Habituation of the metabolic response to cold (shivering) is one of the most frequently reported alterations associated with cold adaptation in humans (Brück 1976). As a consequence, deep body temperature may fall more rapidly in cold adapted individuals (“hypothermic adaptation”), with consequences for groups as diverse as the elderly and divers. The relative contributions of skin and deep body temperature changes in the development of an habituation remain to be elucidated. Golden and Tipton (1988) suggested that shivering habituation required repeated falls in deep body temperature. The present study tested the hypothesis that short-term cold water exposure, resulting in no decrease in deep body temperature, will not result in an habituation of the shivering response to longer-term immersion. The experimental protocol received ethical approval. Seven healthy male participants with no history of repeated cold exposure or cold-induced illness undertook two standard head-out immersions at least a week apart (Imm1 and Imm7) in stirred water at 12°C until either rectal temperature (Tre) fell to 35°C or 90 minutes elapsed. In the intervening period, participants undertook five, 5 minute immersions (Imm2 to Imm6) in 12°C water. Tre and skin temperatures were measured every minute. Inspired respiratory volume (VI) and oxygen consumption (VO2, a surrogate measure of shivering) were measured continuously. A one-way ANOVA for repeated measurement followed by a multiple comparison with Dunnet’s t-test was used to identify differences in the responses obtained during Imm1 to Imm7 over the initial five minutes. A paired Student’s t-test was used to examine differences in the responses between Imm1 and Imm7 from 20 minutes to the end of immersion (20min+). There was no difference between the average [SD] cooling rates of Tre observed in Imm1 and Imm7 (-1.88[0.88] and -1.68[0.71] °C.h-1). The initial response in VI was significantly lower in Imm4, 5, 6 and 7 than in Imm1 (p<0.05, 82.9[30.6] and 58.6[22.2] L.min-1 in Imm1 and 7). The initial VO2 response was significantly lower in Imm 4, 5, 6 than in Imm1 (p<0.05). No difference was observed in VO2 during the period 20min+ in Imm1 and Imm7 (1.61[0.51] and 1.55[0.46] L.min-1). The regression lines of VO2 over Tre for 20min+ showed no difference between Imm1 and Imm7 in their slope or intercept. It is concluded that repeated brief cold water immersions induce an habituation of the initial cardio-respiratory and metabolic responses but not the longer term shivering response to cold. These findings help elucidate the mechanisms underpinning habituation to cold, and the role of skin temperature in the shivering response.
University of Manchester (2010) Proc Physiol Soc 19, C78
Oral Communications: Habituation of shivering in humans
H. Wakabayashi1,2, M. J. Barwood1, M. J. Tipton1
1. Department of Sport and Exercise Science, University of Portsmouth, Portsmouth, United Kingdom. 2. Department of Ergonomics, Faculty of Design, Kyushu Universty, Fukuoka, Japan.
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Where applicable, experiments conform with Society ethical requirements.