Informative Value of Temperatures in Different Areas of the Human Body for Correcting Body Thermal Imbalance during Extravehicular Activities

Abstract

Identification of noninvasive and informative sites on the body reflecting the development of body thermal imbalance during extravehicular activities (EVAs) is highly important for enhancing astronaut safety. Temperature changes were evaluated on several areas of the head (the mastoid fossa ( T mf ), the forehead ( T fo ), and the cheek ( T ch )) and on the fingers ( T fing ). Subjects were dressed in a multicompartment liquid cooling/warming garment. Studies I and II consisted of different combinations of hood versus garment cooling or warming imposed across stages; studies III and IV involved sagittally divided cooling or warming regimes with the hood worn (study III) or with the head uncovered (study IV). In studies I and II, T mf significantly ( P < 0.05) differed between stages 2, when the head was cooled and the rest of the body heated, and 3, when the head was heated and the rest of the body cooled. The T mf changes were consistent with the thermal conditions imposed on the head but not reflective of the developing body heat deficit. In study III, the T mf at stages 2 and 3 on the right or the left followed the thermal conditions on the ipsilateral side of the body ( P < 0.01). In study IV, T fing showed no significant differences across stages. In studies I-IV, T fing showed consistent changes across stages ( P < 0.05), reflecting the developing body heat deficit. In all studies, there were no significant differences in rectal temperature ( T re ) across stages. T mf and temperatures at other head skin sites did not respond in accordance with the actual intensity of a heat or cold flux from the garment and were not reflective of the overall development of body thermal imbalance. T fing was a more adequate indicator of initial thermal destabilization and provided information that would be useful for monitoring the thermal balance and comfort during EVAs.