0427 Assessment of First-Night Effect in Patients with Insomnia Using the Odds-Ratio-Product (ORP)

Abstract Introduction Studies on first-night effect using conventional sleep metrics have been inconclusive. ORP is an objective index of sleep depth and wake propensity ranging from 0 (very deep sleep) to 2.5 (full wakefulness). ORP provides more in-depth information about sleep. We compared several ORP-derived metrics measured during three consecutive PSGs in patients with and without insomnia. Methods Participants (n=119) were screened with the Insomnia Severity Index and clinical interviews and assigned to either control (n=50) or insomnia (n=69) groups. Participants completed 3 nights of in-laboratory polysomnography. After each PSG, participants answered the question “How was your night in the lab compared to a night at home?” on a 1 (much better) to 5 (very mediocre) scale. The following variables were compared across the three nights with repeated-measures ANOVA. Questionnaire response (Q); average ORP during stages wake (ORPW), NREM (ORPNR) and REM (ORPREM) sleep; percent of recording time in deep sleep (ORP< 0.5) and in full wakefulness (ORP>2.25); average instantaneous difference between right and left ORP (R/L ORP difference), a measure of interhemispheric dissociation in sleep depth; frequency (hr-1) of transient increases (>2.0) in ORP during NREM sleep (WII); along with total sleep time (TST), % time awake (%wake), minutes in stages NREM3 (N3 time) and REM sleep (REM time); arousal index (AI). Results There were no differences between nights 2 and 3 in any variable. Q decreased beyond night-1, indicating improvement relative to home. The following significant changes were observed in night-2 in both insomnia and control groups (Tukey’s test): ORPNR and ORPREM decreased (deeper sleep); more time in deep sleep (ORP< 0.5) and less time in full-wakefulness (ORP>2.25); less WII. The following significant changes were observed in night-2 only in participants with insomnia: Lower ORPW, indicating less alertness during stage W, and less R/L ORP differences. TST marginally increased and N3 time and AI marginally decreased in insomnia while %wake decreased marginally in both groups. Conclusion This study demonstrated clear first-night effects in several EEG microstructure variables in both control and insomnia participants, while the latter also showed reduced alertness and improved R/L agreement in sleep depth beyond night-1. Support (if any)