Effect of Local Hand Thermal Insulation on Total and Local Comfort Under Different Levels of Body Heat Deficit

Introduction: There are contradictory opinions regarding the contribution of local hand thermal insulation to support local and total comfort during extravehicular activity (EVA). Instead of a local correction by means of thermal insulation on the periphery of the body to prevent heat dissipation, it may be optimal to prevent heat dissipation from the body core. To examine such a concept, the effects of different insulation levels on the left and right hands on the heat flux and temperature mosaic on the hands was measured. These variables were assessed in relation to the level of heat deficit forming in the core organs and tissues. Methods: Six subjects (4 males, 2 females) were donned in a liquid cooling/warming garment (LCWG) that totally covered the body surface except for the face. Participants wore the Phase VI space gloves including the entire micrometeoroid garment (TMG) on the left hand, and the glove without the TMG on the right hand. The experimental sessions consisted of three stages with inlet water temperatures as follows: Stage 1 baseline - 33°C; Stage 2 cooling - 20°C; Stage 3 warming - 45°C. Skin temperature was measured on the fingers, dorsal part of the hand; rectal temperature was also measured. Results: In Stage 2 cooling, there was a 3.5±0.3 kcal/min heat deficit reflected in the decreasing finger (Tfing) and hand temperature (Tha); there was no significant difference in temperature between the two hands. On both hands, Tfing decreased from 33.4±1.2°C (Stage 1) to 27.8±1.5°C (Stage 2), while Tha decreased from 32±1.2°C to 31.8±0.6°C. In Stage 1, there was a 1.4° C temperature difference between the dorsal part of the hand (32°C) and the distal phalanx of the 4^th finger (33.4°). This difference increased to 4° at the end of the Stage 2 cooling (Tfing 27.8°; Tha 31.8°). Conclusions: Under the development of a general heat deficit/surplus in the body, there was no influence of differing insulation on each hand. The primary influence on local hand and total body thermal status is not distal thermal insulation, but the forming total deficit of heat in the body core organs.