Sleep timing and circadian phase in delayed sleep phase syndrome

Abstract

Delayed sleep phase syndrome (DSPS) is a circadian rhythm sleep disorder in which the timing of the sleep episode occurs later than desired and is associated with difficulty falling asleep, problems awakening on time (e.g., to meet work or school obligations), and daytime sleepiness. The phase relationship between the timing of sleep and endogenous circadian rhythms is critical to the initiation and maintenance of sleep, and significant alteration leads to impairment of sleep quality and duration. The aim of this retrospective study was to determine the phase relationship between sleep-wake times and physiological markers of circadian timing in clinic patients with DSPS. Objective and subjective measures of sleep timing and circadian phase markers (core body temperature and melatonin) were measured in patients with DSPS and compared with age-matched controls. As expected, significant delays in the timing of the major sleep episode and circadian phase of body temperature and melatonin rhythms were seen in the DSPS group when allowed to sleep at their own habitual schedules, but the phase relationship between sleep-wake times and circadian phase was similar between the 2 groups. These results suggest that the symptoms of insomnia and excessive daytime sleepiness in DSPS patients living under entrained real-life conditions cannot be explained by an alteration in the phase relationship between sleep-wake patterns and other physiological circadian rhythms.

Figure 1

Comparison of sleep measures between DSPS and control groups. Three subjective measures collected from sleep diaries are shown in the top panel and 3 objective sleep measures obtained from wrist actigraphy are shown in the bottom panel. Standard error (SE) bars are shown.

Figure 2

Sleep measures during the weekday and weekend for DSPS and control groups. Time in bed (solid + striped bars) is defined as the time between bedtime and wake time. Sleep duration (solid bars) is the time between sleep onset and offset. Sleep latency (striped bars preceding the solid bars) is the time between bedtime and sleep onset. Wake after sleep offset (striped bars following the solid bars) is the time between wake time and getting out of bed.

Figure 3

Comparison of circadian phase and phase angle measures between DSPS and control groups. Mean times of 2 circadian phase markers, dim-light melatonin onset (DLMO), and core body temperature (CBT) nadir, are shown in the top panel. Four phase angle measures were calculated as the difference between a phase measure, DLMO or CBT nadir, and a sleep measure, sleep onset or offset, and are shown in the bottom panel. SE bars are shown.