Changes in sleep architecture during recurrent cycles of sleep restriction: a comparison between stable and variable short sleep schedules.

Study Objectives: To examine how sleep architecture changes over successive cycles of restricted and recovery sleep in young adults, and to determine whether sleep-restricted schedules with differing night-to-night variability in sleep durations lead to different sleep physiological responses. Methods: In this 15-night laboratory-based study, 52 healthy young adults (25 males, age: 21-28) were randomly assigned to one of three sleep schedules: stable short, variable short, or control. They underwent two baseline nights of 8-h time-in-bed (TIB), followed by two cycles of "weekday" sleep opportunity manipulation and "weekend" recovery (8-h TIB). During each manipulation period, the stable short sleep and the control groups received 6-h and 8-h TIBs each night, respectively, while the variable short sleep group received 8-h, 4-h, 8-h, 4-h, and 6-h TIBs from the first to the fifth night. Polysomnography was conducted every night. Results: Sleep architecture changes induced by both short sleep schedules returned to baseline levels following the first or second recovery night and were largely similar between the first and second periods of sleep restriction. Sleep parameters averaged across each sleep restriction or recovery period showed no significant differences between the two short sleep groups. Conclusions: The similar sleep physiological responses in the two sleep restriction periods suggest that in young adults, sleep architecture does not adapt to recurrent weeks of moderate partial sleep loss, and such sleep patterns did not have compounding effects on sleep architecture. Furthermore, overall, increasing night-to-night variability in sleep duration did not have much additional impact on sleep physiological responses relative to a stable short sleep schedule. Clinical Trial: Performance, Mood, and Brain and Metabolic Functions During Different Sleep Schedules (STAVAR), https://www.clinicaltrials.gov/study/NCT04731662, NCT04731662.