Study of Phase Synchronization and Network Structures in Complexes of Physiological Activity in Cardiovascular Pathologies

Obstructive sleep apnea (OSA) is a common sleep-disordered breathing disorder associated with hypoxemia, sleep fragmentation, and significant changes in functional brain activity. This study analyzed polysomnography recordings from 548~patients, including groups with varying OSA severity and healthy volunteers. Wavelet bicoherence was used to assess functional connectivity, and network structure was analyzed using the betweenness centrality index. Synchronization changes in OSA were found to be frequency-specific: in the Δ band (1 -- 4 Hz), a significant decrease in interhemispheric coherence was observed, with significant negative correlations with the apnea-hypopnea index (r = -0.77 to -0.81), while in the high-frequency band (12 - 30 Hz), a relative increase in intrahemispheric connections was observed. Restructuring of network characteristics is significantly evident only during REM sleep, with changes predominantly localized in the occipital leads. The obtained data are consistent with the visceral theory of sleep and indicate a compensatory restructuring of integrative brain processes under conditions of chronic hypoxia, opening up the possibility of using quantitative EEG markers to assess the severity of OSA and associated cognitive impairment.