Heat and simulated high altitude: effects on biochemical indices of stress and performance.
Five healthy, military test volunteers were alternately exposed on separate days to sea level, control conditions (22-23 degrees C, 40-50% RH), a hot wet environment (35 degrees C, 90% RH) or stimulated high altitude (4300 m, 22-23 degrees C, 20-30% RH) while carrying out assigned performance tasks. Acute exposure of 7 h to environmental heat consistently elicited significant increments in plasma levels of cortisol, dopamine-beta-hydroxylase, and uric acid while cholesterol and cyclic AMP levels were unaffected. Alternatively, exposure to altitude for the same duration failed to effect significant alterations in any of the aforementioned biochemical factors. Although both environmental stresses caused similar performance decrements, the responses of biochemical indices of stress were consistently related to the environment itself.