Habituation of the metabolic and ventilatory responses to immersion in humans

An experiment was undertaken to answer long-standing questions concerning the nature of metabolic habituation in repeatedly cooled humans. It was hypothesised that repeated skin and deep-body cooling would produce such a habituation that would be specific to the magnitude of the cooling experienced, and that skin cooling alone would dampen the cold-shock but not the metabolic response to cold-water immersion. Twenty-one male participants were divided into three groups, each of which completed two experimental immersions in 12 degrees C water, lasting until either rectal temperature fell to 35 degrees C or 90 min had elapsed. Between these two immersions, the control group avoided cold exposures, whilst two experimental groups completed five additional immersions (12 degrees C). One experimental group repeatedly immersed for 45 min in average, resulting in deep-body (1.18 degrees C) and skin temperature reductions. The immersions in the second experimental group were designed to result only in skin temperature reductions, and lasted only 5 min. Only the deep-body cooling group displayed a significantly blunted metabolic response during the second experimental immersion until rectal temperature decreased by 1.18 degrees C, but no habituation was observed when they were cooled further. The skin cooling group showed a significant habituation in the ventilatory response during the initial 5 min of the second experimental immersion, but no alteration in the metabolic response. It is concluded that repeated falls of skin and deep-body temperature can habituate the metabolic response, which shows tissue temperature specificity. However, skin temperature cooling only will lower the cold-shock response, but appears not to elicit an alteration in the metabolic response. (C) 2012 Elsevier Ltd. All rights reserved.