LAUSR

Short sleepers (< 6 hours per night) represent a unique phenotype of insomnia associated with more severe biological implications compared to insomnia with normal sleep duration. A primary contributor to shorter sleep duration is more time spent awake after sleep onset (i.e., WASO), which has deleterious effects on long-term cardiac physiology. For instance, short sleepers with higher WASO have lower parasympathetic activity at sleep onset compared to those with lower WASO or greater sleep duration. Results presented here are derived from baseline assessments collected as a part of a clinical trial comparing three modalities of cognitive behavioral therapy for insomnia in middle-aged adults (50-65yrs) with chronic insomnia (N = 23). During their baseline assessment, individuals first completed one night of in-home polysomnography. Total sleep time was PSG derived. The following night, they wore an Equivital Harness equipped with an electrocardiogram (ECG) for 24 hours. In this investigation, inter-beat intervals were derived from ECG in 10-minute segments just before and just after bedtime (i.e., when the individual tried to sleep). WASO was calculated using sleep diaries during the night they wore the Harness and the following week. Preliminary data N = 23) show that high frequency (0.15-0.4Hz) heart rate variability (HRV; i.e., parasympathetic activity) at bedtime is not associated with WASO that night or WASO averaged across the following week. However, when the sample was narrowed to short sleepers only (□6hours; n = 7), lower levels of bedtime HRV (B = -.81, p = .028) is associated with greater WASO during the following week. In short sleepers, mean score of both before and after bedtime HRV predicted 65% of variance in WASO averaged across the next seven nights (R2 = .653, F (1, 5) = 9.41, B = -0.81, p = .28). These effects were not significant in individuals with sleep durations longer than 6 hours. In this small sample, short sleepers display a unique, inverse relationship between cardiac vagal activity and sleep continuity, replicating similar findings regarding parasympathetic activity at sleep onset and subsequent WASO. This project is supported by the Psychology Department at the University of Arizona.