Upper airway collapsibility evaluated by a negative expiratory pressure test in severe obstructive sleep apnea

OBJECTIVES: To investigate the usefulness of measuring upper airway collapsibility with a negative expiratory pressure application as a screening test for severe obstructive sleep apnea (OSA). INTRODUCTION: OSA is a risk factor for cardiovascular disease, and it may have serious consequences. Its recognition may have important implications during the perioperative period. Increased upper airway collapsibility is one of the main determinants of OSA, and its evaluation could be useful for identifying this condition. METHODS: Severe OSA and normal subjects (24 in each group) were matched by body mass index and referred to our sleep laboratory. The subjects were enrolled in an overnight sleep study, and a diurnal negative expiratory pressure test was performed. Flow drop (DeltaV) and expiratory volume were measured in the first 0.2 s (V(0.2)) of the negative expiratory pressure test. RESULTS: DeltaV (%) and V(0.2) (%) values were statistically different between normal and OSA subjects. OSA patients showed a greater decrease in flow than normal subjects. In addition, severely OSA patients exhaled during the first 0.2 s of the negative expiratory pressure application was an average of only 11.2% of the inspired volume compared to 34.2% for the normal subjects. Analysis of the receiver operating characteristics showed that V(0.2) (%) and DeltaV (%) could accurately identify severe OSA in subjects with sensitivities of 95.8% and 91.7%, respectively, and specificities of 95.8% and 91.7%, respectively. CONCLUSIONS: V(0.2) (%) and DeltaV (%) are highly accurate parameters for detecting severe OSA. The pharyngeal collapsibility measurement, which uses negative expiratory pressure during wakefulness, is predictive of collapsibility during sleep.