0430 Odds Ratio Product as a Biological Marker of Hyperarousal in Insomnia with Short Sleep Duration

Abstract Introduction Odds-Ratio-Product (ORP) is an objective, continuous index of sleep depth and wake propensity ranging from 0 (very deep sleep) to 2.5 (full wakefulness) and measured in consecutive 3-second epochs. We investigated differences in ORP metrics in 69 insomnia patients with objectively short and normal sleep duration, and 50 controls. Methods Participants were recruited from the community and were screened with the Insomnia Severity Index and clinical interviews and assigned to either control or insomnia groups. Participants completed three nights of in-laboratory overnight polysomnography and the Odds Ratio Product (ORP) was computed from central EEG signals. Using average total sleep time (TST) of nights 2 and 3, patients with insomnia were divided into those with short sleep duration ( 6 hours; ISSD; n=20) or normal sleep duration (INSD, n=49). Percent of TRT spent in different ORP deciles was calculated along with average ORP over wake time (ORPWAKE, higher values reflect greater alertness), and NREM sleep (ORPNREM, higher values reflect lighter sleep). We also measured the frequency of wake intrusions (transient increases (2.0) in ORP per hour of NREM sleep). Results Patients with ISSD had higher ORPwake than controls (p=.017) when controlling for age, spent more time in full wakefulness (decile 10, ORP2.25) than the other groups (p.001), less time in deep sleep (ORP 0.5) than INSD (p=.018), and had a higher wake intrusion index than patients with INSD (p=.015). Absolute misperception of sleep onset latency was associated with ORPNREM (p=.003), ORPTRT (p=.008), and wake intrusions (p=.012) in ISSD, and ORPTRT (p=.009) and wake intrusions (p=.025) in controls, such that a greater degree of misperception was associated with elevated ORP and greater disruption to sleep. Conclusion Patients with insomnia and short sleep duration had evidence of physiological hyperarousal in EEG measured by ORP compared to controls and patients with insomnia and normal sleep duration. Sleep fragmentation, measured with ORP, was also associated with misperception of sleep onset latency in patients with short sleep duration and controls. These results can assist with the characterization of insomnia phenotypes. Differences in physiological hyperarousal within phenotypes of insomnia could suggest more targeted treatment pathways. Support (if any)