Circadian rhythm of rectal temperature in man with two different types of clothing.

We compared the circadian rhythm of human rectal temperature with two different types of clothing at an ambient temperature of 27.5 degrees +/- 0.5 degrees C and a relative humidity of 40 +/- 10%. One clothing covered the whole body area except for the head, hands and feet (Type A, weight 475 g, 0.98 clo), the other covered the trunk, upper arms and thighs (Type B, weight 366 g, 0.93 clo). Major findings are summarized as follows: (1) Late evening fall after retiring and a morning rise after rising in the rectal temperature rhythm were significantly quicker in Type B than in Type A. (2) Late evening rise after retiring and a morning fall after rising in the skin temperatures of the extremities were quicker in Type B than in Type A. (3) A range of oscillation in the circadian rectal temperature rhythm was significantly larger in Type B than in Type A. It was suggested that the quicker late evening rise and morning fall of the skin temperatures in the extremities after retiring and rising, respectively, might be responsible for the quicker late evening fall and morning rise of the circadian rectal temperature.