Lung Sound Analysis and Airway Inflammation in Bronchial Asthma

Background: Our previous study on lung sound analysis (LSA) revealed that the expiration-to-inspiration sound power ratio in a low-frequency range (E/I LF) was increased in patients with bronchial asthma, even when they have no wheezes.

Objective: We also monitored the expiration-to-inspiration sound power ratio in a mid-frequency range (E/I MF) and the mid- to low-frequency sound power ratio for inspiration and expiration (ie, I MF/LF and E MF/LF, respectively) using a new software program to examine which parameter is most suitable as an index of airway inflammation in patients with asthma.

Methods: A study was conducted in 31 patients with mild-to-moderate bronchial asthma to examine potential correlations of LSA parameters (E/I LF, E/I MF, I MF/LF, and E MF/LF) with spirogram parameters, airway hyperresponsiveness (PC20), fractional exhaled nitric oxide (NO), and sputum eosinophils.

Results: E/I LF was significantly correlated with airway narrowing (forced expiratory volume in 1 second [FEV1.0]/forced vital capacity [FVC]%: r = -0.50, maximal expiratory flow at 50% [V50],%pred: r = -0.50) and peripheral airway inflammation (alveolar NO: r = 0.36, eosinophils in peripheral sputum: r = 0.41). E/I MF was significantly correlated with airway narrowing (FEV1.0/FVC%: r = -0.46, V50,%pred: r = -0.49), airway inflammation (bronchial NO: r = 0.43, alveolar NO: r = 0.47, eosinophils in peripheral sputum: r = 0.50), and airway hyperresponsiveness (logPC20: r = -0.49). E MF/LF was significantly correlated with airway inflammation (NO: r = 0.36, eosinophils in sputum: r = 0.40) and airway hyperresponsiveness (logPC20: r = -0.40). I MF/LF was not significantly correlated with any parameters.

Conclusions: Among the 4 LSA parameters investigated, E/I MF demonstrated the highest correlation with airway inflammation, and also with bronchial hyperresponsiveness.