NREM-AHI greater than REM-AHI versus REM-AHI greater than NREM-AHI in patients with obstructive sleep apnea: clinical and polysomnographic features

Previous studies show a high prevalence of obstructive sleep apnea (OSA) patients with a higher non-rapid eye movement (NREM) apnea-hypopnea index (AHI) (NREM-AHI) than rapid eye movement (REM) AHI (REM-AHI). However, the clinical significance of this phenomenon in patients with OSA is unknown. This study aimed to investigate whether there were significant differences in clinical and polysomnographic features between the NREM-AHI > REM-AHI group and the REM-AHI > NREM-AHI group and to determine whether NREM-AHI > REM-AHI or REM-AHI > NREM-AHI is a specific clinical entity. One hundred forty-two patients with OSA, including 114 males and 28 females, were assessed for specific sleep-related complaints using a semistructured clinical questionnaire, for daytime sleepiness using the Epworth Sleepiness Scale (ESS), for depression using the Beck Depression Inventory (BDI), and for health-related quality of life using the Medical Outcomes Study Short-Form 36 Health Survey questionnaire (SF-36). Anthropometric, clinical, and polysomnographic characteristics were examined between patients with NREM-AHI > REM-AHI and those with REM-AHI > NREM-AHI. A higher NREM-AHI than REM-AHI was found in 54.9% of the 142 patients with OSA. Overall, males predominated in each group, and there were no significant differences in age, body mass index, medical history, and drug intake between the NREM-AHI > REM-AHI group and the REM-AHI > NREM-AHI group. A high occurrence of NREM-AHI > REM-AHI (94.9%) or REM-AHI > NREM-AHI (90.6%) was found in moderate-to-severe cases each group. Although several indexes of OSA were worse in the NREM-AHI > REM-AHI group than in the REM-AHI > NREM-AHI group, no significant differences in specific sleep-related complaints, ESS score, BDI score, the incidence of daytime sleepiness or depression, and scores of sub-dimensions and the total score on SF-36 were present between the two groups. As compared separately, no significant differences in clinical features were observed in the clinical data for males and females between the two groups. Our results show that either NREM-AHI > REM-AHI or REM-AHI > NREM-AHI is more common in moderate-to-severe OSA cases, and there are no significant differences in clinical features between the NREM-AHI > REM-AHI group and the REM-AHI > NREM-AHI group. These findings may suggest that either NREM-AHI > REM-AHI or REM-AHI > NREM-AHI should be considered as a part of the spectrum of OSA, rather than a specific clinical entity.