SLEEP DISORDERED BREATHING Operating characteristics of the negative expiratory pressure technique in predicting obstructive sleep apnoea syndrome in snoring patients

Background: This study examines the operating characteristics of the expiratory flow response to a negative pressure (NEP) applied to the mouth in the prediction of obstructive sleep apnoea syndrome (OSAS) in snoring patients. Methods: Two hundred and thirty eight patients with normal spirometric values were studied. Full laboratory polysomnography was performed and an NEP of 25 cm H2O was applied in the sitting and supine positions. Results: A significant correlation was found between the degree of flow limitation measured by NEP in both positions (expressed as the percentage of the expired tidal volume over which NEP induced flow did not exceed spontaneous flow) and the apnoea-hypopnoea index (AHI). This correlation was significantly higher in the supine position (p,0.0001) where an expiratory flow limitation cut off value of >27.5% of the tidal volume produced a sensitivity of 81.9% and a specificity of 69.1% in predicting OSAS. Conclusion: These findings show that the degree of instability of the upper airway measured by NEP is correlated with the severity of OSAS. NEP had moderate sensitivity and specificity and may be useful in predicting OSAS in a clinic based population.