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Human physiology in extreme environments: lessons from life at the limits?
  1. Michael P W Grocott
  1. Dr M Grocott, Centre for Altitude, Space and Extreme Environment Medicine, UCL Institute of Human Health and Performance, First Floor Charterhouse Building, UCL Archway Campus, Highgate Hill, London N19 5LW; mike.grocott{at}

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Progress in medical science is intimately linked with understanding and advancing the limits of human survival: increases in adult life expectancy and incremental reductions in minimal fetal viable age bear testimony to this relationship. Exploration of human physiology under extreme environmental conditions is another facet of this association. Understanding physiology at the limits of human tolerance to environmental conditions is a worthy goal in itself but may in addition lead to developments in both knowledge and treatments in clinical settings. Recently, larger systematic studies of human responses to extreme environments have used the tools of modern molecular medicine, in combination with detailed physiological phenotyping, in order to identify and explore cellular mechanisms underlying beneficial adaptive processes and detrimental responses.

A robust definition of extreme environment is difficult to frame and is always contextually dependent on the object or person exposed to the environment and the subject of study. Most definitions with respect to the study of human medicine and biology incorporate the requirement for either physiological adaptation or technological innovation in order to survive. Simple stress does not define an extreme environment; there must be a risk of illness or death in some, if not all, exposed individuals in order to justify the requirement for adaptation or innovation in order to survive. Whilst some definitions incorporate the psychological and sociological characteristics of an environment, this can result in difficulty in distinguishing the unpleasant from the dangerous (where survival is at stake).

There is a long tradition of human experimentation (often …

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  • Competing interests: Caudwell Xtreme Everest (CXE) is a research project coordinated by the Centre for Altitude, Space and Extreme Environment Medicine, University College London, UK. The aim of CXE is to conduct research into hypoxia and human performance at high altitude in order to improve understanding of hypoxia in critical illness. Membership, roles and responsibilities of the CXE Research Group can be found at The research was funded from a variety of sources, none of which are public. The entrepreneur John Caudwell, whose name the expedition carries, donated £500 000 specifically to support the research. BOC Medical, now part of Linde Gas Therapeutics, generously supported the research early on and continues to do so. Lilly Critical Care, The London Clinic (a private hospital), Smiths Medical, Deltex Medical and The Rolex Foundation have also donated money to support the research and logistics. All monies were given as unrestricted grants. Specific research grants were awarded by the Association of Anaesthetists of Great Britain and Ireland, and the UK Intensive Care Foundation. The CXE volunteers who trekked to Everest basecamp also kindly donated to support the research.