on thespectral characteristics ofbreath sounds inasthma

BackgroundAnalysis ofbreathsounds bydigital techniques offers an attractive non-invasivemethod of monitoring changesin airwaycalibre. Asthmatic breathsoundshavebeenanalysedand related tochangesinforcedexpiratory volumeinone second(FEVy). MethodsBronchoconstriction was inducedwithmethacholine insixasthmatic subjects on twooccasions andchangesin FEV,and breathsoundspectrawere measured. ResultsAudible wheezeappeared after a mean (SE)fall inFEV,of35%(6-3%) but thelevelwas not reproducible within patients. The mean and median frequency ofthespectraofbreathsounds correlated withthepercentageofpredictedFEV, (r= -0 5 and -0-6 respectively; p < 0^001). Inclusion ofthe quartile frequencies ina stepwise multiple regression reducedthe residual variance bya further 9%. ConclusionDetecting changesinairway calibreby thismethodofsound analysis so farproducesqualitative data onlyandwillnotyieldquantitative data inindividual patients. (Thorax 1992;47:680-683) Breath soundanalysis wouldoffer anattractive non-invasive methodofmonitoring changes in airway calibre ifthesoundswere shownto relate reproducibly toindices ofairflow limitation. Thistoolcould proveespecially useful in