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

Abstract

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 > or = 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 < or = 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.

Figure 1

Supine tidal flow-volume curves (control and during NEP of -5 cmH₂O) and corresponding expiratory flow-time curves (only during NEP) in representative subjects of the different groups. The hatched areas under the flow measure the volume exhaled in the first 0.5 sec. (V,NEP_0.5) and 1 sec. (V,NEP₁) after NEP application.

Figure 2

Individual values of V,NEP _0.5 in seated and supine position at two NEP levels in patients with obstructive sleep apnea-hypopnea (OSAH) (circles, white for mild-to-moderate OSAH and black for severe OSAH), snorers (Sn) (triangles) and controls (C) (squares). *p<0.01 vs C; **p<0.001 vs C; #p<0.05 vs Sn.

Figure 3

The receiver-operating characteristics (ROC) curves are shown for V,NEP_0.5 values during NEP (-5 cmH₂O) both in supine (continuous line) and seated (dashed line) position in 34 patients with OSAH and 21 subjects without OSAH. The area under the ROC curves reflects the ability of V,NEP_0.5 to distinguish subjects without and with OSAH (AHI>5).

Figure 4

Relationship between AHI and V,NEP_0.5 in the supine position during NEP (-5 cmH₂O) in OSAH patients (white circles = mild-to-moderate OSAH; black circles = severe OSAH). The regression line refers only to severe OSAH patients.