In bronchial asthma, the ratio of expiration-to-inspiration sound power in a midfrequency range (E/I MF) may be a useful index in asthma treatment and in the detection of airway narrowing and inflammation, according to study results published in the Journal of Asthma and Allergy.

The E/I MF parameter of lung sound analysis has been found to be a useful index of airway inflammation in bronchial asthma; however, concern remains that although the E/I MF may be an index of airway narrowing that results from airway inflammation, it may not be an accurate index of airway inflammation itself in patients with bronchial asthma who use inhaled corticosteroid (ICS) treatment. The objective of this study was to determine whether the E/I MF may be an index of airway inflammation in bronchial asthma.

In this study, researchers evaluated 131 patients with bronchial asthma who were using ICS treatment and who were free of other respiratory disease complications. They stratified patients into 4 groups according to the presence or absence of airway narrowing and airway inflammation. Normal (N) airway narrowing was defined when forced expiratory volume in one second (FEV)₁/forced vital capacity (FVC) ≥70% and FEV₁ % of predicted value ≥80%, otherwise, the patient was classified as abnormal (A) airway function. Normal fractional exhaled nitric oxide (FeNO) in airway eosinophilic inflammation was defined as FeNO <38 ppb, and abnormal FeNO was defined as FeNO ≥38 ppb. 

The (N) FEV₁ and (N) FeNO group (NN) accounted for 54% of the cohort (n=71); the (N) FEV₁ and (A) FeNO group (NA) accounted for 22% (n=29); the (A) FEV₁ and (N) FeNO group (AN) accounted for 16% (n=21); and the (A) FEV₁ and (A) FeNO group (AA) accounted for 8% (n=10). Researchers compared patient characteristics and E/I MF values among all 4 groups.

Results revealed that patients in the NN group did not have airway narrowing or inflammation and had good asthma control. Patients in the NA group had high serum immunoglobulin E levels of 362 (interquartile range [IQR], 135-1283) IU/mL and high percentages of blood eosinophil (9.3%) and sputum eosinophil (3.5%). Patients in the AN group showed a long disease duration of 8 (IQR, 1-21.5) years, with a high sputum eosinophil percentage of 5% (IQR, 1.5%-16.5%) whereas patients in the AA group showed high patient age of 59 (IQR, 47.5-67.5) years and high percentages of blood and sputum eosinophil (8.3% and 10.3%, respectively). 

Compared with the NN group, the NA, AN, and AA groups had significantly increased airway hyperreactivity. The E/I MF was significantly higher in the NA, AN, and AA groups (P <.05-.01), and also high in patients with airway inflammation and without airway narrowing (P <.01). The E/I MF was also found to be an independent factor involved in FeNO in patients with normal FEV₁ (P =.0281).

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This study had limitations in that ICS treatments were introduced in various situations and the size of the cohort may have been too small.

The study researchers concluded that the E/I MF parameter may be a useful index of airway inflammation in asthma treatment regardless of whether patients have normal respiratory function or airway narrowing.

Reference

Shimoda T, Obase Y, Nagasaka Y, Kishikawa R, Asai S. Lung sound analysis provides a useful index for both airway narrowing and airway inflammation in patients with bronchial asthma. J Asthma Allergy. 2019;12:323-329.