Patterns of heart rate reduction during sleep onset in participants with and without insomnia.

Study objectives: Hyperarousal is common in patients with insomnia. Autonomic stress may reflect hyperarousal and distinguish participants with insomnia vs good sleepers. Slope analysis of heart rate reduction during sleep onset might be a promising measure of such autonomic modulation. We aim to explore the potential utility of this measure with data collected from home settings from the Sleep Heart Health Study.

Methods: In this secondary analysis with 743 participants, we applied two approaches to compute slopes for heart rate reduction during sleep onset. We compared slopes among participants with and without insomnia symptoms, with short versus long sleep onset latency, with or without difficulty falling asleep during the study night, and with sleep-onset insomnia versus other insomnia subtypes. We also explored correlations between heart rate reduction and sleep outcome measures.

Results: We found that the slopes of heart rate reduction during sleep onset were most significantly associated with objectively measured sleep onset latency, followed by subjectively reported sleep onset latency, regardless of the approach used to compute the slopes. Participants with self-reported difficulty falling asleep during the study night had significantly blunted heart rate reduction. The slopes were significantly blunted in participants with self-reported sleep-onset insomnia compared to other types of insomnia.

Conclusions: As measures of autonomic activity, the slopes of heart rate reduction may serve as a physiological biomarker to indicate hyperarousal during wakefulness before sleep onset. Tracking changes of heart rate reduction during sleep onset may have potential value in the evaluation of insomnia treatments, especially those targeting sleep onset difficulties.