The Correlation Between Phase Coherence of Respiratory Sinus Arrhythmia and Slow Wave Brain Activity is Altered in Depressed Patients with and Without Obstructive Sleep Apnea During Sleep.

The aim of this study is to investigate the correlation between slow wave sleep and phase coherence between respiratory sinus arrhythmia (RSA) and respiration in OSA patients with and without major depressive disorder (MDD), and how it differs from healthy subjects. Overnight electroencephalogram (EEG), electrocardiograms (ECG), and breathing using plethysmography were recorded from control subjects (17 CONT), OSA subjects with MDD (17 OSAMDD+) and OSA subjects without MDD (17 OSAMDD-). Slow wave activity was computed by the amplitude envelope of the EEG $\delta$ -wave(0.5-4 Hz). The interbeat intervals (RRI) and respiratory movement were extracted from ECG. RRI and respiration were resampled at 10Hz, and the band passed filtered (0.10-0.4 Hz) before the Hilbert transform was used to extract instantaneous phases of the RSA and respiration. Then, the phase coherence ( $\lambda$ ) between RSA and respiration was quantified. Using cross-correlation, we found that overnight profiles of $\lambda$ and $\delta$ -wave were correlated in only CONT group, with significant cross-correlation coefficient. This coefficient correlation was significantly higher than that obtained for OSAMDD+ and OSAMDD-groups. Our results suggest that the association between $\lambda$ and $\delta$ -wave can be used as trait marker for distinguishing between healthy and OSA patients.