Does shivering thermogenesis enhance the individual's ability to maintain rectal temperature during immersion in cold...

Shivering thermogenesis may enable individuals to maintain rectal temperature during acute cold exposure. This data analysis revisited this hypothesis and compared previously published data with unpublished data from our laboratory on those subjects that were terminated from cold water immersion early because of a reduction in rectal temperature (T(re)) - 35 degrees C. T(re), mean skin temperature (T(sk)), and oxygen uptake (VO2) were recorded at 5, 30, 60, and 90 min of immersion and were used to calculate 3delta readings for each exposure, that is, deltaT(30) minus T5, T60 minus T(30), and T(90) minus T(60). Single group t-tests were used to examine differences in deltaT(re), deltaT(sk), and deltaVO2 between the published data (PD) group and the individual subjects who were terminated early (TE) at each of three water temperatures (18 degrees C, 22 degrees C, 26 degrees C). For deltaVO2 the TE subjects were dichotomized by fatness (low percent fat, 8%-12%; or high percent fat, 18%-22%) to account for the VO2 differences between these groups (i.e., fatness) during cold water immersion. deltaT(re) was significantly (p < 0.05) decreased in TE subjects compared with PD subjects at all timepoints for 18 degrees C and 26 degrees C. At 22 degrees C, the TE subject exhibited a significantly greater (p < 0.05) decrease in deltaT(re) than the PD group at 90 min of immersion only. No significant (p > 0.05) differences in deltaT(sk) between the PD and TE groups were detected for any of the exposure temperatures over all time points. No difference (p > 0.05) between PD subjects and TE subjects for deltaVO2 was exhibited at any time point at any temperature. It appears that with respect to the TE group, elevations in VO2 were comparable to the PD group, but the TE group was unable to maintain T(re) during cold water immersion. In conclusion, from these data it appears that shivering thermogenesis does in part enhance the individual's ability to maintain T(re); however, as evidenced in the TE group, it also appears that the alterations in shivering thermogenesis for certain individuals may not be great enough to offset heat loss.