title: Design and conduct of Xtreme Everest 2: An observational cohort study of Sherpa and lowlander responses to graduated hypobaric hypoxia.
abstract: OBJECTIVE
  Oxygen availability falls with ascent to altitude and also as a consequence of critical illness. Because cellular sequelae and adaptive processes may be shared in both circumstances, high altitude exposure ('physiological hypoxia') assists in the exploration of the response to pathological hypoxia. We therefore studied the response of healthy participants to progressive hypobaric hypoxia at altitude. The primary objective of the study was to identify differences between high altitude inhabitants (Sherpas) and lowland comparators.
  
  
  METHODS
  We performed an observational cohort study of human responses to progressive hypobaric hypoxia (during ascent) and subsequent normoxia (following descent) comparing Sherpas with lowlanders. Studies were conducted in London (35m), Kathmandu (1300m), Namche Bazaar (3500m) and Everest Base Camp (5300m). Of 180 healthy volunteers departing from Kathmandu, 64 were Sherpas and 116 were lowlanders. Physiological, biochemical, genetic and epigenetic data were collected. Core studies focused on nitric oxide metabolism, microcirculatory blood flow and exercise performance. Additional studies performed in nested subgroups examined mitochondrial and metabolic function, and ventilatory and cardiac variables. Of the 180 healthy participants who left Kathmandu, 178 (99%) completed the planned trek. Overall, more than 90% of planned testing was completed. Forty-four study protocols were successfully completed at altitudes up to and including 5300m. A subgroup of identical twins (all lowlanders) was also studied in detail.
  
  
  CONCLUSIONS
  This programme of study (Xtreme Everest 2) will provide a rich dataset relating to human adaptation to hypoxia, and the responses seen on re-exposure to normoxia. It is the largest comprehensive high altitude study of Sherpas yet performed. Translational data generated from this study will be of relevance to diseases in which oxygenation is a major factor.
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, W1T 7HA, UK.
authors.forename: Edward
authors.initials: E
authors.lastname: Gilbert-Kawai
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, W1T 7HA, UK.
authors.forename: Adam
authors.initials: A
authors.lastname: Sheperdigian
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, W1T 7HA, UK.
authors.forename: Thomas
authors.initials: T
authors.lastname: Adams
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, W1T 7HA, UK ; Integrative Physiology and Critical Illness Group, Faculty of Medicine, University Hospital Southampton NHS Foundation Trust, Southampton, SO16 6YD, UK ; Anaesthesia and Critical Care Research Unit, University Hospital Southampton NHS Foundation Trust, Southampton, SO16 6YD, UK ; NIHR Southampton Respiratory Biomedical Research Unit, Southampton, CB2 3EG, UK.
authors.forename: Kay
authors.initials: K
authors.lastname: Mitchell
authors.affiliation: Integrative Physiology and Critical Illness Group, Faculty of Medicine, University Hospital Southampton NHS Foundation Trust, Southampton, SO16 6YD, UK ; NIHR Southampton Respiratory Biomedical Research Unit, Southampton, CB2 3EG, UK.
authors.forename: Martin
authors.initials: M
authors.lastname: Feelisch
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, W1T 7HA, UK ; Department of Physiology, Development & Neuroscience, University of Cambridge, Cambridge, CB2 3EG, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Murray
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, W1T 7HA, UK ; Critical Care Group Portex Unit, UCL, Institute of Child Health, London, WC1N 1EH, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Peters
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, W1T 7HA, UK.
authors.forename: Grace
authors.initials: G
authors.lastname: Gilbert-Kawai
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, W1T 7HA, UK.
authors.forename: Hugh
authors.initials: H
authors.lastname: Montgomery
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, W1T 7HA, UK.
authors.forename: Denny
authors.initials: D
authors.lastname: Levett
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, W1T 7HA, UK ; Nepal Health Research Council, Kathmandu, Nepal.
authors.forename: Rajendra
authors.initials: R
authors.lastname: Kumar
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, W1T 7HA, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Mythen
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, W1T 7HA, UK ; Integrative Physiology and Critical Illness Group, Faculty of Medicine, University Hospital Southampton NHS Foundation Trust, Southampton, SO16 6YD, UK ; Anaesthesia and Critical Care Research Unit, University Hospital Southampton NHS Foundation Trust, Southampton, SO16 6YD, UK ; NIHR Southampton Respiratory Biomedical Research Unit, Southampton, CB2 3EG, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Grocott
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, W1T 7HA, UK.
authors.forename: Daniel
authors.initials: D
authors.lastname: Martin
keywords: Critical care; High altitude; Hypoxia; Microcirculation; Mitochondria; Nitric Oxide; Sherpa