Published Online: October 4, 2014
Persistent airway inflammation in bronchial asthma enhances airway hyper-responsiveness and causes airway narrowing, and is an important factor in the diagnosis and evaluation of the effects of treatment in asthmatic patients. Degree of airway inflammation is currently assessed by 1) performing a bronchial biopsy and bronchial lavage with a fiberoptic bronchoscope, both of which are invasive, 2) by inducing sputum using a hypertonic saline inhalation, which is cumbersome, 3) and by analyzing exhaled breath condensate, or measuring exhaled nitric oxide, which is expensive. If airway inflammation in bronchial asthma can be estimated with a lung sound analysis, which can be performed repeatedly and noninvasively, this tool could be very useful for clinical use. However, this method has not yet been thoroughly evaluated.
In an article recently published in The Journal of Allergy and Clinical Immunology: In Practice, Terufumi Shimoda and colleagues suggest the possibility that a new lung sound analysis can evaluate the eosinophilic airway inflammation in asthmatics, even in those without symptoms.
Using a sound spectrometer, the authors analyzed the recorded lung sounds from 36 asymptomatic asthmatic patients, as well as 14 healthy people. The recorded sounds were analyzed using a mathematical formula involving the sound power during expiration and the sound power during inspiration because expiratory sound power is positively correlated with sputum eosinophils, and inspiratory sound power is correlated inversely. The relationship of the calculated index to airway eosinophilic inflammation was analyzed, and the best cutoff value for predicting airway eosinophilic inflammation was determined.
The calculated index from the lung sound analysis was higher in the asthmatic patients with increased sputum eosinophils than in those without increased sputum eosinophils (0.45 (0.24) vs. 0.20 (0.12), p < 0.001), or in the healthy subjects (0.25 (0.10), p=0.003). A multiple regression analysis showed that the sputum eosinophil ratio and FeNO were independently correlated with the calculated index (respectively p=0.0003 and 0.032). For the prediction of increased sputum eosinophils and increased fractional exhaled nitric oxide levels, the index thresholds of 0.29 and 0.30 showed sensitivities of 0.80 and 0.74 and specificities of 0.83 and 0.77, respectively.
It may be possible to evaluate asthmatic control with this new, non-invasive method for evaluating lung sounds, but further studies will be necessary to confirm this.
The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.