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 cm H(2)O, 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 cm H(2)O 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 cm H(2)O, 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.