Circadian rhythm of temperature in man. Comparative study with two experiment protocols

The circadian rhythm of rectal and skin temperature was studied in man at rest and at thermal neutrality according to two different protocols, to make allowance for the experimental conditions. In the first case, ambient temperature (To) was maintained at a constant value close to thermal neutrality and mean skin temperature (Ts) could evolve freely for 24 h. In the second case, Ts was maintained at 34 degrees C by adequately adjusting To during 90 min-periods divided into 8 equidistant points of the 24-h spans. The results were comparable and brought out a rhythm of rectal temperature (Tre) of a low amplitude, non sinusoidal, with a day-time plateau and a night-time minimum. The Ts and body conductance rhythm, the lack of metabolism and evaporative thermolysis rhythm led to us to confer a major role to the circulatory phenomena to explain the Tre rhythm in these experiments.