Study objectives: To estimate the course of slow-wave
activity (SWA), its amount during the night, and its correlation with
daytime sleepiness in sleep apnea syndrome (SAS) patients. This study
also verified whether continuous positive airway pressure (CPAP)
treatment also restores a normal pattern of SWA in severe SAS
Participants: Ten patients with a diagnosis
of severe SAS who showed a good clinical response to CPAP after
approximately 9 months of treatment were included 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 by 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 treatment. 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 frequency 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 significantly increased their
mean SWA after CPAP treatment in the first (p = 0.024) and second
(p = 0.002) sleep cycles and restored a more physiologic 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