Background: The expiration-to-inspiration sound power ratio in a midfrequency range (E/I MF), a parameter of lung sound analysis (LSA), has been reported to be useful as an index of airway inflammation in patients with bronchial asthma. However, the E/I MF reflects airway narrowing caused by airway inflammation, and there is thus concern that it may not be an index of airway eosinophilic inflammation itself.
Methods: A total of 131 patients with bronchial asthma were classified into four groups according to the presence or absence of airway narrowing and airway inflammation to examine whether the E/I MF could serve as an index of airway inflammation.
Results: The E/I MF was significantly higher in patients with a normal forced expiratory volume in one second (FEV1) and high fractional exhaled nitric oxide (FeNO), those with a low FEV1 and normal FeNO, and those with a low FEV1 and high FeNO than in those with a normal FEV1 and normal FeNO (p < 0.05-0.01). In particular, the E/I MF was high even in the patients who had no airway narrowing but had airway inflammation (p < 0.01). The results of multivariate analysis of factors involved in FeNO in patients with a normal FEV1 revealed that the E/I MF was an independent factor (p = 0.0281).
Conclusion: The E/I MF is a useful index of airway inflammation in the treatment of asthma, regardless of the presence or absence of airway narrowing.
Keywords: E/I MF; FeNO; airway inflammation; bronchial asthma; lung sound analysis.
© 2019 Shimoda et al.