RELATIONSHIP BETWEEN SITES OF AIR-FLOW LIMITATION AND SEVERITY OF CHRONIC AIR-FLOW OBSTRUCTION

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Abstract
Relationship between sites of airflow limitation and severity of chronic obstructive pulmonary disease was studied. Pre- and postbronchodilator physiologic testing was performed in 30 [human] subjects with chronic airflow obstruction (CAO). Pulmonary function, including the increase in maximal expiratory flow at 50% of vital capacity after He-O2 breathing (.DELTA..ovrhdot.VEmax50), was reduced before and after inhalation of 1.3 .mu.mg of metaproterenol. Significant correlations were present between values for .DELTA..ovrhdot.VEmax50 and measurements of expiratory flow (P < 0.001). In subjects with severe CAO (1 s forced expiratory volume .ltoreq. 1.2 l; percentage ratio of 1 s forced expiratory volume to forced vital capacity < 50%), .DELTA..ovrhdot.VEmax50 was always abnormally decreased. An inverse relationship was present between initial .DELTA..ovrhdot.VEmax50 and changes in .DELTA..ovrhdot.VEmax50 after inhalation of metaproterenol (P < 0.001). Apparently, the site of airflow limitation becomes progressively more peripheral as CAO worsens. Apparently, severe CAO is usually associated with peripheral sites of airflow limitation.