O014 Impact of circadian adaptation on sleep architecture and neurobehavioural performance

Abstract Introduction We examined the impact of dynamic lighting schedules on circadian adaptation, sleep architecture, and neurobehavioural performance in a simulated shiftwork paradigm. Methods Healthy adults (n = 19, 10F, mean age[±SD]: 36.2 ± 9.2 years) completed an 8-day inpatient protocol that included 4 consecutive simulated nightshifts in which the sleep–wake schedule was delayed by 8 hours relative to habitual sleep–wake schedule. Participants were randomised to one of three dynamic lighting schedules (DLS). Circadian adaptation was assessed by comparing the plasma dim light melatonin onset measured before and after the nightshifts; sleep architecture was assessed immediately before beginning nightshifts (baseline) and after the fourth nightshift by polysomnography. Neurobehavioural performance (10-minute auditory and visual Psychomotor Vigilance Tasks, and Probed Recall Memory) and alertness (Karolinska Sleepiness Scale) were assessed every 1-2 hours during wake. Results Shiftwork disrupted sleep, compared to baseline, as indicated by significantly reduced total sleep time (TST), stage 2 sleep (N2), and sleep efficiency (SlEff), and increased wake after sleep onset (WASO, all p<.05). Sleep architecture did not differ between DLS schedules. The mean(±SEM) circadian phase-delay shift across the DLS schedules was -5.2 ± 0.4 hours. More circadian adaptation (i.e., larger circadian phase-shifts) was significantly correlated with TST, SlEff, and REM sleep, and decreased WASO (all p<.001). More circadian adaptation was significantly correlated with better alertness and memory function (both p = <0.05), but not PVT reaction time or attentional failure (all p≥.30). Conclusion Better circadian adaptation during nightshift work is associated with better sleep architecture, subjective alertness, and memory function but not reaction time or sustained attention.