Differences in 24-h autonomic nervous activity between hypersomnia and non-hypersomnia with major depressive disorder outpatients: An observational study

Background Hypersomnia, defined as a total sleep time of over 10 h within a 24-h period, is common in patients with major depressive disorder (MDD). The circadian rhythm of patients with hypersomnia and depression is disturbed; however, the difference in patients with non-hypersomnia is unclear. We aimed to clarify the difference in autonomic nervous system (ANS) activity during a 24-h period between hypersomnia and non-hypersomnia patient groups with MDD. Methods This study included outpatients diagnosed with MDD, who were placed in either the hypersomnia or non-hypersomnia group based on the Diagnostic and Statistical Manual of Mental Disorders-5 criteria. Heart rate variability data were collected for 24 h using electrocardiograms. Group differences in ANS activity during daytime and nighttime were compared using the t-test. A general linear model was used with the following variables to compare continuous 24-h data between groups: heart rate; natural logarithm (ln) of the low frequency domain (LF) as sympathetic and parasympathetic nerve activity; ln of the high frequency domain (HF) as parasympathetic nerve activity; ln LF/HF as objective variables indicating sympathetic domination; the presence or absence of hypersomnia every hour during the 24-h period as explanatory variables; age and body mass index as variable effects. Results Nine out of the twenty-five participants with MDD exhibited hypersomnia. The hypersomnia group rarely showed differences in ln HF and ln LF/HF between daytime and nighttime. In the non-hypersomnia group, ln HF was significantly increased and ln LF/HF was significantly decreased in the nighttime compared with daytime. Ln HF was significantly higher in the hypersomnia group versus the non-hypersomnia group in the evening. However, LF/HF was significantly higher in the hypersomnia group early in the morning. Conclusions Patients with hypersomnia had no change in parasympathetic activity between daytime and nighttime. In the hypersomnia group, hourly changes showed that ln HF was significantly higher from 17:00 to 22:00 h and ln LF/HF was significantly higher before waking, at 3:00–4:00 h, relative to the non-hypersomnia group. We observed that ANS activity differed depending on whether hypersomnia, a risk factor for relapse and bipolar disorder, is present.