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The association between lung sound alterations and airways obstruction has long been recognized in clinical practice, but the precise pathophysiological mechanisms of this relationship have not been determined. Therefore, we examined the changes in lung sounds at well-defined levels of methacholine-induced airway narrowing in eight normal and nine asthmatic subjects with normal baseline lung function. All subjects underwent phonopneumography at baseline condition and at &gt; or = 20% fall in forced expiratory volume in one second (FEV1), and in asthmatic subjects also at &gt; or = 40% fall in FEV1. Lung sounds were recorded at three locations on the chest wall during standardized quiet breathing, and during maximal forced breathing. Airflow-dependent power spectra were computed using fast Fourier transform. For each spectrum, we determined the intensity and frequency content of lung sounds, together with the extent of wheezing. The results were analysed using analysis of variance (ANOVA). During acute airway narrowing, the intensity and frequency content of the recorded sounds, as well as the extent of wheezing, were higher than at baseline in both groups of subjects. At similar levels of obstruction, both the pitch and the change in sound intensity with airflow were higher in asthmatics than in normal subjects. Wheezing, being nondiscriminative between the subject groups at baseline, was more prominent in asthmatics than in normal subjects at 20% fall in FEV1. We conclude that, at given levels of acute airway narrowing, lung sounds differ between asthmatics and normal subjects. This suggests that airflow-standardized phonopneumography is a sensitive method for detecting abnormalities in airway dynamics in asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of methacholine-induced acute airway narrowing on lung sounds in normal and asthmatic subjects