Upper airway dynamics during negative expiratory pressure in apneic and non-apneic awake snorers

Background: The ability of negative expiratory pressure (NEP) technique to differentiate between awake snorers with and without obstructive sleep apnea-hypopnea (OSAH) was investigated. Methods: Forty-eight subjects with sleep disordered breathing (SDB) and 7 healthy subjects, as non-snorer controls, underwent the NEP application of -5 and -7 cmH2O in the seated and supine position during wakefulness, after performing a sleep study. The upper airway collapsibility was assessed by computing the volume exhaled during the first 0.5 sec. (V,NEP0.5) and 1 sec. (V,NEP1) following the NEP start. Results: Patients with severe (AHI ≥ 30) (n = 19) and mild-to-moderate (AHI <30 and >5) (n = 15) OSAH had lower V,NEP0.5 (340 ± 88 ml) as compared to snorers (AHI ≤ 5) (n = 14) (427 ± 101 ml; p < 0.01) and controls (n = 7) (492 ± 69 ml; p < 0.001) in the supine position with NEP -5 cmH2O. Less significant differences among the different groups were observed for V,NEP0.5 in the seated position with NEP -5 cmH2O and in both positions with NEP -7 cmH2O (only OSAH patients vs controls, p < 0.001). Similar results were obtained for V,NEP1 in either position by using both NEP -5 cmH2O and -7 cmH2O. In spite of this, a substantial overlapping of V,NEP0.5 and V,NEP1 between snorers and OSAH patients did not allow to identify a reliable diagnostic cut-off level. An inverse correlation with AHI was found for V,NEP0.5 in the supine position with NEP -5 cmH2O (rs = -0.46, p < 0.05) in severe OSAH patients. Conclusion: The awake OSAH patients exhibit values of V,NEP0.5 and V,NEP1 lesser than those of awake snorers. The NEP technique, however, appears to have a limited usefulness as clinical tool for routine screening of the OSAH patients during wakefulness.