HABITUATION OF THE INITIAL RESPONSES TO COLD-WATER IMMERSION IN HUMANS - A CENTRAL OR PERIPHERAL MECHANISM

1. The initial respiratory and cardiac responses to cold water immersi on are thought to be responsible for a significant number of open wate r deaths each year. Previous research has demonstrated that the magnit ude of these responses can be reduced by repeated immersions in cold w ater and the aim of this study was to determine whether the site of ha bituation is central or peripheral. 2. Two groups of subjects undertoo k two 3 min head-out immersions in stirred water at 10 degrees C of th e right-hand side of the body (R). Between these two immersions (3 who le days) the control group (n = 7) were not exposed to cold water, but the habituation group (n = 8) undertook a further six 3 min head-out immersions in stirred water at 10 OC of the left-hand side of the body (L). 3. Repeated L immersions reduced (P < 0.01) the heart rate, resp iratory frequency and volume responses. During the second R immersion a reduction (P < 0.05) in the magnitude of the responses evoked was se en in the habituation group but not in the control group, despite both groups having identical skin temperature profiles. 4. It is concluded that the mechanisms involved in producing habituation of the initial responses are located more centrally than the peripheral receptors.