Modulation of cardiac autonomic activity across consciousness states and levels of sleep depth in individuals with sleep complaints and bipolar disorder or unipolar depressive disorders

OBJECTIVE: Autonomic nervous system dysfunction and reduced heart rate variability (HRV) often co-exist with mood disorders, a phenomenon likely influenced by sleep disturbances. This study investigated heart rate (HR) and HRV across wake, rapid eye movement (REM) sleep, and non-REM (NREM) sleep in individuals with sleep complaints and bipolar or unipolar depressive disorder. METHODS: Polysomnographic data was retrospectively collated for 120 adult patients with sleep complaints and depressive symptoms [60 diagnosed with bipolar disorder, 60 diagnosed with a unipolar depressive disorder], and 60 healthy controls. HR and time-based HRV variables were computed on 30-s segments and averaged across the night for wake, NREM and REM sleep. RESULTS: Significant group by consciousness state interactions showed that the unipolar and bipolar groups had lower standard deviation of normal-to-normal intervals root mean square of successive R-R interval differences compared to controls during NREM and REM sleep, but not during wake (SDNN: F(4, 330) = 3.0, p = .021, np2 = 0.035; RMSSD: F(4, 332) = 5.8, p < .001, np2 = 0.065). The magnitude of these group differences did not vary significantly between NREM 1, NREM 2 and NREM 3 sleep. These interactions persisted after excluding individuals taking 3rd generation antipsychotic, lithium, anticonvulsant, and cardiovascular medications. CONCLUSION: Although further work is required to account for the impact of psychotropic and cardiac medications, as well as manic and euthymic states, these 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.