Lung sound analysis helps localize airway inflammation in patients with bronchial asthma.

PURPOSE: Airway inflammation can be detected by lung sound analysis (LSA) at a single point in the posterior lower lung field. We performed LSA at 7 points to examine whether the technique could identify the location of airway inflammation in patients with asthma.

PATIENTS AND METHODS: Breath sounds were recorded at 7 points on the body surface of 22 asthmatic subjects. Inspiration sound pressure level ( I SPL ), expiration sound pressure level ( E SPL ), and the expiration-to-inspiration sound pressure ratio ( E/I ) were calculated in 6 frequency bands. The data were analyzed for potential correlation with spirometry, airway hyperresponsiveness (PC20 ), and fractional exhaled nitric oxide (FeNO).

RESULTS: The E/I data in the frequency range of 100-400 Hz ( E/I low frequency [LF], E/I mid frequency [MF]) were better correlated with the spirometry, PC20 , and FeNO values than were the I SPL or E SPL data. The left anterior chest and left posterior lower recording positions were associated with the best correlations (forced expiratory volume in 1 second/forced vital capacity: r =-0.55 and r =-0.58; logPC20 : r =-0.46 and r =-0.45; and FeNO: r =0.42 and r =0.46, respectively). The majority of asthmatic subjects with FeNO ≥70 ppb exhibited high E/I MF levels in all lung fields (excluding the trachea) and V 50 %pred <80%, suggesting inflammation throughout the airway. Asthmatic subjects with FeNO <70 ppb showed high or low E/I MF levels depending on the recording position, indicating uneven airway inflammation.

CONCLUSION: E/I LF and E/I MF are more useful LSA parameters for evaluating airway inflammation in bronchial asthma; 7-point lung sound recordings could be used to identify sites of local airway inflammation.