Comparison of core threshold temperatures for forehead sweating based on esophageal and rectal temperatures.

A protocol incorporating successive hot and cold water immersions, causing respective warming and cooling of the body, has been used to determine the core threshold for sweating. Disparate results have been reported for the core threshold of sweating, and these have been attributed to the possible existence of core temperature gradients during such a protocol. Spatial and temporal core temperature (Tc, degree C) gradients during dynamic changes in body temperature may give rise to different values of core temperature thresholds for sweating, depending on the Tc measurement site. In addition, during such an immersion protocol skin temperature transients may influence expression of thresholds using esophageal temperature (Tes). With these considerations, the effects of Tc gradients and skin temperature on Tc thresholds for sweating were examined. Subjects (n = 22) were immersed to the neck in 40 degrees C water until Tes reached 38.5 degrees C (phase 1), followed immediately by cooling in 30.6 degrees C water until extinction of sweating was observed (phase 2). Cooling was continued in the latter bath after the sweating extinction until total immersed time reached 50 min or until shivering was initiated (phase 3). During the trials continuous assessment was made of rectal temperature (Tre) and Tes, mean unweighted skin temperature (Tsk, degree C), forehead sweating rate (Esw, g.m-2.min-1), oxygen consumption (VO2, L.min-1), and surface heat flux (Q, W.m-2). With the current protocol it appeared inappropriate to determine the Tc thresholds for onset of sweating, as sweating was initiated prior to any significant displacement of Tc, but was most likely influenced by Tsk and its rate of change.(ABSTRACT TRUNCATED AT 250 WORDS)