Human physiology in extreme environments: lessons from life at the limits?
- 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;
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 …