Delayed sleep phase disorder in temporal isolation

STUDY OBJECTIVES: This study sought to characterize sleep and the circadian rhythm of body core temperature of an individual with delayed sleep phase disorder (DSPD) in the absence of temporal cues and social entrainment and to compare those measures to age-matched normal control subjects studied under identical conditions. DESIGN: Polysomnography and body temperature were recorded continuously for 4 days in entrained conditions, followed immediately by 17 days in a "free-running" environment. SETTING: Temporal isolation facility in the Laboratory of Human Chronobiology, Weill Cornell Medical College. PARTICIPANTS: One individual who met criteria for delayed sleep phase disorder according to the International Classification of Sleep Disorders Diagnostic and Coding Manual (ICSD-2) and 3 age-matched control subjects. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: The DSPD subject had a spontaneous period length (tau) of 25.38 hours compared to an average tau of 24.44 hours for the healthy controls. The DSPD subject also showed an altered phase relationship between sleep/wake and body temperature rhythms, as well as longer sleep latency, poorer sleep efficiency, and altered distribution of slow wave sleep (SWS) within sleep episodes, compared to control subjects. CONCLUSIONS: Delayed sleep phase disorder may be the reflection of an abnormal circadian timing system characterized not only by a long tau, but also by an altered internal phase relationship between the sleep/wake system and the circadian rhythm of body temperature. The latter results in significantly disturbed sleep, even when DSPD patients are permitted to sleep and wake at their preferred times.