Abnormal lung sounds in patients with asthma during episodes with normal lung function.

Even in patients with clinically stable asthma with normal lung function, the airways are characterized by inflammatory changes, including mucosal swelling. In order to investigate whether lung sounds can distinguish these subjects from normal subjects, we compared lung sound characteristics between eight normal and nine symptom-free subjects with mild asthma. All subjects underwent simultaneous recordings of airflow, lung volume changes, and lung sounds during standardized quiet breathing, and during forced maneuvers. Flow-dependent power spectra were computed using fast Fourier transform. For each spectrum we determined lung sound intensity (LSI), frequencies (Q25%, Q50%, Q75%) wheezing (W), and W%. The results were analyzed by ANOVA. During expiration, LSI was lower in patients with asthma than in healthy controls, in particular at relatively low airflow values. During quiet expiration, Q25% to Q75% were higher in asthmatics than in healthy controls, while the change of Q25% to Q75% with flow was greater in asthmatic than in normal subjects. The W and W% were not different between the subject groups. The results indicate that at given airflows, lung sounds are lower in intensity and higher in pitch in asthmatics as compared with controls. This suggests that the generation and/or transmission of lung sounds in symptom-free patients with stable asthma differ from that in normal subjects, even when lung function is within the normal range. Therefore, airflow standardized phonopneumography might reflect morphologic changes in airways of patients with asthma.