0128 Little Evidence of Day-to-Day Sleep Homeostasis During a Month of 14-hour Nights

Introduction The magnitude of nightly variability in sleep timing and duration in rested healthy people is unknown. This information is important for understanding insomnia and for short-term (within a wake episode) sleep homeostatic processes. Methods 15 healthy individuals participated in a previously reported protocol simulating long nights that included 28 consecutive nights of inpatient sleep in total darkness from 6 pm - 8am. The protocol was approved by the NIH Intramural Research Program IRB; written informed consent was obtained. Polysomnographic records were scored in 30-second epochs using Rechtschaffen and Kales criteria. Consolidated Sleep (CS) duration was defined as the time between the (i) first epoch of 10 consecutive minutes of any stage of sleep and (ii) beginning of consecutive epochs of wake before scheduled wake time. Results The median (across participants) Total Sleep Time (TST), CS, SWS (NREM sleep stages 3 + 4), and REM sleep duration per night declined across the first 7–10 nights and then were stable. For the last 14 nights of this protocol, the median amount of TST ranged from ~7–9 hours with a within-participant across-night range of ~5 hours. For CS duration, the order of median (shortest to longest) duration was different from that for TST; median was ~9–11 hours with across-night range of ~3 hours. For SWS sleep, the order was different; median was ~1.5 hours with across-night range of ~0.5 hr. For REM sleep, the order was different; median was ~2 hours with across-night range of ~2 hours. There was no clear 2-night periodicity (i.e., night with low TST immediately followed by night with high TST). Conclusion The large variability of TST, CS, SWS, and REM sleep without evidence of 2-night periodicity across the final 14 nights in this sleep-satiated population suggests less day-to-day homeostatic control than anticipated in current models of sleep homeostasis. Support (If Any) NIH K24-HL105664 (EBK), P01-AG009975 (CAC, EBK). NIH Intramural funds (TW, GB)