Study objectives: A recent study of 34 patients with mild obstructive sleep apnea syndrome (OSAS) suggested that the number of apneas and hypopneas per hour of sleep (apnea/hypopnea index [AHI]) may show a stronger correlation with sleepiness, as measured by the Multiple Sleep Latency Test (MSLT), when calculated for rapid eye movement (REM) sleep alone (AHIR) as opposed to the entire night. We sought to reexamine this possibility in a larger group of similar patients and in patients who had a wider range of OSAS severity.
Design: Retrospective and observational.
Setting: A large, accredited, academic sleep disorders center where a database of sleep study results is maintained.
Patients: We studied 1,146 persons who had polysomnography and MSLTs for clinical indications.
Results: In linear regression models, the AHI explained 11.0% of the variance in MSLT results, AHIN (AHI during non-REM sleep) explained 10.8%, and AHIR explained only 6.0% (p≤0.0001 for each). Among subjects with AHI <10, the AHI explained 3.1% of the variance (p=0.0012), the AHIN 2.3% (p=0.0049), and the AHIR 0.2% (p=0.40). Among all subjects, the ratio AHIR/AHIN had no influence on the overall relationship between AHI and sleepiness (p=0.23).
Conclusions: We conclude that apneic events during REM and non-REM sleep probably contribute equally to sleepiness as measured by the MSLT.