Effects of indacaterol versus tiotropium on respiratory mechanics assessed by the forced oscillation technique in patients with chronic obstructive pulmonary disease

The forced oscillation technique (FOT) can measure respiratory mechanics and has attracted attention in chronic obstructive pulmonary disease (COPD). We aimed to evaluate the effects of only indacaterol and tiotropium monotherapies on airflow limitation and respiratory impedance. Pulmonary function tests, COPD assessment test (CAT), and multifrequency FOT with MostGraph-01 were performed at the beginning and after 8 weeks of treatment with indacaterol or tiotropium. The resistance index, resistance at 5 Hz (R5), resistance at 20 Hz (R20), reactance index, reactance at 5 Hz (X5), resonant frequency (Fres), and low-frequency reactance area (ALX) were determined at whole-breath, inspiratory, and expiratory phases. Eighty-two patients (mean age: 73 years; mean forced expiratory volume in 1 second (FEV1): 61.6%±19.0% predicted) were randomized to indacaterol or tiotropium treatment. Both bronchodilators improved airflow limitation, with mean trough improvements in FEV1 of 165 mL and 80 mL in the indacaterol and tiotropium groups, respectively. The CAT score decreased in the indacaterol group (P<0.001; 11.2±6.6 to 7.5±5.6). Compared with tiotropium, indacaterol significantly improved FEV1, percent predicted FEV1, and CAT score (P=0.042, P=0.008, and P=0.027, respectively). For respiratory impedance, indacaterol and tiotropium changed R5, X5, Fres, and ALX at whole-breath, inspiratory, and expiratory phases. In the indacaterol group, the changes in R5, R5-R20, X5, Fres, and ALX were significantly correlated with the changes in FEV1. The use of the FOT may enable the evaluation of the effects of bronchodilators in addition to FEV1-indicated therapeutic effects in COPD.