Thermal Responses of Man During Rest and Exercise in a Helium Oxygen Environment

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Abstract
Mean skin temperature [MST], rectal temperature, mean body temperature, sweat loss, and heart rate were measured in man during rest (15 min.), moderate exercise (15 min.), and recovery (45 min.) while exposed either to 79% He-21% O2 or to air. Test conditions were ground level pressure and either 95[degree] F and 90% RH [relative humidity], 95[degree] F and 40%-60% RH, or 71[degree] F and 45%-50% RH. At high temperature irrespective of RH, responses in He-O2 were similar to those in air. At low temperature MST in He-O2 was lower by 1.0[degree] F during rest, by 2.3[degree] F at end of exercise (P <0.05), and by 2.0[degree] F at end of recovery (P<0.05). Rest, exericise, and recovery rectal and mean body temperatures and heart rates were the same in the 2 media, but sweat loss was 27% less (P<0.05) in He-O2. These differences are explained by the higher thermal conductivity of He relative to N2 affecting conductive-convective heat loss in proportion to the skin-to-gas thermal gradient. Calculations indicate that for each [degree] F increase in gradient, MST in He-O2 will be approximately 0.1[degree] F lower than in air.

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