Nonrapid Eye Movement-Predominant Obstructive Sleep Apnea: Detection and Mechanism

Abstract

Study objectives: Obstructive sleep apnea (OSA) can be severe and present in higher numbers during rapid eye movement (REM) than nonrapid eye movement (NREM) sleep; however, OSA occurs in NREM sleep and can be predominant. In general, ventilation decreases an average 10% to 15% during transition from wakefulness to sleep, and there is variability in just how much ventilation decreases. As dynamic changes in ventilation contribute to irregular breathing and breathing during NREM sleep is mainly under chemical control, our hypothesis is that patients with a more pronounced reduction in ventilation during the transition from wakefulness to NREM sleep will have NREM- predominant rather than REM-predominant OSA.

Methods: A retrospective analysis of 451 consecutive patients (apnea-hypopnea index [AHI] > 5) undergoing diagnostic polysomnography was performed, and breath-to-breath analysis of the respiratory cycle duration, tidal volume, and estimated minute ventilation before and after sleep onset were examined. Values were calculated using respiratory inductance plethysmography. The correlation between the percent change in estimated minute ventilation during wake-sleep transitions and the percentage of apnea-hypopneas in NREM sleep (%AHI in NREM; defined as (AHI-NREM) / [(AHI-NREM) + (AHI-REM)] × 100) was the primary outcome.

Results: The decrease in estimated minute ventilation during wake-sleep transitions was 15.0 ± 16.6% (mean ± standard deviation), due to a decrease in relative tidal volume. This decrease in estimated minute ventilation was significantly correlated with %AHI in NREM (r = -0.222, p < 0.01).

Conclusions: A greater dynamic reduction in ventilation back and forth from wakefulness to sleep contributes to the NREM predominant OSA phenotype via induced ventilatory instability.

Keywords: NREM-predominant OSA; obstructive sleep apnea; respiratory physiology during sleep.

Figure 1. The % change in our surrogate of minute ventilation in the transition from wakefulness to sleep for three groups categorized by %AHI in NREM.

Bars represent the mean and standard deviation. The right bar represents those with REM-predominant OSA. The left bar indicates the phenotype of NREM-predominant OSA. There is a significantly different reduction in our surrogate of minute ventilation during transition from wakefulness to sleep. The calculation formula for %change in the surrogate of minute ventilation and %AHI in NREM was: [(minute ventilation after sleep onset) − (minute ventilation before sleep onset)] / (minute ventilation before sleep onset) × 100, or (AHI-NREM) / [(AHI-NREM) + (AHI-REM)] ×100. AHI, apnea-hypopnea index; NREM, nonrapid eye movement; OSA, obstructive sleep apnea; REM, rapid eye movement.

Figure 2. The associations between % change in our surrogate of minute ventilation and %AHI in NREM in different sleeping body position.

The graphs present the data in both supine and nonsupine body positions (A), in supine body position (B), and in lateral body position (C). % change in our surrogate of minute ventilation: the calculation formula was [(minute ventilation after sleep onset) − (minute ventilation before sleep onset)] / (minute ventilation before sleep onset) × 100. %AHI in NREM: (AHI-NREM) / [(AHI-NREM) + (AHI-REM)] × 100. AHI, apnea-hypopnea index; NREM, nonrapid eye movement; r, correlation coefficient of Spearman's correlation analysis; REM, rapid eye movement.