Slow-wave activity in sleep apnea patients before and after continuous positive airway pressure treatment - Contribution to daytime sleepiness

Study objectives: To estimate the course of slow-wave activity (SWA), its a mount during the night, and its correlation with daytime sleepiness in slee p apnea syndrome (SAS) patients. This study also verified whether continuou s positive airway pressure (CPAP) treatment also restores a normal pattern of SWA in severe SAS patients. Participants: Ten patients with a diagnosis of severe SAS who showed a good clinical response to CPAP after approximately 9 months of treatment were i ncluded in this study. These patients were matched for sex and age with 10 control subjects. Design: All subjects underwent 1 night of polysomnography (PSG), followed b y the multiple sleep latency test (MSLT) the next day. For the SAS patients only, the same procedure was repeated after 9 +/- 0.7 months of CPAP treat ment. In addition to traditional scoring of sleep stages, apneas, hypopneas , and microarousals, the SWA, defined as the power in the 0.75- to 4.5-Hz f requency band, was evaluated. Results: A positive correlation between SWA of the first cycle and the MSLT (r = 0.56; p = 0.045) was found before treatment. Moreover, SAS patients s ignificantly increased their mean SWA after CPAP treatment in the first (p = 0.024) and second (p = 0.002) sleep cycles and restored a more physiologi c decay of SWA across the night. Conclusions: These results suggest that daytime sleepiness in SAS patients may be the result of a lack of SWA during the first part of the night, and show that CPAP restores a more physiologic pattern of SWA across the night.