Effect of altitude exposure on thermoregulatory response of man to cold

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Abstract
The thermoregulatory responses to 10.degree. C (for 3 h) were investigated in 12 natives from sea level (lowlanders) at 150 m, and on arrival at 3350 and 4340 m; 6 of these during a 6-wk sojourn at 4360 m and on return to sea level; and 5 natives from each of the 2 altitudes (highlanders) in their respective habitat and after descent to 150 m. The cold-induced increase in the rate of O2 consumption (.ovrhdot.VO2) of the lowlanders was significantly smaller at both altitudes than at sea level. It did not recover substantially during the 6 wk at altitude, but was restored to its initial rate on return to sea level. By contrast, visible shivering activity was augmented on arrival at altitude. It persisted throughout the 6 wk there, but was greatly depressed on return to sea level, despite the increased .ovrhdot.VO2. Mean skin temperatures (.hivin.Tsk) stabilized in the cold at significantly higher values at altitude. Rectal temperature (Tre) decreased similarly at all altitudes. .ovrhdot.VO2 of the highlanders in the cold was significantly greater at sea level than at their resident altitudes, although shivering activity was less intense; .hivin.Tsk stabilized at significantly lower levels at 150 m than at either altitude. Altitude exposure reduces the calorigenic response of man to cold, and this effect is not moderated by acclimatization to altitude, yet is reversible immediately on descent to sea level. The component of cold thermogenesis which appeared to be reduced by altitude exposure was nonshivering thermogenesis rather than visible shivering.

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