conducted during sleep. AHI was reduced using the ER/DS sleep mask compared with the sham (30.1 ± 23.9 events·hr-1 vs. 58.9 ± 34.4 events·hr-1, respectively; p = 0.01). Likewise, oxygen desaturation index and headache severity were reduced (both p < 0.05). There were also benefits on limiting the hypoxia-induced reductions in select measures of reaction speed and attention (p < 0.05). Our study indicates that a simple noninvasive and portable ER/DS mask resulted in reductions (49%) in AHI, and reduced headache severity and aspects of cognitive decline. The field applications of this ER/DS mask should be investigated before recommendations can be made to support its benefit for travel to high altitude.
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Affiliation(s)
- Alexander Patrician
- Center for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Kelowna, Canada
| | - Michael M Tymko
- Center for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Kelowna, Canada
| | - Hannah G Caldwell
- Center for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Kelowna, Canada
| | - Connor A Howe
- Center for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Kelowna, Canada
| | - Geoff B Coombs
- Center for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Kelowna, Canada
| | - Rachel Stone
- Center for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Kelowna, Canada
| | - Allison Hamilton
- Center for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Kelowna, Canada
| | - Ryan L Hoiland
- Center for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Kelowna, Canada
| | - Philip N Ainslie
- Center for Heart, Lung and Vascular Health, University of British Columbia, Okanagan, Kelowna, Canada
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Stone RM, Ainslie PN, Kerstens TP, Wildfong KW, Tymko MM. Sex differences in the circulatory responses to an isocapnic cold pressor test. Exp Physiol 2018; 104:295-305. [PMID: 30578582 DOI: 10.1113/ep087232] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2018] [Accepted: 12/19/2018] [Indexed: 01/04/2023]
Abstract
NEW FINDINGS What is the central question of this study? Do sex differences exist in the cardiorespiratory responses to an isocapnic cold pressor test (CPT)? What is the main finding and its importance? During the CPT, there were no sex differences in the respiratory response; however, females demonstrated a reduced mean arterial pressure and reduced dilatation of the common carotid artery. Given that the CPT is predictive of future cardiovascular events, these data have clinical implications for improving the utility of the CPT to determine cardiovascular health risk. Sex differences should be taken into consideration when conducting and interpreting a CPT. ABSTRACT The cold pressor test (CPT) elicits a transient increase in sympathetic nervous activity, minute ventilation ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mi>E</mml:mi></mml:msub> </mml:math> ), mean arterial pressure (MAP) and common carotid artery (CCA) diameter in healthy individuals. Although the extent of dilatation of the CCA in response to the CPT has been used as a clinical indicator of cardiovascular health status, the potential sex differences have yet to be explored. In response to a CPT, we hypothesized that elevations in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mi>E</mml:mi></mml:msub> </mml:math> and MAP and dilatation of the CCA would be attenuated in females compared with males. In 20 young, healthy participants (10 females), we measured the respiratory, cardiovascular and CCA responses during a CPT, which consisted of a 3 min immersion of the right foot into 0-1 ice water. Blood pressure (via finger photoplethysmography), heart rate (via electrocardiogram) and CCA diameter and velocity (via Duplex ultrasound) were simultaneously recorded immediately before and during the CPT. During the CPT, while controlling end-tidal gases to baseline values, the main findings were as follows: (i) no sex differences were present in absolute or relative changes in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mi>E</mml:mi></mml:msub> </mml:math> (P = 0.801 and P = 0.179, respectively); (ii) the relative MAP and CCA diameter response were reduced in females by 51 and 55%, respectively (P = 0.008 and P = 0.029 versus males, respectively); and (iii) the relative MAP responses was positively correlated with the dilatation of the CCA in males (r = 0.42, P = 0.019), in females (r = 0.43, P = 0.019) and in males and females combined (r = 0.55, P < 0.001). Given that the CPT is used as a clinical tool to assess cardiovascular health status, sex differences should be considered in future studies.
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Affiliation(s)
- Rachel M Stone
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Thijs P Kerstens
- Department of Physiology, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Kevin W Wildfong
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Michael M Tymko
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
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Davis JT, Boulet LM, Hardin AM, Chang AJ, Lovering AT, Foster GE. Ventilatory responses to acute hypoxia and hypercapnia in humans with a patent foramen ovale. J Appl Physiol (1985) 2018; 126:730-738. [PMID: 30521423 DOI: 10.1152/japplphysiol.00741.2018] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Subjects with a patent foramen ovale (PFO) have blunted ventilatory acclimatization to high altitude compared with subjects without PFO. The blunted response observed could be because of differences in central and/or peripheral respiratory chemoreflexes. We hypothesized that compared with subjects without a PFO (PFO-), subjects with a PFO (PFO+) would have blunted ventilatory responses to acute hypoxia and hypercapnia. Sixteen PFO+ subjects (9 female) and 15 PFO- subjects (8 female) completed four 20-min trials on the same day: 1) normoxic hypercapnia (NH), 2) hyperoxic hypercapnia (HH), 3) isocapnic hypoxia (IH), and 4) poikilocapnic hypoxia (PH). Hypercapnic trials were completed before the hypoxic trials, the order of the hypercapnic (NH & HH) and hypoxic (IH & PH) trials were randomized, and trials were separated by ≥40 min. During the NH trials but not the HH trials subjects who were PFO+ had a blunted hypercapnic ventilatory response compared with subjects who were PFO- (1.41 ± 0.46 l·min-1·mmHg-1 vs. 1.98 ± 0.71 l·min-1·mmHg-1, P = 0.02). There were no differences between the PFO+ and PFO- subjects with respect to the acute hypoxic ventilatory response during IH and PH trials. Hypoxic ventilatory depression was similar between subjects who were PFO+ and PFO- during IH. These data suggest that compared with subjects who were PFO-, subjects who were PFO+ have normal ventilatory chemosensitivity to acute hypoxia but blunted ventilatory chemosensitivity to carbon dioxide, possibly because of reduced carbon dioxide sensitivity of either the central and/or the peripheral chemoreceptors. NEW & NOTEWORTHY Patent foramen ovale (PFO) is found in ~25%-40% of the population. The presence of a PFO appears to be associated with blunted ventilatory responses during acute exposure to normoxic hypercapnia. The reason for this blunted ventilatory response during acute exposure to normoxic hypercapnia is unknown but may suggest differences in either central and/or peripheral chemoreflex contribution to hypercapnia.
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Affiliation(s)
- James T Davis
- Indiana State University, Department of Kinesiology, Recreation, and Sport, Terre Haute, Indiana
| | - Lindsey M Boulet
- University of British Columbia, Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science , Kelowna, BC , Canada
| | - Alyssa M Hardin
- University of Oregon, Department of Human Physiology , Eugene, Oregon
| | - Alex J Chang
- University of Oregon, Department of Human Physiology , Eugene, Oregon
| | - Andrew T Lovering
- University of Oregon, Department of Human Physiology , Eugene, Oregon
| | - Glen E Foster
- University of British Columbia, Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science , Kelowna, BC , Canada
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41
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Nowak-Flück D, Ainslie PN, Bain AR, Ahmed A, Wildfong KW, Morris LE, Phillips AA, Fisher JP. Effect of healthy aging on cerebral blood flow, CO2 reactivity, and neurovascular coupling during exercise. J Appl Physiol (1985) 2018; 125:1917-1930. [DOI: 10.1152/japplphysiol.00050.2018] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
We sought to make the first comparisons of duplex Doppler ultrasonography-derived measures of cerebral blood flow during exercise in young and older individuals and to assess whether healthy aging influences the effect of exercise on neurovascular coupling (NVC) and cerebral vascular reactivity to changes in carbon dioxide (CVRco2). In 10 healthy young (23 ± 2 yr; mean ± SD) and 9 healthy older (66 ± 3 yr) individuals, internal carotid artery (ICA) and vertebral artery (VA) blood flows were concurrently measured, along with middle and posterior cerebral artery mean blood velocity (MCAvmean and PCAvmean). Measures were made at rest and during leg cycling (75 W and 35% maximum aerobic workload). ICA and VA blood flow during dynamic exercise, undertaken at matched absolute (ICA: young 336 ± 95, older 352 ± 155; VA: young 95 ± 43, older 100 ± 30 ml/min) and relative (ICA: young 355 ± 125, older 323 ± 153; VA: young 115 ± 48, older 110 ± 32 ml/min) intensities, were not different between groups ( P > 0.670). The PCAvmean responses to visual stimulation (NVC) were blunted in older versus younger group at rest (16 ± 6% vs. 23 ± 7%, P < 0.026) and exercise; however, these responses were not changed from rest to exercise in either group. The ICA and VA CVRco2 were comparable in both groups and unaltered during exercise. Collectively, our findings suggest that 1) ICA and VA blood flow responses to dynamic exercise are similar in healthy young and older individuals, 2) NVC is blunted in healthy older individuals at rest and exercise but is not different between rest to exercise in either group, and 3) CVRco2 is similar during exercise in healthy young and older groups. NEW & NOTEWORTHY Internal carotid artery and vertebral artery blood flow responses to dynamic exercise are similar in healthy young and older individuals. Neurovascular coupling and cerebrovascular carbon dioxide reactivity, two key mechanisms mediating the cerebral blood flow responses to exercise, are generally unaffected by exercise in both healthy young and older individuals.
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Affiliation(s)
- Daniela Nowak-Flück
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Philip N. Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Anthony R. Bain
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Amar Ahmed
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom
| | - Kevin W. Wildfong
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Laura E. Morris
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Aaron A. Phillips
- Departments of Physiology and Pharmacology and Clinical Neurosciences, Libin Cardiovascular Institute, Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - James P. Fisher
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom
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Steventon JJ, Hansen AB, Whittaker JR, Wildfong KW, Nowak-Flück D, Tymko MM, Murphy K, Ainslie PN. Cerebrovascular Function in the Large Arteries Is Maintained Following Moderate Intensity Exercise. Front Physiol 2018; 9:1657. [PMID: 30519192 PMCID: PMC6258791 DOI: 10.3389/fphys.2018.01657] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Accepted: 11/02/2018] [Indexed: 01/13/2023] Open
Abstract
Exercise has been shown to induce cerebrovascular adaptations. However, the underlying temporal dynamics are poorly understood, and regional variation in the vascular response to exercise has been observed in the large cerebral arteries. Here, we sought to measure the cerebrovascular effects of a single 20-min session of moderate-intensity exercise in the one hour period immediately following exercise cessation. We employed transcranial Doppler (TCD) ultrasonography to measure cerebral blood flow velocity (CBFV) in the middle cerebral artery (MCAv) and posterior cerebral artery (PCAv) before, during, and following exercise. Additionally, we simultaneously measured cerebral blood flow (CBF) in the internal carotid artery (ICA) and vertebral artery (VA) before and up to one hour following exercise cessation using Duplex ultrasound. A hypercapnia challenge was used before and after exercise to examine exercise-induced changes in cerebrovascular reactivity (CVR). We found that MCAv and PCAv were significantly elevated during exercise (p = 4.81 × 10-5 and 2.40 × 10-4, respectively). A general linear model revealed that these changes were largely explained by the partial pressure of end-tidal CO2 and not a direct vascular effect of exercise. After exercise cessation, there was no effect of exercise on CBFV or CVR in the intracranial or extracranial arteries (all p > 0.05). Taken together, these data confirm that CBF is rapidly and uniformly regulated following exercise cessation in healthy young males.
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Affiliation(s)
- Jessica J Steventon
- Neuroscience and Mental Health Research Institute, School of Medicine, Cardiff University, Cardiff, United Kingdom.,Cardiff University Brain Research Imaging Centre, School of Physics and Astronomy, Cardiff University, Cardiff, United Kingdom
| | - Alex B Hansen
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Joseph R Whittaker
- Cardiff University Brain Research Imaging Centre, School of Physics and Astronomy, Cardiff University, Cardiff, United Kingdom
| | - Kevin W Wildfong
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Daniela Nowak-Flück
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Michael M Tymko
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, BC, Canada
| | - Kevin Murphy
- Cardiff University Brain Research Imaging Centre, School of Physics and Astronomy, Cardiff University, Cardiff, United Kingdom
| | - Phil N Ainslie
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, BC, Canada
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Willie CK, Stembridge M, Hoiland RL, Tymko MM, Tremblay JC, Patrician A, Steinback C, Moore J, Anholm J, Subedi P, Niroula S, McNeil CJ, McManus A, MacLeod DB, Ainslie PN. UBC-Nepal Expedition: An experimental overview of the 2016 University of British Columbia Scientific Expedition to Nepal Himalaya. PLoS One 2018; 13:e0204660. [PMID: 30379823 PMCID: PMC6209169 DOI: 10.1371/journal.pone.0204660] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Accepted: 09/12/2018] [Indexed: 01/04/2023] Open
Abstract
The University of British Columbia Nepal Expedition took place over several months in the fall of 2016 and was comprised of an international team of 37 researchers. This paper describes the objectives, study characteristics, organization and management of this expedition, and presents novel blood gas data during acclimatization in both lowlanders and Sherpa. An overview and framework for the forthcoming publications is provided. The expedition conducted 17 major studies with two principal goals—to identify physiological differences in: 1) acclimatization; and 2) responses to sustained high-altitude exposure between lowland natives and people of Tibetan descent. We performed observational cohort studies of human responses to progressive hypobaric hypoxia (during ascent), and to sustained exposure to 5050 m over 3 weeks comparing lowlander adults (n = 30) with Sherpa adults (n = 24). Sherpa were tested both with (n = 12) and without (n = 12) descent to Kathmandu. Data collected from lowlander children (n = 30) in Canada were compared with those collected from Sherpa children (n = 57; 3400–3900m). Studies were conducted in Canada (344m) and the following locations in Nepal: Kathmandu (1400m), Namche Bazaar (3440m), Kunde Hospital (3480m), Pheriche (4371m) and the Ev-K2-CNR Research Pyramid Laboratory (5050m). The core studies focused on the mechanisms of cerebral blood flow regulation, the role of iron in cardiopulmonary regulation, pulmonary pressures, intra-ocular pressures, cardiac function, neuromuscular fatigue and function, blood volume regulation, autonomic control, and micro and macro vascular function. A total of 335 study sessions were conducted over three weeks at 5050m. In addition to an overview of this expedition and arterial blood gas data from Sherpa, suggestions for scientists aiming to perform field-based altitude research are also presented. Together, these findings will contribute to our understanding of human acclimatization and adaptation to the stress of residence at high-altitude.
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Affiliation(s)
- Christopher K. Willie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia – Okanagan, Kelowna, British Columbia, Canada
| | - Michael Stembridge
- Cardiff Centre for Exercise and Health, Cardiff School of Sport, Cardiff Metropolitan University, Cardiff, United Kingdom
| | - Ryan L. Hoiland
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia – Okanagan, Kelowna, British Columbia, Canada
| | - Michael M. Tymko
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia – Okanagan, Kelowna, British Columbia, Canada
| | - Joshua C. Tremblay
- Cardiovascular Stress Response Laboratory, School of Kinesiology and Health Studies, Queen’s University, Kingston, Ontario, Canada
| | - Alexander Patrician
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia – Okanagan, Kelowna, British Columbia, Canada
| | | | - Jonathan Moore
- Bangor University, School of Sport, Health & Exercise Sciences, Gwynedd, Wales, United Kingdom
| | - James Anholm
- Pulmonary/Critical Care Section, VA Loma Linda Healthcare System, Loma Linda, California, United States of America
| | - Prajan Subedi
- Paloma Medical Group, San Juan Capistrano, California, United States of America
| | | | - Chris J. McNeil
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia – Okanagan, Kelowna, British Columbia, Canada
| | - Ali McManus
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia – Okanagan, Kelowna, British Columbia, Canada
| | - David B. MacLeod
- Human Pharmacology & Physiology Lab, Duke University Medical Center, Durham, North Carolina, United States of America
| | - Philip N. Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia – Okanagan, Kelowna, British Columbia, Canada
- * E-mail:
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Vermeulen TD, Boulet LM, Stembridge M, Williams AM, Anholm JD, Subedi P, Gasho C, Ainslie PN, Feigl EO, Foster GE. Influence of myocardial oxygen demand on the coronary vascular response to arterial blood gas changes in humans. Am J Physiol Heart Circ Physiol 2018; 315:H132-H140. [PMID: 29600897 DOI: 10.1152/ajpheart.00689.2017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It remains unclear if the human coronary vasculature is inherently sensitive to changes in arterial Po2 and Pco2 or if coronary vascular responses are the result of concomitant increases in myocardial O2 consumption/demand ([Formula: see text]). We hypothesized that the coronary vascular response to Po2 and Pco2 would be attenuated in healthy men when [Formula: see text] was attenuated with β1-adrenergic receptor blockade. Healthy men (age: 25 ± 1 yr, n = 11) received intravenous esmolol (β1-adrenergic receptor antagonist) or volume-matched saline in a double-blind, randomized crossover study and were exposed to poikilocapnic hypoxia, isocapnic hypoxia, and hypercapnic hypoxia. Measurements made at baseline and after 5 min of steady state at each gas manipulation included left anterior descending coronary blood velocity (LADV; Doppler echocardiography), heart rate, and arterial blood pressure. LADV values at the end of each hypoxic condition were compared between esmolol and placebo. The rate-pressure product (RPP) and left ventricular mechanical energy (MELV) were calculated as indexes of [Formula: see text]. All gas manipulations augmented RPP, MELV, and LADV, but only RPP and MELV were attenuated (4-18%) after β1-adrenergic receptor blockade ( P < 0.05). Despite attenuated RPP and MELV responses, β1-adrenergic receptor blockade did not attenuate the mean LADV vasodilatory response compared with placebo during poikilocapnic hypoxia (29.4 ± 2.2 vs. 27.3 ± 1.6 cm/s) and isocapnic hypoxia (29.5 ± 1.5 vs. 30.3 ± 2.2 cm/s). Hypercapnic hypoxia elicited a feedforward coronary dilation that was blocked by β1-adrenergic receptor blockade. These results indicate a direct influence of arterial Po2 on coronary vascular regulation that is independent of [Formula: see text]. NEW & NOTEWORTHY In humans, arterial hypoxemia led to an increase in epicardial coronary artery blood velocity. β1-Adrenergic receptor blockade did not diminish the hypoxemic coronary response despite reduced myocardial O2 demand. These data indicate hypoxemia can regulate coronary blood flow independent of myocardial O2 consumption. A plateau in the mean left anterior descending coronary artery blood velocity-rate-pressure product relationship suggested β1-adrenergic receptor-mediated, feedforward epicardial coronary artery dilation. In addition, we observed a synergistic effect of Po2 and Pco2 during hypercapnic hypoxia.
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Affiliation(s)
- Tyler D Vermeulen
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia , Kelowna, British Columbia , Canada
| | - Lindsey M Boulet
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia , Kelowna, British Columbia , Canada
| | - Mike Stembridge
- Cardiff School of Sport, Cardiff Metropolitan University , Cardiff , United Kingdom
| | - Alexandra M Williams
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia , Kelowna, British Columbia , Canada
| | | | | | - Chris Gasho
- Loma Linda University , Loma Linda, California
| | - Philip N Ainslie
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia , Kelowna, British Columbia , Canada
| | - Eric O Feigl
- Department of Physiology and Biophysics, University of Washington , Seattle, Washington
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia , Kelowna, British Columbia , Canada
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Hansen AB, Hoiland RL, Lewis NCS, Tymko MM, Tremblay JC, Stembridge M, Nowak-Flück D, Carter HH, Bailey DM, Ainslie PN. UBC-Nepal expedition: The use of oral antioxidants does not alter cerebrovascular function at sea level or high altitude. Exp Physiol 2018; 103:523-534. [DOI: 10.1113/ep086887] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2018] [Accepted: 02/05/2018] [Indexed: 12/19/2022]
Affiliation(s)
- Alexander B. Hansen
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences; University of British Columbia, Okanagan Campus; Kelowna BC Canada
| | - Ryan L. Hoiland
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences; University of British Columbia, Okanagan Campus; Kelowna BC Canada
| | - Nia C. S. Lewis
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences; University of British Columbia, Okanagan Campus; Kelowna BC Canada
| | - Michael M. Tymko
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences; University of British Columbia, Okanagan Campus; Kelowna BC Canada
| | - Joshua C. Tremblay
- Cardiovascular Stress Response Laboratory, School of Kinesiology and Health Studies; Queen's University; Kingston ON Canada
| | - Michael Stembridge
- Cardiff Centre for Exercise and Health; Cardiff Metropolitan University; Cardiff UK
| | - Daniela Nowak-Flück
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences; University of British Columbia, Okanagan Campus; Kelowna BC Canada
| | - Howard H. Carter
- Department of Nutrition, Exercise and Sports; University of Copenhagen; Copenhagen Denmark
| | - Damian M. Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education; University of South Wales; Newport UK
| | - Philip N. Ainslie
- Centre for Heart, Lung & Vascular Health, School of Health and Exercise Sciences; University of British Columbia, Okanagan Campus; Kelowna BC Canada
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46
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Caldwell HG, Coombs GB, Tymko MM, Nowak-Flück D, Ainslie PN. Severity-dependent influence of isocapnic hypoxia on reaction time is independent of neurovascular coupling. Physiol Behav 2018; 188:262-269. [PMID: 29458114 DOI: 10.1016/j.physbeh.2018.02.035] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2018] [Revised: 02/16/2018] [Accepted: 02/16/2018] [Indexed: 12/23/2022]
Abstract
With exposure to acute normobaric hypoxia, global cerebral oxygen delivery is maintained via increases in cerebral blood flow (CBF); therefore, regional and localized changes in oxygen tension may explain neurocognitive impairment. Neurovascular coupling (NVC) is the close temporal and regional relationship of CBF to changes in neural activity and may aid in explaining the localized CBF response with cognitive activation. High-altitude related cognitive impairment is likely affected by hypocapnic cerebral vasoconstriction that may influence regional CBF regulation independent of hypoxia. We assessed neurocognition and NVC following 30 min of acute exposure to isocapnic hypoxia (decreased partial pressure of end-tidal oxygen; PETO2) during moderate hypoxia (MOD HX; 55 mm Hg PETO2), and severe hypoxia (SEV HX; 45 mm Hg PETO2) in 10 healthy individuals (25.5 ± 3.3 yrs). Transcranial Doppler ultrasound was used to assess mean posterior and middle cerebral blood velocity (PCAv and MCAv, respectively) and neurocognitive performance was assessed via validated computerized tests. The main finding was that reaction time (i.e., kinesthetic and visual-motor ability via Stroop test) was selectively impaired in SEV HX (-4.6 ± 5.2%, P = 0.04), but not MOD HX, while complex cognitive performance (e.g., psychomotor speed, cognitive flexibility, processing speed, executive function, and motor speed) was unaffected with hypoxia (P > 0.05). Additionally, severity of hypoxia had no effect on NVC (PCAv CON vs. SEV HX relative peak response 13.7 ± 6.4% vs. 16.2 ± 11.5%, P = 0.71, respectively). In summary, severe isocapnic hypoxia impaired reaction time, but not complex cognitive performance or NVC. These findings have implications for recreational and military personnel who may experience acute hypoxia.
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Affiliation(s)
- Hannah G Caldwell
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan, Kelowna, Canada.
| | - Geoff B Coombs
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan, Kelowna, Canada
| | - Michael M Tymko
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan, Kelowna, Canada
| | - Daniela Nowak-Flück
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan, Kelowna, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan, Kelowna, Canada
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47
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Lewis NCS, Bain AR, Wildfong KW, Green DJ, Ainslie PN. Acute hypoxaemia and vascular function in healthy humans. Exp Physiol 2017; 102:1635-1646. [PMID: 28901662 DOI: 10.1113/ep086532] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Accepted: 09/11/2017] [Indexed: 02/03/2023]
Abstract
NEW FINDINGS What is the central question of this study? Endothelium-dependent flow-mediated dilatation (FMD) is impaired during acute (60 min) exposure to moderate hypoxia. We examined whether FMD is impaired to the same degree during exposure to milder hypoxia. Additionally, we assessed whether smooth muscle vasodilatory capacity [glyceryl trinitrate (GTN)-induced dilatation] is impaired during acute hypoxic exposure. What is the main finding and its importance? A graded impairment in FMD and GTN-induced dilatation was evident during acute (≤60 min) exposure to mild and moderate hypoxia. This study is the first to document these graded impairments, and provides rationale to examine the relationship between graded increases in sympathetic nerve activity with hypoxia on FMD and GTN-induced dilatation. Endothelium-dependent flow-mediated dilatation (FMD) and endothelium-independent dilatation [induced with glyceryl trinitrate (GTN)] are impaired at high altitude (5050 m), and FMD is impaired after acute exposure (<60 min) to normobaric hypoxia equivalent to ∼5050 m (inspired oxygen fraction ∼0.11). Whether GTN-induced dilatation is impaired acutely and whether FMD is impaired during milder hypoxia are unknown. Therefore, we assessed brachial FMD at baseline and after 30 min of mild (end-tidal PO2 74 ± 2 mmHg) and moderate (end-tidal PO2 50 ± 3 mmHg) normobaric hypoxia (n = 12) or normoxia (time-control trial; n = 10). We also assessed GTN-induced dilatation after the hypoxic FMD tests and in normoxia on a separate control day (n = 8). Compared with the normoxic baseline, reductions during mild and moderate hypoxic exposure were evident in FMD (mild versus moderate, -1.2 ± 1.1 versus -3.1 ± 1.7%; P = 0.01) and GTN-induced dilatation (-2.1 ± 1.0 versus -4.2 ± 2.0%; P = 0.01); the declines in FMD and GTN-induced dilatation were greater during moderate hypoxia (P < 0.01). When allometrically corrected for baseline diameter and FMD shear rate under the curve, FMD was attenuated in both conditions (mild versus moderate, 0.6 ± 0.9 versus 0.8 ± 0.7%; P ≤ 0.01). After 30 min of normoxic time control, FMD was reduced (-0.6 ± 0.3%; P = 0.02). In summary, there was a graded impairment in FMD during mild and moderate hypoxic exposure, which appears to be influenced by shear patterns and incremental decline in smooth muscle vasodilator capacity (impaired GTN-induced dilatation). Our findings from the normoxic control study suggest the decline in FMD in acute hypoxia also appears to be influenced by 30 min of supine rest/inactivity.
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Affiliation(s)
- N C S Lewis
- Centre for Heart Lung and Vascular Health, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - A R Bain
- Centre for Heart Lung and Vascular Health, University of British Columbia Okanagan, Kelowna, British Columbia, Canada.,Department of Integrative Physiology, Integrative Vascular Biology Laboratory, The University of Colorado Boulder, Boulder, CO, USA
| | - K W Wildfong
- Centre for Heart Lung and Vascular Health, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - D J Green
- School of Sport Science, Exercise and Health, University of Western Australia, Crawley, Perth, Western Australia, Australia
| | - P N Ainslie
- Centre for Heart Lung and Vascular Health, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
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48
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Tymko MM, Kerstens TP, Wildfong KW, Ainslie PN. Cerebrovascular response to the cold pressor test - the critical role of carbon dioxide. Exp Physiol 2017; 102:1647-1660. [DOI: 10.1113/ep086585] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Accepted: 09/15/2017] [Indexed: 11/08/2022]
Affiliation(s)
- Michael M. Tymko
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science; University of British Columbia; Kelowna BC Canada
| | | | - Kevin W. Wildfong
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science; University of British Columbia; Kelowna BC Canada
| | - Philip N. Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science; University of British Columbia; Kelowna BC Canada
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49
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Rieger MG, Hoiland RL, Tremblay JC, Stembridge M, Bain AR, Flück D, Subedi P, Anholm JD, Ainslie PN. One session of remote ischemic preconditioning does not improve vascular function in acute normobaric and chronic hypobaric hypoxia. Exp Physiol 2017; 102:1143-1157. [PMID: 28699679 DOI: 10.1113/ep086441] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2017] [Accepted: 06/30/2017] [Indexed: 01/12/2023]
Abstract
NEW FINDINGS What is the central question of this study? It is suggested that remote ischemic preconditioning (RIPC) might offer protection against ischaemia-reperfusion injuries, but the utility of RIPC in high-altitude settings remains unclear. What is the main finding and its importance? We found that RIPC offers no vascular protection relative to pulmonary artery pressure or peripheral endothelial function during acute, normobaric hypoxia and at high altitude in young, healthy adults. However, peripheral chemosensitivity was heightened 24 h after RIPC at high altitude. Application of repeated short-duration bouts of ischaemia to the limbs, termed remote ischemic preconditioning (RIPC), is a novel technique that might have protective effects on vascular function during hypoxic exposures. In separate parallel-design studies, at sea level (SL; n = 16) and after 8-12 days at high altitude (HA; n = 12; White Mountain, 3800 m), participants underwent either a sham protocol or one session of four bouts of 5 min of dual-thigh-cuff occlusion with 5 min recovery. Brachial artery flow-mediated dilatation (FMD; ultrasound), pulmonary artery systolic pressure (PASP; echocardiography) and internal carotid artery (ICA) flow (ultrasound) were measured at SL in normoxia and isocapnic hypoxia (end-tidal PO2 maintained at 50 mmHg) and during normal breathing at HA. The hypoxic ventilatory response (HVR) was measured at each location. All measures at SL and HA were obtained at baseline (BL) and at 1, 24 and 48 h post-RIPC or sham. At SL, RIPC produced no changes in FMD, PASP, ICA flow, end-tidal gases or HVR in normoxia or hypoxia. At HA, although HVR increased 24 h post-RIPC compared with BL [2.05 ± 1.4 versus 3.21 ± 1.2 l min-1 (% arterial O2 saturation)-1 , P < 0.01], there were no significant differences in FMD, PASP, ICA flow and resting end-tidal gases. Accordingly, a single session of RIPC is insufficient to evoke changes in peripheral, pulmonary and cerebral vascular function in healthy adults. Although chemosensitivity might increase after RIPC at HA, this did not confer any vascular changes. The utility of a single RIPC session seems unremarkable during acute and chronic hypoxia.
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Affiliation(s)
- Mathew G Rieger
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Ryan L Hoiland
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Joshua C Tremblay
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Mike Stembridge
- Cardiff School of Sport, Cardiff Metropolitan University, Cardiff, UK
| | - Anthony R Bain
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada.,University of Colorado, Boulder, Department of Integrative Physiology, Integrative Vascular Biology Laboratory, Boulder, CO, USA
| | - Daniela Flück
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Prajan Subedi
- Pulmonary/Critical Care Section, VA Loma Linda Healthcare System, Loma Linda, CA, USA
| | - James D Anholm
- Pulmonary/Critical Care Section, VA Loma Linda Healthcare System, Loma Linda, CA, USA
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
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50
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Hoiland RL, Smith KJ, Carter HH, Lewis NC, Tymko MM, Wildfong KW, Bain AR, Green DJ, Ainslie PN. Shear-mediated dilation of the internal carotid artery occurs independent of hypercapnia. Am J Physiol Heart Circ Physiol 2017; 313:H24-H31. [DOI: 10.1152/ajpheart.00119.2017] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Revised: 04/03/2017] [Accepted: 04/03/2017] [Indexed: 12/29/2022]
Abstract
Evidence for shear stress as a regulator of carotid artery dilation in response to increased arterial CO2 was recently demonstrated in humans during sustained elevations in CO2 (hypercapnia); however, the relative contributions of CO2 and shear stress to this response remains unclear. We examined the hypothesis that, after a 30-s transient increase in arterial CO2 tension and consequent increase in internal carotid artery shear stress, internal carotid artery diameter would increase, indicating shear-mediated dilation, in the absence of concurrent hypercapnia. In 27 healthy participants, partial pressures of end-tidal O2 and CO2, ventilation (pneumotachography), blood pressure (finger photoplethysmography), heart rate (electrocardiogram), internal carotid artery flow, diameter, and shear stress (high-resolution duplex ultrasound), and middle cerebral artery blood velocity (transcranial Doppler) were measured during 4-min steady-state and transient 30-s hypercapnic tests (both +9 mmHg CO2). Internal carotid artery dilation was lower in the transient compared with steady-state hypercapnia (3.3 ± 1.9 vs. 5.3 ± 2.9%, respectively, P < 0.03). Increases in internal carotid artery shear stress preceded increases in diameter in both transient (time: 16.8 ± 13.2 vs. 59.4 ± 60.3 s, P < 0.01) and steady-state (time: 18.2 ± 14.2 vs. 110.3 ± 79.6 s, P < 0.01) tests. Internal carotid artery dilation was positively correlated with shear rate area under the curve in the transient ( r2 = 0.44, P < 0.01) but not steady-state ( r2 = 0.02, P = 0.53) trial. Collectively, these results suggest that hypercapnia induces shear-mediated dilation of the internal carotid artery in humans. This study further promotes the application and development of hypercapnia as a clinical strategy for the assessment of cerebrovascular vasodilatory function and health in humans. NEW & NOTEWORTHY Shear stress dilates the internal carotid artery in humans. This vasodilatory response occurs independent of other physiological factors, as demonstrated by our transient CO2 test, and is strongly correlated to shear area under the curve. Assessing carotid shear-mediated dilation may provide a future avenue for assessing cerebrovascular health and the risk of cerebrovascular events.
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Affiliation(s)
- Ryan L. Hoiland
- Centre for Heart, Lung, and Vascular Health, University of British Columbia Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Kurt J. Smith
- School of Sport Science, Exercise, and Health, The University of Western Australia, Crawley, Western Australia, Australia
| | - Howard H. Carter
- Department of Nutrition, Exercise, and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Nia C.S. Lewis
- Centre for Heart, Lung, and Vascular Health, University of British Columbia Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Michael M. Tymko
- Centre for Heart, Lung, and Vascular Health, University of British Columbia Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Kevin W. Wildfong
- Centre for Heart, Lung, and Vascular Health, University of British Columbia Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Anthony R. Bain
- Centre for Heart, Lung, and Vascular Health, University of British Columbia Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
- Integrative Vascular Biology Laboratory, Department of Integrative Physiology, University of Colorado Boulder, Boulder, Colorado; and
| | - Daniel J. Green
- School of Sport Science, Exercise, and Health, The University of Western Australia, Crawley, Western Australia, Australia
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom
| | - Philip N. Ainslie
- Centre for Heart, Lung, and Vascular Health, University of British Columbia Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
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