Lung Sound Analysis Provides A Useful Index For Both Airway Narrowing And Airway Inflammation In Patients With Bronchial Asthma

Abstract

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:

• airway inflammation
• bronchial asthma
• E/I MF
• FeNO
• lung sound analysis

Acknowledgments

The authors would like to thank Miss Oda and Miss Kojima for their technical assistance and for performing the statistical analyses.

Abbreviations

LSA, lung sound analysis; FeNO, fractional exhaled nitric oxide; FEV_1, forced expiratory volume in one second; FVC, forced vital capacity; V₅₀ and V_25, maximal expiratory flow at 50% and 25%; E/I LF, the expiration-to-inspiration sound power ratio in a low-frequency range; E/I MF, the expiration-to-inspiration sound power ratio in a midfrequency range; PC_20, provocative concentration of acetylcholine causing a 20% decrease in FEV₁; COPD, chronic obstructive pulmonary disease; ICS, inhaled corticosteroid.

Author Contributions

TS designed the study, participated in the data analysis and wrote the manuscript. YO assisted in the data analysis. YN assisted in the lung sound analysis. RK assisted in the examinations. SA assisted in the design of the study and revised the manuscript. All authors contributed to data analysis, drafting or revising the article, gave final approval of the version to be published, and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.

Additional information

Funding

This study was supported by Fukuoka National Hospital research funding from 2011 to 2015.