Forced Oscillation Technique vs Spirometry to Assess Bronchodilatation in Patients With Asthma and COPD

The forced oscillation technique (FOT) is a noninvasive test used to characterize the mechanical impedance of the respiratory system. The aim of the study was to compare the changes in respiratory conductance (Grs) measured with FOT to those in FEV 1 in 22 patients with asthma and 20 patients with chronic obstructive pulmonary diseases (COPD) after salbutamol inhalation. FEV 1 and Grs indexes, computed as the ratio of the difference between postbronchodilator and prebronchodilator values over the predicted value, were used to express reversibility of airway obstruction. After inhalation of salbutamol in cumulative doses up to 1,200 µ g in ten patients of each group, FEV 1 and Grs indexes showed parallel changes, and most of the increase was observed after the first dose of 200 µ g of salbutamol for the two indexes. In all the 42 patients, we found a linear relationship between the two indexes after inhalation of 200 µ g of salbutamol (r=0.7, p 1 and Grs indexes in terms of sensitivity and specificity for identifying asthmatics among patients with COPD: using a 10% change as the cut-off value, these indexes proved of similar value (sensitivity, 0.91 and 0.95; specificity, 0.95 and 0.85, respectively). We conclude that the use of FOT can be considered as an alternative to forced expiration for detecting bronchodilatation in asthmatics and patients with COPD.