CHANGES IN FREQUENCY-SPECTRA OF BREATH SOUNDS DURING HISTAMINE CHALLENGE TEST IN ADULT ASTHMATICS AND HEALTHY CONTROL SUBJECTS

Air-flow standardized breath sounds were recorded at the chest and at the trachea during histamine challenge test and after subsequent bronc hodilation in 12 asthmatics and 6 healthy controls for spectral analys is, to be compared with simultaneous changes in spirometric variables. Of all the lung sound variables measured, the changes in median frequ ency of the power spectrum (F50) of tracheal expiratory sounds were fo und to correlate best (r = -0.853, p < 0.0001) with changes in FE(1). The increase of F50 during histamine challenge was significantly large r in asthmatics than in healthy control subjects (p < 0.005). The prov ocative dose of histamine inducing a decrease of 15 percent in FEV(1) (PD15FEV(1)) and the provocative dose causing an increase of 30 percen t in tracheal expiratory F50 (PD30F50) were significantly related (r = 0.754, p = 0.012). In asthmatics, the breath sound frequency distribu tion in terms of median frequency reflected acute changes in airways o bstruction with high sensitivity and specificity. The present method f or breath sound analysis can be applied for patients with limited coop eration during bronchial challenge tests.