Seasonal changes in the physiological response of man to an acute cold stress.

Abstract

Eight male human subjects, resting supine, and wearing swim trunks only, were exposed to an ambient temperature of 8.5 °C for 1 hour in the first week of each month from February 1964 to January 1965 inclusive. Skin, rectal, and air temperatures were measured with thermistor probes. Percentage oxygen in expired air and minute ventilation were measured, and heat production was calculated by Weir's method. Electrical activity from the muscles of all four limbs was measured to determine shivering response. Control values of resting respiration and heat production were obtained under comfortably warm conditions and showed marked seasonal variation, with minimum values in spring and maximum values in later summer. In the response to acute cold exposure, marked seasonal changes were found also which were superimposed on the seasonal changes in control values. The response to cold exposure indicated maximum acclimatization to cold in the spring and minimum in later summer. These results are discussed in terms of three modes of response to the cold stress: (i) insulative cooling, (ii) shivering thermogenesis, and (iii) nonshivering thermogenesis. The degree of acclimatization and temperature of exposure may determine the individual mode of response.