"Frontal Slow-Wave Asymmetry in Obstructive Sleep Apnea and Its Modulation During CPAP Titration"

Sleep slow-wave activity (SWA) shows regional and hemispheric variation reflecting local cortical regulation. Obstructive sleep apnea (OSA) introduces recurrent respiratory instability and arousals that may alter cortical dynamics during sleep. It remains unclear whether continuous positive airway pressure (CPAP) affects hemispheric SWA balance.

In this retrospective observational study, we included adult patients who underwent diagnostic polysomnography followed by a CPAP titration study on a separate night. Frontal delta power during N3 sleep was calculated from F3-A2 and F4-A1 using spectral analysis. Hemispheric asymmetry was quantified using a normalized asymmetry index (F4 - F3) / (F4 + F3). Sleep, respiratory, and EEG parameters were compared using paired nonparametric tests.

A total of 143 patients were included (median age 47 years, 76% male). CPAP improved respiratory parameters, with median apnea-hypopnea index decreasing from 27.4 to 3.2 events/h (P < .001). Frontal delta power decreased at both F3 and F4 during CPAP (P < .001). Absolute asymmetry index decreased from 9.35% to 7.55% (P = .008). Signed asymmetry shifted toward left hemispheric dominance (P < .001). Right-dominant patterns were more frequent during the diagnostic night, whereas left-dominant patterns predominated during CPAP. Among patients with non-neutral asymmetry on both nights, dominance direction changed significantly (McNemar P = .008), mainly from right to left.

CPAP is associated with reduced frontal delta power and attenuation of hemispheric SWA asymmetry during deep sleep, suggesting that respiratory stabilization may influence cortical organization. These findings should be interpreted considering potential night-to-night effects.