title: Systemic oxygen extraction during exercise at high altitude.
abstract: BACKGROUND
  Classic teaching suggests that diminished availability of oxygen leads to increased tissue oxygen extraction yet evidence to support this notion in the context of hypoxaemia, as opposed to anaemia or cardiac failure, is limited.
  
  
  METHODS
  At 75 m above sea level, and after 7-8 days of acclimatization to 4559 m, systemic oxygen extraction [C(a-v)O2] was calculated in five participants at rest and at peak exercise. Absolute [C(a-v)O2] was calculated by subtracting central venous oxygen content (CcvO2) from arterial oxygen content [Formula: see text] in blood sampled from central venous and peripheral arterial catheters, respectively. Oxygen uptake [Formula: see text] was determined from expired gas analysis during exercise.
  
  
  RESULTS
  Ascent to altitude resulted in significant hypoxaemia; median (range) [Formula: see text] 87.1 (82.5-90.7)% and [Formula: see text] 6.6 (5.7-6.8) kPa. While absolute C(a-v)O2 was reduced at maximum exercise at 4559 m [83.9 (67.5-120.9) ml litre(-1) vs 99.6 (88.0-151.3) ml litre(-1) at 75 m, P=0.043], there was no change in oxygen extraction ratio (OER) [C(a-v)O2/CaO2] between the two altitudes [0.52 (0.48-0.71) at 4559 m and 0.53 (0.49-0.73) at 75 m, P=0.500]. Comparison of C(a-v)O2 at peak [Formula: see text] at 4559 m and the equivalent [Formula: see text] at sea level for each participant also revealed no significant difference [83.9 (67.5-120.9) ml litre(1) vs 81.2 (73.0-120.7) ml litre(-1), respectively, P=0.225].
  
  
  CONCLUSIONS
  In acclimatized individuals at 4559 m, there was a decline in maximum absolute C(a-v)O2 during exercise but no alteration in OER calculated using central venous oxygen measurements. This suggests that oxygen extraction may have become limited after exposure to 7-8 days of hypoxaemia.
authors.affiliation: UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, University College London Centre for Altitude Space and Extreme Environment Medicine, 170 Tottenham Court Road, London W1 T 7HA, UK daniel.martin@ucl.ac.uk.
authors.forename: D S
authors.initials: DS
authors.lastname: Martin
authors.affiliation: UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, University College London Centre for Altitude Space and Extreme Environment Medicine, 170 Tottenham Court Road, London W1 T 7HA, UK.
authors.forename: A
authors.initials: A
authors.lastname: Cobb
authors.affiliation: UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, University College London Centre for Altitude Space and Extreme Environment Medicine, 170 Tottenham Court Road, London W1 T 7HA, UK.
authors.forename: P
authors.initials: P
authors.lastname: Meale
authors.affiliation: UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, University College London Centre for Altitude Space and Extreme Environment Medicine, 170 Tottenham Court Road, London W1 T 7HA, UK Integrative Physiology and Critical Illness Group, Clinical and Experimental Sciences, Faculty of Medicine, University of Southampton, Mailpoint 810, Sir Henry Wellcome Laboratories, University Hospital Southampton NHS Foundation Trust, Tremona Road, Southampton SO16 6YD, UK Anaesthesia and Critical Care Research Unit, GICU, Mailpoint 27, Level D, Centre Block, University Hospital Southampton NHS Foundation Trust, Tremona Road, Southampton SO16 6YD, UK NIHR Southampton Respiratory Biomedical Research Unit, Southampton, UK.
authors.forename: K
authors.initials: K
authors.lastname: Mitchell
authors.affiliation: UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, University College London Centre for Altitude Space and Extreme Environment Medicine, 170 Tottenham Court Road, London W1 T 7HA, UK Department of Anaesthesia, St George's Hospital, London, UK.
authors.forename: M
authors.initials: M
authors.lastname: Edsell
authors.affiliation: UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, University College London Centre for Altitude Space and Extreme Environment Medicine, 170 Tottenham Court Road, London W1 T 7HA, UK.
authors.forename: M G
authors.initials: MG
authors.lastname: Mythen
authors.affiliation: UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, University College London Centre for Altitude Space and Extreme Environment Medicine, 170 Tottenham Court Road, London W1 T 7HA, UK Integrative Physiology and Critical Illness Group, Clinical and Experimental Sciences, Faculty of Medicine, University of Southampton, Mailpoint 810, Sir Henry Wellcome Laboratories, University Hospital Southampton NHS Foundation Trust, Tremona Road, Southampton SO16 6YD, UK Anaesthesia and Critical Care Research Unit, GICU, Mailpoint 27, Level D, Centre Block, University Hospital Southampton NHS Foundation Trust, Tremona Road, Southampton SO16 6YD, UK NIHR Southampton Respiratory Biomedical Research Unit, Southampton, UK.
authors.forename: M P W
authors.initials: MP
authors.lastname: Grocott
mesh_terms: D000064:Acclimatization; D000328:Adult; D000531:Altitude; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption
chemical_list: D010100:Oxygen
keywords: altitude; blood gas analysis; exercise; hypoxia; oxygen; physiology