Background: Lung sound analysis (LSA) has been reported to be useful for predicting airway obstruction and inflammation in patients with bronchial asthma.
Objectives: We examined whether the exhalation-to-inhalation sound pressure ratio in the middle frequency range (200-400 Hz) (E/I MF) is useful for monitoring therapy in patients with asthma.
Methods: The study population comprised 84 patients with mild to moderate asthma whose LSA data were available before and after 1 year of daily treatment with (budesonide 800 μg). We analyzed whether the E/I MF before and after treatment was associated with the fractional exhaled nitric oxide (FeNO) level, sputum eosinophil percentage, respiratory function, and airway hyperresponsiveness.
Results: Prior to treatment with budesonide, the E/I MF was significantly correlated with respiratory function, airway hyperresponsiveness, FeNO, and sputum eosinophil percentage. The cutoff values for the E/I MF to detect the abnormalities of respiratory function, FeNO, and sputum eosinophil percentage were 0.367, 0.358, and 0.363, respectively. With respect to the reference value, the E/I MF improved significantly in patients whose respiratory function and FeNO benefited from therapy with budesonide compared with patients whose respiratory function did not benefit from budesonide (odds ratios of 6.39 and 4.78, respectively). According to the multivariate analysis, patients whose E/I MF did not improve had a longer history of smoking (P=.038), poorer posttreatment respiratory function (P=.028), and higher posttreatment FeNO (P=.0095).
Conclusion: Similar to respiratory function and FeNO, E/I MF based on LSA is a useful indicator for monitoring the efficacy of therapy in asthmatic patients.

Key words: Bronchial asthma, Fractional exhaled nitric oxide, Induced sputum, Inhaled corticosteroid, Lung sound analysis