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Abstract Introduction Autonomic nervous system dysfunction and reduced heart rate variability (HRV) have been reported in individuals with mood disorders, a phenomenon likely to be influenced by sleep disturbances. Several studies have previously assessed HRV in individuals with major depression or bipolar disorder across the entire sleep period. This study investigated whether distinct heart rate (HR) and HRV profiles across wake, rapid eye movement (REM) sleep, and non-REM (NREM) sleep are linked to unipolar versus bipolar mood disorders in individuals with sleep complaints. Methods Polysomnographic data was retrospectively collated for 120 adult patients with sleep complaints and depressive symptoms referred to a specialized sleep clinic for sleep assessment 60 diagnosed with bipolar disorder (70% female, mean age= 43.4±11.6 years) and 60 age-matched cases diagnosed with a unipolar depressive disorder (68.3% female, mean age= 43.2±11.6 years), and 60 age-matched healthy controls (68.3% female, mean age= 43.4±12.6 years). HR and time-based HRV parameters were computed on 30-second segments and averaged across the night for wake and sleep stages. Results Significant group by sleep stage interactions showed that the unipolar and bipolar groups had lower standard deviation of normal-to-normal intervals (SDNN) and vagal tone root mean square of successive R-R interval differences (RMSSD) compared to controls during NREM sleep ( p≤.001) and REM sleep (p≤.003), but not during wake (p.050). The unipolar group had significantly higher heart rate than controls regardless of sleep stages (all, p≤ .042), while the bipolar group had higher heart rate than controls only during NREM 2 (p=.012) and NREM 3 (p=.009) sleep. These interactions persisted after excluding individuals taking antipsychotic, lithium, anticonvulsant, and cardiovascular medications. Conclusion While additional research is required to account for manic and euthymic states, as well as the impact of psychotropic and cardiac medications, and potential confounders like variations in body mass index, the present findings suggest that the sleep-based autonomic signature of depressive states differs across different types of mood disorders and could potentially inform the development of biomarkers and therapeutic targets. Support (if any) This project was supported by the Ottawa Region for Advanced Cardiovascular Research Excellence (ORACLE) funding program.
Leveille et al. (Sat,) studied this question.