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Buxton RB. Thermodynamic limitations on brain oxygen metabolism: physiological implications. J Physiol 2024; 602:683-712. [PMID: 38349000 DOI: 10.1113/jp284358] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Accepted: 01/03/2024] [Indexed: 02/20/2024] Open
Abstract
Recent thermodynamic modelling indicates that maintaining the brain tissue ratio of O2 to CO2 (abbreviated tissue O2 /CO2 ) is critical for preserving the entropy increase available from oxidative metabolism of glucose, with a fall of that available entropy leading to a reduction of the phosphorylation potential and impairment of brain energy metabolism. This provides a novel perspective for understanding physiological responses under different conditions in terms of preserving tissue O2 /CO2 . To enable estimation of tissue O2 /CO2 in the human brain, a detailed mathematical model of O2 and CO2 transport was developed, and applied to reported physiological responses to different challenges, asking: how well is tissue O2 /CO2 preserved? Reported experimental results for increased neural activity, hypercapnia and hypoxia due to high altitude are consistent with preserving tissue O2 /CO2 . The results highlight two physiological mechanisms that control tissue O2 /CO2 : cerebral blood flow, which modulates tissue O2 ; and ventilation rate, which modulates tissue CO2 . The hypoxia modelling focused on humans at high altitude, including acclimatized lowlanders and Tibetan and Andean adapted populations, with a primary finding that decreasing CO2 by increasing ventilation rate is more effective for preserving tissue O2 /CO2 than increasing blood haemoglobin content to maintain O2 delivery to tissue. This work focused on the function served by particular physiological responses, and the underlying mechanisms require further investigation. The modelling provides a new framework and perspective for understanding how blood flow and other physiological factors support energy metabolism in the brain under a wide range of conditions. KEY POINTS: Thermodynamic modelling indicates that preserving the O2 /CO2 ratio in brain tissue is critical for preserving the entropy change available from oxidative metabolism of glucose and the phosphorylation potential underlying energy metabolism. A detailed model of O2 and CO2 transport was developed to allow estimation of the tissue O2 /CO2 ratio in the human brain in different physiological states. Reported experimental results during hypoxia, hypercapnia and increased oxygen metabolic rate in response to increased neural activity are consistent with maintaining brain tissue O2 /CO2 ratio. The hypoxia modelling of high-altitude acclimatization and adaptation in humans demonstrates the critical role of reducing CO2 with increased ventilation for preserving tissue O2 /CO2 . Preservation of tissue O2 /CO2 provides a novel perspective for understanding the function of observed physiological responses under different conditions in terms of preserving brain energy metabolism, although the mechanisms underlying these functions are not well understood.
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Affiliation(s)
- Richard B Buxton
- Center for Functional Magnetic Resonance Imaging, Department of Radiology, University of California, San Diego, California, USA
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Wang S, Ma J, Qiu H, Liu S, Zhang S, Liu H, Zhang P, Ge RL, Li G, Cui S. Plasma exosomal microRNA expression profiles in patients with high-altitude polycythemia. Blood Cells Mol Dis 2023; 98:102707. [DOI: 10.1016/j.bcmd.2022.102707] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2022] [Revised: 10/19/2022] [Accepted: 10/26/2022] [Indexed: 11/06/2022]
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Liu H, Tang F, Su J, Ma J, Qin Y, Ji L, Geng H, Wang S, Zhang P, Liu J, Cui S, Ge RL, Li Z. EPAS1 regulates proliferation of erythroblasts in chronic mountain sickness. Blood Cells Mol Dis 2020; 84:102446. [PMID: 32470757 DOI: 10.1016/j.bcmd.2020.102446] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 05/14/2020] [Accepted: 05/15/2020] [Indexed: 01/13/2023]
Abstract
Excessive erythrocytosis (EE) is a characteristic of chronic mountain sickness (CMS). Currently, the pathogenesis of CMS remains unclear. This study was intended to investigate the role of EPAS1 in the proliferation of erythroblasts in CMS. Changes of HIF-1α and EPAS1/HIF-2α in the bone marrow erythroblasts of 21 patients with CMS and 14 control subjects residing at the same altitudes were determined by RT-qPCR and western blotting. We also developed a lentiviral vector, Lv-EPAS1/sh-EPAS1, to over-express/silence EPAS1 in K562 cells. Cells cycle and proliferation were detected by flow cytometry. Transcriptome analyses were carried out on Illumina. CMS patients showed a higher expression of EPAS1/HIF-2α in the bone marrow erythroblasts than those of controls. Variations in EPAS1 expression in CMS patients were positively correlated with RBC levels, and negatively correlated with SaO2. Over-expressing of EPAS1 in K562 cells accelerated the erythroid cells cycle progression and promoted the erythroid cells proliferation-and vice versa. Transcriptome data indicated that proliferation-related DEGs were significantly enriched in EPAS1 overexpression/silencing K562 cells. Our results suggest that EPAS1 might participate in the pathogenesis of EE by regulating the proliferation of erythroblasts.
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Affiliation(s)
- Huihui Liu
- Research Center for High Altitude Medicine, Qinghai University, Xining, China; Qinghai Key Laboratory of Science and Technology for High Altitude Medicine, Xining, China; Qinghai-Utah Joint Research Key Lab for High Altitude Medicine, Xining, China; Department of Rheumatology, Affiliated Hospital of Qinghai University, Xining, China
| | - Feng Tang
- Research Center for High Altitude Medicine, Qinghai University, Xining, China; Qinghai Key Laboratory of Science and Technology for High Altitude Medicine, Xining, China; Qinghai-Utah Joint Research Key Lab for High Altitude Medicine, Xining, China
| | - Juan Su
- Department of Rheumatology, Affiliated Hospital of Qinghai University, Xining, China
| | - Jie Ma
- Department of Hematology, Affiliated Hospital of Qinghai University, Xining, China
| | - Yajing Qin
- Department of Rheumatology, Affiliated Hospital of Qinghai University, Xining, China
| | - Linhua Ji
- Department of Hematology, Affiliated Hospital of Qinghai University, Xining, China
| | - Hui Geng
- Department of Rheumatology, Affiliated Hospital of Qinghai University, Xining, China
| | - Shengyan Wang
- Research Center for High Altitude Medicine, Qinghai University, Xining, China; Qinghai Key Laboratory of Science and Technology for High Altitude Medicine, Xining, China; Qinghai-Utah Joint Research Key Lab for High Altitude Medicine, Xining, China
| | - Peili Zhang
- Research Center for High Altitude Medicine, Qinghai University, Xining, China; Qinghai Key Laboratory of Science and Technology for High Altitude Medicine, Xining, China; Qinghai-Utah Joint Research Key Lab for High Altitude Medicine, Xining, China
| | - Junli Liu
- Research Center for High Altitude Medicine, Qinghai University, Xining, China; Qinghai Key Laboratory of Science and Technology for High Altitude Medicine, Xining, China; Qinghai-Utah Joint Research Key Lab for High Altitude Medicine, Xining, China
| | - Sen Cui
- Department of Hematology, Affiliated Hospital of Qinghai University, Xining, China
| | - Ri-Li Ge
- Research Center for High Altitude Medicine, Qinghai University, Xining, China; Qinghai Key Laboratory of Science and Technology for High Altitude Medicine, Xining, China; Qinghai-Utah Joint Research Key Lab for High Altitude Medicine, Xining, China
| | - Zhanquan Li
- Department of Rheumatology, Affiliated Hospital of Qinghai University, Xining, China.
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Zhang S, Liu D, Gesang DZ, Lv M. Characteristics of Cerebral Stroke in the Tibet Autonomous Region of China. Med Sci Monit 2020; 26:e919221. [PMID: 31917778 PMCID: PMC6977622 DOI: 10.12659/msm.919221] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2019] [Accepted: 10/03/2019] [Indexed: 11/09/2022] Open
Abstract
It is well known that cerebrovascular disease has become an important cause of adult death and disability. Strikingly, the Tibet Autonomous Region (TAR) ranks on the top in China for the incidence of stroke. To help explain this phenomenon, we have searched for and analyzed stroke-related literature for the TAR in the past 2 decades and have referenced reports from other regions at similar altitudes. This article focuses on epidemiology features, risk factors, and pathogenesis of stroke in the TAR in an effort to generate a better understanding of the characteristics of stroke in this region. The special plateau-related factors such as its high elevation, limited oxygen, the high incidence of hypertension, smoking, and the unique dietary habits of the region are correlated with the high incidence of stroke. In addition to these factors, the pathogenesis of stroke in this high-altitude area is also unique. However, there is no established explanation for the unique occurrence and high incidence of stroke in the TAR. Our study provides an important rationale not only for the clinic to prevent and treat this disease, but also for the government to develop appropriate health policies for the prevention of stroke in the TAR.
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Affiliation(s)
- Shuai Zhang
- Department of Neurosurgery, Beijing Aerospace General Hospital, Beijing, P.R. China
| | - Dong Liu
- Department of Neurosurgery, Sanbo Brain Hospital, Capital Medical University, Beijing, P.R. China
| | - Dun Zhu Gesang
- Department of Neurosurgery, Second People’s Hospital of Tibet Autonomous Region, Lhasa, Tibet Autonomous Region, P.R. China
| | - Ming Lv
- Department of Interventional Neuroradiology, Beijing Neurosurgical Institute and Beijing Tiantan Hospital, Capital Medical University, Beijing, P.R. China
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Hoiland RL, Howe CA, Carter HH, Tremblay JC, Willie CK, Donnelly J, MacLeod DB, Gasho C, Stembridge M, Boulet LM, Niroula S, Ainslie PN. UBC‐Nepal expedition: phenotypical evidence for evolutionary adaptation in the control of cerebral blood flow and oxygen delivery at high altitude. J Physiol 2019; 597:2993-3008. [DOI: 10.1113/jp277596] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 04/09/2019] [Indexed: 01/26/2023] Open
Affiliation(s)
- Ryan L. Hoiland
- Centre for Heart, Lung and Vascular HealthUniversity of British Columbia–Okanagan Campus, School of Health and Exercise Sciences 3333 University Way Kelowna British Columbia Canada V1V 1V7
| | - Connor A. Howe
- Centre for Heart, Lung and Vascular HealthUniversity of British Columbia–Okanagan Campus, School of Health and Exercise Sciences 3333 University Way Kelowna British Columbia Canada V1V 1V7
| | - Howard H. Carter
- Department of Nutrition, Exercise and SportsUniversity of Copenhagen Nørre Allé 51 DK‐2200 Copenhagen Denmark
| | - Joshua C. Tremblay
- Cardiovascular Stress Response Laboratory, School of Kinesiology and Health StudiesQueen's University 28 Division Street Kingston Ontario Canada K7L 3N6
| | - Chris K. Willie
- Centre for Heart, Lung and Vascular HealthUniversity of British Columbia–Okanagan Campus, School of Health and Exercise Sciences 3333 University Way Kelowna British Columbia Canada V1V 1V7
| | - Joseph Donnelly
- Brain Physics Laboratory, Division of Neurosurgery, Department of Clinical NeurosciencesCambridge Biomedical Campus, University of Cambridge Cambridge CB2 0QQ UK
| | - David B. MacLeod
- Human Pharmacology and Physiology Lab, Department of AnesthesiologyDuke University Medical Center Durham NC 27708 USA
| | - Chris Gasho
- VA Loma Linda Healthcare System and Loma Linda University School of Medicine Loma Linda CA USA
| | - Mike Stembridge
- Cardiff Centre for Exercise and HealthCardiff Metropolitan University Cyncoed Road Cardiff CF23 6XD UK
| | - Lindsey M. Boulet
- Centre for Heart, Lung and Vascular HealthUniversity of British Columbia–Okanagan Campus, School of Health and Exercise Sciences 3333 University Way Kelowna British Columbia Canada V1V 1V7
| | | | - Philip N. Ainslie
- Centre for Heart, Lung and Vascular HealthUniversity of British Columbia–Okanagan Campus, School of Health and Exercise Sciences 3333 University Way Kelowna British Columbia Canada V1V 1V7
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Sleep Disordered Breathing at High Altitude in Adults and Its Interaction with Cardiovascular Homeostasis. CURRENT SLEEP MEDICINE REPORTS 2019. [DOI: 10.1007/s40675-019-00138-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Human Genetic Adaptation to High Altitude: Evidence from the Andes. Genes (Basel) 2019; 10:genes10020150. [PMID: 30781443 PMCID: PMC6410003 DOI: 10.3390/genes10020150] [Citation(s) in RCA: 67] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Revised: 01/29/2019] [Accepted: 02/11/2019] [Indexed: 12/31/2022] Open
Abstract
Whether Andean populations are genetically adapted to high altitudes has long been of interest. Initial studies focused on physiological changes in the O₂ transport system that occur with acclimatization in newcomers and their comparison with those of long-resident Andeans. These as well as more recent studies indicate that Andeans have somewhat larger lung volumes, narrower alveolar to arterial O₂ gradients, slightly less hypoxic pulmonary vasoconstrictor response, greater uterine artery blood flow during pregnancy, and increased cardiac O2 utilization, which overall suggests greater efficiency of O₂ transfer and utilization. More recent single nucleotide polymorphism and whole-genome sequencing studies indicate that multiple gene regions have undergone recent positive selection in Andeans. These include genes involved in the regulation of vascular control, metabolic hemostasis, and erythropoiesis. However, fundamental questions remain regarding the functional links between these adaptive genomic signals and the unique physiological attributes of highland Andeans. Well-designed physiological and genome association studies are needed to address such questions. It will be especially important to incorporate the role of epigenetic processes (i.e.; non-sequence-based features of the genome) that are vital for transcriptional responses to hypoxia and are potentially heritable across generations. In short, further exploration of the interaction among genetic, epigenetic, and environmental factors in shaping patterns of adaptation to high altitude promises to improve the understanding of the mechanisms underlying human adaptive potential and clarify its implications for human health.
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Bailey DM, Brugniaux JV, Filipponi T, Marley CJ, Stacey B, Soria R, Rimoldi SF, Cerny D, Rexhaj E, Pratali L, Salmòn CS, Murillo Jáuregui C, Villena M, Smirl JD, Ogoh S, Pietri S, Scherrer U, Sartori C. Exaggerated systemic oxidative-inflammatory-nitrosative stress in chronic mountain sickness is associated with cognitive decline and depression. J Physiol 2019; 597:611-629. [PMID: 30397919 PMCID: PMC6332753 DOI: 10.1113/jp276898] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Accepted: 11/05/2018] [Indexed: 12/15/2022] Open
Abstract
KEY POINTS Chronic mountain sickness (CMS) is a maladaptation syndrome encountered at high altitude (HA) characterised by severe hypoxaemia that carries a higher risk of stroke and migraine and is associated with increased morbidity and mortality. We examined if exaggerated oxidative-inflammatory-nitrosative stress (OXINOS) and corresponding decrease in vascular nitric oxide bioavailability in patients with CMS (CMS+) is associated with impaired cerebrovascular function and adverse neurological outcome. Systemic OXINOS was markedly elevated in CMS+ compared to healthy HA (CMS-) and low-altitude controls. OXINOS was associated with blunted cerebral perfusion and vasoreactivity to hypercapnia, impaired cognition and, in CMS+, symptoms of depression. These findings are the first to suggest that a physiological continuum exists for hypoxaemia-induced systemic OXINOS in HA dwellers that when excessive is associated with accelerated cognitive decline and depression, helping identify those in need of more specialist neurological assessment and targeted support. ABSTRACT Chronic mountain sickness (CMS) is a maladaptation syndrome encountered at high altitude (HA) characterised by severe hypoxaemia that carries a higher risk of stroke and migraine and is associated with increased morbidity and mortality. The present cross-sectional study examined to what extent exaggerated systemic oxidative-inflammatory-nitrosative stress (OXINOS), defined by an increase in free radical formation and corresponding decrease in vascular nitric oxide (NO) bioavailability, is associated with impaired cerebrovascular function, accelerated cognitive decline and depression in CMS. Venous blood was obtained from healthy male lowlanders (80 m, n = 17), and age- and gender-matched HA dwellers born and bred in La Paz, Bolivia (3600 m) with (CMS+, n = 23) and without (CMS-, n = 14) CMS. We sampled blood for oxidative (electron paramagnetic resonance spectroscopy, HPLC), nitrosative (ozone-based chemiluminescence) and inflammatory (fluorescence) biomarkers. We employed transcranial Doppler ultrasound to measure cerebral blood flow (CBF) and reactivity. We utilised psychometric tests and validated questionnaires to assess cognition and depression. Highlanders exhibited elevated systemic OXINOS (P < 0.05 vs. lowlanders) that was especially exaggerated in the more hypoxaemic CMS+ patients (P < 0.05 vs. CMS-). OXINOS was associated with blunted cerebral perfusion and vasoreactivity to hypercapnia, impaired cognition and, in CMS+, symptoms of depression. Collectively, these findings are the first to suggest that a physiological continuum exists for hypoxaemia-induced OXINOS in HA dwellers that when excessive is associated with accelerated cognitive decline and depression, helping identify those in need of specialist neurological assessment and support.
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Affiliation(s)
- Damian M. Bailey
- Neurovascular Research LaboratoryFaculty of Life Sciences and Education, University of South WalesUK
| | - Julien V. Brugniaux
- Neurovascular Research LaboratoryFaculty of Life Sciences and Education, University of South WalesUK
- HP2 Laboratory, INSERM U1042Grenoble Alpes UniversityGrenobleFrance
| | - Teresa Filipponi
- Neurovascular Research LaboratoryFaculty of Life Sciences and Education, University of South WalesUK
| | - Christopher J. Marley
- Neurovascular Research LaboratoryFaculty of Life Sciences and Education, University of South WalesUK
| | - Benjamin Stacey
- Neurovascular Research LaboratoryFaculty of Life Sciences and Education, University of South WalesUK
| | - Rodrigo Soria
- Department of Cardiology and Clinical ResearchUniversity HospitalBernSwitzerland
| | - Stefano F. Rimoldi
- Department of Cardiology and Clinical ResearchUniversity HospitalBernSwitzerland
| | - David Cerny
- Department of Cardiology and Clinical ResearchUniversity HospitalBernSwitzerland
| | - Emrush Rexhaj
- Department of Cardiology and Clinical ResearchUniversity HospitalBernSwitzerland
| | | | | | | | | | - Jonathan D. Smirl
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise ScienceUniversity of British Columbia OkanaganKelownaBritish ColumbiaCanada
| | | | | | - Urs Scherrer
- Department of Cardiology and Clinical ResearchUniversity HospitalBernSwitzerland
- Facultad de Ciencias, Departamento de BiologíaUniversidad de TarapacáAricaChile
| | - Claudio Sartori
- Department of Internal MedicineUniversity HospitalUNIL‐LausanneSwitzerland
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Li Y, Zhang Y, Zhang Y. Research advances in pathogenesis and prophylactic measures of acute high altitude illness. Respir Med 2018; 145:145-152. [DOI: 10.1016/j.rmed.2018.11.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2018] [Revised: 09/14/2018] [Accepted: 11/06/2018] [Indexed: 12/30/2022]
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Wang X, Wei W, Yuan F, Li S, Lin J, Zhang J. Regional cerebral blood flow in natives at high altitude: An arterial spin labeled MRI study. J Magn Reson Imaging 2018; 48:708-717. [PMID: 29493838 DOI: 10.1002/jmri.25996] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2017] [Accepted: 02/13/2018] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND It is known that a neurologic sequence occurs at high altitudes (HA); hence, cerebral blood flow (CBF) might vary by altitude. PURPOSE To use arterial spin labeled (ASL) MRI to evaluate absolute CBF differences between subjects who live at HA and lowlands. STUDY TYPE Cohort prospective trial. POPULATION In all, 64 HA Tibetans, 19 lowland Tibetans, and 25 lowland Han subjects. FIELD STRENGTH/SEQUENCE CBF was measured with the pulsed ASL sequence at 3T. ASSESSMENT CBF was correlated with abode altitude in HA Tibetans; CBF differences among HA Tibetans, lowland Tibetans, and lowland Han subjects was assessed. STATISTICAL TESTS Pearson correlation assessed the correlation. Independent t-tests analyzed group differences. RESULTS In HA Tibetans, CBF decreased with altitude in the bilateral anterior and posterior cingulate gyri, fusiform gyrus, cerebellar tonsil and cortices, and thalamus as well as left middle and inferior temporal gyri and right insula (P < 0.05); HA Tibetans (vs. lowland Tibetans) had lower CBF in the left hemisphere (precuneus, anterior cingulate gyrus, fusiform gyrus, and lingual gyrus) and right hemisphere (superior parietal lobule, precuneus, posterior cingulate gyrus, and cerebellar tonsil), while they had higher CBF in the left inferior parietal lobule, lentiform nucleus, and inferior frontal gyrus (P < 0.05). The overlapping regions, in which CBF in HA Tibetans correlated with altitude and decreased (vs. lowland Tibetans), were selected for region of interest analysis, and the results showed lower CBF in HA Tibetans than lowland Han subjects (P < 0.05). DATA CONCLUSION HA adaptation in Tibetans is associated with a decrease of regional CBF. LEVEL OF EVIDENCE 2 Technical Efficacy: Stage 4 J. Magn. Reson. Imaging 2018.
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Affiliation(s)
- Xiaochuan Wang
- Department of Neurology, Affiliated Hospital of Hangzhou Normal University, Hangzhou, China
| | - Wenping Wei
- MRI Center, First Affiliated Hospital of Xiamen University, Xiamen, China
| | - Fengjuan Yuan
- Institute of Brain Diseases and Cognition, Medical College of Xiamen University, Xiamen, China
| | - Shanhua Li
- Institute of Brain Diseases and Cognition, Medical College of Xiamen University, Xiamen, China
| | - Jianzhong Lin
- Magnetic Resonance Center, Zhongshan Hospital Xiamen University, Xiamen, China
| | - Jiaxing Zhang
- Institute of Brain Diseases and Cognition, Medical College of Xiamen University, Xiamen, China
- Institute for Brain Research and Rehabilitation, South China Normal University, Guangzhou, China
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Moore LG. Measuring high-altitude adaptation. J Appl Physiol (1985) 2017; 123:1371-1385. [PMID: 28860167 DOI: 10.1152/japplphysiol.00321.2017] [Citation(s) in RCA: 113] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Revised: 08/15/2017] [Accepted: 08/15/2017] [Indexed: 12/12/2022] Open
Abstract
High altitudes (>8,000 ft or 2,500 m) provide an experiment of nature for measuring adaptation and the physiological processes involved. Studies conducted over the past ~25 years in Andeans, Tibetans, and, less often, Ethiopians show varied but distinct O2 transport traits from those of acclimatized newcomers, providing indirect evidence for genetic adaptation to high altitude. Short-term (acclimatization, developmental) and long-term (genetic) responses to high altitude exhibit a temporal gradient such that, although all influence O2 content, the latter also improve O2 delivery and metabolism. Much has been learned concerning the underlying physiological processes, but additional studies are needed on the regulation of blood flow and O2 utilization. Direct evidence of genetic adaptation comes from single-nucleotide polymorphism (SNP)-based genome scans and whole genome sequencing studies that have identified gene regions acted upon by natural selection. Efforts have begun to understand the connections between the two with Andean studies on the genetic factors raising uterine blood flow, fetal growth, and susceptibility to Chronic Mountain Sickness and Tibetan studies on genes serving to lower hemoglobin and pulmonary arterial pressure. Critical for future studies will be the selection of phenotypes with demonstrable effects on reproductive success, the calculation of actual fitness costs, and greater inclusion of women among the subjects being studied. The well-characterized nature of the O2 transport system, the presence of multiple long-resident populations, and relevance for understanding hypoxic disorders in all persons underscore the importance of understanding how evolutionary adaptation to high altitude has occurred.NEW & NOTEWORTHY Variation in O2 transport characteristics among Andean, Tibetan, and, when available, Ethiopian high-altitude residents supports the existence of genetic adaptations that improve the distribution of blood flow to vital organs and the efficiency of O2 utilization. Genome scans and whole genome sequencing studies implicate a broad range of gene regions. Future studies are needed using phenotypes of clear relevance for reproductive success for determining the mechanisms by which naturally selected genes are acting.
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Affiliation(s)
- Lorna G Moore
- Division of Reproductive Sciences, Department of Obstetrics & Gynecology, University of Colorado Denver-Anschutz Medical Campus, Aurora, Colorado
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Flück D, Morris LE, Niroula S, Tallon CM, Sherpa KT, Stembridge M, Ainslie PN, McManus AM. UBC-Nepal expedition: markedly lower cerebral blood flow in high-altitude Sherpa children compared with children residing at sea level. J Appl Physiol (1985) 2017; 123:1003-1010. [PMID: 28572497 DOI: 10.1152/japplphysiol.00292.2017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Revised: 05/28/2017] [Accepted: 05/30/2017] [Indexed: 12/12/2022] Open
Abstract
Developmental cerebral hemodynamic adaptations to chronic high-altitude exposure, such as in the Sherpa population, are largely unknown. To examine hemodynamic adaptations in the developing human brain, we assessed common carotid (CCA), internal carotid (ICA), and vertebral artery (VA) flow and middle cerebral artery (MCA) velocity in 25 (9.6 ± 1.0 yr old, 129 ± 9 cm, 27 ± 8 kg, 14 girls) Sherpa children (3,800 m, Nepal) and 25 (9.9 ± 0.7 yr old, 143 ± 7 cm, 34 ± 6 kg, 14 girls) age-matched sea level children (344 m, Canada) during supine rest. Resting gas exchange, blood pressure, oxygen saturation and heart rate were assessed. Despite comparable age, height and weight were lower (both P < 0.01) in Sherpa compared with sea level children. Mean arterial pressure, heart rate, and ventilation were similar, whereas oxygen saturation (95 ± 2 vs. 99 ± 1%, P < 0.01) and end-tidal Pco2 (24 ± 3 vs. 36 ± 3 Torr, P < 0.01) were lower in Sherpa children. Global cerebral blood flow was ∼30% lower in Sherpa compared with sea level children. This was reflected in a lower ICA flow (283 ± 108 vs. 333 ± 56 ml/min, P = 0.05), VA flow (78 ± 26 vs. 118 ± 35 ml/min, P < 0.05), and MCA velocity (72 ± 14 vs. 88 ± 14 cm/s, P < 0.01). CCA flow was similar between Sherpa and sea level children (425 ± 92 vs. 441 ± 81 ml/min, P = 0.52). Scaling flow and oxygen uptake for differences in vessel diameter and body size, respectively, led to the same findings. A lower cerebral blood flow in Sherpa children may reflect specific cerebral hemodynamic adaptations to chronic hypoxia.NEW & NOTEWORTHY Cerebral blood flow is lower in Sherpa children compared with children residing at sea level; this may reflect a cerebral hemodynamic pattern, potentially due to adaptation to a hypoxic environment.
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Affiliation(s)
- Daniela Flück
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, British Columbia, Canada;
| | - Laura E Morris
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, British Columbia, Canada
| | - Shailesh Niroula
- Institute of Medicine, Tribhuvan University, Kirtipur, Nepal.,Khunde Hospital, Khunde, Nepal; and
| | - Christine M Tallon
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, British Columbia, Canada
| | | | - Mike Stembridge
- Cardiff School of Sport, Cardiff Metropolitan University, Cardiff, United Kingdom
| | - Philip N Ainslie
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, British Columbia, Canada
| | - Ali M McManus
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, University of British Columbia, Kelowna, British Columbia, Canada
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Azad P, Zhao HW, Cabrales PJ, Ronen R, Zhou D, Poulsen O, Appenzeller O, Hsiao YH, Bafna V, Haddad GG. Senp1 drives hypoxia-induced polycythemia via GATA1 and Bcl-xL in subjects with Monge's disease. J Exp Med 2016; 213:2729-2744. [PMID: 27821551 PMCID: PMC5110013 DOI: 10.1084/jem.20151920] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Revised: 06/02/2016] [Accepted: 10/06/2016] [Indexed: 01/17/2023] Open
Abstract
Azad and collaborators propose that Senp1 drives excessive erythropoiesis in high-altitude Andean dwellers suffering from chronic mountain sickness. In this study, because excessive polycythemia is a predominant trait in some high-altitude dwellers (chronic mountain sickness [CMS] or Monge’s disease) but not others living at the same altitude in the Andes, we took advantage of this human experiment of nature and used a combination of induced pluripotent stem cell technology, genomics, and molecular biology in this unique population to understand the molecular basis for hypoxia-induced excessive polycythemia. As compared with sea-level controls and non-CMS subjects who responded to hypoxia by increasing their RBCs modestly or not at all, respectively, CMS cells increased theirs remarkably (up to 60-fold). Although there was a switch from fetal to adult HgbA0 in all populations and a concomitant shift in oxygen binding, we found that CMS cells matured faster and had a higher efficiency and proliferative potential than non-CMS cells. We also established that SENP1 plays a critical role in the differential erythropoietic response of CMS and non-CMS subjects: we can convert the CMS phenotype into that of non-CMS and vice versa by altering SENP1 levels. We also demonstrated that GATA1 is an essential downstream target of SENP1 and that the differential expression and response of GATA1 and Bcl-xL are a key mechanism underlying CMS pathology.
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Affiliation(s)
- Priti Azad
- Division of Respiratory Medicine, Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093
| | - Huiwen W Zhao
- Division of Respiratory Medicine, Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093
| | - Pedro J Cabrales
- Department of Bioengineering, University of California, San Diego, La Jolla, CA 92093
| | - Roy Ronen
- Bioinformatics and Systems Biology Graduate Program, University of California, San Diego, La Jolla, CA 92093
| | - Dan Zhou
- Division of Respiratory Medicine, Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093
| | - Orit Poulsen
- Division of Respiratory Medicine, Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093
| | - Otto Appenzeller
- Department of Neurology, New Mexico Health Enhancement and Marathon Clinics Research Foundation, Albuquerque, NM 87122
| | - Yu Hsin Hsiao
- Division of Respiratory Medicine, Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093
| | - Vineet Bafna
- Department of Computer Science and Engineering, University of California, San Diego, La Jolla, CA 92093
| | - Gabriel G Haddad
- Division of Respiratory Medicine, Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093 .,Department of Neurosciences, University of California, San Diego, La Jolla, CA 92093.,Rady Children's Hospital, San Diego, CA 92123
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14
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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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15
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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: 20] [Impact Index Per Article: 2.5] [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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16
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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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17
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Feddersen B, Neupane P, Thanbichler F, Hadolt I, Sattelmeyer V, Pfefferkorn T, Waanders R, Noachtar S, Ausserer H. Regional differences in the cerebral blood flow velocity response to hypobaric hypoxia at high altitudes. J Cereb Blood Flow Metab 2015; 35:1846-51. [PMID: 26082017 PMCID: PMC4635241 DOI: 10.1038/jcbfm.2015.142] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Revised: 03/16/2015] [Accepted: 05/15/2015] [Indexed: 11/09/2022]
Abstract
Symptoms of acute mountain sickness (AMS) may appear above 2,500 m altitude, if the time allowed for acclimatization is insufficient. As the mechanisms underlying brain adaptation to the hypobaric hypoxic environment are not fully understood, a prospective study was performed investigating neurophysiological changes by means of near infrared spectroscopy, electroencephalograpy (EEG), and transcranial doppler sonography at 100, 3,440 and 5,050 m above sea level in the Khumbu Himal, Nepal. Fourteen of the 26 mountaineers reaching 5,050 m altitude developed symptoms of AMS between 3,440 and 5,050 m altitude (Lake-Louise Score ⩾3). Their EEG frontal beta activity and occipital alpha activity increased between 100 and 3,440 m altitude, i.e., before symptoms appeared. Cerebral blood flow velocity (CBFV) in the anterior and middle cerebral arteries (MCAs) increased in all mountaineers between 100 and 3,440 m altitude. During further ascent to 5,050 altitude, mountaineers with AMS developed a further increase in CBFV in the MCA, whereas in all mountaineers CBFV decreased continuously with increasing altitude in the posterior cerebral arteries. These results indicate that hypobaric hypoxia causes different regional changes in CBFV despite similar electrophysiological changes.
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Affiliation(s)
- Berend Feddersen
- Department of Neurology, Klinikum Grosshadern, University of Munich, Munich, Germany.,Department of Palliative Medicine, Specialized Palliative Home Care Team, University of Munich, Munich, Germany
| | - Pritam Neupane
- Department of Internal Medicine, Sinai Hospital, Johns Hopkins University, Baltimore, Maryland, USA
| | - Florian Thanbichler
- Department of Neurology, Klinikum Grosshadern, University of Munich, Munich, Germany
| | - Irmgard Hadolt
- Research Unit of Biomedical Engineering in Anesthesia and Intensive Care Medicine, Medical University of Graz, Graz, Austria
| | - Vera Sattelmeyer
- Klinik für Neurochirurgie, Dr Horst Schmidt Klinik, Wiesbaden, Germany
| | - Thomas Pfefferkorn
- Department of Neurology, Klinikum Grosshadern, University of Munich, Munich, Germany
| | - Robb Waanders
- Department of Neuropsychology, Landeskrankenhaus Rankweil, Rankweil, Austria
| | - Soheyl Noachtar
- Department of Neurology, Klinikum Grosshadern, University of Munich, Munich, Germany
| | - Harald Ausserer
- Department of Neurology, Klinikum Grosshadern, University of Munich, Munich, Germany.,Department of Neurology, Franz-Tappeiner Krankenhaus, Meran, Italy
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18
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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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19
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The Andean adaptive toolkit to counteract high altitude maladaptation: genome-wide and phenotypic analysis of the Collas. PLoS One 2014; 9:e93314. [PMID: 24686296 PMCID: PMC3970967 DOI: 10.1371/journal.pone.0093314] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2014] [Accepted: 03/03/2014] [Indexed: 12/03/2022] Open
Abstract
During their migrations out of Africa, humans successfully colonised and adapted to a wide range of habitats, including extreme high altitude environments, where reduced atmospheric oxygen (hypoxia) imposes a number of physiological challenges. This study evaluates genetic and phenotypic variation in the Colla population living in the Argentinean Andes above 3500 m and compares it to the nearby lowland Wichí group in an attempt to pinpoint evolutionary mechanisms underlying adaptation to high altitude hypoxia. We genotyped 730,525 SNPs in 25 individuals from each population. In genome-wide scans of extended haplotype homozygosity Collas showed the strongest signal around VEGFB, which plays an essential role in the ischemic heart, and ELTD1, another gene crucial for heart development and prevention of cardiac hypertrophy. Moreover, pathway enrichment analysis showed an overrepresentation of pathways associated with cardiac morphology. Taken together, these findings suggest that Colla highlanders may have evolved a toolkit of adaptative mechanisms resulting in cardiac reinforcement, most likely to counteract the adverse effects of the permanently increased haematocrit and associated shear forces that characterise the Andean response to hypoxia. Regulation of cerebral vascular flow also appears to be part of the adaptive response in Collas. These findings are not only relevant to understand the evolution of hypoxia protection in high altitude populations but may also suggest new avenues for medical research into conditions where hypoxia constitutes a detrimental factor.
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20
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Smirl JD, Lucas SJE, Lewis NCS, duManoir GR, Smith KJ, Bakker A, Basnyat AS, Ainslie PN, Ainslie PN. Cerebral pressure-flow relationship in lowlanders and natives at high altitude. J Cereb Blood Flow Metab 2014; 34:248-57. [PMID: 24169852 PMCID: PMC3915197 DOI: 10.1038/jcbfm.2013.178] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Revised: 08/13/2013] [Accepted: 09/09/2013] [Indexed: 12/30/2022]
Abstract
We investigated if dynamic cerebral pressure-flow relationships in lowlanders are altered at high altitude (HA), differ in HA natives and after return to sea level (SL). Lowlanders were tested at SL (n=16), arrival to 5,050 m, after 2-week acclimatization (with and without end-tidal PO2 normalization), and upon SL return. High-altitude natives (n=16) were tested at 5,050 m. Testing sessions involved resting spontaneous and driven (squat-stand maneuvers at very low (VLF, 0.05 Hz) and low (LF, 0.10 Hz) frequencies) measures to maximize blood pressure (BP) variability and improve assessment of the pressure-flow relationship using transfer function analysis (TFA). Blood flow velocity was assessed in the middle (MCAv) and posterior (PCAv) cerebral arteries. Spontaneous VLF and LF phases were reduced and coherence was elevated with acclimatization to HA (P<0.05), indicating impaired pressure-flow coupling. However, when BP was driven, both the frequency- and time-domain metrics were unaltered and comparable with HA natives. Acute mountain sickness was unrelated to TFA metrics. In conclusion, the driven cerebral pressure-flow relationship (in both frequency and time domains) is unaltered at 5,050 m in lowlanders and HA natives. Our findings indicate that spontaneous changes in TFA metrics do not necessarily reflect physiologically important alterations in the capacity of the brain to regulate BP.
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Affiliation(s)
- Jonathan D Smirl
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Samuel J E Lucas
- 1] Department of Physiology, University of Otago, Dunedin, New Zealand [2] School of Physical Education, University of Otago, Dunedin, New Zealand [3] School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK
| | - Nia C S Lewis
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | | | - Kurt J Smith
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Akke Bakker
- University of Twente, Enschede, The Netherlands
| | | | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, School of Health and Exercise Science, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
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