The Correlation between Lung Sound Distribution and Pulmonary Function in COPD Patients

BACKGROUND Regional lung sound intensity in chronic obstructive pulmonary disease (COPD) patients is influenced by the severity and distribution of emphysema, obstructed peripheral airways, and altered ribcage and diaphragm configurations and movements due to hyperinflation. Changes in the lung sound distribution accompanied by pulmonary function improvements in COPD patients were observed after bronchodilator inhalation. We investigated the association of lung sound distribution with pulmonary functions, and the effects of emphysematous lesions on this association. These studies were designed to acquire the basic knowledge necessary for the application of lung sound analysis in the physiological evaluation of COPD patients. METHODS Pulmonary function tests and the percentage of upper- and lower-lung sound intensity (quantitative lung data [QLD]) were evaluated in 47 stable male COPD patients (54 - 82 years of age). In 39 patients, computed tomography taken within 6 months of the study was available and analyzed. RESULTS The ratio of lower QLD to upper QLD showed significant positive correlations with FEV1 %predicted (%FEV1; ρ=0.45, p<0.005) and MEF50 %predicted (%MEF50; ρ=0.46, p<0.005). These correlations were not observed in COPD patients with dominant emphysema (% low attenuation area >40%, n=20) and were stronger in less emphysematous patients (n=19, %FEV1; ρ=0.64, p<0.005, %MEF50; ρ=0.71, p<0.001). CONCLUSIONS In COPD patients, the ratio of lower- to upper-lung sound intensities decreased according to the severity of obstructive changes, although emphysematous lesions considerably affected lung sound distribution.