A gas-stream heater to control local skin temperature under evaporative sweat capsules

A compact 4-W gas-stream heater for use with ventilated sweating capsules is described. The heating element is constructed from two modified 75-omega power resistors connected in parallel and contained in the capsule gas inlet tube. Heater power is controlled with integrated circuits which compare the output of a thermocouple, measuring either capsule skin or air temperature, with a predetermined target temperature. The unit responds fairly slowly to sudden large changes in target temperature, but once a steady state is achieved, maintains target temperature levels despite changes in evaporative heat loss. The device is well suited for studies in which local skin temperature or capsule air temperature must be elevated and clamped while the effects of other local stimuli or central thermoregulatory activity are studied, and in studies where the skin temperature effect on transepidermal water loss must be controlled.