title: Sublingual microcirculatory blood flow and vessel density in Sherpas at high altitude.
abstract: Anecdotal reports suggest that Sherpa highlanders demonstrate extraordinary tolerance to hypoxia at high altitude, despite exhibiting lower arterial oxygen content than acclimatized lowlanders. This study tested the hypothesis that Sherpas exposed to hypobaric hypoxia on ascent to 5,300 m develop increased microcirculatory blood flow as a means of maintaining tissue oxygen delivery. Incident dark-field imaging was used to obtain images of the sublingual microcirculation from 64 Sherpas and 69 lowlanders. Serial measurements were obtained from participants undertaking an ascent from baseline testing (35 m or 1,300 m) to Everest base camp (5,300 m) and following subsequent descent in Kathmandu (1,300 m). Microcirculatory flow index and heterogeneity index were used to provide indexes of microcirculatory flow, while capillary density was assessed using small vessel density. Sherpas demonstrated significantly greater microcirculatory blood flow at Everest base camp, but not at baseline testing or on return in Kathmandu, than lowlanders. Additionally, blood flow exhibited greater homogeneity at 5,300 and 1,300 m (descent) in Sherpas than lowlanders. Sublingual small vessel density was not different between the two cohorts at baseline testing or at 1,300 m; however, at 5,300 m, capillary density was up to 30% greater in Sherpas. These data suggest that Sherpas can maintain a significantly greater microcirculatory flow per unit time and flow per unit volume of tissue at high altitude than lowlanders. These findings support the notion that peripheral vascular factors at the microcirculatory level may be important in the process of adaptation to hypoxia.NEW & NOTEWORTHYSherpa highlanders demonstrate extraordinary tolerance to hypoxia at high altitude, yet the physiological mechanisms underlying this tolerance remain unknown. In our prospective study, conducted on healthy volunteers ascending to Everest base camp (5,300 m), we demonstrated that Sherpas have a higher sublingual microcirculatory blood flow and greater capillary density at high altitude than lowlanders. These findings support the notion that the peripheral microcirculation plays a key role in the process of long-term adaptation to hypoxia.
authors.affiliation: University College London Centre for Altitude, Space, and Extreme Environment Medicine, University College London Hospitals National Institute for Health Research Biomedical Research Centre, Institute of Sport and Exercise Health, London, United Kingdom; e.gilbert@ucl.ac.uk.
authors.forename: Edward
authors.initials: E
authors.lastname: Gilbert-Kawai
authors.affiliation: University College London Centre for Altitude, Space, and Extreme Environment Medicine, University College London Hospitals National Institute for Health Research Biomedical Research Centre, Institute of Sport and Exercise Health, London, United Kingdom.
authors.forename: Jonny
authors.initials: J
authors.lastname: Coppel
authors.affiliation: University College London Centre for Altitude, Space, and Extreme Environment Medicine, University College London Hospitals National Institute for Health Research Biomedical Research Centre, Institute of Sport and Exercise Health, London, United Kingdom.
authors.forename: Jo
authors.initials: J
authors.lastname: Court
authors.affiliation: University College London Centre for Altitude, Space, and Extreme Environment Medicine, University College London Hospitals National Institute for Health Research Biomedical Research Centre, Institute of Sport and Exercise Health, London, United Kingdom.
authors.forename: Jildou
authors.initials: J
authors.lastname: van der Kaaij
authors.affiliation: University College London Centre for Altitude, Space, and Extreme Environment Medicine, University College London Hospitals National Institute for Health Research Biomedical Research Centre, Institute of Sport and Exercise Health, London, United Kingdom.
authors.forename: Andre
authors.initials: A
authors.lastname: Vercueil
authors.affiliation: University College London Centre for Altitude, Space, and Extreme Environment Medicine, University College London Hospitals National Institute for Health Research Biomedical Research Centre, Institute of Sport and Exercise Health, London, United Kingdom.|Integrative Physiology and Critical Illness Group, Clinical and Experimental Sciences, Faculty of Medicine, University of Southampton, Southampton, United Kingdom.
authors.forename: Martin
authors.initials: M
authors.lastname: Feelisch
authors.affiliation: University College London Centre for Altitude, Space, and Extreme Environment Medicine, University College London Hospitals National Institute for Health Research Biomedical Research Centre, Institute of Sport and Exercise Health, London, United Kingdom.|Anaesthesia and Critical Care Research Area, National Institute for Health Research Respiratory Biomedical Research Unit, University Hospital Southampton National Health Service Foundation Trust, Southampton, United Kingdom; and.|Integrative Physiology and Critical Illness Group, Clinical and Experimental Sciences, Faculty of Medicine, University of Southampton, Southampton, United Kingdom.
authors.forename: Denny
authors.initials: D
authors.lastname: Levett
authors.affiliation: University College London Centre for Altitude, Space, and Extreme Environment Medicine, University College London Hospitals National Institute for Health Research Biomedical Research Centre, Institute of Sport and Exercise Health, London, United Kingdom.
authors.forename: Monty
authors.initials: M
authors.lastname: Mythen
authors.affiliation: University College London Centre for Altitude, Space, and Extreme Environment Medicine, University College London Hospitals National Institute for Health Research Biomedical Research Centre, Institute of Sport and Exercise Health, London, United Kingdom.|Anaesthesia and Critical Care Research Area, National Institute for Health Research Respiratory Biomedical Research Unit, University Hospital Southampton National Health Service Foundation Trust, Southampton, United Kingdom; and.|Integrative Physiology and Critical Illness Group, Clinical and Experimental Sciences, Faculty of Medicine, University of Southampton, Southampton, United Kingdom.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Grocott
authors.affiliation: University College London Centre for Altitude, Space, and Extreme Environment Medicine, University College London Hospitals National Institute for Health Research Biomedical Research Centre, Institute of Sport and Exercise Health, London, United Kingdom.
authors.forename: Daniel
authors.initials: D
authors.lastname: Martin
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D000531:Altitude; D001783:Blood Flow Velocity / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008833:Microcirculation / Q000502:physiology*; D008875:Middle Aged; D009060:Mouth Floor / Q000098:blood supply* / Q000502:physiology*; D009390:Nepal / Q000453:epidemiology; D006113:United Kingdom / Q000453:epidemiology; D055815:Young Adult
keywords: Sherpa; altitude; capillary; hypoxia; microcirculation