Lung sound analysis can detect airway inflammation in asthma patients during attack-free period

Published Online: March 2016

Bronchial asthma is a chronic inflammatory disease with airway inflammation even when the respiratory function is normal and no wheezing is heard. Airway inflammation is assessed primarily by fractional exhaled nitric oxide (FeNO) and induced sputum examination. Computer-aided lung sound analysis (LSA) is capable of analyzing subtle changes in sounds that are inaudible on auscultation but detect the presence of airway inflammation.

We investigated whether new LSA-based parameters are useful in detecting airway inflammation in asthma patients during attack-free periods. Analysis was conducted in a single breathing cycle of entire inspiration and expiration, under the definitions of a low-frequency (LF) range between 100 and 200 Hz and a mid-frequency (MF) range between 200 and 400 Hz. Four LSA parameters used in the analysis were: the expiration-to-inspiration sound power ratio in a low-frequency range (E/I LF), the expiration-to-inspiration sound power ratio in a mid-frequency range (E/I MF), the expiration sound power ratio in a low-frequency range to that in a mid-frequency range (E LF/MF), and the inspiration sound power ratio in a low-frequency range to that in a mid-frequency range (I LF/MF). These four LSA parameters were examined for correlations with FeNO and/or induced sputum eosinophil percentage to determine which parameter is most suitable as an indicator of airway inflammation in asthmatic patients, including the location of inflammation in the airway.

Of the four parameters (E/I LF, E/I MF, I MF/LF, and E MF/LF), E/I MF was the best indicator of central and peripheral airway inflammation. E/I MF was significantly correlated with airway narrowing, FeNO, airway inflammation, eosinophils in peripheral sputum, and airway hyperresponsiveness.

LSA is a simple and noninvasive examination, which can detect airway inflammation in asthmatic patients during attack-free periods.

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.

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