Changes in inhaler inhalation acoustic features during induced bronchoconstriction: A pilot study

Asthma is a chronic respiratory disease affecting millions of people worldwide, and is consequently a major issue for global health. Exacerbations are acute events involving the worsening of asthma's primary respiratory symptoms and are a major cause of morbidity in asthma patients, largely due to the unpredictability of their onset. This study aimed to investigate the relationship between changes in acoustic features of inhaler inhalations and changes in forced expiratory volume in one second (FEV1) that occur during a simulated exacerbation, a bronchial challenge test (BCT). This is a clinical test that simulates an asthma exacerbation through the administration of a bronchoconstrictor agent. Eight patients indicated for a BCT were recruited for this study. Non-contact and tracheal microphones were employed to record Diskus™ inhaler inhalations throughout the course of a BCT. A spirometer was employed to measure inhaler peak inspiratory flow rate (PIFR). In patients responsive to the BCT (n=4), significant correlations between changes in FEV1 and acoustic features on both microphones existed, with fractal increment of Katz fractal dimension yielding the strongest correlation (R^2=0.58), and between FEV1 and PIFR (R^2=0.62). These findings suggest that inhaler inhalation acoustic features may assist in the early detection of exacerbations. Future research will determine whether this is the case in a larger cohort of patients with non-simulated exacerbations.