Negative Expiratory Pressure in the Assessment of Bronchodilator Response: Comparison of Spirometry and the Interrupter Method

Abstract

The negative expiratory pressure (NEP) method offers a simple and rapid assessment of expiratory flow limitation (EFL) during tidal respiration. This study compared the value of NEP in the assessment of the bronchodilator test (BDT) with those of spirometry and the interrupter method. Thirty two patients referred to the lung function laboratory for BDT were investigated. All patients underwent spirometry, interrupter airway resistance (Rint) and NEP measurements in the sitting position before and after inhalation of 500 microg of terbutaline. A positive BDT was defined as an increase in the forced expiratory volume in 1 second (FEV1) of > or = 12%. The ratio of FEV1 to forced vital capacity (FVC) was less than 70% in 21 (65.6%) patients, but EFL as demonstrated by NEP (EFL-N) was present in only 10 patients (31.3%). The baseline EFL-N was only weakly correlated with FEV1 (r = -0.36, p = 0.04), but not with Rint or FEV1/FVC. Among the 14 patients with positive BDT results, the change in FEV1 was correlated with the change in Rint (r = -0.69, p < 0.01), but not with the change in EFL-N. These data suggest that, compared with spirometry and the interrupter method, NEP applied in the sitting position is not sensitive in the assessment of bronchodilator response in patients with obstructive airway disorders.