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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.
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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
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Rosenberg AJ, Anderson GK, McKeefer HJ, Bird J, Pentz B, Byman BRM, Jendzjowsky N, Wilson RJ, Day TA, Rickards CA. Hemorrhage at high altitude: impact of sustained hypobaric hypoxia on cerebral blood flow, tissue oxygenation, and tolerance to simulated hemorrhage in humans. Eur J Appl Physiol 2024:10.1007/s00421-024-05450-1. [PMID: 38489034 DOI: 10.1007/s00421-024-05450-1] [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: 08/23/2023] [Accepted: 02/22/2024] [Indexed: 03/17/2024]
Abstract
With ascent to high altitude (HA), compensatory increases in cerebral blood flow and oxygen delivery must occur to preserve cerebral metabolism and consciousness. We hypothesized that this compensation in cerebral blood flow and oxygen delivery preserves tolerance to simulated hemorrhage (via lower body negative pressure, LBNP), such that tolerance is similar during sustained exposure to HA vs. low altitude (LA). Healthy humans (4F/4 M) participated in LBNP protocols to presyncope at LA (1130 m) and 5-7 days following ascent to HA (3800 m). Internal carotid artery (ICA) blood flow, cerebral delivery of oxygen (CDO2) through the ICA, and cerebral tissue oxygen saturation (ScO2) were determined. LBNP tolerance was similar between conditions (LA: 1276 ± 304 s vs. HA: 1208 ± 306 s; P = 0.58). Overall, ICA blood flow and CDO2 were elevated at HA vs. LA (P ≤ 0.01) and decreased with LBNP under both conditions (P < 0.0001), but there was no effect of altitude on ScO2 responses (P = 0.59). Thus, sustained exposure to hypobaric hypoxia did not negatively impact tolerance to simulated hemorrhage. These data demonstrate the robustness of compensatory physiological mechanisms that preserve human cerebral blood flow and oxygen delivery during sustained hypoxia, ensuring cerebral tissue metabolism and neuronal function is maintained.
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Affiliation(s)
- Alexander J Rosenberg
- Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
- Integrative Physiology Laboratory, Department of Kinesiology and Nutrition, University of Illinois at Chicago, Chicago, IL, USA
- Physiology Department, Midwestern University, Downers Grove, IL, USA
| | - Garen K Anderson
- Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Haley J McKeefer
- Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
| | | | | | | | - Nicholas Jendzjowsky
- University of Calgary, Calgary, AB, Canada
- Institute of Respiratory Medicine & Exercise Physiology, The Lundquist Institute at UCLA Harbor Medical, Torrance, CA, USA
| | | | | | - Caroline A Rickards
- Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA.
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Manferdelli G, Narang BJ, Bourdillon N, Giardini G, Debevec T, Millet GP. Impaired cerebrovascular CO 2 reactivity at high altitude in prematurely born adults. J Physiol 2023. [PMID: 38116893 DOI: 10.1113/jp285048] [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: 05/19/2023] [Accepted: 11/30/2023] [Indexed: 12/21/2023] Open
Abstract
Premature birth impairs cardiac and ventilatory responses to both hypoxia and hypercapnia, but little is known about cerebrovascular responses. Both at sea level and after 2 days at high altitude (3375 m), 16 young preterm-born (gestational age, 29 ± 1 weeks) and 15 age-matched term-born (40 ± 0 weeks) adults were exposed to two consecutive 4 min bouts of hyperoxic hypercapnic conditions (3% CO2 -97% O2 ; 6% CO2 -94% O2 ), followed by two periods of voluntary hyperventilation-induced hypocapnia. We measured middle cerebral artery blood velocity, end-tidal CO2 , pulmonary ventilation, beat-by-beat mean arterial pressure and arterialized capillary blood gases. Baseline middle cerebral artery blood velocity increased at high altitude compared with sea level in term-born (+24 ± 39%, P = 0.036), but not in preterm-born (-4 ± 27%, P = 0.278) adults. The end-tidal CO2 , pulmonary ventilation and mean arterial pressure were similar between groups at sea level and high altitude. Hypocapnic cerebrovascular reactivity was higher at high altitude compared with sea level in term-born adults (+173 ± 326%, P = 0.026) but not in preterm-born adults (-21 ± 107%, P = 0.572). Hypercapnic reactivity was altered at altitude only in preterm-born adults (+125 ± 144%, P < 0.001). Collectively, at high altitude, term-born participants showed higher hypocapnic (P = 0.012) and lower hypercapnic (P = 0.020) CO2 reactivity compared with their preterm-born peers. In conclusion, exposure to high altitude revealed different cerebrovascular responses in preterm- compared with term-born adults, despite similar ventilatory responses. These findings suggest a blunted cerebrovascular response at high altitude in preterm-born adults, which might predispose these individuals to an increased risk of high-altitude illnesses. KEY POINTS: Cerebral haemodynamics and cerebrovascular reactivity in normoxia are known to be similar between term-born and prematurely born adults. In contrast, acute exposure to high altitude unveiled different cerebrovascular responses to hypoxia, hypercapnia and hypocapnia. In particular, cerebral vasodilatation was impaired in prematurely born adults, leading to an exaggerated cerebral vasoconstriction. Cardiovascular and ventilatory responses to both hypo- and hypercapnia at sea level and at high altitude were similar between control subjects and prematurely born adults. Other mechanisms might therefore underlie the observed blunted cerebral vasodilatory responses in preterm-born adults at high altitude.
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Affiliation(s)
| | - Benjamin J Narang
- Department of Automatics, Biocybernetics and Robotics, Jožef Stefan Institute, Ljubljana, Slovenia
- Faculty of Sport, University of Ljubljana, Ljubljana, Slovenia
| | - Nicolas Bourdillon
- Institute of Sport Sciences, University of Lausanne, Lausanne, Switzerland
| | - Guido Giardini
- Mountain Medicine and Neurology Centre, Valle D'Aosta Regional Hospital, Aosta, Italy
| | - Tadej Debevec
- Department of Automatics, Biocybernetics and Robotics, Jožef Stefan Institute, Ljubljana, Slovenia
- Faculty of Sport, University of Ljubljana, Ljubljana, Slovenia
| | - Grégoire P Millet
- Institute of Sport Sciences, University of Lausanne, Lausanne, Switzerland
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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.
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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
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Pathophysiology and Therapy of High-Altitude Sickness: Practical Approach in Emergency and Critical Care. J Clin Med 2022; 11:jcm11143937. [PMID: 35887706 PMCID: PMC9325098 DOI: 10.3390/jcm11143937] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Revised: 06/21/2022] [Accepted: 06/24/2022] [Indexed: 12/26/2022] Open
Abstract
High altitude can be a hostile environment and a paradigm of how environmental factors can determine illness when human biological adaptability is exceeded. This paper aims to provide a comprehensive review of high-altitude sickness, including its epidemiology, pathophysiology, and treatments. The first section of our work defines high altitude and considers the mechanisms of adaptation to it and the associated risk factors for low adaptability. The second section discusses the main high-altitude diseases, highlighting how environmental factors can lead to the loss of homeostasis, compromising important vital functions. Early recognition of clinical symptoms is important for the establishment of the correct therapy. The third section focuses on high-altitude pulmonary edema, which is one of the main high-altitude diseases. With a deeper understanding of the pathogenesis of high-altitude diseases, as well as a reasoned approach to environmental or physical factors, we examine the main high-altitude diseases. Such an approach is critical for the effective treatment of patients in a hostile environment, or treatment in the emergency room after exposure to extreme physical or environmental factors.
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Baker J, Safarzadeh MA, Incognito AV, Jendzjowsky NG, Foster GE, Bird JD, Raj SR, Day TA, Rickards CA, Zubieta-DeUrioste N, Alim U, Wilson RJA. Functional optical coherence tomography at altitude: retinal microvascular perfusion and retinal thickness at 3,800 meters. J Appl Physiol (1985) 2022; 133:534-545. [PMID: 35771223 DOI: 10.1152/japplphysiol.00132.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cerebral hypoxia is a serious consequence of several cardiorespiratory illnesses. Measuring the retinal microvasculature at high altitude provides a surrogate for cerebral microvasculature, offering potential insight into cerebral hypoxia in critical illness. Additionally, while sex-specific differences in cardiovascular diseases are strongly supported, few have focused on differences in ocular blood flow. We evaluated the retinal microvasculature in males (n=11) and females (n=7) using functional optical coherence tomography at baseline (1,130m) (Day 0), following rapid ascent (Day 2) and prolonged exposure (Day 9) to high altitude (3,800m). Retinal vascular perfusion density (rVPD; an index of total blood supply), retinal thickness (RT; reflecting vascular and neural tissue volume) and arterial blood were acquired. As a group, rVPD increased on Day 2 vs. Day 0 (p<0.001) and was inversely related to PaO2 (R2=0.45; p=0.006). By Day 9, rVPD recovered to baseline, but was significantly lower in males vs. females (p=0.007). RT was not different on Day 2 vs. Day 0 (p>0.99) but was reduced by Day 9 relative to Day 0 and Day 2 (p<0.001). RT changes relative to Day 0 were inversely related to changes in PaO2 on Day 2 (R2=0.6; p=0.001) and Day 9 (R2=0.4; p=0.02). RT did not differ between sexes. These data suggest differential time course and regulation of the retina during rapid ascent and prolonged exposure to high altitude and are the first to demonstrate sex-specific differences in rVPD at high altitude. The ability to assess intact microvasculature contiguous with the brain has widespread research and clinical applications.
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Affiliation(s)
- Jacquie Baker
- Libin Cardiovascular Institute, Department of Cardiac Sciences, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.,Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada
| | - Mohammad Amin Safarzadeh
- Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada.,Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada.,Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Alberta, Canada
| | - Anthony V Incognito
- Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada.,Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada.,Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Alberta, Canada
| | - Nicholas G Jendzjowsky
- Division of Respiratory and Critical Care Physiology and Medicine, The Lundquist Institute for Biomedical Innovation at Harbor-UCLA Medical Center, Torrance, California, United States
| | - Glen Edward Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | - Jordan D Bird
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Satish R Raj
- Libin Cardiovascular Institute, Department of Cardiac Sciences, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Trevor A Day
- Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Caroline A Rickards
- Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Natalia Zubieta-DeUrioste
- Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada.,Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada.,High Altitude Pulmonary and Pathology Institute (HAPPI - IPPA), La Paz, Bolivia
| | - Usman Alim
- Department of Computer Science, University of Calgary, Calgary, Alberta, Canada
| | - Richard J A Wilson
- Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada.,Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada.,Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Alberta, Canada
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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.
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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
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Falla M, Giardini G, Angelini C. Recommendations for traveling to altitude with neurological disorders. J Cent Nerv Syst Dis 2021; 13:11795735211053448. [PMID: 34955663 PMCID: PMC8695750 DOI: 10.1177/11795735211053448] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 09/02/2021] [Accepted: 09/28/2021] [Indexed: 11/16/2022] Open
Abstract
BACKGROUND Several neurological conditions might worsen with the exposure to high altitude (HA). The aim of this review was to summarize the available knowledge on the neurological HA illnesses and the risk for people with neurological disorders to attend HA locations. METHODS A search of literature was conducted for several neurological disorders in PubMed and other databases since 1970. The neurological conditions searched were migraine, different cerebrovascular disease, intracranial space occupying mass, multiple sclerosis, peripheral neuropathies, neuromuscular disorders, epileptic seizures, delirium, dementia, and Parkinson's disease (PD). RESULTS Attempts were made to classify the risk posed by each condition and to provide recommendations regarding medical evaluation and advice for or against traveling to altitude. Individual cases should be advised after careful examination and risk evaluation performed either in an outpatient mountain medicine service or by a physician with knowledge of HA risks. Preliminary diagnostic methods and anticipation of neurological complications are needed. CONCLUSIONS Our recommendations suggest absolute contraindications to HA exposure for the following neurological conditions: (1) Unstable conditions-such as recent strokes, (2) Diabetic neuropathy, (3) Transient ischemic attack in the last month, (4) Brain tumors, and 5. Neuromuscular disorders with a decrease of forced vital capacity >60%. We consider the following relative contraindications where decision has to be made case by case: (1) Epilepsy based on recurrence of seizure and stabilization with the therapy, (2) PD (± obstructive sleep apnea syndrome-OSAS), (3) Mild Cognitive Impairment (± OSAS), and (4) Patent foramen ovale and migraine have to be considered risk factors for acute mountain sickness.
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Affiliation(s)
- Marika Falla
- Institute of Mountain Emergency
Medicine, Eurac Research, Bolzano, Italy
- Center for Mind/Brain Sciences,
CIMeC, University of Trento, Rovereto, Italy
| | - Guido Giardini
- Mountain Medicine and Neurology
Centre, Valle D’Aosta Regional
Hospital, Aosta, Italy
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10
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The influence of short-term high-altitude acclimatization on cerebral and leg tissue oxygenation post-orthostasis. Eur J Appl Physiol 2021; 121:3095-3102. [PMID: 34319446 DOI: 10.1007/s00421-021-04765-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Accepted: 07/06/2021] [Indexed: 10/20/2022]
Abstract
PURPOSE Orthostasis at sea level decreases brain tissue oxygenation and increases risk of syncope. High altitude reduces brain and peripheral muscle tissue oxygenation. This study determined the effect of short-term altitude acclimatization on cerebral and peripheral leg tissue oxygenation index (TOI) post-orthostasis. METHOD Seven lowlanders completed a supine-to-stand maneuver at sea level (450 m) and for 3 consecutive days at high altitude (3776 m). Cardiorespiratory measurements and near-infrared spectroscopy-derived oxygenation of the frontal lobe (cerebral TOI) and vastus lateralis (leg TOI) were measured at supine and 5-min post-orthostasis. RESULTS After orthostasis at sea level, cerebral TOI decreased [mean Δ% (95% confidential interval): - 4.5%, (- 7.5, - 1.5), P < 0.001], whilst leg TOI was unchanged [- 4.6%, (- 10.9, 1.7), P = 0.42]. High altitude had no effect on cerebral TOI following orthostasis [days 1-3: - 2.3%, (- 5.3, 0.7); - 2.4%, (- 5.4, 0.6); - 2.1%, (- 5.1, 0.9), respectively, all P > 0.05], whereas leg TOI decreased [days 1-3: - 12.0%, (- 18.3, - 5.7); - 12.1%, (- 18.4, - 5.8); - 10.2%, (- 16.5, - 3.9), respectively, all P < 0.001]. This response did not differ with days spent at high altitude, despite evidence of cardiorespiratory acclimatization [increased peripheral oxygen saturation (supine: P = 0.01; stand: P = 0.02) and decreased end-tidal carbon dioxide (supine: P = 0.003; stand: P = 0.01)]. CONCLUSION Cerebral oxygenation is preferentially maintained over leg oxygenation post-orthostasis at high altitude, suggesting different vascular regulation between cerebral and peripheral circulations. Short-term acclimatization to high altitude did not alter cerebral and leg oxygenation responses to orthostasis.
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Manferdelli G, Marzorati M, Easton C, Porcelli S. Changes in prefrontal cerebral oxygenation and microvascular blood volume in hypoxia and possible association with acute mountain sickness. Exp Physiol 2020; 106:76-85. [DOI: 10.1113/ep088515] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Accepted: 07/24/2020] [Indexed: 01/30/2023]
Affiliation(s)
- Giorgio Manferdelli
- Institute of Biomedical Technologies National Research Council Segrate Italy
- School of Health and Exercise Sciences University of the West of Scotland Paisley UK
| | - Mauro Marzorati
- Institute of Biomedical Technologies National Research Council Segrate Italy
| | - Chris Easton
- School of Health and Exercise Sciences University of the West of Scotland Paisley UK
| | - Simone Porcelli
- Institute of Biomedical Technologies National Research Council Segrate Italy
- Department of Molecular Physiology University of Pavia Pavia Italy
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12
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Gibbons TD, Tymko MM, Thomas KN, Wilson LC, Stembridge M, Caldwell HG, Howe CA, Hoiland RL, Akerman AP, Dawkins TG, Patrician A, Coombs GB, Gasho C, Stacey BS, Ainslie PN, Cotter JD. Global REACH 2018: The influence of acute and chronic hypoxia on cerebral haemodynamics and related functional outcomes during cold and heat stress. J Physiol 2020; 598:265-284. [PMID: 31696936 DOI: 10.1113/jp278917] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2019] [Accepted: 10/28/2019] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Thermal and hypoxic stress commonly coexist in environmental, occupational and clinical settings, yet how the brain tolerates these multi-stressor environments is unknown Core cooling by 1.0°C reduced cerebral blood flow (CBF) by 20-30% and cerebral oxygen delivery (CDO2 ) by 12-19% at sea level and high altitude, whereas core heating by 1.5°C did not reliably reduce CBF or CDO2 Oxygen content in arterial blood was fully restored with acclimatisation to 4330 m, but concurrent cold stress reduced CBF and CDO2 Gross indices of cognition were not impaired by any combination of thermal and hypoxic stress despite large reductions in CDO2 Chronic hypoxia renders the brain susceptible to large reductions in oxygen delivery with concurrent cold stress, which might make monitoring core temperature more important in this context ABSTRACT: Real-world settings are composed of multiple environmental stressors, yet the majority of research in environmental physiology investigates these stressors in isolation. The brain is central in both behavioural and physiological responses to threatening stimuli and, given its tight metabolic and haemodynamic requirements, is particularly susceptible to environmental stress. We measured cerebral blood flow (CBF, duplex ultrasound), cerebral oxygen delivery (CDO2 ), oesophageal temperature, and arterial blood gases during exposure to three commonly experienced environmental stressors - heat, cold and hypoxia - in isolation, and in combination. Twelve healthy male subjects (27 ± 11 years) underwent core cooling by 1.0°C and core heating by 1.5°C in randomised order at sea level; acute hypoxia ( P ET , O 2 = 50 mm Hg) was imposed at baseline and at each thermal extreme. Core cooling and heating protocols were repeated after 16 ± 4 days residing at 4330 m to investigate any interactions with high altitude acclimatisation. Cold stress decreased CBF by 20-30% and CDO2 by 12-19% (both P < 0.01) irrespective of altitude, whereas heating did not reliably change either CBF or CDO2 (both P > 0.08). The increases in CBF with acute hypoxia during thermal stress were appropriate to maintain CDO2 at normothermic, normoxic values. Reaction time was faster and slower by 6-9% with heating and cooling, respectively (both P < 0.01), but central (brain) processes were not impaired by any combination of environmental stressors. These findings highlight the powerful influence of core cooling in reducing CDO2 . Despite these large reductions in CDO2 with cold stress, gross indices of cognition remained stable.
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Affiliation(s)
- T D Gibbons
- School of Physical Education, Sport & Exercise Science, University of Otago, 55/47 Union St W, Dunedin, 9016, New Zealand
| | - M M Tymko
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - K N Thomas
- Department of Surgical Sciences, University of Otago, 201 Great King St, Dunedin, 9016, New Zealand
| | - L C Wilson
- Department of Medicine, University of Otago, 201 Great King St, Dunedin, 9016, New Zealand
| | - M Stembridge
- Cardiff Centre for Exercise and Health, Cardiff Metropolitan University, Cyncoed Road, Cardiff, CF23 6XD, UK
| | - H G Caldwell
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - C A Howe
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - R L Hoiland
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - A P Akerman
- Faculty of Health Sciences, University of Ottawa, 125 University St, Ottawa, Ontario, Canada, K1N 6N5
| | - T G Dawkins
- Cardiff Centre for Exercise and Health, Cardiff Metropolitan University, Cyncoed Road, Cardiff, CF23 6XD, UK
| | - A Patrician
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - G B Coombs
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - C Gasho
- Division of Pulmonary, Critical Care, Hyperbaric and Sleep Medicine, Loma Linda University School of Medicine, Loma Linda, CA, USA
| | - B S Stacey
- Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, UK
| | - P N Ainslie
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan Campus, School of Health and Exercise Sciences, 3333 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - J D Cotter
- School of Physical Education, Sport & Exercise Science, University of Otago, 55/47 Union St W, Dunedin, 9016, New Zealand
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Hsieh DT, Warden GI, Butler JM, Nakanishi E, Asano Y. Multiple Sclerosis Exacerbation Associated With High-Altitude Climbing Exposure. Mil Med 2019; 185:e1322-e1325. [DOI: 10.1093/milmed/usz421] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Abstract
The spectrum of the neurological effects of high-altitude exposure can range from high-altitude headache and acute mountain sickness, to the more severe end of the spectrum with high-altitude cerebral edema. In general, patients with known unstable preexisting neurological conditions and those patients with residual neurological deficits from a preexisting neurological condition are discouraged from climbing to high altitudes because of the risk of exacerbation or worsening of symptoms. Although multiple sclerosis exacerbations can be triggered by environmental factors, high-altitude exposure has not been reported as a potential trigger. We are reporting the case of a multiple sclerosis exacerbation presenting in an active duty U.S. Air Force serviceman upon ascending and descending Mt. Fuji within the same day.
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Affiliation(s)
- David T Hsieh
- Department of Pediatrics, 374th Medical Group, Yokota AB, Unit 5071, APO, AP 96328, Japan
- The Office of the Chief, manuscript writing and revision and provided Japanese translation capabilities Medical Staff, 374th Medical Group, Yokota AB, Unit 5071, APO, AP 96328, Japan
| | - Graham I Warden
- Radiology, 374th Medical Group, Yokota AB, Unit 5071, APO, AP 96328, Japan
| | - Jay M Butler
- Optometry, Department of Pediatrics, 374th Medical Group, Yokota AB, Unit 5071, APO, AP 96328, Japan
| | - Erika Nakanishi
- The Office of the Chief, manuscript writing and revision and provided Japanese translation capabilities Medical Staff, 374th Medical Group, Yokota AB, Unit 5071, APO, AP 96328, Japan
| | - Yuri Asano
- Department of Neurology, patient and contributed to the writing and revision of the manuscript, Tokyo Metropolitan Neurological Hospital, 2-6-1 Musashi dai Fuchu-City, Tokyo 183-0042, Japan
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14
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15
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Howe CA, Ainslie PN, Tremblay JC, Carter HH, Patrician A, Stembridge M, Williams A, Drane AL, Delorme E, Rieger MG, Tymko MM, Gasho C, Santoro A, MacLeod DB, Hoiland RL. UBC-Nepal Expedition: Haemoconcentration underlies the reductions in cerebral blood flow observed during acclimatization to high altitude. Exp Physiol 2019; 104:1963-1972. [PMID: 31410899 DOI: 10.1113/ep087663] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2019] [Accepted: 08/13/2019] [Indexed: 12/16/2022]
Abstract
NEW FINDINGS What is the central question of this study? The aim was to evaluate the degree to which increases in haematocrit alter cerebral blood flow and cerebral oxygen delivery during acclimatization to high altitude. What is the main finding and its importance? Through haemodilution, we determined that, after 1 week of acclimatization, the primary mechanism contributing to the cerebral blood flow response during acclimatization is an increase in haemoglobin and haematocrit. The remaining contribution to the cerebral blood flow response during acclimatization is likely to be attributable to ventilatory acclimatization. ABSTRACT At high altitude, an increase in haematocrit (Hct) is achieved through altitude-induced diuresis and erythropoiesis, both of which result in increased arterial oxygen content. Given the impact of alterations in Hct on oxygen content, haemoconcentration has been hypothesized to mediate, in part, the attenuation of the initial elevation in cerebral blood flow (CBF) at high altitude. To test this hypothesis, healthy men (n = 13) ascended to 5050 m over 9 days without the aid of prophylactic acclimatization medications. After 1 week of acclimatization at 5050 m, participants were haemodiluted by rapid saline infusion (2.10 ± 0.28 l) to return Hct towards pre-acclimatization values. Arterial blood gases, Hct, global CBF (duplex ultrasound) and haemodynamic variables were measured after initial arrival at 5050 m and after 1 week of acclimatization at high altitude, before and after the haemodilution protocol. After 1 week at 5050 m, the Hct increased from 42.5 ± 2.5 to 49.6 ± 2.5% (P < 0.001), and it was subsequently reduced to 45.6 ± 2.3% (P < 0.001) after haemodilution. Global CBF decreased from 844 ± 160 to 619 ± 136 ml min-1 (P = 0.033) after 1 week of acclimatization and increased to 714 ± 204 ml min -1 (P = 0.045) after haemodilution. Despite the significant changes in Hct, and thus oxygen content, cerebral oxygen delivery was unchanged at all time points. Furthermore, these observations occurred in the absence of any changes in mean arterial blood pressure, cardiac output, arterial blood pH or oxygen saturation pre- and posthaemodilution. These data highlight the influence of Hct in the regulation of CBF and are the first to demonstrate experimentally that haemoconcentration contributes to the reduction in CBF during acclimatization to altitude.
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Affiliation(s)
- Connor A Howe
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
| | - 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
| | - Joshua C Tremblay
- Cardiovascular Stress Response Laboratory, School of Kinesiology and Health Studies, Queen's University, Kingston, ON, Canada
| | - Howard H Carter
- Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Alex Patrician
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
| | - Mike Stembridge
- Cardiff Centre for Exercise and Health, Cardiff Metropolitan University, Cardiff, UK
| | - Alex Williams
- International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada
| | - Aimee L Drane
- Cardiff Centre for Exercise and Health, Cardiff Metropolitan University, Cardiff, UK
| | - Eric Delorme
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan Campus, Kelowna, BC, Canada
| | - Mathew G Rieger
- 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
| | - Chris Gasho
- VA Loma Linda Healthcare System and Loma Linda University School of Medicine, Loma Linda, CA, USA
| | - Antoinette Santoro
- Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - David B MacLeod
- Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - 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
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16
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Heinrich EC, Djokic MA, Gilbertson D, DeYoung PN, Bosompra NO, Wu L, Anza-Ramirez C, Orr JE, Powell FL, Malhotra A, Simonson TS. Cognitive function and mood at high altitude following acclimatization and use of supplemental oxygen and adaptive servoventilation sleep treatments. PLoS One 2019; 14:e0217089. [PMID: 31188839 PMCID: PMC6561544 DOI: 10.1371/journal.pone.0217089] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 05/03/2019] [Indexed: 11/19/2022] Open
Abstract
Impairments in cognitive function, mood, and sleep quality occur following ascent to high altitude. Low oxygen (hypoxia) and poor sleep quality are both linked to impaired cognitive performance, but their independent contributions at high altitude remain unknown. Adaptive servoventilation (ASV) improves sleep quality by stabilizing breathing and preventing central apneas without supplemental oxygen. We compared the efficacy of ASV and supplemental oxygen sleep treatments for improving daytime cognitive function and mood in high-altitude visitors (N = 18) during acclimatization to 3,800 m. Each night, subjects were randomly provided with ASV, supplemental oxygen (SpO2 > 95%), or no treatment. Each morning subjects completed a series of cognitive function tests and questionnaires to assess mood and multiple aspects of cognitive performance. We found that both ASV and supplemental oxygen (O2) improved daytime feelings of confusion (ASV: p < 0.01; O2: p < 0.05) and fatigue (ASV: p < 0.01; O2: p < 0.01) but did not improve other measures of cognitive performance at high altitude. However, performance improved on the trail making tests (TMT) A and B (p < 0.001), the balloon analog risk test (p < 0.0001), and the psychomotor vigilance test (p < 0.01) over the course of three days at altitude after controlling for effects of sleep treatments. Compared to sea level, subjects reported higher levels of confusion (p < 0.01) and performed worse on the TMT A (p < 0.05) and the emotion recognition test (p < 0.05) on nights when they received no treatment at high altitude. These results suggest that stabilizing breathing (ASV) or increasing oxygenation (supplemental oxygen) during sleep can reduce feelings of fatigue and confusion, but that daytime hypoxia may play a larger role in other cognitive impairments reported at high altitude. Furthermore, this study provides evidence that some aspects of cognition (executive control, risk inhibition, sustained attention) improve with acclimatization.
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Affiliation(s)
- Erica C. Heinrich
- Department of Medicine, Division of Pulmonary, Critical Care, and Sleep Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Matea A. Djokic
- Department of Medicine, Division of Pulmonary, Critical Care, and Sleep Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Dillon Gilbertson
- Department of Medicine, Division of Pulmonary, Critical Care, and Sleep Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Pamela N. DeYoung
- Department of Medicine, Division of Pulmonary, Critical Care, and Sleep Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Naa-Oye Bosompra
- Department of Medicine, Division of Pulmonary, Critical Care, and Sleep Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Lu Wu
- Department of Medicine, Division of Pulmonary, Critical Care, and Sleep Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Cecilia Anza-Ramirez
- Departamento de Ciencias Biológicas y Fisiológicas, Facultad de Ciencias y Filosofía, Universidad Peruana Cayetano Heredia, Lima, Peru
| | - Jeremy E. Orr
- Department of Medicine, Division of Pulmonary, Critical Care, and Sleep Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Frank L. Powell
- Department of Medicine, Division of Pulmonary, Critical Care, and Sleep Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Atul Malhotra
- Department of Medicine, Division of Pulmonary, Critical Care, and Sleep Medicine, University of California San Diego, La Jolla, California, United States of America
| | - Tatum S. Simonson
- Department of Medicine, Division of Pulmonary, Critical Care, and Sleep Medicine, University of California San Diego, La Jolla, California, United States of America
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17
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Leacy JK, Zouboules SM, Mann CR, Peltonen JDB, Saran G, Nysten CE, Nysten HE, Brutsaert TD, O’Halloran KD, Sherpa MT, Day TA. Neurovascular Coupling Remains Intact During Incremental Ascent to High Altitude (4240 m) in Acclimatized Healthy Volunteers. Front Physiol 2018; 9:1691. [PMID: 30546319 PMCID: PMC6279846 DOI: 10.3389/fphys.2018.01691] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Accepted: 11/09/2018] [Indexed: 12/21/2022] Open
Abstract
Neurovascular coupling (NVC) is the temporal link between neuronal metabolic activity and regional cerebral blood flow (CBF), supporting adequate delivery of nutrients. Exposure to high altitude (HA) imposes several stressors, including hypoxia and hypocapnia, which modulate cerebrovascular tone in an antagonistic fashion. Whether these contrasting stressors and subsequent adaptations affect NVC during incremental ascent to HA is unclear. The aim of this study was to assess whether incremental ascent to HA influences the NVC response. Given that CBF is sensitive to changes in arterial blood gasses, in particular PaCO2, we hypothesized that the vasoconstrictive effect of hypocapnia during ascent would decrease the NVC response. 10 healthy study participants (21.7 ± 1.3 years, 23.57 ± 2.00 kg/m2, mean ± SD) were recruited as part of a research expedition to HA in the Nepal Himalaya. Resting posterior cerebral artery velocity (PCAv), arterial blood gasses (PaO2, SaO2, PaCO2, [HCO3 -], base excess and arterial blood pH) and NVC response of the PCA were measured at four pre-determined locations: Calgary/Kathmandu (1045/1400 m, control), Namche (3440 m), Deboche (3820 m) and Pheriche (4240 m). PCAv was measured using transcranial Doppler ultrasound. Arterial blood draws were taken from the radial artery and analyzed using a portable blood gas/electrolyte analyzer. NVC was determined in response to visual stimulation (VS; Strobe light; 6 Hz; 30 s on/off × 3 trials). The NVC response was averaged across three VS trials at each location. PaO2, SaO2, and PaCO2 were each significantly decreased at 3440, 3820, and 4240 m. No significant differences were found for pH at HA (P > 0.05) due to significant reductions in [HCO3 -] (P < 0.043). As expected, incremental ascent to HA induced a state of hypoxic hypocapnia, whereas normal arterial pH was maintained due to renal compensation. NVC was quantified as the delta (Δ) PCAv from baseline for mean PCAv, peak PCAv and total area under the curve (ΔPCAv tAUC) during VS. No significant differences were found for Δmean, Δpeak or ΔPCAv tAUC between locations (P > 0.05). NVC remains remarkably intact during incremental ascent to HA in healthy acclimatized individuals. Despite the array of superimposed stressors associated with ascent to HA, CBF and NVC regulation may be preserved coincident with arterial pH maintenance during acclimatization.
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Affiliation(s)
- Jack K. Leacy
- Department of Biology, Mount Royal University, Calgary, AB, Canada
- Department of Physiology, School of Medicine, College of Medicine & Health, University College Cork, Cork, Ireland
| | | | - Carli R. Mann
- Department of Biology, Mount Royal University, Calgary, AB, Canada
| | | | - Gurkan Saran
- Department of Biology, Mount Royal University, Calgary, AB, Canada
| | | | | | - Tom D. Brutsaert
- School of Education, Syracuse University, Syracuse, NY, United States
| | - Ken D. O’Halloran
- Department of Physiology, School of Medicine, College of Medicine & Health, University College Cork, Cork, Ireland
| | | | - Trevor A. Day
- Department of Biology, Mount Royal University, Calgary, AB, Canada
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18
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Ventilatory and cerebrovascular regulation and integration at high-altitude. Clin Auton Res 2018; 28:423-435. [PMID: 29574504 DOI: 10.1007/s10286-018-0522-2] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2017] [Accepted: 03/09/2018] [Indexed: 01/17/2023]
Abstract
Ascent to high-altitude elicits compensatory physiological adaptations in order to improve oxygenation throughout the body. The brain is particularly vulnerable to the hypoxemia of terrestrial altitude exposure. Herein we review the ventilatory and cerebrovascular changes at altitude and how they are both implicated in the maintenance of oxygen delivery to the brain. Further, the interdependence of ventilation and cerebral blood flow at altitude is discussed. Following the acute hypoxic ventilatory response, acclimatization leads to progressive increases in ventilation, and a partial mitigation of hypoxemia. Simultaneously, cerebral blood flow increases during initial exposure to altitude when hypoxemia is the greatest. Following ventilatory acclimatization to altitude, and an increase in hemoglobin concentration-which both underscore improvements in arterial oxygen content over time at altitude-cerebral blood flow progressively decreases back to sea-level values. The complimentary nature of these responses (ventilatory, hematological and cerebral) lead to a tightly maintained cerebral oxygen delivery while at altitude. Despite this general maintenance of global cerebral oxygen delivery, the manner in which this occurs reflects integration of these physiological responses. Indeed, ventilation directly influences cerebral blood flow by determining the prevailing blood gas and acid/base stimuli at altitude, but cerebral blood flow may also influence ventilation by altering central chemoreceptor stimulation via central CO2 washout. The causes and consequences of the integration of ventilatory and cerebral blood flow regulation at high altitude are outlined.
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19
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Liu X, Xu D, Hall JR, Ross S, Chen S, Liu H, Mallet RT, Shi X. Enhanced cerebral perfusion during brief exposures to cyclic intermittent hypoxemia. J Appl Physiol (1985) 2017; 123:1689-1697. [DOI: 10.1152/japplphysiol.00647.2017] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cerebral vasodilation and increased cerebral oxygen extraction help maintain cerebral oxygen uptake in the face of hypoxemia. This study examined cerebrovascular responses to intermittent hypoxemia in eight healthy men breathing 10% O2 for 5 cycles, each 6 min, interspersed with 4 min of room air breathing. Hypoxia exposures raised heart rate ( P < 0.01) without altering arterial pressure, and increased ventilation ( P < 0.01) by expanding tidal volume. Arterial oxygen saturation ([Formula: see text]) and cerebral tissue oxygenation ([Formula: see text]) fell ( P < 0.01) less appreciably in the first bout (from 97.0 ± 0.3% and 72.8 ± 1.6% to 75.5 ± 0.9% and 54.5 ± 0.9%, respectively) than the fifth bout (from 94.9 ± 0.4% and 70.8 ± 1.0% to 66.7 ± 2.3% and 49.2 ± 1.5%, respectively). Flow velocity in the middle cerebral artery ( VMCA) and cerebrovascular conductance increased in a sigmoid fashion with decreases in [Formula: see text] and [Formula: see text]. These stimulus-response curves shifted leftward and upward from the first to the fifth hypoxia bouts; thus, the centering points fell from 79.2 ± 1.4 to 74.6 ± 1.1% ( P = 0.01) and from 59.8 ± 1.0 to 56.6 ± 0.3% ( P = 0.002), and the minimum VMCA increased from 54.0 ± 0.5 to 57.2 ± 0.5 cm/s ( P = 0.0001) and from 53.9 ± 0.5 to 57.1 ± 0.3 cm/s ( P = 0.0001) for the [Formula: see text]- VMCA and [Formula: see text]- VMCA curves, respectively. Cerebral oxygen extraction increased from prehypoxia 0.22 ± 0.01 to 0.25 ± 0.02 in minute 6 of the first hypoxia bout, and remained elevated between 0.25 ± 0.01 and 0.27 ± 0.01 throughout the fifth hypoxia bout. These results demonstrate that cerebral vasodilation combined with enhanced cerebral oxygen extraction fully compensated for decreased oxygen content during acute, cyclic hypoxemia. NEW & NOTEWORTHY Five bouts of 6-min intermittent hypoxia (IH) exposures to 10% O2 progressively reduce arterial oxygen saturation ([Formula: see text]) to 67% without causing discomfort or distress. Cerebrovascular responses to hypoxemia are dynamically reset over the course of a single IH session, such that threshold and saturation for cerebral vasodilations occurred at lower [Formula: see text] and cerebral tissue oxygenation ([Formula: see text]) during the fifth vs. first hypoxia bouts. Cerebral oxygen extraction is augmented during acute hypoxemia, which compensates for decreased arterial O2 content.
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Affiliation(s)
- Xiaoli Liu
- Institute of Cardiovascular & Metabolic Disease, University of North Texas Health Science Center, Fort Worth, Texas
- Department of Physical Therapy, University of North Texas Health Science Center, Fort Worth, Texas
| | - Diqun Xu
- Institute of Cardiovascular & Metabolic Disease, University of North Texas Health Science Center, Fort Worth, Texas
| | - James R. Hall
- Hubei University for Nationalities, Enshi, Hubei, China
| | - Sarah Ross
- Hubei University for Nationalities, Enshi, Hubei, China
| | - Shande Chen
- Hubei University for Nationalities, Enshi, Hubei, China
- Institute of Healthy Aging, University of North Texas Health Science Center, Fort Worth, Texas
| | - Howe Liu
- Department of Biostatistics, University of North Texas Health Science Center, Fort Worth, Texas
| | - Robert T. Mallet
- Institute of Cardiovascular & Metabolic Disease, University of North Texas Health Science Center, Fort Worth, Texas
| | - Xiangrong Shi
- Institute of Cardiovascular & Metabolic Disease, University of North Texas Health Science Center, Fort Worth, Texas
- Institute of Healthy Aging, University of North Texas Health Science Center, Fort Worth, Texas
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20
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Rieger MG, Hoiland RL, Tremblay JC, Stembridge M, Bain AR, Flück D, Subedi P, Anholm JD, Ainslie PN. One session of remote ischemic preconditioning does not improve vascular function in acute normobaric and chronic hypobaric hypoxia. Exp Physiol 2017; 102:1143-1157. [PMID: 28699679 DOI: 10.1113/ep086441] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2017] [Accepted: 06/30/2017] [Indexed: 01/12/2023]
Abstract
NEW FINDINGS What is the central question of this study? It is suggested that remote ischemic preconditioning (RIPC) might offer protection against ischaemia-reperfusion injuries, but the utility of RIPC in high-altitude settings remains unclear. What is the main finding and its importance? We found that RIPC offers no vascular protection relative to pulmonary artery pressure or peripheral endothelial function during acute, normobaric hypoxia and at high altitude in young, healthy adults. However, peripheral chemosensitivity was heightened 24 h after RIPC at high altitude. Application of repeated short-duration bouts of ischaemia to the limbs, termed remote ischemic preconditioning (RIPC), is a novel technique that might have protective effects on vascular function during hypoxic exposures. In separate parallel-design studies, at sea level (SL; n = 16) and after 8-12 days at high altitude (HA; n = 12; White Mountain, 3800 m), participants underwent either a sham protocol or one session of four bouts of 5 min of dual-thigh-cuff occlusion with 5 min recovery. Brachial artery flow-mediated dilatation (FMD; ultrasound), pulmonary artery systolic pressure (PASP; echocardiography) and internal carotid artery (ICA) flow (ultrasound) were measured at SL in normoxia and isocapnic hypoxia (end-tidal PO2 maintained at 50 mmHg) and during normal breathing at HA. The hypoxic ventilatory response (HVR) was measured at each location. All measures at SL and HA were obtained at baseline (BL) and at 1, 24 and 48 h post-RIPC or sham. At SL, RIPC produced no changes in FMD, PASP, ICA flow, end-tidal gases or HVR in normoxia or hypoxia. At HA, although HVR increased 24 h post-RIPC compared with BL [2.05 ± 1.4 versus 3.21 ± 1.2 l min-1 (% arterial O2 saturation)-1 , P < 0.01], there were no significant differences in FMD, PASP, ICA flow and resting end-tidal gases. Accordingly, a single session of RIPC is insufficient to evoke changes in peripheral, pulmonary and cerebral vascular function in healthy adults. Although chemosensitivity might increase after RIPC at HA, this did not confer any vascular changes. The utility of a single RIPC session seems unremarkable during acute and chronic hypoxia.
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Affiliation(s)
- Mathew G Rieger
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Ryan L Hoiland
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Joshua C Tremblay
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Mike Stembridge
- Cardiff School of Sport, Cardiff Metropolitan University, Cardiff, UK
| | - Anthony R Bain
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada.,University of Colorado, Boulder, Department of Integrative Physiology, Integrative Vascular Biology Laboratory, Boulder, CO, USA
| | - Daniela Flück
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
| | - Prajan Subedi
- Pulmonary/Critical Care Section, VA Loma Linda Healthcare System, Loma Linda, CA, USA
| | - James D Anholm
- Pulmonary/Critical Care Section, VA Loma Linda Healthcare System, Loma Linda, CA, USA
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, BC, Canada
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21
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Smith ZM, Krizay E, Sá RC, Li ET, Scadeng M, Powell FL, Dubowitz DJ. Evidence from high-altitude acclimatization for an integrated cerebrovascular and ventilatory hypercapnic response but different responses to hypoxia. J Appl Physiol (1985) 2017; 123:1477-1486. [PMID: 28705997 DOI: 10.1152/japplphysiol.00341.2017] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Ventilation and cerebral blood flow (CBF) are both sensitive to hypoxia and hypercapnia. To compare chemosensitivity in these two systems, we made simultaneous measurements of ventilatory and cerebrovascular responses to hypoxia and hypercapnia in 35 normal human subjects before and after acclimatization to hypoxia. Ventilation and CBF were measured during stepwise changes in isocapnic hypoxia and iso-oxic hypercapnia. We used MRI to quantify actual cerebral perfusion. Measurements were repeated after 2 days of acclimatization to hypoxia at 3,800 m altitude (partial pressure of inspired O2 = 90 Torr) to compare plasticity in the chemosensitivity of these two systems. Potential effects of hypoxic and hypercapnic responses on acute mountain sickness (AMS) were assessed also. The pattern of CBF and ventilatory responses to hypercapnia were almost identical. CO2 responses were augmented to a similar degree in both systems by concomitant acute hypoxia or acclimatization to sustained hypoxia. Conversely, the pattern of CBF and ventilatory responses to hypoxia were markedly different. Ventilation showed the well-known increase with acute hypoxia and a progressive decline in absolute value over 25 min of sustained hypoxia. With acclimatization to hypoxia for 2 days, the absolute values of ventilation and O2 sensitivity increased. By contrast, O2 sensitivity of CBF or its absolute value did not change during sustained hypoxia for up to 2 days. The results suggest a common or integrated control mechanism for CBF and ventilation by CO2 but different mechanisms of O2 sensitivity and plasticity between the systems. Ventilatory and cerebrovascular responses were the same for all subjects irrespective of AMS symptoms. NEW & NOTEWORTHY Ventilatory and cerebrovascular hypercapnic response patterns show similar plasticity in CO2 sensitivity following hypoxic acclimatization, suggesting an integrated control mechanism. Conversely, ventilatory and cerebrovascular hypoxic responses differ. Ventilation initially increases but adapts with prolonged hypoxia (hypoxic ventilatory decline), and ventilatory sensitivity increases following acclimatization. In contrast, cerebral blood flow hypoxic sensitivity remains constant over a range of hypoxic stimuli, with no cerebrovascular acclimatization to sustained hypoxia, suggesting different mechanisms for O2 sensitivity in the two systems.
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Affiliation(s)
- Zachary M Smith
- Department of Radiology, Center for Functional MRI, University of California San Diego School of Medicine , La Jolla, California
| | - Erin Krizay
- Department of Radiology, Center for Functional MRI, University of California San Diego School of Medicine , La Jolla, California
| | - Rui Carlos Sá
- Division of Physiology, Department of Medicine, University of California San Diego School of Medicine , La Jolla, California
| | - Ethan T Li
- Department of Radiology, Center for Functional MRI, University of California San Diego School of Medicine , La Jolla, California
| | - Miriam Scadeng
- Department of Radiology, Center for Functional MRI, University of California San Diego School of Medicine , La Jolla, California
| | - Frank L Powell
- Division of Physiology, Department of Medicine, University of California San Diego School of Medicine , La Jolla, California.,White Mountain Research Station, University of California , Bishop, California
| | - David J Dubowitz
- Department of Radiology, Center for Functional MRI, University of California San Diego School of Medicine , La Jolla, California
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22
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Liu W, Liu J, Lou X, Zheng D, Wu B, Wang DJJ, Ma L. A longitudinal study of cerebral blood flow under hypoxia at high altitude using 3D pseudo-continuous arterial spin labeling. Sci Rep 2017; 7:43246. [PMID: 28240265 PMCID: PMC5327438 DOI: 10.1038/srep43246] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Accepted: 01/20/2017] [Indexed: 12/14/2022] Open
Abstract
Changes in cerebral blood flow (CBF) may occur with acute exposure to high altitude; however, the CBF of the brain parenchyma has not been studied to date. In this study, identical magnetic resonance scans using arterial spin labeling (ASL) were performed to study the haemodynamic changes at both sea level and high altitude. We found that with acute exposure to high altitude, the CBF in acute mountain sickness (AMS) subjects was higher (P < 0.05), while the CBF of non-AMS subjects was lower (P > 0.05) compared with those at sea level. Moreover, magnetic resonance angiography in both AMS and non-AMS subjects showed a significant increase in the cross-sectional areas of the internal carotid, basilar, and middle cerebral arteries on the first day at high altitude. These findings support that AMS may be related to increased CBF rather than vasodilation; these results contradict most previous studies that reported no relationship between CBF changes and the occurrence of AMS. This discrepancy may be attributed to the use of ASL for CBF measurement at both sea level and high altitude in this study, which has substantial advantages over transcranial Doppler for the assessment of CBF.
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Affiliation(s)
- Wenjia Liu
- Department of Radiology, Chinese PLA General Hospital, Beijing, China
| | - Jie Liu
- Department of Radiology, Tibet Military General Hospital, Lhasa, Tibet, China
| | - Xin Lou
- Department of Radiology, Chinese PLA General Hospital, Beijing, China.,Department of Neurology, University of California, Los Angeles, CA, USA
| | - Dandan Zheng
- GE Healthcare, MR Research China, Beijing, China
| | - Bing Wu
- GE Healthcare, MR Research China, Beijing, China
| | - Danny J J Wang
- Department of Neurology, University of California, Los Angeles, CA, USA
| | - Lin Ma
- Department of Radiology, Chinese PLA General Hospital, Beijing, China
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23
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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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Analysis of High-altitude Syndrome and the Underlying Gene Polymorphisms Associated with Acute Mountain Sickness after a Rapid Ascent to High-altitude. Sci Rep 2016; 6:38323. [PMID: 27982053 PMCID: PMC5159877 DOI: 10.1038/srep38323] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Accepted: 11/08/2016] [Indexed: 11/08/2022] Open
Abstract
To investigated the objective indicators and potential genotypes for acute mountain sickness (AMS). 176 male subjects were evaluated for symptoms scores and physiological parameters at 3700 m. EPAS1 gene polymorphisms were explored and verified effects of potential genotypes on pulmonary function by inhaled budesonide. The incidence of AMS was 53.98% (95/176). The individuals who suffered from headache with anxiety and greater changes in heart rate (HR), the forced vital capacity (FVC), and mean flow velocity of basilar artery (Vm-BA), all of which were likely to develop AMS. The rs4953348 polymorphism of EPAS1 gene had a significant correlation with the SaO2 level and AMS, and a significant difference in the AG and GG genotype distribution between the AMS and non-AMS groups. The spirometric parameters were significantly lower, but HR (P = 0.036) and Vm-BA (P = 0.042) significantly higher in the AMS subjects with the G allele than those with the A allele. In summary, changes in HR (≥82 beats/min), FVC (≤4.2 Lt) and Vm-BA (≥43 cm/s) levels may serve as predictors for diagnosing AMS accompanied by high-altitude syndrome. The A allele of rs4953348 is a protective factor for AMS through HR and Vm-BA compensation, while the G allele may contribute to hypoxic pulmonary hypertension in AMS.
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25
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Peacock CA, Weber R, Sanders GJ, Seo Y, Kean D, Pollock BS, Burns KJ, Cain M, LaScola P, Glickman EL. Pilot physiology, cognition and flight performance during flight simulation exposed to a 3810-m hypoxic condition. INTERNATIONAL JOURNAL OF OCCUPATIONAL SAFETY AND ERGONOMICS 2016; 23:44-49. [DOI: 10.1080/10803548.2016.1234685] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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26
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Imray C. Lessons from altitude: cerebral perfusion insights and their potential translational clinical significance. Exp Physiol 2016; 101:1167-1172. [PMID: 27061345 DOI: 10.1113/ep085813] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 03/30/2016] [Indexed: 01/28/2023]
Abstract
What is the topic of this review? The long-held assumption that transcranial Doppler middle cerebral artery velocity is a surrogate for cerebral blood flow has been questioned in certain circumstances, particularly where tissue oxygenation changes. What advances does it highlight? Cerebral venous outflow restriction appears to be implicated in the development of high-altitude cerebral oedema. Rapid ascent to high altitude commonly results in acute mountain sickness and, on occasion, potentially fatal high-altitude cerebral oedema. The exact pathophysiological mechanisms behind these syndromes remain to be determined. One of the main theories to explain the development of acute mountain sickness is an increase in intracranial pressure. Vasogenic (extracellular water accumulation attributable to increased permeability of the blood-brain barrier) and cytotoxic (intracellular) oedema have also been postulated as potential mechanisms that underlie high-altitude cerebral oedema. Recently published findings derived from a very challenging field study (obtained at altitudes of up to 7950 m), substantiated by sea-level hypoxic magnetic resonance angiography studies, have given new insights into the maintenance of cerebral blood flow at altitude. This report provides new perspectives and potential mechanisms to account for the maintenance of cerebral oxygen delivery at high and extreme altitude. In particular, the long-held assumption that transcranial Doppler middle cerebral artery velocity is a surrogate for cerebral blood flow has been shown to be incorrect in certain circumstances. The emerging evidence for a potential third mechanism, namely the restrictive venous outflow hypothesis, in the development of high-altitude cerebral oedema, over and above the accepted vasogenic and cytotoxic hypotheses, is also appraised.
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Affiliation(s)
- Chris Imray
- Department of Vascular Surgery, University Hospitals Coventry and Warwickshire NHS Trust, Coventry, UK.,Warwick Medical School, Warwick University, Coventry, UK.,Coventry University, Coventry, UK
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27
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Liu J, Liu Y, Ren LH, Li L, Wang Z, Liu SS, Li SZ, Cao TS. Effects of race and sex on cerebral hemodynamics, oxygen delivery and blood flow distribution in response to high altitude. Sci Rep 2016; 6:30500. [PMID: 27503416 PMCID: PMC4977556 DOI: 10.1038/srep30500] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Accepted: 07/06/2016] [Indexed: 11/25/2022] Open
Abstract
To assess racial, sexual, and regional differences in cerebral hemodynamic response to high altitude (HA, 3658 m). We performed cross-sectional comparisons on total cerebral blood flow (TCBF = sum of bilateral internal carotid and vertebral arterial blood flows = QICA + QVA), total cerebrovascular resistance (TCVR), total cerebral oxygen delivery (TCOD) and QVA/TCBF (%), among six groups of young healthy subjects: Tibetans (2-year staying) and Han (Han Chinese) at sea level, Han (2-day, 1-year and 5-year) and Tibetans at HA. Bilateral ICA and VA diameters and flow velocities were derived from duplex ultrasonography; and simultaneous measurements of arterial pressure, oxygen saturation, and hemoglobin concentration were conducted. Neither acute (2-day) nor chronic (>1 year) responses showed sex differences in Han, except that women showed lower TCOD compared with men. Tibetans and Han exhibited different chronic responses (percentage alteration relative to the sea-level counterpart value) in TCBF (−17% vs. 0%), TCVR (22% vs. 12%), TCOD (0% vs. 10%) and QVA/TCBF (0% vs. 2.4%, absolute increase), with lower resting TCOD found in SL- and HA-Tibetans. Our findings indicate racial but not sex differences in cerebral hemodynamic adaptations to HA, with Tibetans (but not Han) demonstrating an altitude-related change of CBF distribution.
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Affiliation(s)
- Jie Liu
- Department of Ultrasound Diagnostics, Tangdu Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China
| | - Yang Liu
- Department of Cardiovascular Surgery, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China
| | - Li-Hua Ren
- General Hospital of Tibet Military Area Command, Lhasa, Tibet Autonomous Region, China
| | - Li Li
- Department of Ultrasonic Medicine, Affiliated Hospital of Tibet University for Nationalities, Xianyang, Shaanxi, China
| | - Zhen Wang
- Department of Ultrasound Diagnostics, Tangdu Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China
| | - Shan-Shan Liu
- Department of Ultrasound Diagnostics, Tangdu Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China
| | - Su-Zhi Li
- General Hospital of Tibet Military Area Command, Lhasa, Tibet Autonomous Region, China
| | - Tie-Sheng Cao
- Department of Ultrasound Diagnostics, Tangdu Hospital, Fourth Military Medical University, Xi'an, Shaanxi, China
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28
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Keramidas ME, Kölegård R, Mekjavic IB, Eiken O. PlanHab: hypoxia exaggerates the bed-rest-induced reduction in peak oxygen uptake during upright cycle ergometry. Am J Physiol Heart Circ Physiol 2016; 311:H453-64. [PMID: 27342877 DOI: 10.1152/ajpheart.00304.2016] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Accepted: 06/20/2016] [Indexed: 11/22/2022]
Abstract
The study examined the effects of hypoxia and horizontal bed rest, separately and in combination, on peak oxygen uptake (V̇o2 peak) during upright cycle ergometry. Ten male lowlanders underwent three 21-day confinement periods in a counterbalanced order: 1) normoxic bed rest [NBR; partial pressure of inspired O2 (PiO2 ) = 133.1 ± 0.3 mmHg]; 2) hypoxic bed rest (HBR; PiO2 = 90.0 ± 0.4 mmHg), and 3) hypoxic ambulation (HAMB; PiO2 = 90.0 ± 0.4 mmHg). Before and after each confinement, subjects performed two incremental-load trials to exhaustion, while inspiring either room air (AIR), or a hypoxic gas (HYPO; PiO2 = 90.0 ± 0.4 mmHg). Changes in regional oxygenation of the vastus lateralis muscle and the frontal cerebral cortex were monitored with near-infrared spectroscopy. Cardiac output (CO) was recorded using a bioimpedance method. The AIR V̇o2 peak was decreased by both HBR (∼13.5%; P ≤ 0.001) and NBR (∼8.6%; P ≤ 0.001), with greater drop after HBR (P = 0.01). The HYPO V̇o2 peak was also reduced by HBR (-9.7%; P ≤ 0.001) and NBR (-6.1%; P ≤ 0.001). Peak CO was lower after both bed-rest interventions, and especially after HBR (HBR: ∼13%, NBR: ∼7%; P ≤ 0.05). Exercise-induced alterations in muscle and cerebral oxygenation were blunted in a similar manner after both bed-rest confinements. No changes were observed in HAMB. Hence, the bed-rest-induced decrease in V̇o2 peak was exaggerated by hypoxia, most likely due to a reduction in convective O2 transport, as indicated by the lower peak values of CO.
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Affiliation(s)
- Michail E Keramidas
- Department of Environmental Physiology, Swedish Aerospace Physiology Center, School of Technology and Health, Royal Institute of Technology, Stockholm, Sweden;
| | - Roger Kölegård
- Department of Environmental Physiology, Swedish Aerospace Physiology Center, School of Technology and Health, Royal Institute of Technology, Stockholm, Sweden
| | - Igor B Mekjavic
- Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia; and Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Ola Eiken
- Department of Environmental Physiology, Swedish Aerospace Physiology Center, School of Technology and Health, Royal Institute of Technology, Stockholm, Sweden
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Lawley JS, Levine BD, Williams MA, Malm J, Eklund A, Polaner DM, Subudhi AW, Hackett PH, Roach RC. Cerebral spinal fluid dynamics: effect of hypoxia and implications for high-altitude illness. J Appl Physiol (1985) 2016; 120:251-62. [DOI: 10.1152/japplphysiol.00370.2015] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2015] [Accepted: 08/17/2015] [Indexed: 12/24/2022] Open
Abstract
The pathophysiology of acute mountain sickness and high-altitude cerebral edema, the cerebral forms of high-altitude illness, remain uncertain and controversial. Persistently elevated or pathological fluctuations in intracranial pressure are thought to cause symptoms similar to those reported by individuals suffering cerebral forms of high-altitude illness. This review first focuses on the basic physiology of the craniospinal system, including a detailed discussion of the long-term and dynamic regulation of intracranial pressure. Thereafter, we critically examine the available literature, based primarily on invasive pressure monitoring, that suggests intracranial pressure is acutely elevated at altitude due to brain swelling and/or elevated sagittal sinus pressure, but normalizes over time. We hypothesize that fluctuations in intracranial pressure occur around a slightly elevated or normal mean intracranial pressure, in conjunction with oscillations in arterial Po2 and arterial blood pressure. Then these modest fluctuations in intracranial pressure, in concert with direct vascular stretch due to dilatation and/or increased blood pressure transmission, activate the trigeminal vascular system and cause symptoms of acute mountain sickness. Elevated brain water (vasogenic edema) may be due to breakdown of the blood-brain barrier. However, new information suggests cerebral spinal fluid flux into the brain may be an important factor. Regardless of the source (or mechanisms responsible) for the excess brain water, brain swelling occurs, and a “tight fit” brain would be a major risk factor to produce symptoms; activities that produce large changes in brain volume and cause fluctuations in blood pressure are likely contributing factors.
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Affiliation(s)
- Justin S. Lawley
- Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas, Texas
- UT Southwestern Medical Center, Dallas, Texas
| | - Benjamin D. Levine
- Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas, Texas
- UT Southwestern Medical Center, Dallas, Texas
| | - Michael A. Williams
- Sandra and Malcolm Berman Brain & Spine Institute, Dept. of Neurology, Sinai Hospital, Baltimore, Maryland
| | - Jon Malm
- Department of Clinical Neuroscience, Umeå University, Umeå, Sweden
| | - Anders Eklund
- Department of Radiation Sciences, Umeå University, Umeå, Sweden
| | - David M. Polaner
- Departments of Anesthesiology and Pediatrics, University of Colorado School of Medicine and Children's Hospital Colorado, Aurora, Colorado
| | - Andrew W. Subudhi
- Department of Biology, University of Colorado, Colorado Springs, Colorado
- Altitude Research Center, Department of Emergency Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado; and
| | | | - Robert C. Roach
- Altitude Research Center, Department of Emergency Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado; and
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Fan JL, Subudhi AW, Duffin J, Lovering AT, Roach RC, Kayser B. AltitudeOmics: Resetting of Cerebrovascular CO2 Reactivity Following Acclimatization to High Altitude. Front Physiol 2016; 6:394. [PMID: 26779030 PMCID: PMC4705915 DOI: 10.3389/fphys.2015.00394] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Accepted: 12/03/2015] [Indexed: 12/25/2022] Open
Abstract
Previous studies reported enhanced cerebrovascular CO2 reactivity upon ascent to high altitude using linear models. However, there is evidence that this response may be sigmoidal in nature. Moreover, it was speculated that these changes at high altitude are mediated by alterations in acid-base buffering. Accordingly, we reanalyzed previously published data to assess middle cerebral blood flow velocity (MCAv) responses to modified rebreathing at sea level (SL), upon ascent (ALT1) and following 16 days of acclimatization (ALT16) to 5260 m in 21 lowlanders. Using sigmoid curve fitting of the MCAv responses to CO2, we found the amplitude (95 vs. 129%, SL vs. ALT1, 95% confidence intervals (CI) [77, 112], [111, 145], respectively, P = 0.024) and the slope of the sigmoid response (4.5 vs. 7.5%/mmHg, SL vs. ALT1, 95% CIs [3.1, 5.9], [6.0, 9.0], respectively, P = 0.026) to be enhanced at ALT1, which persisted with acclimatization at ALT16 (amplitude: 177, 95% CI [139, 215], P < 0.001; slope: 10.3%/mmHg, 95% CI [8.2, 12.5], P = 0.003) compared to SL. Meanwhile, the sigmoidal response midpoint was unchanged at ALT1 (SL: 36.5 mmHg; ALT1: 35.4 mmHg, 95% CIs [34.0, 39.0], [33.1, 37.7], respectively, P = 0.982), while it was reduced by ~7 mmHg at ALT16 (28.6 mmHg, 95% CI [26.4, 30.8], P = 0.001 vs. SL), indicating leftward shift of the cerebrovascular CO2 response to a lower arterial partial pressure of CO2 (PaCO2) following acclimatization to altitude. Sigmoid fitting revealed a leftward shift in the midpoint of the cerebrovascular response curve which could not be observed with linear fitting. These findings demonstrate that there is resetting of the cerebrovascular CO2 reactivity operating point to a lower PaCO2 following acclimatization to high altitude. This cerebrovascular resetting is likely the result of an altered acid-base buffer status resulting from prolonged exposure to the severe hypocapnia associated with ventilatory acclimatization to high altitude.
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Affiliation(s)
- Jui-Lin Fan
- Centre for Translational Physiology, University of OtagoWellington, New Zealand; Department of Surgery and Anaesthesia, University of OtagoWellington, New Zealand
| | - Andrew W Subudhi
- Department of Emergency Medicine, Altitude Research Center, University of Colorado DenverAurora, CO, USA; Department of Biology, University of Colorado Colorado SpringsColorado Springs, CO, USA
| | - James Duffin
- Department of Physiology, University of TorontoToronto, ON, Canada; Department of Anaesthesiology, University of TorontoToronto, ON, Canada; University Health NetworkToronto, ON, Canada
| | - Andrew T Lovering
- Department of Human Physiology, University of Oregon Eugene, Oregon, OR, USA
| | - Robert C Roach
- Department of Emergency Medicine, Altitude Research Center, University of Colorado DenverAurora, CO, USA; Department of Biology, University of Colorado Colorado SpringsColorado Springs, CO, USA
| | - Bengt Kayser
- Institute of Sports Sciences, Faculty of Biology and Medicine, University of LausanneLausanne, Switzerland; Department of Physiology, Faculty of Biology and Medicine, University of LausanneLausanne, Switzerland
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31
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Steinback CD, Poulin MJ. Influence of Hypoxia on Cerebral Blood Flow Regulation in Humans. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 903:131-44. [PMID: 27343093 DOI: 10.1007/978-1-4899-7678-9_9] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The brain is a vital organ that relies on a constant and adequate supply of blood to match oxygen and glucose delivery with the local metabolic demands of active neurones. It is well established that cerebral blood flow is altered in response to both neural activity and humoral stimuli. Thus, augmented neural activation (e.g. visual stimulation) leads to locally increased cerebral blood flow via functional hyperaemia, whereas humoral stimuli (i.e. alterations in arterial PO2 and PCO2) produce global increases in cerebral blood flow. Perhaps not surprisingly, cerebrovascular responses to neural activity and humoral stimuli may not be highly correlated because they reflect different physiological mechanisms for vasodilation. Exquisite regulation of cerebral blood flow is particularly important under hypoxic conditions when cerebral PO2 can be reduced substantially. Indeed, cerebrovascular reactivity to hypoxia determines the capacity of cerebral vessels to respond and compensate for a reduced oxygen supply. This reactivity is dynamic, changing with prolonged exposure to hypoxic environments, and in patients and healthy individuals exposed to chronic intermittent periods of hypoxia. More recently, a number of animal studies have provided evidence that glial cells (i.e. astrocytes) play an important role in regulating cerebral blood flow under normoxic and hypoxic conditions. This review aims to summarize our current understanding of cerebral blood flow control during hypoxia in humans and put into context the underlying neurovascular mechanisms that may contribute to this regulation.
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Affiliation(s)
- Craig D Steinback
- Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada
| | - Marc J Poulin
- Departments of Physiology and Pharmacology and Clinical Neurosciences, Faculty of Medicine, Hotchkiss Brain Institute, The Libin Cardiovascular Institute of Alberta, Calgary, AB, Canada.
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Hoiland RL, Bain AR, Rieger MG, Bailey DM, Ainslie PN. Hypoxemia, oxygen content, and the regulation of cerebral blood flow. Am J Physiol Regul Integr Comp Physiol 2015; 310:R398-413. [PMID: 26676248 DOI: 10.1152/ajpregu.00270.2015] [Citation(s) in RCA: 150] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2015] [Accepted: 11/30/2015] [Indexed: 01/13/2023]
Abstract
This review highlights the influence of oxygen (O2) availability on cerebral blood flow (CBF). Evidence for reductions in O2 content (CaO2 ) rather than arterial O2 tension (PaO2 ) as the chief regulator of cerebral vasodilation, with deoxyhemoglobin as the primary O2 sensor and upstream response effector, is discussed. We review in vitro and in vivo data to summarize the molecular mechanisms underpinning CBF responses during changes in CaO2 . We surmise that 1) during hypoxemic hypoxia in healthy humans (e.g., conditions of acute and chronic exposure to normobaric and hypobaric hypoxia), elevations in CBF compensate for reductions in CaO2 and thus maintain cerebral O2 delivery; 2) evidence from studies implementing iso- and hypervolumic hemodilution, anemia, and polycythemia indicate that CaO2 has an independent influence on CBF; however, the increase in CBF does not fully compensate for the lower CaO2 during hemodilution, and delivery is reduced; and 3) the mechanisms underpinning CBF regulation during changes in O2 content are multifactorial, involving deoxyhemoglobin-mediated release of nitric oxide metabolites and ATP, deoxyhemoglobin nitrite reductase activity, and the downstream interplay of several vasoactive factors including adenosine and epoxyeicosatrienoic acids. The emerging picture supports the role of deoxyhemoglobin (associated with changes in CaO2 ) as the primary biological regulator of CBF. The mechanisms for vasodilation therefore appear more robust during hypoxemic hypoxia than during changes in CaO2 via hemodilution. Clinical implications (e.g., disorders associated with anemia and polycythemia) and future study directions are considered.
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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, British Columbia, Canada; and
| | - Anthony R Bain
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan Campus, Kelowna, British Columbia, Canada; and
| | - Mathew G Rieger
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan Campus, Kelowna, British Columbia, Canada; and
| | - Damian M Bailey
- Neurovascular Research Laboratory, Research Institute of Science and Health, University of South Wales, Glamorgan, United Kingdom
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia-Okanagan Campus, Kelowna, British Columbia, Canada; and Neurovascular Research Laboratory, Research Institute of Science and Health, University of South Wales, Glamorgan, United Kingdom
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Tipton MJ. Environmental extremes: origins, consequences and amelioration in humans. Exp Physiol 2015; 101:1-14. [DOI: 10.1113/ep085362] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2015] [Accepted: 09/08/2015] [Indexed: 01/26/2023]
Affiliation(s)
- M. J. Tipton
- Extreme Environments Laboratory, Department of Sport & Exercise Science; University of Portsmouth; Portsmouth UK
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Wilson MH, Imray CHE. The cerebral venous system and hypoxia. J Appl Physiol (1985) 2015; 120:244-50. [PMID: 26294747 DOI: 10.1152/japplphysiol.00327.2015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2015] [Accepted: 08/13/2015] [Indexed: 01/24/2023] Open
Abstract
Most hypobaric hypoxia studies have focused on oxygen delivery and therefore cerebral blood inflow. Few have studied venous outflow. However, the volume of blood entering and leaving the skull (∼700 ml/min) is considerably greater than cerebrospinal fluid production (0.35 ml/min) or edema formation rates and slight imbalances of in- and outflow have considerable effects on intracranial pressure. This dynamic phenomenon is not necessarily appreciated in the currently taught static "Monro-Kellie" doctrine, which forms the basis of the "Tight-Fit" hypothesis thought to underlie high altitude headache, acute mountain sickness, and high altitude cerebral edema. Investigating both sides of the cerebral circulation was an integral part of the 2007 Xtreme Everest Expedition. The results of the relevant studies performed as part of and subsequent to this expedition are reviewed here. The evidence from recent studies suggests a relative venous outflow insufficiency is an early step in the pathogenesis of high altitude headache. Translation of knowledge gained from high altitude studies is important. Many patients in a critical care environment develop hypoxemia akin to that of high altitude exposure. An inability to drain the hypoxemic induced increase in cerebral blood flow could be an underappreciated regulatory mechanism of intracranial pressure.
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Affiliation(s)
- Mark H Wilson
- The Centre for Altitude, Space and Extreme Environment Medicine, University College London, London, United Kingdom; The Birmingham Medical Research Expeditionary Society, Queen Elizabeth Hospital, Edgbaston, Birmingham, United Kingdom; Imperial Neurotrauma Centre, Imperial College, St Mary's Hospital, London, United Kingdom; Institute of Pre-Hospital Care, London's Air Ambulance, Royal London Hospital, Whitechapel, United Kingdom; and
| | - Christopher H E Imray
- The Centre for Altitude, Space and Extreme Environment Medicine, University College London, London, United Kingdom; The Birmingham Medical Research Expeditionary Society, Queen Elizabeth Hospital, Edgbaston, Birmingham, United Kingdom; Department of Surgery, Warwick Medical School, UHCW NHS Trust, Warwick, United Kingdom
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35
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Abstract
In 1875, Paul Bert linked high altitude danger to the low partial pressure of oxygen when 2 of 3 French balloonists died euphorically at about 8,600 m altitude. World War I fatal crashes of high altitude fighter pilots led to a century of efforts to use oximetry to warn pilots. The carotid body, discovered in 1932 to be the hypoxia detector, led to most current physiologic understanding of the body's respiratory responses to hypoxia and CO2. The author describes some of his UCSF group's work: In 1963, we reported both the brain's ventral medullary near-surface CO2 (and pH) chemosensors and the role of cerebrospinal fluid in acclimatization to altitude. In 1966, we reported the effect of altitude on cerebral blood flow and later the changes of carotid body sensitivity at altitude and the differences in natives of high altitude. In 1973, pulse oximetry was invented when Japanese biophysicist Takuo Aoyagi read and applied to pulses a largely forgotten 35-year-old discovery by English medical student J. R. Squire of a method of computing oxygen saturation from red and infrared light passing through both perfused and blanched tissue.
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Affiliation(s)
- John W Severinghaus
- Department of Anesthesia and Cardiovascular Research Institute, University of California San Francisco, San Francisco, California
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36
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Flück D, Siebenmann C, Keiser S, Cathomen A, Lundby C. Cerebrovascular reactivity is increased with acclimatization to 3,454 m altitude. J Cereb Blood Flow Metab 2015; 35:1323-30. [PMID: 25806704 PMCID: PMC4528007 DOI: 10.1038/jcbfm.2015.51] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Revised: 02/11/2015] [Accepted: 03/02/2015] [Indexed: 12/27/2022]
Abstract
Controversy exists regarding the effect of high-altitude exposure on cerebrovascular CO2 reactivity (CVR). Confounding factors in previous studies include the use of different experimental approaches, ascent profiles, duration and severity of exposure and plausibly environmental factors associated with altitude exposure. One aim of the present study was to determine CVR throughout acclimatization to high altitude when controlling for these. Middle cerebral artery mean velocity (MCAv mean) CVR was assessed during hyperventilation (hypocapnia) and CO2 administration (hypercapnia) with background normoxia (sea level (SL)) and hypoxia (3,454 m) in nine healthy volunteers (26 ± 4 years (mean ± s.d.)) at SL, and after 30 minutes (HA0), 3 (HA3) and 22 (HA22) days of high-altitude (3,454 m) exposure. At altitude, ventilation was increased whereas MCAv mean was not altered. Hypercapnic CVR was decreased at HA0 (1.16% ± 0.16%/mm Hg, mean ± s.e.m.), whereas both hyper- and hypocapnic CVR were increased at HA3 (3.13% ± 0.18% and 2.96% ± 0.10%/mm Hg) and HA22 (3.32% ± 0.12% and 3.24% ± 0.14%/mm Hg) compared with SL (1.98% ± 0.22% and 2.38% ± 0.10%/mm Hg; P < 0.01) regardless of background oxygenation. Cerebrovascular conductance (MCAv mean/mean arterial pressure) CVR was determined to account for blood pressure changes and revealed an attenuated response. Collectively our results show that hypocapnic and hypercapnic CVR are both elevated with acclimatization to high altitude.
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Affiliation(s)
- Daniela Flück
- 1] Zurich Center for Integrative Human Physiology (ZIHP), Zurich, Switzerland [2] Institute of Physiology, ZIHP, University of Zurich, Zurich, Switzerland
| | | | - Stefanie Keiser
- 1] Zurich Center for Integrative Human Physiology (ZIHP), Zurich, Switzerland [2] Institute of Physiology, ZIHP, University of Zurich, Zurich, Switzerland
| | - Adrian Cathomen
- Institute of Human Movement Sciences, ETH Zurich, Zurich, Switzerland
| | - Carsten Lundby
- 1] Zurich Center for Integrative Human Physiology (ZIHP), Zurich, Switzerland [2] Institute of Physiology, ZIHP, University of Zurich, Zurich, Switzerland [3] Department of Food and Nutrition and Sport Science, Gothenburg University, Gothenburg, Sweden
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37
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Cerebral Hemodynamics at Altitude: Effects of Hyperventilation and Acclimatization on Cerebral Blood Flow and Oxygenation. Wilderness Environ Med 2015; 26:133-41. [DOI: 10.1016/j.wem.2014.10.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2014] [Revised: 07/15/2014] [Accepted: 10/08/2014] [Indexed: 11/22/2022]
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Willie CK, MacLeod DB, Smith KJ, Lewis NC, Foster GE, Ikeda K, Hoiland RL, Ainslie PN. The contribution of arterial blood gases in cerebral blood flow regulation and fuel utilization in man at high altitude. J Cereb Blood Flow Metab 2015; 35:873-81. [PMID: 25690474 PMCID: PMC4420871 DOI: 10.1038/jcbfm.2015.4] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 12/16/2014] [Accepted: 12/25/2014] [Indexed: 11/09/2022]
Abstract
The effects of partial acclimatization to high altitude (HA; 5,050 m) on cerebral metabolism and cerebrovascular function have not been characterized. We hypothesized (1) increased cerebrovascular reactivity (CVR) at HA; and (2) that CO2 would affect cerebral metabolism more than hypoxia. PaO2 and PaCO2 were manipulated at sea level (SL) to simulate HA exposure, and at HA, SL blood gases were simulated; CVR was assessed at both altitudes. Arterial-jugular venous differences were measured to calculate cerebral metabolic rates and cerebral blood flow (CBF). We observed that (1) partial acclimatization yields a steeper CO2-H(+) relation in both arterial and jugular venous blood; yet (2) CVR did not change, despite (3) mean arterial pressure (MAP)-CO2 reactivity being doubled at HA, thus indicating effective cerebral autoregulation. (4) At SL hypoxia increased CBF, and restoration of oxygen at HA reduced CBF, but neither had any effect on cerebral metabolism. Acclimatization resets the cerebrovasculature to chronic hypocapnia.
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Affiliation(s)
- Christopher K Willie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - David B MacLeod
- Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina, USA
| | - Kurt J Smith
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Nia C Lewis
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Glen E Foster
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
| | - Keita Ikeda
- Department of Anesthesiology, University of Virginia School of Medicine, Charlottesville, Virginia, USA
| | - 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
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada
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39
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Abstract
This brief review traces the last 50 years of research related to cerebral blood flow (CBF) in humans exposed to high altitude. The increase in CBF within the first 12 hours at high altitude and its return to near sea level values after 3-5 days of acclimatization was first documented with use of the Kety-Schmidt technique in 1964. The degree of change in CBF at high altitude is influenced by many variables, including arterial oxygen and carbon dioxide tensions, oxygen content, cerebral spinal fluid pH, and hematocrit, but can be collectively summarized in terms of the relative strengths of four key integrated reflexes: 1) hypoxic cerebral vasodilatation; 2) hypocapnic cerebral vasoconstriction; 3) hypoxic ventilatory response; and 4) hypercapnic ventilatory response. Understanding the mechanisms underlying these reflexes and their interactions with one another is critical to advance our understanding of global and regional CBF regulation. Whether high altitude populations exhibit cerebrovascular adaptations to chronic levels of hypoxia or if changes in CBF are related to the development of acute mountain sickness are currently unknown; yet overall, the integrated CBF response to high altitude appears to be sufficient to meet the brain's large and consistent demand for oxygen. This short review is organized as follows: An historical overview of the earliest CBF measurements collected at high altitude introduces a summary of reported CBF changes at altitude over the last 50 years in both lowlanders and high-altitude natives. The most tenable candidate mechanism(s) regulating CBF at altitude are summarized with a focus on available data in humans, and a role for these mechanisms in the pathophysiology of AMS is considered. Finally, suggestions for future directions are provided.
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Affiliation(s)
- Philip N Ainslie
- 1 School of Health and Exercise Sciences, University of British Columbia , Okanagan Campus, Kelowna, British Columbia, Canada
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40
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Tao X, Lin MT, Thorington GU, Wilson SM, Longo LD, Hessinger DA. Long-term hypoxia increases calcium affinity of BK channels in ovine fetal and adult cerebral artery smooth muscle. Am J Physiol Heart Circ Physiol 2015; 308:H707-22. [PMID: 25599571 DOI: 10.1152/ajpheart.00564.2014] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Accepted: 01/14/2015] [Indexed: 01/31/2023]
Abstract
Acclimatization to high-altitude, long-term hypoxia (LTH) reportedly alters cerebral artery contraction-relaxation responses associated with changes in K(+) channel activity. We hypothesized that to maintain oxygenation during LTH, basilar arteries (BA) in the ovine adult and near-term fetus would show increased large-conductance Ca(2+) activated potassium (BK) channel activity. We measured BK channel activity, expression, and cell surface distribution by use of patch-clamp electrophysiology, flow cytometry, and confocal microscopy, respectively, in myocytes from normoxic control and LTH adult and near-term fetus BA. Electrophysiological data showed that BK channels in LTH myocytes exhibited 1) lowered Ca(2+) set points, 2) left-shifted activation voltages, and 3) longer dwell times. BK channels in LTH myocytes also appeared to be more dephosphorylated. These differences collectively make LTH BK channels more sensitive to activation. Studies using flow cytometry showed that the LTH fetus exhibited increased BK β1 subunit surface expression. In addition, in both fetal groups confocal microscopy revealed increased BK channel clustering and colocalization to myocyte lipid rafts. We conclude that increased BK channel activity in LTH BA occurred in association with increased channel affinity for Ca(2+) and left-shifted voltage activation. Increased cerebrovascular BK channel activity may be a mechanism by which LTH adult and near-term fetal sheep can acclimatize to long-term high altitude hypoxia. Our findings suggest that increasing BK channel activity in cerebral myocytes may be a therapeutic target to ameliorate the adverse effects of high altitude in adults or of intrauterine hypoxia in the fetus.
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Affiliation(s)
- Xiaoxiao Tao
- Division of Pharmacology, School of Medicine, Loma Linda University, Loma Linda, California
| | - Mike T Lin
- Division of Physiology, School of Medicine, Loma Linda University, Loma Linda, California; Department of Physiology and Cell Biology, University of South Alabama, Mobile, Alabama
| | - Glyne U Thorington
- Division of Physiology, School of Medicine, Loma Linda University, Loma Linda, California
| | - Sean M Wilson
- Division of Pharmacology, School of Medicine, Loma Linda University, Loma Linda, California; Center for Perinatal Biology, School of Medicine, Loma Linda University, Loma Linda, California; and
| | - Lawrence D Longo
- Division of Physiology, School of Medicine, Loma Linda University, Loma Linda, California; Center for Perinatal Biology, School of Medicine, Loma Linda University, Loma Linda, California; and
| | - David A Hessinger
- Division of Pharmacology, School of Medicine, Loma Linda University, Loma Linda, California; Division of Physiology, School of Medicine, Loma Linda University, Loma Linda, California;
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41
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Regulation of brain blood flow and oxygen delivery in elite breath-hold divers. J Cereb Blood Flow Metab 2015; 35:66-73. [PMID: 25370857 PMCID: PMC4294396 DOI: 10.1038/jcbfm.2014.170] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Revised: 09/05/2014] [Accepted: 09/08/2014] [Indexed: 01/07/2023]
Abstract
The roles of involuntary breathing movements (IBMs) and cerebral oxygen delivery in the tolerance to extreme hypoxemia displayed by elite breath-hold divers are unknown. Cerebral blood flow (CBF), arterial blood gases (ABGs), and cardiorespiratory metrics were measured during maximum dry apneas in elite breath-hold divers (n=17). To isolate the effects of apnea and IBM from the concurrent changes on ABG, end-tidal forcing ('clamp') was then used to replicate an identical temporal pattern of decreasing arterial PO2 (PaO2) and increasing arterial PCO2 (PaCO2) while breathing. End-apnea PaO2 ranged from 23 to 37 mm Hg (30 ± 7 mm Hg). Elevation in mean arterial pressure was greater during apnea than during clamp reaching +54 ± 24% versus 34 ± 26%, respectively; however, CBF increased similarly between apnea and clamp (93.6 ± 28% and 83.4 ± 38%, respectively). This latter observation indicates that during the overall apnea period IBM per se do not augment CBF and that the brain remains sufficiently protected against hypertension. Termination of apnea was not determined by reduced cerebral oxygen delivery; despite 40% to 50% reductions in arterial oxygen content, oxygen delivery was maintained by commensurately increased CBF.
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42
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Smith KJ, MacLeod D, Willie CK, Lewis NCS, Hoiland RL, Ikeda K, Tymko MM, Donnelly J, Day TA, MacLeod N, Lucas SJE, Ainslie PN. Influence of high altitude on cerebral blood flow and fuel utilization during exercise and recovery. J Physiol 2014; 592:5507-27. [PMID: 25362150 PMCID: PMC4270509 DOI: 10.1113/jphysiol.2014.281212] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2014] [Accepted: 10/18/2014] [Indexed: 11/08/2022] Open
Abstract
We examined the hypotheses that: (1) during incremental exercise and recovery following 4-6 days at high altitude (HA) global cerebral blood flow (gCBF) increases to preserve cerebral oxygen delivery (CDO2) in excess of that required by an increasing cerebral metabolic rate of oxygen ( CM RO2); (2) the trans-cerebral exchange of oxygen vs. carbohydrates (OCI; carbohydrates = glucose + ½lactate) would be similar during exercise and recovery at HA and sea level (SL). Global CBF, intra-cranial arterial blood velocities, extra-cranial blood flows, and arterial-jugular venous substrate differences were measured during progressive steady-state exercise (20, 40, 60, 80, 100% maximum workload (Wmax)) and through 30 min of recovery. Measurements (n = 8) were made at SL and following partial acclimatization to 5050 m. At HA, absolute Wmax was reduced by ∼50%. During submaximal exercise workloads (20-60% Wmax), despite an elevated absolute gCBF (∼20%, P < 0.05) the relative increases in gCBF were not different at HA and SL. In contrast, gCBF was elevated at HA compared with SL during 80 and 100% Wmax and recovery. Notwithstanding a maintained CDO2 and elevated absolute CM RO2 at HA compared with SL, the relative increase in CM RO2 was similar during 20-80% Wmax but half that of the SL response (i.e. 17 vs. 27%; P < 0.05 vs. SL) at 100% Wmax. The OCI was reduced at HA compared with SL during 20, 40, and 60% Wmax but comparable at 80 and 100% Wmax. At HA, OCI returned almost immediately to baseline values during recovery, whereas at SL it remained below baseline. In conclusion, the elevations in gCBF during exercise and recovery at HA serve to maintain CDO2. Despite adequate CDO2 at HA the brain appears to increase non-oxidative metabolism during exercise and recovery.
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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, BC, Canada
| | - D MacLeod
- Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - C K Willie
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | - N C S Lewis
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | - R L Hoiland
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | - K Ikeda
- Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - M M Tymko
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
| | - J Donnelly
- University of Otago, Dunedin, New Zealand University Division of Neurosurgery, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK
| | - T A Day
- Department of Biology, Mount Royal Univeristy, Calgary, AB, Canada
| | - N MacLeod
- Carolina Friends School, Durham, NC, USA
| | - S J E Lucas
- University of Otago, Dunedin, New Zealand University of Birmingham, Birmingham, UK
| | - P N Ainslie
- Centre for Heart Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada
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43
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Abstract
High altitude headache (HAH) has been defined by the International Headache Society as a headache that appears within 24 hours after ascent to 2,500 m or higher [1••]. The headache can appear in isolation or as part of acute mountain sickness (AMS), which has more dramatic symptoms than the headache alone. If symptoms are ignored, more serious conditions such as high altitude cerebral edema (HACE), high altitude pulmonary edema (HAPE), or even death may ensue. While there is no definitive understanding of the underlying pathophysiologic mechanism, it is speculated that HAH occurs from the combination of hypoxemia-induced intracranial vasodilation and subsequent cerebral edema. There are a number of preventive measures that can be adopted prior to ascending, including acclimatization and various medications. A variety of pharmacological interventions are also available to clinicians to treat this extremely widespread condition.
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Affiliation(s)
- J Ivan Lopez
- University of Nevada School of Medicine, Reno, Nevada,
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44
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Goodall S, Twomey R, Amann M. Acute and chronic hypoxia: implications for cerebral function and exercise tolerance. FATIGUE-BIOMEDICINE HEALTH AND BEHAVIOR 2014; 2:73-92. [PMID: 25593787 DOI: 10.1080/21641846.2014.909963] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
PURPOSE To outline how hypoxia profoundly affects neuronal functionality and thus compromise exercise-performance. METHODS Investigations using electroencephalography (EEG) and transcranial magnetic stimulation (TMS) detecting neuronal changes at rest and those studying fatiguing effects on whole-body exercise performance in acute (AH) and chronic hypoxia (CH) were evaluated. RESULTS At rest during very early hypoxia (<1-h), slowing of cerebral neuronal activity is evident despite no change in corticospinal excitability. As time in hypoxia progresses (3-h), increased corticospinal excitability becomes evident; however, changes in neuronal activity are unknown. Prolonged exposure (3-5 d) causes a respiratory alkalosis which modulates Na+ channels, potentially explaining reduced neuronal excitability. Locomotor exercise in AH exacerbates the development of peripheral-fatigue; as the severity of hypoxia increases, mechanisms of peripheral-fatigue become less dominant and CNS hypoxia becomes the predominant factor. The greatest central-fatigue in AH occurs when SaO2 is ≤75%, a level that coincides with increasing impairments in neuronal activity. CH does not improve the level of peripheral-fatigue observed in AH; however, it attenuates the development of central-fatigue paralleling increases in cerebral O2 availability and corticospinal excitability. CONCLUSIONS The attenuated development of central-fatigue in CH might explain, the improvements in locomotor exercise-performance commonly observed after acclimatisation to high altitude.
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Affiliation(s)
- Stuart Goodall
- Faculty of Health and Life Sciences, Northumbria University, Newcastle, UK
| | - Rosie Twomey
- School of Sport and Service Management, University of Brighton, Eastbourne, UK
| | - Markus Amann
- Department of Medicine, University of Utah, Salt Lake City, UT, USA
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45
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Subudhi AW, Fan JL, Evero O, Bourdillon N, Kayser B, Julian CG, Lovering AT, Panerai RB, Roach RC. AltitudeOmics: cerebral autoregulation during ascent, acclimatization, and re-exposure to high altitude and its relation with acute mountain sickness. J Appl Physiol (1985) 2014; 116:724-9. [DOI: 10.1152/japplphysiol.00880.2013] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Cerebral autoregulation (CA) acts to maintain brain blood flow despite fluctuations in perfusion pressure. Acute hypoxia is thought to impair CA, but it is unclear if CA is affected by acclimatization or related to the development of acute mountain sickness (AMS). We assessed changes in CA using transfer function analysis of spontaneous fluctuations in radial artery blood pressure (indwelling catheter) and resulting changes in middle cerebral artery blood flow velocity (transcranial Doppler) in 21 active individuals at sea level upon arrival at 5,260 m (ALT1), after 16 days of acclimatization (ALT16), and upon re-exposure to 5,260 m after 7 days at 1,525 m (POST7). The Lake Louise Questionnaire was used to evaluate AMS symptom severity. CA was impaired upon arrival at ALT1 ( P < 0.001) and did not change with acclimatization at ALT16 or upon re-exposure at POST7. CA was not associated with AMS symptoms (all R < 0.50, P > 0.05). These findings suggest that alterations in CA are an intrinsic consequence of hypoxia and are not directly related to the occurrence or severity of AMS.
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Affiliation(s)
- Andrew W. Subudhi
- University of Colorado Altitude Research Center, Department of Emergency Medicine, Anschutz Medical Campus, Aurora, Colorado
- University of Colorado Colorado Springs, Department of Biology, Colorado Springs, Colorado
| | - Jui-Lin Fan
- University of Lausanne, Institute of Sports Sciences, Lausanne, Switzerland
- University of Geneva, Lemanic Doctoral School of Neuroscience, Geneva, Switzerland
| | - Oghenero Evero
- University of Colorado Altitude Research Center, Department of Emergency Medicine, Anschutz Medical Campus, Aurora, Colorado
| | - Nicolas Bourdillon
- University of Lausanne, Institute of Sports Sciences, Lausanne, Switzerland
| | - Bengt Kayser
- University of Lausanne, Institute of Sports Sciences, Lausanne, Switzerland
| | - Colleen G. Julian
- University of Colorado Altitude Research Center, Department of Emergency Medicine, Anschutz Medical Campus, Aurora, Colorado
| | - Andrew T. Lovering
- University of Oregon, Department of Human Physiology, Eugene, Oregon; and
| | - Ronney B. Panerai
- University of Leicester, Leicester Royal Infirmary, Department of Cardiovascular Sciences, Leicester, United Kingdom
| | - Robert C. Roach
- University of Colorado Altitude Research Center, Department of Emergency Medicine, Anschutz Medical Campus, Aurora, Colorado
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46
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Ogoh S, Nakahara H, Ueda S, Okazaki K, Shibasaki M, Subudhi AW, Miyamoto T. Effects of acute hypoxia on cerebrovascular responses to carbon dioxide. Exp Physiol 2014; 99:849-58. [PMID: 24632495 DOI: 10.1113/expphysiol.2013.076802] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
In normoxic conditions, a reduction in arterial carbon dioxide tension causes cerebral vasoconstriction, thereby reducing cerebral blood flow and modifying dynamic cerebral autoregulation (dCA). It is unclear to what extent these effects are altered by acute hypoxia and the associated hypoxic ventilatory response (respiratory chemoreflex). This study tested the hypothesis that acute hypoxia attenuates arterial CO2 tension-mediated regulation of cerebral blood flow to help maintain cerebral O2 homeostasis. Eight subjects performed three randomly assigned respiratory interventions following a resting baseline period, as follows: (1) normoxia (21% O2); (2) hypoxia (12% O2); and (3) hypoxia with wilful restraint of the respiratory chemoreflex. During each intervention, 0, 2.0, 3.5 or 5.0% CO2 was sequentially added (8 min stages) to inspired gas mixtures to assess changes in steady-state cerebrovascular CO2 reactivity and dCA. During normoxia, the addition of CO2 increased internal carotid artery blood flow and middle cerebral artery mean blood velocity (MCA Vmean), while reducing dCA (change in phase = -0.73 ± 0.22 rad, P = 0.005). During acute hypoxia, internal carotid artery blood flow and MCA Vmean remained unchanged, but cerebrovascular CO2 reactivity (internal carotid artery, P = 0.003; MCA Vmean, P = 0.031) and CO2-mediated effects on dCA (P = 0.008) were attenuated. The effects of hypoxia were not further altered when the respiratory chemoreflex was restrained. These findings support the hypothesis that arterial CO2 tension-mediated effects on the cerebral vasculature are reduced during acute hypoxia. These effects could limit the degree of hypocapnic vasoconstriction and may help to regulate cerebral blood flow and cerebral O2 homeostasis during acute periods of hypoxia.
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Affiliation(s)
- Shigehiko Ogoh
- Department of Biomedical Engineering, Toyo University, Kawagoe-Shi, Saitama, Japan
| | | | - Shinya Ueda
- Morinomiya University of Medical Sciences, Osaka, Japan
| | - Kazunobu Okazaki
- Department of Environmental Physiology for Exercise, Osaka City University Graduate School of Medicine, Osaka, Japan
| | - Manabu Shibasaki
- Department of Environmental Health, Nara Women's University, Nara, Japan
| | - Andrew W Subudhi
- Department of Biology, University of Colorado, Colorado Springs, CO, USA
| | - Tadayoshi Miyamoto
- Morinomiya University of Medical Sciences, Osaka, Japan Department of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, Osaka, Japan
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47
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Lewis NCS, Messinger L, Monteleone B, Ainslie PN. Effect of acute hypoxia on regional cerebral blood flow: effect of sympathetic nerve activity. J Appl Physiol (1985) 2014; 116:1189-96. [PMID: 24610534 DOI: 10.1152/japplphysiol.00114.2014] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
We examined 1) whether global cerebral blood flow (CBF) would increase across a 6-h bout of normobaric poikilocapnic hypoxia and be mediated by a larger increase in blood flow in the vertebral artery (VA) than in the internal carotid artery (ICA); and 2) whether additional increases in global CBF would be evident following an α1-adrenergic blockade via further dilation of the ICA and VA. In 11 young normotensive individuals, ultrasound measures of ICA and VA flow were obtained in normoxia (baseline) and following 60, 210, and 330 min of hypoxia (FiO2 = 0.11). Ninety minutes prior to final assessment, participants received an α1-adrenoreceptor blocker (prazosin, 1 mg/20 kg body mass) or placebo. Compared with baseline, following 60, 220, and 330 min of hypoxia, global CBF [(ICAFlow + VAFlow) ∗ 2] increased by 160 ± 52 ml/min (+28%; P = 0.05), 134 ± 23 ml/min (+23%; P = 0.02), and 113 ± 51 (+19%; P = 0.27), respectively. Compared with baseline, ICAFlow increased by 23% following 60 min of hypoxia (P = 0.06), after which it progressively declined. The percentage increase in VA flow was consistently larger than ICA flow during hypoxia by ∼20% (P = 0.002). Compared with baseline, ICA and VA diameters increased during hypoxia by ∼9% and ∼12%, respectively (P ≤ 0.05), and were correlated with reductions in SaO2. Flow and diameters were unaltered following α1 blockade (P ≥ 0.10). In conclusion, elevations in global CBF during acute hypoxia are partly mediated via greater increases in VA flow compared with ICA flow; this regional difference was unaltered following α1 blockade, indicating that a heightened sympathetic nerve activity with hypoxia does not constrain further dilation of larger extracranial blood vessels.
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Affiliation(s)
- Nia C S Lewis
- Centre for Heart, Lung and Vascular Health, University of British Columbia, Kelowna, British Columbia, Canada
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48
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Imray C, Chan C, Stubbings A, Rhodes H, Patey S, Wilson MH, Bailey DM, Wright AD. Time Course Variations in the Mechanisms by Which Cerebral Oxygen Delivery Is Maintained on Exposure to Hypoxia/Altitude. High Alt Med Biol 2014; 15:21-7. [DOI: 10.1089/ham.2013.1079] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- Christopher Imray
- Warwick Medical School, University Hospitals Coventry and Warwickshire NHS Trust, Warwick, United Kingdom
| | - Colin Chan
- Wirral University Teaching Hospital, Wirral, United Kingdom
| | | | - Hannah Rhodes
- Department Paediatric Surgery, Bristol Royal Hospital for Children, Bristol, United Kingdom
| | - Susannah Patey
- Department of Anaesthetics, University Hospital of South Manchester, Wythenshawe, Manchester, United Kingdom
| | - Mark H. Wilson
- Department of Neurosurgery, Imperial College, St Mary's Hospital, Paddington London, United Kingdom
| | - Damian M. Bailey
- Department of Physiology, University of Glamorgan, Pontypridd, Wales, United Kingdom
| | - Alex D. Wright
- Birmingham Medical Research Expeditionary Society, The Medical School, Birmingham University, Edgbaston, Birmingham, United Kingdom
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49
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Rupp T, Esteve F, Bouzat P, Lundby C, Perrey S, Levy P, Robach P, Verges S. Cerebral hemodynamic and ventilatory responses to hypoxia, hypercapnia, and hypocapnia during 5 days at 4,350 m. J Cereb Blood Flow Metab 2014; 34:52-60. [PMID: 24064493 PMCID: PMC3887348 DOI: 10.1038/jcbfm.2013.167] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Revised: 07/31/2013] [Accepted: 08/26/2013] [Indexed: 01/18/2023]
Abstract
This study investigated the changes in cerebral near-infrared spectroscopy (NIRS) signals, cerebrovascular and ventilatory responses to hypoxia and CO2 during altitude exposure. At sea level (SL), after 24 hours and 5 days at 4,350 m, 11 healthy subjects were exposed to normoxia, isocapnic hypoxia, hypercapnia, and hypocapnia. The following parameters were measured: prefrontal tissue oxygenation index (TOI), oxy- (HbO2), deoxy- and total hemoglobin (HbTot) concentrations with NIRS, blood velocity in the middle cerebral artery (MCAv) with transcranial Doppler and ventilation. Smaller prefrontal deoxygenation and larger ΔHbTot in response to hypoxia were observed at altitude compared with SL (day 5: ΔHbO2-0.6±1.1 versus -1.8±1.3 μmol/cmper mm Hg and ΔHbTot 1.4±1.3 versus 0.7±1.1 μmol/cm per mm Hg). The hypoxic MCAv and ventilatory responses were enhanced at altitude. Prefrontal oxygenation increased less in response to hypercapnia at altitude compared with SL (day 5: ΔTOI 0.3±0.2 versus 0.5±0.3% mm Hg). The hypercapnic MCAv and ventilatory responses were decreased and increased, respectively, at altitude. Hemodynamic responses to hypocapnia did not change at altitude. Short-term altitude exposure improves cerebral oxygenation in response to hypoxia but decreases it during hypercapnia. Although these changes may be relevant for conditions such as exercise or sleep at altitude, they were not associated with symptoms of acute mountain sickness.
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Affiliation(s)
- Thomas Rupp
- 1] INSERM U1042, Grenoble, France [2] HP2 laboratory, Joseph Fourier University, Grenoble, France
| | - François Esteve
- 1] U836/team 6, INSERM, Grenoble, France [2] Grenoble Institute of Neurosciences, Joseph Fourier University, Grenoble, France
| | - Pierre Bouzat
- 1] U836/team 6, INSERM, Grenoble, France [2] Grenoble Institute of Neurosciences, Joseph Fourier University, Grenoble, France
| | - Carsten Lundby
- Institute of Physiology, University of Zurich, Zurich, Switzerland
| | - Stéphane Perrey
- Movement To Health (M2H), Montpellier-1 University, Euromov, France
| | - Patrick Levy
- 1] INSERM U1042, Grenoble, France [2] HP2 laboratory, Joseph Fourier University, Grenoble, France
| | - Paul Robach
- 1] INSERM U1042, Grenoble, France [2] HP2 laboratory, Joseph Fourier University, Grenoble, France [3] Ecole Nationale de Ski et d'Alpinisme, Chamonix, France
| | - Samuel Verges
- 1] INSERM U1042, Grenoble, France [2] HP2 laboratory, Joseph Fourier University, Grenoble, France
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50
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Subudhi AW, Fan JL, Evero O, Bourdillon N, Kayser B, Julian CG, Lovering AT, Roach RC. AltitudeOmics: effect of ascent and acclimatization to 5260 m on regional cerebral oxygen delivery. Exp Physiol 2013; 99:772-81. [PMID: 24243839 DOI: 10.1113/expphysiol.2013.075184] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Cerebral hypoxaemia associated with rapid ascent to high altitude can be life threatening; yet, with proper acclimatization, cerebral function can be maintained well enough for humans to thrive. We investigated adjustments in global and regional cerebral oxygen delivery (DO2) as 21 healthy volunteers rapidly ascended and acclimatized to 5260 m. Ultrasound indices of cerebral blood flow in internal carotid and vertebral arteries were measured at sea level, upon arrival at 5260 m (ALT1; atmospheric pressure 409 mmHg) and after 16 days of acclimatization (ALT16). Cerebral DO2 was calculated as the product of arterial oxygen content and flow in each respective artery and summed to estimate global cerebral blood flow. Vascular resistances were calculated as the quotient of mean arterial pressure and respective flows. Global cerebral blood flow increased by ∼70% upon arrival at ALT1 (P < 0.001) and returned to sea-level values at ALT16 as a result of changes in cerebral vascular resistance. A reciprocal pattern in arterial oxygen content maintained global cerebral DO2 throughout acclimatization, although DO2 to the posterior cerebral circulation was increased by ∼25% at ALT1 (P = 0.032). We conclude that cerebral DO2 is well maintained upon acute exposure and acclimatization to hypoxia, particularly in the posterior and inferior regions of the brain associated with vital homeostatic functions. This tight regulation of cerebral DO2 was achieved through integrated adjustments in local vascular resistances to alter cerebral perfusion during both acute and chronic exposure to hypoxia.
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Affiliation(s)
- Andrew W Subudhi
- University of Colorado Denver Anschutz Medical Campus, Department of Emergency Medicine, Altitude Research Center, Aurora, CO, USA University of Colorado Colorado Springs, Department of Biology, Colorado Springs, CO, USA
| | - Jui-Lin Fan
- University of Lausanne, Institute of Sport Sciences, Lausanne, Switzerland University of Geneva, Lemanic Doctoral School of Neuroscience, Geneva, Switzerland
| | - Oghenero Evero
- University of Colorado Denver Anschutz Medical Campus, Department of Emergency Medicine, Altitude Research Center, Aurora, CO, USA
| | - Nicolas Bourdillon
- University of Lausanne, Institute of Sport Sciences, Lausanne, Switzerland
| | - Bengt Kayser
- University of Lausanne, Institute of Sport Sciences, Lausanne, Switzerland
| | - Colleen G Julian
- University of Colorado Denver Anschutz Medical Campus, Department of Emergency Medicine, Altitude Research Center, Aurora, CO, USA
| | - Andrew T Lovering
- University of Oregon, Department of Human Physiology, Eugene, OR, USA
| | - Robert C Roach
- University of Colorado Denver Anschutz Medical Campus, Department of Emergency Medicine, Altitude Research Center, Aurora, CO, USA
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