Awake flow limitation with negative expiratory pressure in sleep disordered breathing

Abstract

Background and purpose Although upper airway collapsibility (UAC) is theoretically useful to anticipate severity of sleep-disordered breathing (SDB), inspiratory UAC measurements are poorly correlated with obstructive sleep apnea (OSA) severity. Patients and methods We investigated in 15 healthy and 35 SDB awake subjects whether negative expiratory pressure (NEP) could be a technique which would allow us to anticipate SDB severity. We characterized in these subjects, both in supine and sitting position, at −5 and −10 cmH 2O, the flow-volume curves and a new NEP quantitative index (ratio of the ‘areas under the curve’ of NEP flow-volume loop vs. spontaneous flow-volume loop). Results Abnormal flow-volume curves were significantly more frequent in patients with SDB than in healthy subjects, for both negative pressures in sitting posture and −10 cmH 2O in supine position. The quantitative index decreased with the severity of SDB, independently of confounding factors (age, body mass index (BMI) and expiratory reserve volume (ERV)). In the supine position, at −5 and −10 cmH 2O, thresholds of less than 160 and 180% respectively identified in 96.6% of SDB, whereas thresholds of greater than 160 and 180% were adequately classified in 76.9% of controls. Conclusions NEP flow-volume curves and quantitative index during wakefulness are useful methods to detect UAC. These results, however, should be confirmed by a prospective study in the general population.