1
|
McCrone JC, Osei-Boateng C. Haemoconcentrating on cerebral blood flow regulation during early acclimatization: does altitude severity matter? J Physiol 2024. [PMID: 39087848 DOI: 10.1113/jp286928] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2024] [Accepted: 07/15/2024] [Indexed: 08/02/2024] Open
Affiliation(s)
- Jenna C McCrone
- Integrative Cerebrovascular and Environmental Physiology SB Laboratory, Department of Human Health and Nutritional Sciences, College of Biological Science, University of Guelph, Guelph, Ontario, Canada
| | - Christabel Osei-Boateng
- Integrative Cerebrovascular and Environmental Physiology SB Laboratory, Department of Human Health and Nutritional Sciences, College of Biological Science, University of Guelph, Guelph, Ontario, Canada
| |
Collapse
|
2
|
Howe CA. Haemoconcentration and cerebral blood flow: absence of evidence is not evidence of absence. J Physiol 2024. [PMID: 38970619 DOI: 10.1113/jp287042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/08/2024] Open
Affiliation(s)
- Connor A Howe
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia - Okanagan Campus, British Columbia, Canada
| |
Collapse
|
3
|
Turner R, Rasmussen P, Gatterer H, Tremblay JC, Roche J, Strapazzon G, Roveri G, Lawley J, Siebenmann C. Cerebral blood flow regulation in hypobaric hypoxia: role of haemoconcentration. J Physiol 2024. [PMID: 38687185 DOI: 10.1113/jp285169] [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: 06/19/2023] [Accepted: 04/04/2024] [Indexed: 05/02/2024] Open
Abstract
During acute hypoxic exposure, cerebral blood flow (CBF) increases to compensate for the reduced arterial oxygen content (CaO2). Nevertheless, as exposure extends, both CaO2 and CBF progressively normalize. Haemoconcentration is the primary mechanism underlying the CaO2 restoration and may therefore explain, at least in part, the CBF normalization. Accordingly, we tested the hypothesis that reversing the haemoconcentration associated with extended hypoxic exposure returns CBF towards the values observed in acute hypoxia. Twenty-three healthy lowlanders (12 females) completed two identical 4-day sojourns in a hypobaric chamber, one in normoxia (NX) and one in hypobaric hypoxia (HH, 3500 m). CBF was measured by ultrasound after 1, 6, 12, 48 and 96 h and compared between sojourns to assess the time course of changes in CBF. In addition, CBF was measured at the end of the HH sojourn after hypervolaemic haemodilution. Compared with NX, CBF was increased in HH after 1 h (P = 0.001) but similar at all later time points (all P > 0.199). Haemoglobin concentration was higher in HH than NX from 12 h to 96 h (all P < 0.001). While haemodilution reduced haemoglobin concentration from 14.8 ± 1.0 to 13.9 ± 1.2 g·dl-1 (P < 0.001), it did not increase CBF (974 ± 282 to 872 ± 200 ml·min-1; P = 0.135). We thus conclude that, at least at this moderate altitude, haemoconcentration is not the primary mechanism underlying CBF normalization with acclimatization. These data ostensibly reflect the fact that CBF regulation at high altitude is a complex process that integrates physiological variables beyond CaO2. KEY POINTS: Acute hypoxia causes an increase in cerebral blood flow (CBF). However, as exposure extends, CBF progressively normalizes. We investigated whether hypoxia-induced haemoconcentration contributes to the normalization of CBF during extended hypoxia. Following 4 days of hypobaric hypoxic exposure (corresponding to 3500 m altitude), we measured CBF before and after abolishing hypoxia-induced haemoconcentration by hypervolaemic haemodilution. Contrary to our hypothesis, the haemodilution did not increase CBF in hypoxia. Our findings do not support haemoconcentration as a stimulus for the CBF normalization during extended hypoxia.
Collapse
Affiliation(s)
- Rachel Turner
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
- Institut für Sportwissenschaft, Universität Innsbruck, Tyrol, Austria
| | | | - Hannes Gatterer
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Joshua C Tremblay
- School of Sport and Health Sciences, Cardiff Metropolitan University, Wales, UK
| | - Johanna Roche
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Giacomo Strapazzon
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Giulia Roveri
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Justin Lawley
- Institut für Sportwissenschaft, Universität Innsbruck, Tyrol, Austria
| | | |
Collapse
|
4
|
Patrician A, Willie C, Hoiland RL, Gasho C, Subedi P, Anholm JD, Tymko MM, Ainslie PN. Manipulation of iron status on cerebral blood flow at high altitude in lowlanders and adapted highlanders. J Cereb Blood Flow Metab 2023; 43:1166-1179. [PMID: 36883428 PMCID: PMC10291452 DOI: 10.1177/0271678x231152734] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 01/27/2023] [Accepted: 12/05/2022] [Indexed: 03/09/2023]
Abstract
Cerebral blood flow (CBF) increases during hypoxia to counteract the reduction in arterial oxygen content. The onset of tissue hypoxemia coincides with the stabilization of hypoxia-inducible factor (HIF) and transcription of downstream HIF-mediated processes. It has yet to be determined, whether HIF down- or upregulation can modulate hypoxic vasodilation of the cerebral vasculature. Therefore, we examined whether: 1) CBF would increase with iron depletion (via chelation) and decrease with repletion (via iron infusion) at high-altitude, and 2) explore whether genotypic advantages of highlanders extend to HIF-mediated regulation of CBF. In a double-blinded and block-randomized design, CBF was assessed in 82 healthy participants (38 lowlanders, 20 Sherpas and 24 Andeans), before and after the infusion of either: iron(III)-hydroxide sucrose, desferrioxamine or saline. Across both lowlanders and highlanders, baseline iron levels contributed to the variability in cerebral hypoxic reactivity at high altitude (R2 = 0.174, P < 0.001). At 5,050 m, CBF in lowlanders and Sherpa were unaltered by desferrioxamine or iron. At 4,300 m, iron infusion led to 4 ± 10% reduction in CBF (main effect of time p = 0.043) in lowlanders and Andeans. Iron status may provide a novel, albeit subtle, influence on CBF that is potentially dependent on the severity and length-of-stay at high altitude.
Collapse
Affiliation(s)
- Alexander Patrician
- Centre for Heart, Lung, & Vascular Health, School of Health and Exercise Sciences, University of British Columbia – Okanagan, Kelowna, BC, Canada
| | - Christopher Willie
- Centre for Heart, Lung, & Vascular Health, School of Health and Exercise Sciences, University of British Columbia – Okanagan, Kelowna, BC, Canada
| | - Ryan L Hoiland
- Centre for Heart, Lung, & Vascular Health, School of Health and Exercise Sciences, University of British Columbia – Okanagan, Kelowna, BC, Canada
- Department of Anesthesiology, Pharmacology and Therapeutics, Faculty of Medicine, Vancouver General Hospital, University of British Columbia, Vancouver, BC, Canada
- Department of Cellular and Physiological Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada
- International Collaboration on Repair Discoveries (ICORD), University of British Columbia, Vancouver, British Columbia, Canada
| | - Christopher Gasho
- Pulmonary/Critical Care Section, VA Loma Linda Healthcare System and Department of Medicine, Loma Linda University, Loma Linda, CA, USA
| | - Prajan Subedi
- Pulmonary/Critical Care Section, VA Loma Linda Healthcare System and Department of Medicine, Loma Linda University, Loma Linda, CA, USA
| | - James D Anholm
- Pulmonary/Critical Care Section, VA Loma Linda Healthcare System and Department of Medicine, Loma Linda University, Loma Linda, CA, USA
| | - Michael M Tymko
- Centre for Heart, Lung, & Vascular Health, School of Health and Exercise Sciences, University of British Columbia – Okanagan, Kelowna, BC, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung, & Vascular Health, School of Health and Exercise Sciences, University of British Columbia – Okanagan, Kelowna, BC, Canada
| |
Collapse
|
5
|
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.
Collapse
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
| |
Collapse
|
6
|
Hao GS, Fan QL, Hu QZ, Hou Q. Research progress on the mechanism of cerebral blood flow regulation in hypoxia environment at plateau. Bioengineered 2022; 13:6353-6358. [PMID: 35235760 PMCID: PMC8973622 DOI: 10.1080/21655979.2021.2024950] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The plateau is a special environment with low air pressure and low oxygen content. The average altitude of Qinghai-Tibet is 3,500 m, and the atmospheric oxygen partial pressure in most areas is lower than 60% of that at sea level. In order to adapt to the plateau low-oxygen environment, the human body has developed corresponding physiological structure and functions adjust. In the present review, the regulation mechanism of cerebral blood flow (CBF) under high-altitude environments was elaborated in eight aspects: the arterial blood gas, endogenous substances in the nerve and blood, the cerebral neovascularization, the hematocrit, cerebral auto-regulation mechanism, cerebrovascular reactivity, pulmonary vasoconstriction, and sympathetic automatic regulation, aiming to further explore the characteristics of changes in brain tissue and cerebral blood flow in a hypoxic environment.
Collapse
Affiliation(s)
- Gui-Sheng Hao
- Department of Neurology, Qinghai Provincial People's Hospital, Xining, Qinghai, China
| | - Qing-Li Fan
- Department of Neurology, Qinghai Provincial People's Hospital, Xining, Qinghai, China
| | - Quan-Zhong Hu
- Department of Neurology, Qinghai Provincial People's Hospital, Xining, Qinghai, China
| | - Qian Hou
- Department of Neurology, Qinghai Provincial People's Hospital, Xining, Qinghai, China
| |
Collapse
|
7
|
Stembridge M, Hoiland RL, Williams AM, Howe CA, Donnelly J, Dawkins TG, Drane A, Tymko MM, Gasho C, Anholm J, Simpson LL, Moore JP, Bailey DM, MacLeod DB, Ainslie PN. The influence of hemoconcentration on hypoxic pulmonary vasoconstriction in acute, prolonged, and lifelong hypoxemia. Am J Physiol Heart Circ Physiol 2021; 321:H738-H747. [PMID: 34448634 DOI: 10.1152/ajpheart.00357.2021] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Hemoconcentration can influence hypoxic pulmonary vasoconstriction (HPV) via increased frictional force and vasoactive signaling from erythrocytes, but whether the balance of these mechanism is modified by the duration of hypoxia remains to be determined. We performed three sequential studies: 1) at sea level, in normoxia and isocapnic hypoxia with and without isovolumic hemodilution (n = 10, aged 29 ± 7 yr); 2) at altitude (6 ± 2 days acclimatization at 5,050 m), before and during hypervolumic hemodilution (n = 11, aged 27 ± 5 yr) with room air and additional hypoxia [fraction of inspired oxygen ([Formula: see text])= 0.15]; and 3) at altitude (4,340 m) in Andean high-altitude natives with excessive erythrocytosis (EE; n = 6, aged 39 ± 17 yr), before and during isovolumic hemodilution with room air and hyperoxia (end-tidal Po2 = 100 mmHg). At sea level, hemodilution mildly increased pulmonary artery systolic pressure (PASP; +1.6 ± 1.5 mmHg, P = 0.01) and pulmonary vascular resistance (PVR; +0.7 ± 0.8 wu, P = 0.04). In contrast, after acclimation to 5,050 m, hemodilution did not significantly alter PASP (22.7 ± 5.2 vs. 24.5 ± 5.2 mmHg, P = 0.14) or PVR (2.2 ± 0.9 vs. 2.3 ± 1.2 wu, P = 0.77), although both remained sensitive to additional acute hypoxia. In Andeans with EE at 4,340 m, hemodilution lowered PVR in room air (2.9 ± 0.9 vs. 2.3 ± 0.8 wu, P = 0.03), but PASP remained unchanged (31.3 ± 6.7 vs. 30.9 ± 6.9 mmHg, P = 0.80) due to an increase in cardiac output. Collectively, our series of studies reveal that HPV is modified by the duration of exposure and the prevailing hematocrit level. In application, these findings emphasize the importance of accounting for hematocrit and duration of exposure when interpreting the pulmonary vascular responses to hypoxemia.NEW & NOTEWORTHY Red blood cell concentration influences the pulmonary vasculature via direct frictional force and vasoactive signaling, but whether the magnitude of the response is modified with duration of exposure is not known. By assessing the pulmonary vascular response to hemodilution in acute normobaric and prolonged hypobaric hypoxia in lowlanders and lifelong hypobaric hypoxemia in Andean natives, we demonstrated that a reduction in red cell concentration augments the vasoconstrictive effects of hypoxia in lowlanders. In high-altitude natives, hemodilution lowered pulmonary vascular resistance, but a compensatory increase in cardiac output following hemodilution rendered PASP unchanged.
Collapse
Affiliation(s)
- Mike Stembridge
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, United Kingdom
| | - Ryan L Hoiland
- Centre for Heart, Lung and Vascular Health, 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
| | - Alexandra M Williams
- Centre for Heart, Lung and Vascular Health, University of British Columbia Okanagan, Kelowna, British Columbia, Canada.,Faculty of Medicine, Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Connor A Howe
- Centre for Heart, Lung and Vascular Health, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Joseph Donnelly
- Department of Anaesthesiology, University of Auckland, Auckland, New Zealand
| | - Tony G Dawkins
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, United Kingdom
| | - Aimee Drane
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, United Kingdom
| | - Michael M Tymko
- Centre for Heart, Lung and Vascular Health, University of British Columbia Okanagan, Kelowna, British Columbia, Canada.,Neurovascular Health Laboratory, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Christopher Gasho
- Division of Pulmonary and Critical Care, School of Medicine, Loma Linda University, Loma Linda, California
| | - James Anholm
- Division of Pulmonary and Critical Care, School of Medicine, Loma Linda University, Loma Linda, California
| | - Lydia L Simpson
- Extremes Research Group, School of Sport, Health and Exercise Sciences, Bangor University, Wales, United Kingdom
| | - Jonathan P Moore
- Extremes Research Group, School of Sport, Health and Exercise Sciences, Bangor University, Wales, United Kingdom
| | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, United Kingdom
| | - David B MacLeod
- Human Pharmacology and Physiology Laboratory, Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| |
Collapse
|
8
|
Steele AR, Skow RJ, Fraser GM, Berthelsen LF, Steinback CD. Sympathetic neurovascular transduction following acute hypoxia. Clin Auton Res 2021; 31:755-765. [PMID: 34528146 DOI: 10.1007/s10286-021-00824-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Accepted: 08/18/2021] [Indexed: 01/29/2023]
Abstract
PURPOSE Following an acute exposure to hypoxia, sympathetic nerve activity remains elevated. However, this elevated sympathetic nerve activity does not elicit a parallel increase in vascular resistance suggesting a blunted sympathetic signaling [i.e. blunted sympathetic neurovascular transduction (sNVT)]. Therefore, we sought to quantify spontaneous sympathetic bursts and related changes in total peripheral resistance following hypoxic exposure. We hypothesized that following hypoxia sNVT would be blunted. METHODS Nine healthy participants (n = 6 men; mean age 25 ± 2 years) were recruited. We collected data on muscle sympathetic nerve activity (MSNA) using microneurography and beat-by-beat total peripheral resistance (TPR) via finger photoplethysmography at baseline, during acute hypoxia and during two periods of recovery (recovery period 1, 0-10 min post hypoxia; recovery period 2, 10-20 min post hypoxia). MSNA burst sequences (i.e. singlets, doublets, triplets and quads+) were identified and coupled to changes in TPR over 15 cardiac cycles as an index of sNVT for burst sequences. A sNVT slope for each participant was calculated from the slope of the relationship between TPR plotted against normalized burst amplitude. RESULTS The sNVT slope was blunted during hypoxia [Δ 0.0044 ± 0.0014 (mmHg/L/min)/(a.u.)], but unchanged following termination of hypoxia [recovery 1, Δ 0.031 ± 0.0019 (mmHg/L/min)/(a.u.); recovery 2, Δ 0.0038 ± 0.0014 (mmHg/L/min)/(a.u.) compared to baseline (Δ 0.038 ± 0.0015 (L/min/mmHg)/(a.u.)] (main effect of group p = 0.012). CONCLUSIONS Contrary to our hypothesis, we have demonstrated that systemic sNVT is unchanged following hypoxia in young healthy adults.
Collapse
Affiliation(s)
- Andrew R Steele
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, , University of Alberta, 1-059D Li Ka Shing Centre for Health Research Innovation, Edmonton, AB, Canada, T6G 2E1
| | - Rachel J Skow
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, , University of Alberta, 1-059D Li Ka Shing Centre for Health Research Innovation, Edmonton, AB, Canada, T6G 2E1
- Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
- Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
| | - Graham M Fraser
- Division of BioMedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, NL, Canada
| | - Lindsey F Berthelsen
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, , University of Alberta, 1-059D Li Ka Shing Centre for Health Research Innovation, Edmonton, AB, Canada, T6G 2E1
| | - Craig D Steinback
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, , University of Alberta, 1-059D Li Ka Shing Centre for Health Research Innovation, Edmonton, AB, Canada, T6G 2E1.
- Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada.
- Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada.
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada.
| |
Collapse
|
9
|
Carr JMJR, Caldwell HG, Ainslie PN. Cerebral blood flow, cerebrovascular reactivity and their influence on ventilatory sensitivity. Exp Physiol 2021; 106:1425-1448. [PMID: 33932955 DOI: 10.1113/ep089446] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2021] [Accepted: 04/26/2021] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the topic of this review? Cerebrovascular reactivity to CO2 , which is a principal factor in determining ventilatory responses to CO2 through the role reactivity plays in determining cerebral extra- and intracellular pH. What advances does it highlight? Recent animal evidence suggests central chemoreceptor vasculature may demonstrate regionally heterogeneous cerebrovascular reactivity to CO2 , potentially as a protective mechanism against excessive CO2 washout from the central chemoreceptors, thereby allowing ventilation to reflect the systemic acid-base balance needs (respiratory changes in P aC O 2 ) rather than solely the cerebral needs. Ventilation per se does not influence cerebrovascular reactivity independent of changes in P aC O 2 . ABSTRACT Alveolar ventilation and cerebral blood flow are both predominantly regulated by arterial blood gases, especially arterial P C O 2 , and so are intricately entwined. In this review, the fundamental mechanisms underlying cerebrovascular reactivity and central chemoreceptor control of breathing are covered. We discuss the interaction of cerebral blood flow and its reactivity with the control of ventilation and ventilatory responsiveness to changes in P C O 2 , as well as the lack of influence of ventilation itself on cerebrovascular reactivity. We briefly summarize the effects of arterial hypoxaemia on the relationship between ventilatory and cerebrovascular response to both P C O 2 and P O 2 . We then highlight key methodological considerations regarding the interaction of reactivity and ventilatory sensitivity, including the following: regional heterogeneity of cerebrovascular reactivity; a pharmacological approach for the reduction of cerebral blood flow; reactivity assessment techniques; the influence of mean arterial blood pressure; and sex-related differences. Finally, we discuss ventilatory and cerebrovascular control in the context of high altitude and congestive heart failure. Future research directions and pertinent questions of interest are highlighted throughout.
Collapse
Affiliation(s)
- Jay M J R Carr
- Centre for Heart, Lung and Vascular Health, University of British Columbia - Okanagan Campus, British Columbia, Canada
| | - Hannah G Caldwell
- Centre for Heart, Lung and Vascular Health, University of British Columbia - Okanagan Campus, British Columbia, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, University of British Columbia - Okanagan Campus, British Columbia, Canada
| |
Collapse
|
10
|
Bailey DM, Stacey BS, Iannetelli A. Cerebral oxygen sensing and the integrated regulation of hypoxic vasodilatation. Exp Physiol 2019; 104:1751-1753. [PMID: 31565816 DOI: 10.1113/ep088090] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2019] [Accepted: 09/27/2019] [Indexed: 11/08/2022]
Affiliation(s)
- Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Benjamin S Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Angelo Iannetelli
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| |
Collapse
|