Lung sound analysis can be an index of the control of bronchial asthma.
BACKGROUND
We assessed whether lung sound analysis (LSA) is a valid measure of airway obstruction and inflammation in patients with bronchial asthma during treatment with inhaled corticosteroids (ICSs).


METHODS
63 good adherence patients with bronchial asthma and 18 poor adherence patients were examined by LSA, spirometry, fractional exhaled nitric oxide (FeNO), and induced sputum. The expiration-to-inspiration lung sound power ratio at low frequencies between 100 and 200 Hz (E/I LF) obtained by LSA was compared between healthy volunteers and bronchial asthma patients. Next, post-ICS treatment changes were compared in bronchial asthma patients between the good adherence patients and the poor adherence patients.


RESULTS
E/I LF was significantly higher in bronchial asthma patients (0.62 ± 0.21) than in healthy volunteers (0.44 ± 0.12, p < 0.001). The good adherence patients demonstrated a significant reduction in E/I LF from pre-treatment to post-treatment (0.55 ± 0.21 to 0.46 ± 0.16, p = 0.002), whereas the poor adherence patients did not show a significant change. The decrease of E/I LF correlated with the improvement of FEV1/FVC ratio during the ICS treatment (r = -0.26, p = 0.04). The subjects with higher pre-treatment E/I LF values had significantly lower FEV1/FVC and V50,%pred (p < 0.001), and significantly higher FeNO and sputum eosinophil percentages (p = 0.008 and p < 0.001, respectively).


CONCLUSIONS
The E/I LF measurement obtained by LSA is useful as an indicator of changes in airway obstruction and inflammation and can be used for monitoring the therapeutic course of bronchial asthma patients.