Abbreviated method for assessing upper airway function in obstructive sleep apnea

Objectives: Previous studies have shown that the level of flow through the upper airway in patients with obstructive sleep apnea (OSA) is determined b y the critical closing pressure (Pcrit) and the upstream resistance (RN). W e developed a standardized protocol for delineating quasisteady-state press ure-flow relationships for the upper airway from which these variables coul d be derived. In addition, we investigated the effect of body position and sleep stage on these variables by determining Pcrit and RN, and their confi dence intervals (CIs), for each condition. Design: Pressure-flow relationships were constructed in the supine and late ral recumbent positions (nonrapid eye movement [NREM] sleep, n = 10) and in the supine position (rapid eye movement [REM] sleep, n = 5). Setting: University Hospital Antwerp, Belgium. Patients: Ten obese patients (body mass index, 32.0 +/- 5.6 kg/m(2)) with s evere OSA (respiratory disturbance index, 63.0 +/- 14.6 events/h) were stud ied. Interventions: Pressure-flow relationships were constructed from breaths ob tained during a series of step decreases in nasal pressure (34.1 +/- 6.5 ru ns over 3.6 +/- 1.2 h) in NREM sleep and during 7.8 +/- 2.2 runs over 0.8 /- 0.6 h in REM sleep. Results: Maximal inspiratory airflow reached a steady state in the third th rough fifth breaths following a decrease in nasal pressure. Analysis of pre ssure-flow relationships derived from these breaths showed that Pcrit fell from 1.8 (95% CI, -0.1 to 2.7) cm H2O in the supine position to -1.1 cm H2O (95% CI, -1.8 to 0.4 cm H2O; p = 0.009) in the lateral recumbent position, whereas RN did not change significantly. In contrast, no significant effec t of sleep stage was found on either Pcrit or RN. Conclusions: Our methods for delineating upper airway pressure-flow relatio nships during sleep allow for multiple determinations of Pcrit within a sin gle night from which small yet significant differences can be discerned bet ween study conditions.