Cardiovascular autonomic dysfunction in insomnia patients with objective short sleep duration.

Two phenotypes have been proposed: insomnia with objective near-normal sleep duration, related to increased psychological symptoms, and insomnia with objective short sleep duration, associated with cardiometabolic morbidity. Reduced heart rate variability has also been implicated in the pathophysiology of cardiometabolic disease; however, there are little data on whether cardiovascular function differs between patients with objective short sleep duration and near-normal sleep duration. Participants (M  = 49.9 ± 11.3 years; 62.8% female) were 180 adults with chronic insomnia (M  = 15.7 ± 13.6). Objective sleep duration was based on total sleep time averaged across two consecutive nights of polysomnography and subjective sleep duration was based on 2-week sleep diaries. The sample was divided into two groups, with sleep duration shorter (polysomnography-total sleep time: n = 46; sleep diary: n = 95) or equal/longer (polysomnography-total sleep time: n = 134; sleep diary: n = 85) than 6 hr. Electrocardiogram data derived from polysomnography were used to obtain heart rate and heart rate variability during stage 2 (N2) and rapid eye movement sleep. Heart rate variability measures included absolute and normalized high-frequency component, an index of parasympathetic activation, and the ratio of low- to high-frequency (LF/HF ratio), an index of sympathovagal balance. After controlling for covariates (e.g., co-morbidity), patients with objective short sleep duration had reduced high-frequency (p < .05) and elevated low-frequency/high-frequency ratio (p = .036) and heart rate (p = .051) compared with patients with near-normal sleep duration. No differences were observed between phenotypes when subjective sleep duration was used. Insomnia patients with objective short sleep duration showed significantly dampened parasympathetic activation and increased sympathovagal imbalance relative to their counterparts with near-normal sleep duration. These findings highlight the importance of treating insomnia, as treatment may reduce the risk of cardiovascular disease.