Effect of continuous cold exposure on nocturnal body temperatures of man

¹ Physiology Branch, Environmental Protection Research Division, Quartermaster Research and Engineering Command, U.S. Army, Natick, Massachusetts

Effects of continuous cold stress on 24-hour patterns of body temperature were studied in five men. Cold stress consisted in living at 15.6°C (60°F) for 14 days wearing only shorts. The cold period was preceded and followed by 2 weeks at 26.7°C (80°F). Activity (minimal) and diet were the same for all periods. One blanket was used at night. Rectal temperature (T_r) and skin temperature (T_s) were measured. T_r during sleep fell more rapidly and to lower values during cold exposure (35.6°C) than during the control period (36.1°C). T_s during sleep was slightly lower in the cold than in the control period; also, T_s did not exhibit the gradual drop characteristic of sleep in the control period. Comparison of T_r and T_s between early and later cold days revealed the following differences: a) nocturnal T_r fell to lower levels on the later cold days; b) nocturnal toe temperatures were 15°C (27°F) higher on the later cold days. The arch temperatures followed the same pattern as the toes. No significant differences were found in daytime temperatures between early and later cold days. The data suggest that evidence for acclimatization to cold in terms of altered body temperature responses may be fruitfully sought in responses during rewarming and/or sleep.

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