0181 NREM Delta Power Is Conserved in Nighttime Recovery Sleep After Repeated Simulated Nightshift Duty Cycles

Abstract Introduction Slow wave sleep (SWS) has been reported to be conserved, relative to baseline, across days in schedules with repeated simulated nightshift duty cycles. We investigated whether this SWS characteristic extends to delta power (0.6–4.0Hz) in the NREM sleep EEG of nighttime sleep after each of two consecutive nightshift duty cycles, to quantify post-duty homeostatic recovery. Methods N=27 health adults (ages 22–39y; 13f) completed a 14-day laboratory study. After 10h nighttime baseline sleep (TIB 22:00–08:00), subjects were randomized to a simulated dayshift condition (n=15; 6f) with all nights 10h TIB (22:00–08:00) or a simulated nightshift condition (n=12; 7f) with two repeated simulated nighttime duty cycles. Each nighttime duty cycle involved a transition nap (15:00–20:00), 4 consecutive daytime sleep opportunities (10:00–20:00), and another transition nap (10:00–15:00), followed by nighttime recovery sleep (22:00–08:00). Analyses focused on the nighttime baseline sleep and both recovery sleep opportunities in the nightshift condition and the equivalent nights in the dayshift condition. Sleep was scored using AASM criteria and subjected to NREM EEG spectral analysis to assess cumulative delta power for each night. Results were analyzed using repeated-measures ANOVA with factors for condition, night, and their interaction, and covariates for age and sex. Results There was a trend for an overall reduction in delta power in the nightshift condition compared to the dayshift condition (F[1,23]=3.0, P=0.097), but no effect of night (F[2,48]=0.51, P=0.60) and no interaction (F[2,48]=0.45, P=0.64). Results were consistent with two-process model simulations of homeostatic pressure, which predicted reduced delta power during recovery sleep in the nightshift condition. The correlation between group-average observations and predictions was 0.44. Conclusion NREM delta power was conserved in nighttime recovery sleep after repeated nightshift duty cycles. Compared to nighttime sleep in simulated dayshift, the observed NREM delta power was marginally reduced in simulated nightshift, as moderately correlated with two-process model predictions. The minimal dynamic response to simulated nightshift in NREM delta power is congruent with observations in repeated cycles of simulated dayshift with sleep restriction, and may underlie cumulative deficits in neurobehavioral performance across repeated nightshift duty cycles. Support (if any) FMCSA DTMC75-07-D-00006 and CDMRP W81XWH-05-1-0099.