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.