RATIONALE
Rapid eye movement sleep (REM) is associated with reduced ventilation and greater obstructive sleep apnea (OSA) severity versus non-REM (nREM) for reasons not fully elucidated. Here we use direct physiological measurements to determine whether the pharyngeal compromise in REM OSA is most consistent with 1) withdrawal of neural ventilatory drive or 2) deficits in pharyngeal pathophysiology per se (i.e. increased collapsibility, decreased muscle responsiveness).
METHODS
63 OSA participants completed sleep studies with gold-standard measurements of ventilatory "drive" (calibrated intra-esophageal diaphragm EMG), ventilation (oronasal "ventilation"), and genioglossus EMG (EMGgg). Drive withdrawal was assessed by examining these measurements at nadir drive (1st decile drive within stage). Pharyngeal physiology was assessed by examining collapsibility (lowered ventilation at eupneic drive) and responsiveness (ventilation-drive slope). Mixed model analysis compared REM vs. nREM; sensitivity analysis examined phasic REM.
RESULTS
REM (≥10 min) was obtained in 25 patients. Compared with nREM, drive in REM dipped to markedly-lower nadir values (1st decile: -21.8[-31.2,-12.4]%eupnea; P<0.0001, estimate[95%CI]), with an accompanying reduction in ventilation (-25.8[-31.8,-19.8]%eupnea; P<0.0001). However, there was no effect of REM on collapsibility (ventilation at eupneic drive), baseline EMGgg activity, or responsiveness. REM was associated with increased OSA severity (+10.1[1.8,19.8] events/hr), but not after adjusting for nadir drive (+4.3[-4.2,14.6]). Drive withdrawal was exacerbated in phasic REM.
CONCLUSIONS
In OSA patients, the pharyngeal compromise characteristic of REM appears to be explained by ventilatory drive withdrawal rather than preferential decrements in muscle activity or responsiveness. Preventing drive withdrawal may be the leading target for REM OSA.