0046 Impact of Circadian Adaptation on Sleep Architecture in Simulated Shiftwork

Abstract

Introduction: Shift workers commonly experience circadian misalignment, which disrupts sleep. We examined the impact of a dynamic lighting schedule on circadian adaptation and sleep architecture in a simulated shiftwork paradigm. Methods: Healthy adults (n= 19, 10F, mean age [±SD] 36.20 ± 9.20 years) completed an 8-day inpatient protocol that included 4 consecutive nightshifts during which the sleep-wake schedule was delayed by 8 hours relative to each participant's habitual schedule. Participants were randomized to one of three dynamic lighting interventions during the four nightshifts that differed in illuminance, spectrum, and timing through the waking day and were expected to induce a phase delay. Circadian adaptation was assessed by comparing the plasma dim light melatonin onset (DLMO) measured before and after the nightshifts. Sleep during an 8-hour sleep opportunity was measured polysomnographically before the first nightshift (baseline) and after the fourth nightshift. Results: The mean (±SEM) circadian phase-delay shift was -5.15±0.37 hours (range: -8.16 to -1.88 hours) of the targeted 8-hours. Sleep architecture did not differ across the three conditions, so data were combined for analyses. Compared to baseline, sleep after the fourth nightshift was associated with significantly reduced total sleep time (TST, 415.40±20.24 vs. 377.2±15.02 minutes, p < 0.01), stage 2 sleep (N2, 187.3±13.16 vs. 151.7±9.47 minutes, p< 0.01), and sleep efficiency (SlpEff, 86.05±4.19 vs. 78.52±3.11 %, p< 0.01), and increased wake after sleep onset (WASO, 52.92±19.15 vs. 84.79±15.10 mins, p< 0.05). Sleep onset latency (SOL) did not differ (18.02±5.32 v 14.68±2.45 mins, p=0.76). Greater circadian phase shifts, corresponding to more adaptation to the shifted sleep-wake schedule were correlated with increased TST (r2 = 0.49, p< 0.001), SlpEff (r2 = 0.49, p< 0.001), REM (r2 = 0.38, p< 0.01), and decreased WASO (r2 = 0.53, p< 0.001), but not SOL (r2 = 0.10, p=0.19).Conclusion: The results show that greater circadian adaptation is associated with better sleep architecture. Additional studies are needed to optimize details of dynamic lighting schedules and lighting characteristics for preserving sleep quality in various shiftwork schedules.