Long-term ambulatory temperature monitoring in a subject with a hypernychthemeral sleep--wake cycle disturbance.

A portable temperature data logger was used for prolonged rectal temperature monitoring in an ambulatory subject with a longer than 24 hr (hypernychthemeral) sleep-wake cycle. The mean period of the sleep-wake and circadian temperature cycles was 24.8 hr. However, the period of the sleep-wake cycle fluctuated considerably, being less than 24.8 hr when he slept during the socially desirable sleep hours and more than 24.8 hr when he slept during the day. In the first instance, the daily temperature fall occurred later than, and in the second earlier than, sleep onset. During the times of desynchronization of the two cycles, he complained of insomnia, fatigue, and reduced performance. We postulate that his hypernychthemeral cycles were the result of either a primary defect in the mechanism of entrainment or "weakened" social zeitgebers due to a personality disorder. These concepts are supported by a sleep-wake pattern resembling that of relative coordination. We therefore raise the possibility that 24 hr was beyond the range of entrainment of the subject's circadian temperature cycle during the study.