Insidious hypothermia during raft use.

It is commonly thought that increasing protection against cold water results in greater physiological efficiency in maintaining core temperature. To examine the relationship of physiological changes resulting from cold exposures as a function of increased insulation, five subjects (4 males, 1 female) wearing anti-exposure ensembles covering the entire body and head were exposed in a pool to water temperatures (Twater) = 4.4 degrees C and air temperatures (Tair) = 5.6 degrees C. Trials consisted of subjects undergoing either head-out immersions with mean exposure time (t = 150 +/- 9 S.E.M. min) or enclosed within a raft (t = 398 +/- 126 min). Rectal temperatures were higher, and their relative change from baseline (delta Tre) smaller, for 3 of the 5 subjects at minute 122 in the water than in the raft. While no correlation was found between mean weighted skin temperature (Tsk), hand temperature (Thand), or foot temperature (Tfoot) with Tre, close correlation was found between delta Tre and forehead temperature (Tfore) (r = 0.97, p less than 0.05) and change in forehead temperature (r = 0.97, p less than 0.05). The results suggest that, during cold exposure, increased insulation, under specific conditions, may result in a lower Tre.