title: Caudwell Xtreme Everest: A prospective study of the effects of environmental hypoxia on cognitive functioning.
abstract: BACKGROUND
  The neuropsychological consequences of exposure to environmental hypobaric hypoxia (EHH) remain unclear. We thus investigated them in a large group of healthy volunteers who trekked to Mount Everest base camp (5,300 m).
  
  
  METHODS
  A neuropsychological (NP) test battery assessing memory, language, attention, and executive function was administered to 198 participants (age 44.5±13.7 years; 60% male). These were studied at baseline (sea level), 3,500 m (Namche Bazaar), 5,300 m (Everest Base Camp) and on return to 1,300 m (Kathmandu) (attrition rate 23.7%). A comparable control group (n = 25; age 44.5±14.1 years; 60% male) for comparison with trekkers was tested at/or near sea level over an equivalent timeframe so as to account for learning effects associated with repeat testing. The Reliable Change Index (RCI) was used to calculate changes in cognition and neuropsychological function during and after exposure to EHH relative to controls.
  
  
  RESULTS
  Overall, attention, verbal ability and executive function declined in those exposed to EHH when the performance of the control group was taken into account (RCI .05 to -.95) with decline persisting at descent. Memory and psychomotor function showed decline at highest ascent only (RCI -.08 to -.56). However, there was inter-individual variability in response: whilst NP performance declined in most, this improved in some trekkers. Cognitive decline was greater amongst older people (r = .42; p < .0001), but was otherwise not consistently associated with socio-demographic, mood, or physiological variables.
  
  
  CONCLUSIONS
  After correcting for learning effects, attention, verbal abilities and executive functioning declined with exposure to EHH. There was considerable individual variability in the response of brain function to sustained hypoxia with some participants not showing any effects of hypoxia. This might have implications for those facing sustained hypoxia as a result of any disease.
authors.affiliation: Health Services Research Group, City University London, College Building Room A224, London, United Kingdom.|Department of Psychology, National University of Singapore, 9 Arts Link AS4-02-28, Singapore, Singapore.
authors.forename: Konstadina
authors.identifier: http://orcid.org/0000-0001-8173-5663
authors.initials: K
authors.lastname: Griva
authors.affiliation: Health Services Research Group, City University London, College Building Room A224, London, United Kingdom.
authors.forename: Jan
authors.initials: J
authors.lastname: Stygall
authors.affiliation: The Traumatic Brain Injury Centre, Imperial College, London and London's Air Ambulance (Queen Mary University), London, United Kingdom.
authors.forename: Mark H
authors.initials: MH
authors.lastname: Wilson
authors.affiliation: Institute for Human Health and Performance, University College London, London, United Kingdom.
authors.forename: Daniel
authors.initials: D
authors.lastname: Martin
authors.affiliation: Anaesthesia and Critical Care Research Unit, University Hospital Southampton, Southampton, United Kingdom.
authors.forename: Denny
authors.initials: D
authors.lastname: Levett
authors.affiliation: Institute for Human Health and Performance, University College London, London, United Kingdom.
authors.forename: Kay
authors.initials: K
authors.lastname: Mitchell
authors.affiliation: Institute for Human Health and Performance, University College London, London, United Kingdom.
authors.forename: Monty
authors.initials: M
authors.lastname: Mythen
authors.affiliation: Institute for Human Health and Performance, University College London, London, United Kingdom.
authors.forename: Hugh E
authors.initials: HE
authors.lastname: Montgomery
authors.affiliation: Institute for Human Health and Performance, University College London, London, United Kingdom.|Anaesthesia and Critical Care Research Unit, University Hospital Southampton, Southampton, United Kingdom.|Integrative Physiology and Critical Illness Group, Division of Clinical and Experimental Science, Faculty of Medicine, University of Southampton, Southampton, United Kingdom.|Southampton NIHR Respiratory Biomedical Research Unit, Southampton, Southampton, United Kingdom.
authors.forename: Mike P
authors.initials: MP
authors.lastname: Grocott
authors.affiliation: Division of Psychiatry, University College London, London, United Kingdom.
authors.forename: Golnar
authors.initials: G
authors.lastname: Aref-Adib
authors.affiliation: St George's Hospital, London, United Kingdom.
authors.forename: Mark
authors.initials: M
authors.lastname: Edsell
authors.affiliation: MRC Centre for Inflammation Research, The Queen's Medical Research Institute, The University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Tracie
authors.initials: T
authors.lastname: Plant
authors.affiliation: Division of Translational and Systems Medicine, Warwick Medical School, Warwick, United Kingdom.
authors.forename: Chris
authors.initials: C
authors.lastname: Imray
authors.affiliation: School of Health Sciences, Faculty of Health & Medical Sciences, University of Surrey, Surrey, United Kingdom.
authors.forename: Debbie
authors.initials: D
authors.lastname: Cooke
authors.affiliation: Division of Psychiatry, University College London, London, United Kingdom.
authors.forename: Jane
authors.initials: J
authors.lastname: Harrington
authors.affiliation: Institute for Human Health and Performance, University College London, London, United Kingdom.
authors.forename: Maryam
authors.initials: M
authors.lastname: Khosravi
authors.affiliation: Health Services Research Group, City University London, College Building Room A224, London, United Kingdom.
authors.forename: Stanton P
authors.initials: SP
authors.lastname: Newman
mesh_terms: D000328:Adult; D000367:Age Factors; D000531:Altitude; D001288:Attention; D003071:Cognition; D060825:Cognitive Dysfunction / Q000209:etiology* / Q000503:physiopathology; D056344:Executive Function; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000150:complications* / Q000503:physiopathology; D015994:Incidence; D007802:Language; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D011446:Prospective Studies; D012307:Risk Factors