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Hoiland RL, Bain AR, Tymko MM, Rieger MG, Howe CA, Willie CK, Hansen AB, Flück D, Wildfong KW, Stembridge M, Subedi P, Anholm J, Ainslie PN. Adenosine receptor-dependent signaling is not obligatory for normobaric and hypobaric hypoxia-induced cerebral vasodilation in humans. J Appl Physiol (1985) 2017; 122:795-808. [PMID: 28082335 DOI: 10.1152/japplphysiol.00840.2016] [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: 09/19/2016] [Revised: 01/09/2017] [Accepted: 01/09/2017] [Indexed: 01/11/2023] Open
Abstract
Hypoxia increases cerebral blood flow (CBF) with the underlying signaling processes potentially including adenosine. A randomized, double-blinded, and placebo-controlled design, was implemented to determine if adenosine receptor antagonism (theophylline, 3.75 mg/Kg) would reduce the CBF response to normobaric and hypobaric hypoxia. In 12 participants the partial pressures of end-tidal oxygen ([Formula: see text]) and carbon dioxide ([Formula: see text]), ventilation (pneumotachography), blood pressure (finger photoplethysmography), heart rate (electrocardiogram), CBF (duplex ultrasound), and intracranial blood velocities (transcranial Doppler ultrasound) were measured during 5-min stages of isocapnic hypoxia at sea level (98, 90, 80, and 70% [Formula: see text]). Ventilation, [Formula: see text] and [Formula: see text], blood pressure, heart rate, and CBF were also measured upon exposure (128 ± 31 min following arrival) to high altitude (3,800 m) and 6 h following theophylline administration. At sea level, although the CBF response to hypoxia was unaltered pre- and postplacebo, it was reduced following theophylline (P < 0.01), a finding explained by a lower [Formula: see text] (P < 0.01). Upon mathematical correction for [Formula: see text], the CBF response to hypoxia was unaltered following theophylline. Cerebrovascular reactivity to hypoxia (i.e., response slope) was not different between trials, irrespective of [Formula: see text] At high altitude, theophylline (n = 6) had no effect on CBF compared with placebo (n = 6) when end-tidal gases were comparable (P > 0.05). We conclude that adenosine receptor-dependent signaling is not obligatory for cerebral hypoxic vasodilation in humans.NEW & NOTEWORTHY The signaling pathways that regulate human cerebral blood flow in hypoxia remain poorly understood. Using a randomized, double-blinded, and placebo-controlled study design, we determined that adenosine receptor-dependent signaling is not obligatory for the regulation of human cerebral blood flow at sea level; these findings also extend to high altitude.
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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;
| | - 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
| | - 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
| | - Mathew G Rieger
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Connor A Howe
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Christopher K Willie
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Alex B Hansen
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Okanagan Campus, School of Health and Exercise Sciences, Kelowna, British Columbia, Canada
| | - Daniela Flück
- 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
| | - Mike Stembridge
- Cardiff Centre for Exercise and Health, Cardiff Metropolitan University, Cardiff, United Kingdom; and
| | - Prajan Subedi
- VA Loma Linda Healthcare System and Loma Linda University School of Medicine, Loma Linda, California
| | - James Anholm
- VA Loma Linda Healthcare System and Loma Linda University School of Medicine, Loma Linda, California
| | - 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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52
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Boulet LM, Stembridge M, Tymko MM, Tremblay JC, Foster GE. The effects of graded changes in oxygen and carbon dioxide tension on coronary blood velocity independent of myocardial energy demand. Am J Physiol Heart Circ Physiol 2016; 311:H326-36. [PMID: 27233761 DOI: 10.1152/ajpheart.00107.2016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Accepted: 05/19/2016] [Indexed: 11/22/2022]
Abstract
In humans, coronary blood flow is tightly regulated by microvessels within the myocardium to match myocardial energy demand. However, evidence regarding inherent sensitivity of the microvessels to changes in arterial partial pressure of carbon dioxide and oxygen is conflicting because of the accompanied changes in myocardial energy requirements. This study aimed to investigate the changes in coronary blood velocity while manipulating partial pressures of end-tidal CO2 (Petco2) and O2 (Peto2). It was hypothesized that an increase in Petco2 (hypercapnia) or decrease in Peto2 (hypoxia) would result in a significant increase in mean blood velocity in the left anterior descending artery (LADVmean) due to an increase in both blood gases and energy demand associated with the concomitant cardiovascular response. Cardiac energy demand was assessed through noninvasive measurement of the total left ventricular mechanical energy. Healthy subjects (n = 13) underwent a euoxic CO2 test (Petco2 = -8, -4, 0, +4, and +8 mmHg from baseline) and an isocapnic hypoxia test (Peto2 = 64, 52, and 45 mmHg). LADVmean was assessed using transthoracic Doppler echocardiography. Hypercapnia evoked a 34.6 ± 8.5% (mean ± SE; P < 0.01) increase in mean LADVmean, whereas hypoxia increased LADVmean by 51.4 ± 8.8% (P < 0.05). Multiple stepwise regressions revealed that both mechanical energy and changes in arterial blood gases are important contributors to the observed changes in LADVmean (P < 0.01). In summary, regulation of the coronary vasculature in humans is mediated by metabolic changes within the heart and an inherent sensitivity to arterial blood gases.
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Affiliation(s)
- Lindsey M Boulet
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada; and
| | - Mike Stembridge
- Cardiff School of Sport, Cardiff Metropolitan University, Cardiff, United Kingdom
| | - Michael M Tymko
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada; and
| | - Joshua C Tremblay
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada; and
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada; and
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53
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Farra SD, Kessler C, Duffin J, Wells GD, Jacobs I. Clamping end-tidal carbon dioxide during graded exercise with control of inspired oxygen. Respir Physiol Neurobiol 2016; 231:28-36. [PMID: 27236039 DOI: 10.1016/j.resp.2016.05.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Revised: 03/31/2016] [Accepted: 05/25/2016] [Indexed: 11/29/2022]
Abstract
Exercise- and hypoxia-induced hyperventilation decreases the partial pressure of end-tidal carbon dioxide (PETCO2), which in turn exerts many physiological effects. Several breathing circuits that control PETCO2 have been previously described, but their designs are not satisfactory for exercise studies where changes in inspired oxygen (FIO2) may be desired. This study is the first report of a breathing system that can maintain PETCO2 constant within a single session of graded submaximal exercise and graded hypoxia. Thirteen fit and healthy subjects completed two bouts of exercise consisting of three 3min stages on a cycle ergometer with increasing exercise intensity in normoxia (Part A; 142±14, 167±14, 192±14W) or with decreasing FIO2 at a constant exercise intensity (Part B; 21, 18, and 14%). One bout was a control (CON) where PETCO2 was not manipulated, while during the other bout the investigator clamped PETCO2 within 2mmHg (CO2Clamp) using sequential gas delivery (SGD). During the final 30s of each exercise stage during CO2Clamp, PETCO2 was successfully maintained in Part A (43±4, 44±4, 44±3mmHg; P=0.44) and Part B (45±3, 46±3, 45±3mmHg; P=0.68) despite the increases in ventilation due to exercise. These findings demonstrate that this SGD circuit can be used to maintain isocapania in exercising humans during progressively increasing exercise intensities and changing FIO2.
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Affiliation(s)
- Saro D Farra
- Faculty of Kinesiology & Physical Education, University of Toronto, Toronto, Canada
| | - Cathie Kessler
- Faculty of Kinesiology & Physical Education, University of Toronto, Toronto, Canada
| | - James Duffin
- Department of Physiology, University of Toronto, Toronto, Canada
| | - Greg D Wells
- Faculty of Kinesiology & Physical Education, University of Toronto, Toronto, Canada
| | - Ira Jacobs
- Faculty of Kinesiology & Physical Education, University of Toronto, Toronto, Canada.
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54
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Hoiland RL, Tymko MM, Bain AR, Wildfong KW, Monteleone B, Ainslie PN. Carbon dioxide-mediated vasomotion of extra-cranial cerebral arteries in humans: a role for prostaglandins? J Physiol 2016; 594:3463-81. [PMID: 26880615 DOI: 10.1113/jp272012] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 02/01/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Cerebral blood flow increases during hypercapnia and decreases during hypocapnia; it is unknown if vasomotion of the internal carotid artery is implicated in these responses. Indomethacin, a non-selective cyclooxygenase inhibitor (used to inhibit prostaglandin synthesis), has a unique ability to blunt cerebrovascular carbon dioxide reactivity, while other cyclooxygenase inhibitors have no effect. We show significant dilatation and constriction of the internal carotid artery during hypercapnia and hypocapnia, respectively. Indomethacin, but not ketorolac or naproxen, reduced the dilatatory response of the internal carotid artery to hypercapnia The differential effect of indomethacin compared to ketorolac and naproxen suggests that indomethacin inhibits vasomotion of the internal carotid artery independent of prostaglandin synthesis inhibition. ABSTRACT Extra-cranial cerebral blood vessels are implicated in the regulation of cerebral blood flow during changes in arterial CO2 ; however, the mechanisms governing CO2 -mediated vasomotion of these vessels in humans remain unclear. We determined if cyclooxygenase inhibition with indomethacin (INDO) reduces the vasomotor response of the internal carotid artery (ICA) to changes in end-tidal CO2 (P ETC O2). Using a randomized single-blinded placebo-controlled study, participants (n = 10) were tested on two occasions, before and 90 min following oral INDO (1.2 mg kg(-1) ) or placebo. Concurrent measurements of beat-by-beat velocity, diameter and blood flow of the ICA were made at rest and during steady-state stages (4 min) of iso-oxic hypercapnia (+3, +6, +9 mmHg P ETC O2) and hypocapnia (-3, -6, -9 mmHg P ETC O2). To examine if INDO affects ICA vasomotion independent of cyclooxygenase inhibition, two participant subsets (each n = 5) were tested before and following oral ketorolac (post 45 min, 0.25 mg kg(-1) ) or naproxen (post 90 min, 4.2 mg kg(-1) ). During pre-drug testing in the INDO trial, the ICA dilatated during hypercapnia at +6 mmHg (4.72 ± 0.45 vs. 4.95 ± 0.51 mm; P < 0.001) and +9 mmHg (4.72 ± 0.45 mm vs. 5.12 ± 0.47 mm; P < 0.001), and constricted during hypocapnia at -6 mmHg (4.95 ± 0.33 vs. 4.88 ± 0.27 mm; P < 0.05) and -9 mmHg (4.95 ± 0.33 vs. 4.82 ± 0.27 mm; P < 0.001). Following INDO, vasomotor responsiveness of the ICA to hypercapnia was reduced by 67 ± 28% (0.045 ± 0.015 vs. 0.015 ± 0.012 mm mmHg P ETC O2(-1) ). There was no effect of the drug in the ketorolac and naproxen trials. We conclude that: (1) INDO markedly reduces the vasomotor response of the ICA to changes in P ETC O2; and (2) INDO may be reducing CO2 -mediated vasomotion via a mechanism(s) independent of cyclooxygenase inhibition.
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Affiliation(s)
- 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
| | - 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
| | - Anthony R Bain
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
| | - Kevin W Wildfong
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
| | - Brad Monteleone
- 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
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55
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Pfoh JR, Tymko MM, Abrosimova M, Boulet LM, Foster GE, Bain AR, Ainslie PN, Steinback CD, Bruce CD, Day TA. Comparing and characterizing transient and steady-state tests of the peripheral chemoreflex in humans. Exp Physiol 2016; 101:432-47. [DOI: 10.1113/ep085498] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Accepted: 11/30/2015] [Indexed: 11/08/2022]
Affiliation(s)
- Jamie R. Pfoh
- Department of Biology, Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
| | - Michael M. Tymko
- School of Health and Exercise Sciences, Faculty of Health and Social Development; University of British Columbia Okanagan; Kelowna British Columbia Canada
| | - Maria Abrosimova
- Department of Biology, Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
| | - Lindsey M. Boulet
- Department of Biology, Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
- School of Health and Exercise Sciences, Faculty of Health and Social Development; University of British Columbia Okanagan; Kelowna British Columbia Canada
| | - Glen E. Foster
- School of Health and Exercise Sciences, Faculty of Health and Social Development; University of British Columbia Okanagan; Kelowna British Columbia Canada
| | - Anthony R. Bain
- School of Health and Exercise Sciences, Faculty of Health and Social Development; University of British Columbia Okanagan; Kelowna British Columbia Canada
| | - Philip N. Ainslie
- School of Health and Exercise Sciences, Faculty of Health and Social Development; University of British Columbia Okanagan; Kelowna British Columbia Canada
| | - Craig D. Steinback
- Faculty of Physical Education and Recreation; University of Alberta; Edmonton Alberta Canada
| | - Christina D. Bruce
- Department of Biology, Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
| | - Trevor A. Day
- Department of Biology, Faculty of Science and Technology; Mount Royal University; Calgary Alberta Canada
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56
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Evans RG. Oxygen regulation in biological systems. Am J Physiol Regul Integr Comp Physiol 2016; 310:R673-8. [PMID: 26911461 DOI: 10.1152/ajpregu.00004.2016] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Accepted: 02/17/2016] [Indexed: 01/25/2023]
Affiliation(s)
- Roger G Evans
- Cardiovascular Disease Program, Biomedicine Discovery Institute and Department of Physiology, Monash University, Clayton, Melbourne, Australia
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57
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Tymko MM, Hoiland RL, Kuca T, Boulet LM, Tremblay JC, Pinske BK, Williams AM, Foster GE. Measuring the human ventilatory and cerebral blood flow response to CO2: a technical consideration for the end-tidal-to-arterial gas gradient. J Appl Physiol (1985) 2016; 120:282-96. [DOI: 10.1152/japplphysiol.00787.2015] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Accepted: 10/19/2015] [Indexed: 11/22/2022] Open
Abstract
Our aim was to quantify the end-tidal-to-arterial gas gradients for O2 (PET-PaO2) and CO2 (Pa-PETCO2) during a CO2 reactivity test to determine their influence on the cerebrovascular (CVR) and ventilatory (HCVR) response in subjects with (PFO+, n = 8) and without (PFO−, n = 7) a patent foramen ovale (PFO). We hypothesized that 1) the Pa-PETCO2 would be greater in hypoxia compared with normoxia, 2) the Pa-PETCO2 would be similar, whereas the PET-PaO2 gradient would be greater in those with a PFO, 3) the HCVR and CVR would be underestimated when plotted against PETCO2 compared with PaCO2, and 4) previously derived prediction algorithms will accurately target PaCO2. PETCO2 was controlled by dynamic end-tidal forcing in steady-state steps of −8, −4, 0, +4, and +8 mmHg from baseline in normoxia and hypoxia. Minute ventilation (V̇E), internal carotid artery blood flow (Q̇ICA), middle cerebral artery blood velocity (MCAv), and temperature corrected end-tidal and arterial blood gases were measured throughout experimentation. HCVR and CVR were calculated using linear regression analysis by indexing V̇E and relative changes in Q̇ICA, and MCAv against PETCO2, predicted PaCO2, and measured PaCO2. The Pa-PETCO2 was similar between hypoxia and normoxia and PFO+ and PFO−. The PET-PaO2 was greater in PFO+ by 2.1 mmHg during normoxia ( P = 0.003). HCVR and CVR plotted against PETCO2 underestimated HCVR and CVR indexed against PaCO2 in normoxia and hypoxia. Our PaCO2 prediction equation modestly improved estimates of HCVR and CVR. In summary, care must be taken when indexing reactivity measures to PETCO2 compared with PaCO2.
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Affiliation(s)
- Michael M. Tymko
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada; and
| | - Ryan L. Hoiland
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada; and
| | - Tomas Kuca
- Department of Anesthesia, Pain and Perioperative Medicine, Department of Critical Care Medicine, Dalhousie University, Halifax, Canada
| | - Lindsey M. Boulet
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada; and
| | - Joshua C. Tremblay
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada; and
| | - Bryenna K. Pinske
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada; and
| | - Alexandra M. Williams
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada; and
| | - Glen E. Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada; and
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58
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Smith KJ, Wildfong KW, Hoiland RL, Harper M, Lewis NC, Pool A, Smith SL, Kuca T, Foster GE, Ainslie PN. Role of CO2 in the cerebral hyperemic response to incremental normoxic and hyperoxic exercise. J Appl Physiol (1985) 2016; 120:843-54. [PMID: 26769951 DOI: 10.1152/japplphysiol.00490.2015] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Accepted: 01/11/2016] [Indexed: 11/22/2022] Open
Abstract
Cerebral blood flow (CBF) is temporally related to exercise-induced changes in partial pressure of end-tidal carbon dioxide (PetCO2 ); hyperoxia is known to enhance this relationship. We examined the hypothesis that preventing PetCO2 from rising (isocapnia) during submaximal exercise with and without hyperoxia [end-tidal Po2(PetO2 ) = 300 mmHg] would attenuate the increases in CBF. Additionally, we aimed to identify the magnitude that breathing, per se, influences the CBF response to normoxic and hyperoxic exercise. In 14 participants, CBF (intra- and extracranial) measurements were measured during exercise [20, 40, 60, and 80% of maximum workload (Wmax)] and during rest while ventilation (V̇e) was volitionally increased to mimic volumes achieved during exercise (isocapnic hyperpnea). While V̇ewas uncontrolled during poikilocapnic exercise, during isocapnic exercise and isocapnic hyperpnea, V̇ewas increased to prevent PetCO2 from rising above resting values (∼40 mmHg). Although PetCO2 differed by 2 ± 3 mmHg during normoxic poikilocapnic and isocapnic exercise, except for a greater poikilocapnic compared with isocapnic increase in blood velocity in the posterior cerebral artery at 60% Wmax, the between condition increases in intracranial (∼12-15%) and extracranial (15-20%) blood flow were similar at each workload. The poikilocapnic hyperoxic increases in both intra- and extracranial blood-flow (∼17-29%) were greater compared with poikilocapnic normoxia (∼8-20%) at intensities >40% Wmax(P< 0.01). During both normoxic and hyperoxic conditions, isocapnia normalized both the intracranial and extracranial blood-flow differences. Isocapnic hyperpnea did not alter CBF. Our findings demonstrate a differential effect of PetCO2 on CBF during exercise influenced by the prevailing PetO2.
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Affiliation(s)
- K J Smith
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada; and
| | - K W Wildfong
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada; and
| | - R L Hoiland
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada; and
| | - M Harper
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada; and
| | - N C Lewis
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada; and
| | - A Pool
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada; and
| | - S L Smith
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada; and
| | - T Kuca
- Department of Anesthesia, Pain and Perioperative Medicine, Department of Critical Care Medicine, Dalhousie University, Halifax, Nova Scotia, Canada
| | - G E Foster
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada; and
| | - P N Ainslie
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada; and
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59
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Foster GE, Davies-Thompson J, Dominelli PB, Heran MKS, Donnelly J, duManoir GR, Ainslie PN, Rauscher A, Sheel AW. Changes in cerebral vascular reactivity and structure following prolonged exposure to high altitude in humans. Physiol Rep 2015; 3:3/12/e12647. [PMID: 26660556 PMCID: PMC4760444 DOI: 10.14814/phy2.12647] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Although high‐altitude exposure can lead to neurocognitive impairment, even upon return to sea level, it remains unclear the extent to which brain volume and regional cerebral vascular reactivity (CVR) are altered following high‐altitude exposure. The purpose of this study was to simultaneously determine the effect of 3 weeks at 5050 m on: (1) structural brain alterations; and (2) regional CVR after returning to sea level for 1 week. Healthy human volunteers (n = 6) underwent baseline and follow‐up structural and functional magnetic resonance imaging (MRI) at rest and during a CVR protocol (end‐tidal PCO2 reduced by −10, −5 and increased by +5, +10, and +15 mmHg from baseline). CVR maps (% mmHg−1) were generated using BOLD MRI and brain volumes were estimated. Following return to sea level, whole‐brain volume and gray matter volume was reduced by 0.4 ± 0.3% (P < 0.01) and 2.6 ± 1.0% (P < 0.001), respectively; white matter was unchanged. Global gray matter CVR and white matter CVR were unchanged following return to sea level, but CVR was selectively increased (P < 0.05) in the brainstem (+30 ± 12%), hippocampus (+12 ± 3%), and thalamus (+10 ± 3%). These changes were the result of improvement and/or reversal of negative CVR to positive CVR in these regions. Three weeks of high‐altitude exposure is reflected in loss of gray matter volume and improvements in negative CVR.
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Affiliation(s)
- Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada School of Kinesiology, University of British Columbia, Vancouver, Canada
| | - Jodie Davies-Thompson
- Department of Ophthalmology and Visual Sciences, Faculty of Medicine, University of British Columbia, Vancouver, Canada
| | - Paolo B Dominelli
- School of Kinesiology, University of British Columbia, Vancouver, Canada
| | - Manraj K S Heran
- Diagnostic and Therapeutic Neuroradiology, Vancouver General Hospital University of British Columbia, Vancouver, Canada
| | - Joseph Donnelly
- Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK
| | - Gregory R duManoir
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, Canada
| | - Alexander Rauscher
- Department of Radiology, UBC MRI Research Centre University of British Columbia, Vancouver, Canada
| | - A William Sheel
- School of Kinesiology, University of British Columbia, Vancouver, Canada
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60
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Bain AR, Dujic Z, Hoiland RL, Barak OF, Madden D, Drvis I, Stembridge M, MacLeod DB, MacLeod DM, Ainslie PN. Peripheral chemoreflex inhibition with low-dose dopamine: new insight into mechanisms of extreme apnea. Am J Physiol Regul Integr Comp Physiol 2015; 309:R1162-71. [PMID: 26290106 DOI: 10.1152/ajpregu.00271.2015] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2015] [Accepted: 08/11/2015] [Indexed: 01/02/2023]
Abstract
The purpose of this study was to determine the impact of peripheral chemoreflex inhibition with low-dose dopamine on maximal apnea time, and the related hemodynamic and cerebrovascular responses in elite apnea divers. In a randomized order, participants performed a maximal apnea while receiving either intravenous 2 μg·kg(-1)·min(-1) dopamine or volume-matched saline (placebo). The chemoreflex and hemodynamic response to dopamine was also assessed during hypoxia [arterial O2 tension, (PaO2 ) ∼35 mmHg] and mild hypercapnia [arterial CO2 tension (PaCO2 ) ∼46 mmHg] that mimicked the latter parts of apnea. Outcome measures included apnea duration, arterial blood gases (radial), heart rate (HR, ECG), mean arterial pressure (MAP, intra-arterial), middle (MCAv) and posterior (PCAv) cerebral artery blood velocity (transcranial ultrasound), internal carotid (ICA) and vertebral (VA) artery blood flow (ultrasound), and the chemoreflex responses. Although dopamine depressed the ventilatory response by 27 ± 41% (vs. placebo; P = 0.01), the maximal apnea duration was increased by only 5 ± 8% (P = 0.02). The PaCO2 and PaO2 at apnea breakpoint were similar (P > 0.05). When compared with placebo, dopamine increased HR and decreased MAP during both apnea and chemoreflex test (P all <0.05). At rest, dopamine compared with placebo dilated the ICA (3.0 ± 4.1%, P = 0.05) and VA (6.6 ± 5.0%, P < 0.01). During apnea and chemoreflex test, conductance of the cerebral vessels (ICA, VA, MCAv, PCAv) was increased with dopamine; however, flow (ICA and VA) was similar. At least in elite apnea divers, the small increase in apnea time and similar PaO2 at breakpoint (∼31 mmHg) suggest the apnea breakpoint is more related to PaO2 , rather than peripheral chemoreflex drive to breathe.
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Affiliation(s)
- Anthony R Bain
- Center for Heart Lung and Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada;
| | - Zeljko Dujic
- School of Medicine, University of Split, Split, Croatia
| | - Ryan L Hoiland
- Center for Heart Lung and Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
| | - Otto F Barak
- School of Medicine, University of Split, Split, Croatia
| | - Dennis Madden
- School of Medicine, University of Split, Split, Croatia
| | - Ivan Drvis
- School of Kinesiology, University of Zagreb, Zagreb, Croatia
| | | | - David B MacLeod
- Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina; and
| | | | - Philip N Ainslie
- Center for Heart Lung and Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
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Hurr C, Harrison ML, Brothers RM. Acute flavanol consumption improves the cerebral vasodilatory capacity in college-aged African Americans. Exp Physiol 2015; 100:1030-8. [DOI: 10.1113/ep085269] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Accepted: 06/16/2015] [Indexed: 11/08/2022]
Affiliation(s)
- Chansol Hurr
- Environmental and Autonomic Physiology Laboratory, Department of Kinesiology and Health Education; The University of Texas at Austin; Austin TX USA
| | - Michelle L. Harrison
- Environmental and Autonomic Physiology Laboratory, Department of Kinesiology and Health Education; The University of Texas at Austin; Austin TX USA
| | - R. Matthew Brothers
- Environmental and Autonomic Physiology Laboratory, Department of Kinesiology and Health Education; The University of Texas at Austin; Austin TX USA
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