Thermoregulation and heat exchange in a nonuniform thermal environment during simulated extended EVA

Background: Nonuniform heating and cooling of the body, a possibility during extended duration extravehicular activities (EVA); was studied by means of a specially designed water circulating garment that independently heated or cooled the right and left sides of the body. The purpose was to assess whether there was a generalized reaction on the finger in extreme contradictory temperatures on the body surface, as a potential heat status controller. Method: Eight subjects, six men and two women, were studied while wearing a sagitally divided experimental garment with hands exposed in the following conditions: Stage 1 baseline - total body garment inlet water temperature at 33°C; Stage 2 - left side inlet water temperature heated to 45 °C; right side cooled to 8°C; Stage 3 - left side inlet water temperature cooled to 8°C, right side heated to 45°C. Results: Temperatures on each side of the body surface as well as ear canal temperature (T(ec)) showed statistically significant Stage X Side interactions, demonstrating responsivess to the thermal manipulations. Right and left finger temperatures (T(fing)) were not significantly different across stages; their dynamic across time was similar. Rectal temperature (T(re)) was not reactive to prevailing cold on the body surface, and therefore not informative. Subjective perception of heat and cold on the left and right sides of the body was consistent with actual temperature manipulations. Conclusions: T(ec) and T(re) estimates of internal temperature do not provide accurate data for evaluating overall thermal status in nonuniform thermal conditions on the body surface. The use of T(fing) has significant potential in providing more accurate information on thermal status and as a feedback method for more precise thermal regulation of the astronaut within the EVA space suit.