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Doneddu A, Roberto S, Guicciardi M, Pazzona R, Manca A, Monni A, Fanni M, Leban B, Ghiani G, Spranger MD, Mulliri G, Crisafulli A. Hemodynamics and cerebral oxygenation during acute exercise in moderate normobaric hypoxia and with concurrent cognitive task in young healthy males. Appl Physiol Nutr Metab 2024. [PMID: 39088843 DOI: 10.1139/apnm-2023-0629] [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: 08/03/2024]
Abstract
The present investigation aimed to study the cardiovascular responses and the cerebral oxygenation (Cox) during exercise in acute hypoxia and with contemporary mental stress. Fifteen physically active, healthy males (age 29.0 ± 5.9 years) completed a cardiopulmonary test on a cycle ergometer to determine the workload at their gas exchange threshold (GET). On a separate day, participants performed two randomly assigned exercise tests pedaling for 6 min at a workload corresponding to 80% of the GET: (1) during normoxia (NORMO), and (2) during acute, normobaric hypoxia at 13.5% inspired oxygen (HYPO). During the last 3 min of the exercise, they also performed a mental task (MT). Hemodynamics were assessed with impedance cardiography, and peripheral arterial oxygen saturation and Cox were continuously measured by near-infrared spectroscopy. The main results were that both in NORMO and HYPO conditions, the MT caused a significant increase in the heart rate and ventricular filling rate. Moreover, MT significantly reduced (74.8 ± 5.5 vs. 62.0 ± 5.2 A.U.) Cox, while the reaction time (RT) increased (813.3 ± 110.2 vs. 868.2 ± 118.1 ms) during the HYPO test without affecting the correctness of the answers. We conclude that in young, healthy males, adding an MT during mild intensity exercise in both normoxia and acute moderate (normobaric) hypoxia induces a similar hemodynamic response. However, MT and exercise in HYPO cause a decrease in Cox and an impairment in RT.
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Affiliation(s)
- Azzurra Doneddu
- Department of Medical Sciences and Public Health, University of Cagliari, Italy
- International PhD in Innovation Sciences and Technologies, University of Cagliari, Italy
| | - Silvana Roberto
- Department of Medical Sciences and Public Health, University of Cagliari, Italy
| | - Marco Guicciardi
- Department of Education, Psychology and Philosophy, Faculty of Humanities, University of Cagliari, Italy
| | - Riccardo Pazzona
- Department of Education, Psychology and Philosophy, Faculty of Humanities, University of Cagliari, Italy
| | - Andrea Manca
- Department of Education, Psychology and Philosophy, Faculty of Humanities, University of Cagliari, Italy
| | - Alessandra Monni
- Department of Education, Psychology and Philosophy, Faculty of Humanities, University of Cagliari, Italy
| | - Massimo Fanni
- Department of Medical Sciences and Public Health, University of Cagliari, Italy
- International PhD in Innovation Sciences and Technologies, University of Cagliari, Italy
| | - Bruno Leban
- Department of Mechanical, Chemical and Material Engineering, Faculty of Engineering and Architecture, University of Cagliari, Italy
| | - Giovanna Ghiani
- Department of Medical Sciences and Public Health, University of Cagliari, Italy
| | - Marty D Spranger
- Department of Physiology, Michigan State University, East Lansing, MI, USA
| | - Gabriele Mulliri
- Department of Medical Sciences and Public Health, University of Cagliari, Italy
| | - Antonio Crisafulli
- Department of Medical Sciences and Public Health, University of Cagliari, Italy
- International PhD in Innovation Sciences and Technologies, University of Cagliari, Italy
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Shaw DM, Harrell JW. Integrating physiological monitoring systems in military aviation: a brief narrative review of its importance, opportunities, and risks. ERGONOMICS 2023; 66:2242-2254. [PMID: 36946542 DOI: 10.1080/00140139.2023.2194592] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Accepted: 03/18/2023] [Indexed: 06/18/2023]
Abstract
Military pilots risk their lives during training and operations. Advancements in aerospace engineering, flight profiles, and mission demands may require the pilot to test the safe limits of their physiology. Monitoring pilot physiology (e.g. heart rate, oximetry, and respiration) inflight is in consideration by several nations to inform pilots of reduced performance capacity and guide future developments in aircraft and life-support system design. Numerous challenges, however, prevent the immediate operationalisation of physiological monitoring sensors, particularly their unreliability in the aerospace environment and incompatibility with pilot clothing and protective equipment. Human performance and behaviour are also highly variable and measuring these in controlled laboratory settings do not mirror the real-world conditions pilots must endure. Misleading or erroneous predictive models are unacceptable as these could compromise mission success and lose operator trust. This narrative review provides an overview of considerations for integrating physiological monitoring systems within the military aviation environment.Practitioner summary: Advancements in military technology can conflictingly enhance and compromise pilot safety and performance. We summarise some of the opportunities, limitations, and risks of integrating physiological monitoring systems within military aviation. Our intent is to catalyse further research and technological development.Abbreviations: AGS: anti-gravity suit; AGSM: anti-gravity straining manoeuvre; A-LOC: almost loss of consciousness; CBF: cerebral blood flow; ECG: electrocardiogram; EEG: electroencephalogram; fNIRS: functional near-infrared spectroscopy; G-forces: gravitational forces; G-LOC: gravity-induced loss of consciousness; HR: heart rate; HRV: heart rate variability; LSS: life-support system; NATO: North Atlantic Treaty Organisation; PE: Physiological Episode; PCO2: partial pressure of carbon dioxide; PO2: partial pressure of oxygen; OBOGS: on board oxygen generating systems; SpO2: peripheral blood haemoglobin-oxygen saturation; STANAG: North Atlantic Treaty Organisation Standardisation Agreement; UPE: Unexplained Physiological Episode; WBV: whole body vibration.
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Affiliation(s)
- David M Shaw
- Aviation Medicine Unit, Royal New Zealand Air Force Base Auckland, Auckland, New Zealand
- School of Sport, Exercise and Nutrition, Massey University, Auckland, New Zealand
| | - John W Harrell
- 711th Human Performance Wing, Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, OH, USA
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Ando S, Tsukamoto H, Stacey BS, Washio T, Owens TS, Calverley TA, Fall L, Marley CJ, Iannetelli A, Hashimoto T, Ogoh S, Bailey DM. Acute hypoxia impairs posterior cerebral bioenergetics and memory in man. Exp Physiol 2023; 108:1516-1530. [PMID: 37898979 PMCID: PMC10988469 DOI: 10.1113/ep091245] [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: 04/06/2023] [Accepted: 10/03/2023] [Indexed: 10/31/2023]
Abstract
Hypoxia has the potential to impair cognitive function; however, it is still uncertain which cognitive domains are adversely affected. We examined the effects of acute hypoxia (∼7 h) on central executive (Go/No-Go) and non-executive (memory) tasks and the extent to which impairment was potentially related to regional cerebral blood flow and oxygen delivery (CDO2 ). Twelve male participants performed cognitive tasks following 0, 2, 4 and 6 h of passive exposure to both normoxia and hypoxia (12% O2 ), in a randomized block cross-over single-blinded design. Middle cerebral artery (MCA) and posterior cerebral artery (PCA) blood velocities and corresponding CDO2 were determined using bilateral transcranial Doppler ultrasound. In hypoxia, MCA DO2 was reduced during the Go/No-Go task (P = 0.010 vs. normoxia, main effect), and PCA DO2 was attenuated during memorization (P = 0.005 vs. normoxia) and recall components (P = 0.002 vs. normoxia) in the memory task. The accuracy of the memory task was also impaired in hypoxia (P = 0.049 vs. normoxia). In contrast, hypoxia failed to alter reaction time (P = 0.19 vs. normoxia) or accuracy (P = 0.20 vs. normoxia) during the Go/No-Go task, indicating that selective attention and response inhibition were preserved. Hypoxia did not affect cerebral blood flow or corresponding CDO2 responses to cognitive activity (P > 0.05 vs. normoxia). Collectively, these findings highlight the differential sensitivity of cognitive domains, with memory being selectively vulnerable in hypoxia. NEW FINDINGS: What is the central question of this study? We sought to examine the effects of acute hypoxia on central executive (selective attention and response inhibition) and non-executive (memory) performance and the extent to which impairments are potentially related to reductions in regional cerebral blood flow and oxygen delivery. What is the main finding and its importance? Memory was impaired in acute hypoxia, and this was accompanied by a selective reduction in posterior cerebral artery oxygen delivery. In contrast, selective attention and response inhibition remained well preserved. These findings suggest that memory is selectively vulnerable to hypoxia.
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Affiliation(s)
- Soichi Ando
- Graduate School of Informatics and EngineeringThe University of Electro‐CommunicationsTokyoJapan
| | - Hayato Tsukamoto
- Neurovascular Research Laboratory, Faculty of Life Sciences and EducationUniversity of South WalesPontypriddUK
- Faculty of Sports ScienceWaseda UniversitySaitamaJapan
| | - Benjamin S. Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and EducationUniversity of South WalesPontypriddUK
| | - Takuro Washio
- Department of Biomedical EngineeringToyo UniversityKawagoeSaitamaJapan
| | - Thomas S. Owens
- Neurovascular Research Laboratory, Faculty of Life Sciences and EducationUniversity of South WalesPontypriddUK
| | - Thomas A. Calverley
- Neurovascular Research Laboratory, Faculty of Life Sciences and EducationUniversity of South WalesPontypriddUK
| | - Lewis Fall
- Neurovascular Research Laboratory, Faculty of Life Sciences and EducationUniversity of South WalesPontypriddUK
| | - Christopher J. Marley
- Neurovascular Research Laboratory, Faculty of Life Sciences and EducationUniversity of South WalesPontypriddUK
| | - Angelo Iannetelli
- Neurovascular Research Laboratory, Faculty of Life Sciences and EducationUniversity of South WalesPontypriddUK
| | | | - Shigehiko Ogoh
- Neurovascular Research Laboratory, Faculty of Life Sciences and EducationUniversity of South WalesPontypriddUK
- Department of Biomedical EngineeringToyo UniversityKawagoeSaitamaJapan
| | - Damian M. Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and EducationUniversity of South WalesPontypriddUK
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Shaw DM, Bloomfield PM, Benfell A, Hughes I, Gant N. Recovery from acute hypoxia: A systematic review of cognitive and physiological responses during the 'hypoxia hangover'. PLoS One 2023; 18:e0289716. [PMID: 37585402 PMCID: PMC10431643 DOI: 10.1371/journal.pone.0289716] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Accepted: 07/21/2023] [Indexed: 08/18/2023] Open
Abstract
Recovery of cognitive and physiological responses following a hypoxic exposure may not be considered in various operational and research settings. Understanding recovery profiles and influential factors can guide post-hypoxia restrictions to reduce the risk of further cognitive and physiological deterioration, and the potential for incidents and accidents. We systematically evaluated the available evidence on recovery of cognitive and basic physiological responses following an acute hypoxic exposure to improve understanding of the performance and safety implications, and to inform post-hypoxia restrictions. This systematic review summarises 30 studies that document the recovery of either a cognitive or physiological index from an acute hypoxic exposure. Titles and abstracts from PubMed (MEDLINE) and Scopus were searched from inception to July 2022, of which 22 full text articles were considered eligible. An additional 8 articles from other sources were identified and also considered eligible. The overall quality of evidence was moderate (average Rosendal score, 58%) and there was a large range of hypoxic exposures. Heart rate, peripheral blood haemoglobin-oxygen saturation and heart rate variability typically normalised within seconds-to-minutes following return to normoxia or hyperoxia. Whereas, cognitive performance, blood pressure, cerebral tissue oxygenation, ventilation and electroencephalogram indices could persist for minutes-to-hours following a hypoxic exposure, and one study suggested regional cerebral tissue oxygenation requires up to 24 hours to recover. Full recovery of most cognitive and physiological indices, however, appear much sooner and typically within ~2-4 hours. Based on these findings, there is evidence to support a 'hypoxia hangover' and a need to implement restrictions following acute hypoxic exposures. The severity and duration of these restrictions is unclear but should consider the population, subsequent requirement for safety-critical tasks and hypoxic exposure.
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Affiliation(s)
- David M. Shaw
- Aviation Medicine Unit, Royal New Zealand Air Force Base Auckland, Whenuapai, Auckland, New Zealand
| | - Peter M. Bloomfield
- Department of Exercise Sciences, University of Auckland, Auckland, New Zealand
| | - Anthony Benfell
- Department of Medicine, University of Auckland, Auckland, New Zealand
| | - Isadore Hughes
- Department of Medicine, University of Auckland, Auckland, New Zealand
| | - Nicholas Gant
- Department of Exercise Sciences, University of Auckland, Auckland, New Zealand
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Bloomfield PM, Fisher JP, Shaw DM, Gant N. Cocoa flavanols protect cognitive function, cerebral oxygenation, and mental fatigue during severe hypoxia. J Appl Physiol (1985) 2023; 135:475-484. [PMID: 37471213 DOI: 10.1152/japplphysiol.00219.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2023] [Revised: 07/06/2023] [Accepted: 07/06/2023] [Indexed: 07/22/2023] Open
Abstract
We tested the hypothesis that ingestion of cocoa flavanols would improve cognition during acute hypoxia equivalent to 5,500 m altitude (partial pressure of end-tidal oxygen = 45 mmHg). Using placebo-controlled double-blind trials, 12 participants ingested 15 mg·kg-1 of cocoa flavanols 90 min before completing cognitive tasks during normoxia and either poikilocapnic or isocapnic hypoxia (partial pressure of end-tidal carbon dioxide uncontrolled or maintained at the baseline value, respectively). Cerebral oxygenation was measured using functional near-infrared spectroscopy. Overall cognition was impaired by poikilocapnic hypoxia (main effect of hypoxia, P = 0.008). Cocoa flavanols improved a measure of overall cognitive performance by 4% compared with placebo (effect of flavanols, P = 0.033) during hypoxia, indicating a change in performance from "low average" to "average." The hypoxia-induced decrease in cerebral oxygenation was two-fold greater with placebo than with cocoa flavanols (effect of flavanols, P = 0.005). Subjective fatigue was increased by 900% with placebo compared with flavanols during poikilocapnic hypoxia (effect of flavanols, P = 0.004). Overall cognition was impaired by isocapnic hypoxia (effect of hypoxia, P = 0.001) but was not improved by cocoa flavanols (mean improvement = 1%; effect of flavanols, P = 0.72). Reaction time was impaired by 8% with flavanols during normoxia and further impaired by 11% during isocapnic hypoxia (effect of flavanols, P = 0.01). Our findings are the first to show that flavanol-mediated improvements in cognition and mood during normoxia persist during severe oxygen deprivation, conferring a neuroprotective effect.NEW & NOTEWORTHY We show for the first time that cocoa flavanols exert a neuroprotective effect during severe hypoxia. Following acute cocoa flavanol ingestion, we observed improvements in cognition, cerebral oxygenation, and subjective fatigue during normoxia and severe poikilocapnic hypoxia. Cocoa flavanols did not improve cognition during severe isocapnic hypoxia, suggesting a possible interaction with carbon dioxide.
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Affiliation(s)
- Peter M Bloomfield
- Exercise Neurometabolism Laboratory, University of Auckland, Auckland, New Zealand
| | - James P Fisher
- Department of Physiology, Faculty of Medical & Health Sciences, Manaaki Mānawa - The Centre for Heart Research, University of Auckland, Auckland, New Zealand
| | - David M Shaw
- Aviation Medicine Unit, Royal New Zealand Air Force Base Auckland, Whenuapai, Auckland, New Zealand
| | - Nicholas Gant
- Exercise Neurometabolism Laboratory, University of Auckland, Auckland, New Zealand
- Centre for Brain Research, University of Auckland, Auckland, New Zealand
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Ogoh S, Washio T, Stacey BS, Tsukamoto H, Iannetelli A, Owens TS, Calverley TA, Fall L, Marley CJ, Saito S, Watanabe H, Hashimoto T, Ando S, Miyamoto T, Bailey DM. Integrated respiratory chemoreflex-mediated regulation of cerebral blood flow in hypoxia: Implications for oxygen delivery and acute mountain sickness. Exp Physiol 2021; 106:1922-1938. [PMID: 34318560 DOI: 10.1113/ep089660] [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: 04/12/2021] [Accepted: 07/20/2021] [Indexed: 12/30/2022]
Abstract
NEW FINDINGS What is the central question of this study? To what extent do hypoxia-induced changes in the peripheral and central respiratory chemoreflex modulate anterior and posterior cerebral oxygen delivery, with corresponding implications for susceptibility to acute mountain sickness? What is the main finding and its importance? We provide evidence for site-specific regulation of cerebral blood flow in hypoxia that preserves oxygen delivery in the posterior but not the anterior cerebral circulation, with minimal contribution from the central respiratory chemoreflex. External carotid artery vasodilatation might prove to be an alternative haemodynamic risk factor that predisposes to acute mountain sickness. ABSTRACT The aim of the present study was to determine the extent to which hypoxia-induced changes in the peripheral and central respiratory chemoreflex modulate anterior and posterior cerebral blood flow (CBF) and oxygen delivery (CDO2 ), with corresponding implications for the pathophysiology of the neurological syndrome, acute mountain sickness (AMS). Eight healthy men were randomly assigned single blind to 7 h of passive exposure to both normoxia (21% O2 ) and hypoxia (12% O2 ). The peripheral and central respiratory chemoreflex, internal carotid artery, external carotid artery (ECA) and vertebral artery blood flow (duplex ultrasound) and AMS scores (questionnaires) were measured throughout. A reduction in internal carotid artery CDO2 was observed during hypoxia despite a compensatory elevation in perfusion. In contrast, vertebral artery and ECA CDO2 were preserved, and the former was attributable to a more marked increase in perfusion. Hypoxia was associated with progressive activation of the peripheral respiratory chemoreflex (P < 0.001), whereas the central respiratory chemoreflex remained unchanged (P > 0.05). Symptom severity in participants who developed clinical AMS was positively related to ECA blood flow (Lake Louise score, r = 0.546-0.709, P = 0.004-0.043; Environmental Symptoms Questionnaires-Cerebral symptoms score, r = 0.587-0.771, P = 0.001-0.027, n = 4). Collectively, these findings highlight the site-specific regulation of CBF in hypoxia that maintains CDO2 selectively in the posterior but not the anterior cerebral circulation, with minimal contribution from the central respiratory chemoreflex. Furthermore, ECA vasodilatation might represent a hitherto unexplored haemodynamic risk factor implicated in the pathophysiology of AMS.
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Affiliation(s)
- Shigehiko Ogoh
- Department of Biomedical Engineering, Toyo University, Kawagoe, Saitama, Japan.,Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Takuro Washio
- Department of Biomedical Engineering, Toyo University, Kawagoe, Saitama, Japan
| | - Benjamin S Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Hayato Tsukamoto
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK.,Faculty of Sport and Health Science, Ritsumeikan University, Shiga, Japan
| | - Angelo Iannetelli
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Thomas S Owens
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Thomas A Calverley
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Lewis Fall
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Christopher J Marley
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
| | - Shotaro Saito
- Department of Biomedical Engineering, Toyo University, Kawagoe, Saitama, Japan
| | - Hironori Watanabe
- Department of Biomedical Engineering, Toyo University, Kawagoe, Saitama, Japan
| | - Takeshi Hashimoto
- Faculty of Sport and Health Science, Ritsumeikan University, Shiga, Japan
| | - Soichi Ando
- Graduate School of Informatics and Engineering, The University of Electro-Communications, Tokyo, Japan
| | | | - Damian M Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK
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Shaw DM, Cabre G, Gant N. Hypoxic Hypoxia and Brain Function in Military Aviation: Basic Physiology and Applied Perspectives. Front Physiol 2021; 12:665821. [PMID: 34093227 PMCID: PMC8171399 DOI: 10.3389/fphys.2021.665821] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Accepted: 04/22/2021] [Indexed: 01/04/2023] Open
Abstract
Acute hypobaric hypoxia (HH) is a major physiological threat during high-altitude flight and operations. In military aviation, although hypoxia-related fatalities are rare, incidences are common and are likely underreported. Hypoxia is a reduction in oxygen availability, which can impair brain function and performance of operational and safety-critical tasks. HH occurs at high altitude, due to the reduction in atmospheric oxygen pressure. This physiological state is also partially simulated in normobaric environments for training and research, by reducing the fraction of inspired oxygen to achieve comparable tissue oxygen saturation [normobaric hypoxia (NH)]. Hypoxia can occur in susceptible individuals below 10,000 ft (3,048 m) in unpressurised aircrafts and at higher altitudes in pressurised environments when life support systems malfunction or due to improper equipment use. Between 10,000 ft and 15,000 ft (4,572 m), brain function is mildly impaired and hypoxic symptoms are common, although both are often difficult to accurately quantify, which may partly be due to the effects of hypocapnia. Above 15,000 ft, brain function exponentially deteriorates with increasing altitude until loss of consciousness. The period of effective and safe performance of operational tasks following exposure to hypoxia is termed the time-of-useful-consciousness (TUC). Recovery of brain function following hypoxia may also lag beyond arterial reoxygenation and could be exacerbated by repeated hypoxic exposures or hyperoxic recovery. This review provides an overview of the basic physiology and implications of hypoxia for military aviation and discusses the utility of hypoxia recognition training.
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Affiliation(s)
- David M Shaw
- Aviation Medicine Unit, Royal New Zealand Air Force Base Auckland, Auckland, New Zealand.,School of Sport, Exercise and Nutrition, Massey University, Auckland, New Zealand
| | - Gus Cabre
- Aviation Medicine Unit, Royal New Zealand Air Force Base Auckland, Auckland, New Zealand
| | - Nicholas Gant
- Department of Exercise Sciences, University of Auckland, Auckland, New Zealand
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Cardio-respiratory, oxidative stress and acute mountain sickness responses to normobaric and hypobaric hypoxia in prematurely born adults. Eur J Appl Physiol 2020; 120:1341-1355. [PMID: 32270264 DOI: 10.1007/s00421-020-04366-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Accepted: 04/04/2020] [Indexed: 10/24/2022]
Abstract
PURPOSE We compared the effects of hypobaric and normobaric hypoxia on select cardio-respiratory responses, oxidative stress and acute mountain sickness (AMS) severity in prematurely born individuals, known to exhibit blunted hypoxic ventilatory response. METHODS Sixteen prematurely born but otherwise healthy males underwent two 8-h hypoxic exposures under: (1) hypobaric hypoxic [HH; terrestrial altitude 3840 m; PiO2:90.2 (0.5) mmHg; BP: 478 (2) mmHg] and (2) normobaric hypoxic [NH; PiO2:90.6 (0.9) mmHg; FiO2:0.142 (0.001)] condition. Resting values of capillary oxyhemoglobin saturation (SpO2), heart rate (HR) and blood pressure were measured before and every 2 h during the exposures. Ventilatory responses and middle cerebral artery blood flow velocity (MCAv) were assessed at rest and during submaximal cycling before and at 4 and 8 h. Plasmatic levels of selected oxidative stress and antioxidant markers and AMS symptoms were also determined at these time points. RESULTS HH resulted in significantly lower resting (P = 0.010) and exercise (P = 0.004) SpO2 as compared to NH with no significant differences in the ventilatory parameters, HR or blood pressure. No significant differences between conditions were found in resting or exercising MCAv and measured oxidative stress markers. Significantly lower values of ferric-reducing antioxidant power (P = 0.037) were observed during HH as opposed to NH. AMS severity was higher at 8 h compared to baseline (P = 0.002) with no significant differences between conditions. CONCLUSION These data suggest that, in prematurely born adults, 8-h exposure to hypobaric, as opposed to normobaric hypoxia, provokes greater reductions in systemic oxygenation and antioxidant capacity. Further studies investigating prolonged hypobaric exposures in this population are warranted. REGISTRATION NCT02780908 (ClinicalTrials.gov).
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Lefferts WK, DeBlois JP, Soriano JE, Mann L, Rampuri Z, Herrington B, Thrall S, Bird J, Harman TS, Day TA, Heffernan KS, Brutsaert TD. Preservation of Neurovascular Coupling to Cognitive Activity in Anterior Cerebrovasculature During Incremental Ascent to High Altitude. High Alt Med Biol 2019; 21:20-27. [PMID: 31750741 DOI: 10.1089/ham.2019.0050] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Background: High altitude sojourn challenges blood flow regulation in the brain, which may contribute to cognitive dysfunction. Neurovascular coupling (NVC) describes the ability to increase blood flow to working regions of the brain. Effects of high altitude on NVC in frontal regions undergoing cognitive activation are unclear but may be relevant to executive function in high-altitude hypoxia. This study sought to examine the effect of incremental ascent to very high altitude on NVC by measuring anterior cerebral artery (ACA) and middle cerebral artery (MCA) hemodynamic responses to sustained cognitive activity. Materials and Methods: Eight adults (23 ± 7 years, four female) underwent bilateral measurement of ACA and MCA mean velocity and pulsatility index (PI) through transcranial Doppler during a 3-minute Stroop task at 1400, 3440, and 4240 m. Results: Resting MCA and ACA PI decreased with high-altitude hypoxia (p < 0.05). Cognitive activity at all altitudes resulted in similar increases in MCA and ACA mean velocity, and decreases in ACA and MCA PI (p < 0.05 for MCA, p = 0.07 for ACA). No significant altitude-by-Stroop interactions were detected, indicating NVC was stable with increasing altitude. Conclusions: Ascent to very high altitude (4240 m) using an incremental profile that supports partial acclimatization does not appear to disturb (1) increases in cerebral blood velocity and (2) reductions in pulsatility that characterize optimal NVC in frontal regions of the brain during cognitive activity.
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Affiliation(s)
- Wesley K Lefferts
- Integrative Physiology Laboratory, Department of Kinesiology and Nutrition, University of Illinois at Chicago, Chicago, Illinois.,Department of Exercise Science, Syracuse University, Syracuse, New York
| | - Jacob P DeBlois
- Department of Exercise Science, Syracuse University, Syracuse, New York
| | | | - Leah Mann
- Department of Biology, Mount Royal University, Calgary, Alberta, Canada
| | - Zahrah Rampuri
- Department of Biology, Mount Royal University, Calgary, Alberta, Canada
| | | | - Scott Thrall
- Department of Biology, Mount Royal University, Calgary, Alberta, Canada
| | - Jordan Bird
- Department of Biology, Mount Royal University, Calgary, Alberta, Canada
| | - Taylor S Harman
- Department of Exercise Science, Syracuse University, Syracuse, New York
| | - Trevor A Day
- Department of Biology, Mount Royal University, Calgary, Alberta, Canada
| | - Kevin S Heffernan
- Department of Exercise Science, Syracuse University, Syracuse, New York
| | - Tom D Brutsaert
- Department of Exercise Science, Syracuse University, Syracuse, New York
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Ando S, Komiyama T, Sudo M, Higaki Y, Ishida K, Costello JT, Katayama K. The interactive effects of acute exercise and hypoxia on cognitive performance: A narrative review. Scand J Med Sci Sports 2019; 30:384-398. [PMID: 31605635 DOI: 10.1111/sms.13573] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2019] [Revised: 09/09/2019] [Accepted: 10/04/2019] [Indexed: 12/13/2022]
Abstract
Acute moderate intensity exercise has been shown to improve cognitive performance. In contrast, hypoxia is believed to impair cognitive performance. The detrimental effects of hypoxia on cognitive performance are primarily dependent on the severity and duration of exposure. In this review, we describe how acute exercise under hypoxia alters cognitive performance, and propose that the combined effects of acute exercise and hypoxia on cognitive performance are mainly determined by interaction among exercise intensity and duration, the severity of hypoxia, and duration of exposure to hypoxia. We discuss the physiological mechanism(s) of the interaction and suggest that alterations in neurotransmitter function, cerebral blood flow, and possibly cerebral metabolism are the primary candidates that determine cognitive performance when acute exercise is combined with hypoxia. Furthermore, acclimatization appears to counteract impaired cognitive performance during prolonged exposure to hypoxia although the precise physiological mechanism(s) responsible for this amelioration remain to be elucidated. This review has implications for sporting, occupational, and recreational activities at terrestrial high altitude where cognitive performance is essential. Further studies are required to understand physiological mechanisms that determine cognitive performance when acute exercise is performed in hypoxia.
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Affiliation(s)
- Soichi Ando
- Graduate School of Informatics and Engineering, The University of Electro-Communications, Tokyo, Japan
| | - Takaaki Komiyama
- Center for Education in Liberal Arts and Sciences, Osaka University, Osaka, Japan
| | - Mizuki Sudo
- Meiji Yasuda Life Foundation of Health and Welfare, Tokyo, Japan
| | - Yasuki Higaki
- Faculty of Sports Science, Fukuoka University, Fukuoka, Japan
| | - Koji Ishida
- Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, Japan
| | - Joseph T Costello
- Extreme Environments Laboratory, Department of Sport and Exercise Science, University of Portsmouth, Portsmouth, UK
| | - Keisho Katayama
- Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, Japan
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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
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12
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Williams TB, Corbett J, McMorris T, Young JS, Dicks M, Ando S, Thelwell RC, Tipton MJ, Costello JT. Cognitive performance is associated with cerebral oxygenation and peripheral oxygen saturation, but not plasma catecholamines, during graded normobaric hypoxia. Exp Physiol 2019; 104:1384-1397. [DOI: 10.1113/ep087647] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2019] [Accepted: 06/11/2019] [Indexed: 11/08/2022]
Affiliation(s)
- Thomas B. Williams
- Extreme Environments LaboratoryDepartment of Sport and Exercise SciencesUniversity of Portsmouth Portsmouth UK
| | - Jo Corbett
- Extreme Environments LaboratoryDepartment of Sport and Exercise SciencesUniversity of Portsmouth Portsmouth UK
| | - Terry McMorris
- Extreme Environments LaboratoryDepartment of Sport and Exercise SciencesUniversity of Portsmouth Portsmouth UK
- Department of Sport and Exercise SciencesUniversity of Chichester Chichester UK
| | - John S. Young
- School of Pharmacy and Biomedical ScienceUniversity of Portsmouth Portsmouth UK
| | - Matt Dicks
- Extreme Environments LaboratoryDepartment of Sport and Exercise SciencesUniversity of Portsmouth Portsmouth UK
| | - Soichi Ando
- Graduate School of Informatics and EngineeringThe University of Electro‐Communications Tokyo Japan
| | - Richard C. Thelwell
- Extreme Environments LaboratoryDepartment of Sport and Exercise SciencesUniversity of Portsmouth Portsmouth UK
| | - Michael J. Tipton
- Extreme Environments LaboratoryDepartment of Sport and Exercise SciencesUniversity of Portsmouth Portsmouth UK
| | - Joseph T. Costello
- Extreme Environments LaboratoryDepartment of Sport and Exercise SciencesUniversity of Portsmouth Portsmouth UK
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Bain AR, Drvis I, Dujic Z, MacLeod DB, Ainslie PN. Physiology of static breath holding in elite apneists. Exp Physiol 2019; 103:635-651. [PMID: 29512224 DOI: 10.1113/ep086269] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 03/02/2018] [Indexed: 12/16/2022]
Abstract
NEW FINDINGS What is the topic of this review? This review provides an up-to-date assessment of the physiology involved with extreme static dry-land breath holding in trained apneists. What advances does it highlight? We specifically highlight the recent findings involved with the cardiovascular, cerebrovascular and metabolic function during a maximal breath hold in elite apneists. ABSTRACT Breath-hold-related activities have been performed for centuries, but only recently, within the last ∼30 years, has it emerged as an increasingly popular competitive sport. In apnoea sport, competition relates to underwater distances or simply maximal breath-hold duration, with the current (oxygen-unsupplemented) static breath-hold record at 11 min 35 s. Remarkably, many ultra-elite apneists are able to suppress respiratory urges to the point where consciousness fundamentally limits a breath-hold duration. Here, arterial oxygen saturations as low as ∼50% have been reported. In such cases, oxygen conservation to maintain cerebral functioning is critical, where responses ascribed to the mammalian dive reflex, e.g. sympathetically mediated peripheral vasoconstriction and vagally mediated bradycardia, are central. In defence of maintaining global cerebral oxygen delivery during prolonged breath holds, the cerebral blood flow may increase by ∼100% from resting values. Interestingly, near the termination of prolonged dry static breath holds, recent studies also indicate that reductions in the cerebral oxidative metabolism can occur, probably attributable to the extreme hypercapnia and irrespective of the hypoxaemia. In this review, we highlight and discuss the recent data on the cardiovascular, metabolic and, particularly, cerebrovascular function in competitive apneists performing maximal static breath holds. The physiological adaptation and maladaptation with regular breath-hold training are also summarized, and future research areas in this unique physiological field are highlighted; particularly, the need to determine the potential long-term health impacts of extreme breath holding.
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Affiliation(s)
- Anthony R Bain
- Center for Heart, Lung and Vascular Health, University of British Columbia, Kelowna, BC, Canada.,Integrative Physiology, University of Colorado, Boulder, CO, USA
| | - Ivan Drvis
- Faculty of Kinesiology, University of Zagreb, Zagreb, Croatia
| | - Zeljko Dujic
- Department of Integrative Physiology, University of Split School of Medicine, Split, Croatia
| | - David B MacLeod
- Human Pharmacology and Physiology Laboratory, Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - Philip N Ainslie
- Center for Heart, Lung and Vascular Health, University of British Columbia, Kelowna, BC, Canada
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14
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Huang M, Brothers RM, Ganio MS, Lucas RAI, Cramer MN, Moralez G, Convertino VA, Crandall CG. Tolerance to a haemorrhagic challenge during heat stress is improved with inspiratory resistance breathing. Exp Physiol 2018; 103:1243-1250. [PMID: 29947436 PMCID: PMC6119106 DOI: 10.1113/ep087102] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2018] [Accepted: 06/22/2018] [Indexed: 02/06/2023]
Abstract
NEW FINDINGS What is the central question of this study? Does inspiratory resistance breathing improve tolerance to simulated haemorrhage in individuals with elevated internal temperatures? What is the main finding and its importance? The main finding of this study is that inspiratory resistance breathing modestly improves tolerance to a simulated progressive haemorrhagic challenge during heat stress. These findings demonstrate a scenario in which exploitation of the respiratory pump can ameliorate serious conditions related to systemic hypotension. ABSTRACT Heat exposure impairs human blood pressure control and markedly reduces tolerance to a simulated haemorrhagic challenge. Inspiratory resistance breathing enhances blood pressure control and improves tolerance during simulated haemorrhage in normothermic individuals. However, it is unknown whether similar improvements occur with this manoeuvre in heat stress conditions. In this study, we tested the hypothesis that inspiratory resistance breathing improves tolerance to simulated haemorrhage in individuals with elevated internal temperatures. On two separate days, eight subjects performed a simulated haemorrhage challenge [lower-body negative pressure (LBNP)] to presyncope after an increase in internal temperature of 1.3 ± 0.1°C. During one trial, subjects breathed through an inspiratory impedance device set at 0 cmH2 O of resistance (Sham), whereas on a subsequent day the device was set at -7 cmH2 O of resistance (ITD). Tolerance was quantified as the cumulative stress index. Subjects were more tolerant to the LBNP challenge during the ITD protocol, as indicated by a > 30% larger cumulative stress index (Sham, 520 ± 306 mmHg min; ITD, 682 ± 324 mmHg min; P < 0.01). These data indicate that inspiratory resistance breathing modestly improves tolerance to a simulated progressive haemorrhagic challenge during heat stress.
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Affiliation(s)
- Mu Huang
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX, USA
- Department of Health Care Sciences, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - R Matthew Brothers
- Department of Kinesiology, University of Texas, Arlington, Arlington, TX, USA
| | - Matthew S Ganio
- Department of Health, Human Performance and Recreation, University of Arkansas, Fayetteville, AR, USA
| | - Rebekah A I Lucas
- School of Sport, Exercise & Rehabilitation Sciences, The University of Birmingham, Edgbaston, Birmingham, UK
| | - Matthew N Cramer
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX, USA
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Gilbert Moralez
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX, USA
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | | | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX, USA
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
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15
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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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16
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Caldwell HG, Ainslie PN, Ellis LA, Phillips AA, Flück D. Stability in neurovascular function at 3800 m. Physiol Behav 2017; 182:62-68. [DOI: 10.1016/j.physbeh.2017.09.023] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 09/26/2017] [Accepted: 09/26/2017] [Indexed: 01/19/2023]
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17
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Bailey DM, Willie CK, Hoiland RL, Bain AR, MacLeod DB, Santoro MA, DeMasi DK, Andrijanic A, Mijacika T, Barak OF, Dujic Z, Ainslie PN. Surviving Without Oxygen: How Low Can the Human Brain Go? High Alt Med Biol 2017; 18:73-79. [DOI: 10.1089/ham.2016.0081] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Affiliation(s)
- Damian M. Bailey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Glamorgan, United Kingdom
- Faculty of Medicine, University of British Columbia-Okanagan, Kelowna, 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
| | - 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
| | - 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
| | - David B. MacLeod
- Human Pharmacology and Physiology Laboratory, Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - Maria A. Santoro
- Human Pharmacology and Physiology Laboratory, Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - Daniel K. DeMasi
- Human Pharmacology and Physiology Laboratory, Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - Andrea Andrijanic
- School of Management, Libertas International University, Zagreb, Croatia
| | | | - Otto F. Barak
- School of Medicine, University of Split, Split, Croatia
- Faculty of Medicine, University of Novi Sad, Novi Sad, Serbia
| | - Zeljko Dujic
- School of Medicine, University of Split, Split, Croatia
| | - Philip N. Ainslie
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Glamorgan, United Kingdom
- 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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18
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Lawley JS, Macdonald JH, Oliver SJ, Mullins PG. Unexpected reductions in regional cerebral perfusion during prolonged hypoxia. J Physiol 2016; 595:935-947. [PMID: 27506309 DOI: 10.1113/jp272557] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Accepted: 08/04/2016] [Indexed: 01/06/2023] Open
Abstract
KEY POINTS Cognitive performance is impaired by hypoxia despite global cerebral oxygen delivery and metabolism being maintained. Using arterial spin labelled (ASL) magnetic resonance imaging, this is the first study to show regional reductions in cerebral blood flow (CBF) in response to decreased oxygen supply (hypoxia) at 2 h that increased in area and became more pronounced at 10 h. Reductions in CBF were seen in brain regions typically associated with the 'default mode' or 'task negative' network. Regional reductions in CBF, and associated vasoconstriction, within the default mode network in hypoxia is supported by increased vasodilatation in these regions to a subsequent hypercapnic (5% CO2 ) challenge. These results suggest an anatomical mechanism through which hypoxia may cause previously reported deficits in cognitive performance. ABSTRACT Hypoxia causes an increase in global cerebral blood flow, which maintains global cerebral oxygen delivery and metabolism. However, neurological deficits are abundant under hypoxic conditions. We investigated regional cerebral microvascular responses to acute (2 h) and prolonged (10 h) poikilocapnic normobaric hypoxia. We found that 2 h of hypoxia caused an expected increase in frontal cortical grey matter perfusion but unexpected perfusion decreases in regions of the brain normally associated with the 'default mode' or 'task negative' network. After 10 h in hypoxia, decreased blood flow to the major nodes of the default mode network became more pronounced and widespread. The use of a hypercapnic challenge (5% CO2 ) confirmed that these reductions in cerebral blood flow from hypoxia were related to vasoconstriction. Our findings demonstrate steady-state deactivation of the default network under acute hypoxia, which become more pronounced over time. Moreover, these data provide a unique insight into the nuanced localized cerebrovascular response to hypoxia that is not attainable through traditional methods. The observation of reduced perfusion in the posterior cingulate and cuneal cortex, which are regions assumed to play a role in declarative and procedural memory, provides an anatomical mechanism through which hypoxia may cause deficits in working memory.
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Affiliation(s)
- Justin S Lawley
- Extremes Research Group, School of Sport, Health and Exercise Sciences, Bangor University, Gwynedd, UK.,Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas, TX, USA
| | - Jamie H Macdonald
- Extremes Research Group, School of Sport, Health and Exercise Sciences, Bangor University, Gwynedd, UK
| | - Samuel J Oliver
- Extremes Research Group, School of Sport, Health and Exercise Sciences, Bangor University, Gwynedd, UK
| | - Paul G Mullins
- Bangor Imaging Centre, School of Psychology, Bangor University, Gwynedd, UK
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