RELATIONSHIP BETWEEN THE SITE OF AIR-FLOW LIMITATION AND LOCALIZATION OF THE BRONCHODILATOR RESPONSE IN ASTHMA

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Abstract
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 (.DELTA..ovrhdot.VEmax50) after breathing 80% He-20% O2 (He-O2) was reduced (P < 0.001). Prebronchodilator values of .DELTA..ovrhdot.VEmax50 correlated linearly with .DELTA..ovrhdot.VEmax50 breathing air (r [correlation coefficient = .+-. 0.68, P < 0.001). Airflow limitation becomes more peripheral as asthma becomes more severe. After the bronchodilator administration, the results of routine pulmonary function studies improved; .DELTA..ovrhdot.VEmax50 increased or decreased, depending on the prebtonchodilator values. Density-dependence tended to increase in subjects with low prebronchodilator values of .DELTA..ovrhdot.VEmax50 and decrease in subjects with high prebronchodilator values of .DELTA..ovrhdot.VEmax50. Predominant sites of bronchodilatation in asthmatics are related to the prebronchodilator sites of airflow limitation.