GENERALIZED RESPONSE IN SWEAT RATE TO PERIODIC CUTANEOUS HEATING WITH SPECIAL REFERENCE TO ITS RELATIONSHIP TO HEAT TOLERANCE

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Periodic radiant heat was applied to the back of the human trunk by the use of an infrared lamp and the sweat rate of non-irradiated regions was recorded continuously by means of resistance hygrometry. A general trend was observed that the sweat rate increased as the irradiated area was warmed during the lamp-on phase and decreased with the cooling of the area during the lamp-off phase, with a delay of a few seconds. The degree of such synchronization of sweat rate withthe heating cycle was largely affected by the length of the on-off period, and varied with individuals. The individuality appeared to be most distinct with repetitive irradiation of a two-minute period, consisting of one minute each of lamp-on and lamp-off phases.
The magnitude of the sweat response was affected by the basal level of sweat rate and by the skin region, but the pattern of the sweat response was not significantly influenced by them. No significant seasonal differences were noted in the pattern of sweat response.
Well-synchronized sweat response was observed in a majority of natives from warm regions and in many athletes, but in few non-athletic individuals from cool districts. This type of sweat response is considered to be mediated through neural reflex pathways involving the central thermoregulatory mechanism. Improvement in sweat responsiveness may result from facilitation somewhere along these pathways, which may be acquired only by long-term heat acclimatization or adaptation to torrid climate.