Chapter 2 - The Circadian Rhythm of Deep Body Temperature

Abstract

The deep body temperature at any moment results from the imbalance between heat gain and heat loss, though the thermal capacity of the human body is such that changes in body temperature take place rather slowly when heat imbalances occur. This chapter discusses some methods for the measurement of the circadian rhythm of deep body temperature. Rectal temperature is an accurate measure of deep body temperature and is the preferred method, but it is often unpopular with subjects and, therefore, in practice, alternative sites of measurement have often been used. A number of experimental approaches, such as experiments in which exogenous influences are decreased, free-running experiments, experiments with phase shifts, and experiments with non-24-hour days, indicate that the circadian rhythm of deep body temperature has a large endogenous component. Though the endogenous component of the temperature rhythm is marked, an exogenous component is present too. The exogenous component results from the pattern of sleep and wakefulness—that is, the alternation between inactivity and activity. The chapter explains the interaction between exogenous and endogenous influences, implications and usefulness of circadian rhythm, and the nychthemeral rhythm.