O006 Tracking wake propensity across night shift lighting conditions with ORP

Introduction Odds ratio product (ORP) provides a continuous metric of sleep depth and wake propensity that may be a useful marker of sleep and circadian disruption effects on sleepiness and subsequent performance. Thus, the present study examined wakefulness during simulated shift work under different lighting conditions that were previously shown to differentially impact circadian rhythm and performance. Methods Nineteen healthy sleepers (7 female, mean ± SD 29 ± 10yrs) underwent two continuous 8-day sessions, each with either circadian-informed or standard lighting. During days 3-7, participants underwent a night-shift schedule, sleeping from 10:00-9:00. Participants competed three 7-minute drowsiness test batteries throughout each night shift. ORP, ranging from 0 (deep sleep) to 2.5 (full wakefulness), was calculated using C3 and C4 electrodes in 3-sec epochs. Results Generalized linear mixed models demonstrated significant three-way interactions (Condition × Day × Test Battery) for both C3 ORP (χ2 = 79.11, p<.001) and C4 ORP (χ2 = 21.99, p=.001). ORP was consistently higher in test battery 3 in the circadian-informed lighting compared to standard lighting. Day 6 showed lower ORP in circadian-informed lighting at battery 1 and battery 2 for both channels (p<.010), while C3 ORP was highest across all batteries on Day 7. Discussion These results support that ORP is sensitive to circadian-informed lighting effects that progressively alter wakefulness over consecutive night shifts, whilst remaining sensitive to within-shift dips in wakefulness. Thus, where continuous electroencephalographic measurement is feasible, ORP may be a useful metric for evaluating differential wakefulness levels, alertness and safety in the context of shift work.