REPRODUCIBILITY OF CORE TEMPERATURE THRESHOLD FOR SWEATING ONSET IN HUMANS

The control of sweating in humans has been described quantitatively in terms of skin and core temperatures (T-sk and T-core, respectively). However, the precision with which features of the relationship between sweat rate and T-core at a given T-sk can be reproduced in the short term is not known. We focused on the threshold T-core. We held T-sk at 38 degrees C until sweating began for two periods separated by a period of cooling with T-sk at 32 degrees C in six men and three women. The esophageal temperature (T-sk) at which sweating began was invariably lower in the second period of heating (average difference 0.09 degrees C, maximum 0.17 degrees C). Also, the rate of rise in T-es was invariably higher (average 148%) during the second period of heating. Thus, although a threshold cannot be reproduced within the error of T-es measurement, the consistency and small magnitude of the downward shift recommend our protocol as a practical method for evaluating other influences on thermoregulation, provided that the effects are big enough to be seen against a background of an expected small decrease. From the fundamental point of view, the consistency of the downward displacement has provocative implications, e.g., the rate of change in T-core influences sweating or thermosensitive units in slow-responding thermal compartments contribute to the T-core input signal.