Apnoea–Hypopnoea Index during Rapid Eye Movement and Non-Rapid Eye Movement Sleep in Obstructive Sleep Apnoea

This study investigated the differences in apnoea-hypopnoea index (AHI) during rapid eye movement (REM) sleep (AHI-REM) and AHI during non-REM (NREM) sleep (AHI-NREM) in patients with obstructive sleep apnoea (OSA). Nocturnal polysomnography was performed in 102 Japanese OSA patients and their AHI along with a variety of other factors were retrospectively evaluated. Regardless of the severity of AHI, mean apnoea duration was longer and patients' lowest recorded oxygen saturation measured by pulse oximetry was lower during REM sleep than during NREM sleep. Approximately half of the patients (n = 50) had a higher AHI-NREM than AHI-REM. In subjects with AHI ≤ 60 events/h, AHI-NREM was significantly higher than AHI-REM. On multivariate logistic regression, severe AHI ≤ 30 events/h was the only predictor of a higher AHI-NREM than AHI-REM. This may indicate that important, but unknown, factors related to the mechanism responsible for the severity of OSA are operative during NREM sleep.