Impulse oscillometry for estimation of airway obstruction and bronchodilation in adults with mild obstructive asthma

Background: Clinical validity of impulse oscillometry (IOS) for the evaluation of airway obstruction and bronchodilation is a controversial issue in adults with asthma. Methods: This study enrolled 195 outpatients from October 1998 to October 2004. We performed IOS in 158 asthmatic adults, including 70 asthmatic adults with a forced expiratory volume in 1 second (FEV₁) reversibility (group 1), 88 asthmatic adults with hyperresponsiveness to methacholine or sputum eosinophilia (group 2) who did not meet the FEV, criteria, and 37 nonasthmatic adults (group 3). Results: Baseline respiratory resistance at 5 Hz (R₅), respiratory resistance at 10 Hz, frequency dependency of resistance (R_{5 to 20}), and resonance frequency were discriminative between asthmatic patients and nonasthmatic patients. The IOS parameters were decreased after bronchodilation in both asthmatic groups compared with the nonasthmatic group. Among these patients, R₅ and R_{5 to 20} were the most discriminative parameters for evaluation of bronchodilation. Approximately one third of the patients with positive methacholine challenge test results or sputum eosinophilia manifested bronchodilation evaluated by these IOS parameters. Overall sensitivities of these parameters were comparable to FEV₁ for diagnosis of bronchodilation in 158 asthmatic adults. Logistic regression analysis showed that R_{5 to 20} was the most reliable parameter for prediction of R₅ reversibility for all asthmatic adults. Conclusions: IOS may complement the estimation of obstruction and bronchodilation for asthmatic adults. Its discriminative power for airway obstruction and sensitivities for bronchodilation were comparable to FEV₁.