Relationship Between the Site of Airflow Limitation and Localization of the Bronchodilator Response in Asthma1,2

In an effort to determine the relationship between the major sites of airflow limitation and bronchodilator action, physiologic studies were performed in 65 asthmatics before and after the administration of isoproterenol, metaproterenol, or terbutaline. Before the administration of a bronchodilator, the results of routine pulmonary function tests were abnormal; the mean increment in maximal expiratory flow at 50% of forced vital capacity after breathing 80% helium-20% oxygen (He-O2) was reduced (p < 0.001). Prebronchodilator values of correlated linearly with breathing air (r = + 0.68, p < 0.001). These data suggested that airflow limitation becomes more peripheral as asthma becomes more severe. After the bronchodilator administration, the results of routine pulmonary function studies improved; either increased or decreased, depending upon the prebronchodilator values. Density-dependence tended to (1) increase in subjects with low prebronchodilator values of , and (2) decrease in subjects with high prebro...