Effect of methacholine induced bronchoconstriction on the spectral characteristics of breath sounds in asthma.

Abstract

Analysis of breath sounds by digital techniques offers an attractive non-invasive method of monitoring changes in airway calibre. Asthmatic breath sounds have been analysed and related to changes in forced expiratory volume in one second (FEV1). Bronchoconstriction was induced with methacholine in six asthmatic subjects on two occasions and changes in FEV1 and breath sound spectra were measured. Audible wheeze appeared after a mean (SE) fall in FEV1 of 35% (6.3%) but the level was not reproducible within patients. The mean and median frequency of the spectra of breath sounds correlated with the percentage of predicted FEV1 (r = -0.5 and -0.6 respectively; p < 0.001). Inclusion of the quartile frequencies in a stepwise multiple regression reduced the residual variance by a further 9%. Detecting changes in airway calibre by this method of sound analysis so far produces qualitative data only and will not yield quantitative data in individual patients.