Abstract

The aim of this study was to define the most useful index of expressing bronchodilator response and to distinguish between asthma and COPD. A prospective study was carried out of bronchodilator response in 142 asthmatics and 58 COPD patients in a university hospital. Reversibility was expressed as: 1. absolute change (dabs); 2. % of initial (A %init); 3. % of predicted (A %pred) and 4. % of maximum possible response (A %max). Dependence on forced expirations volume in 1 set (FEV,) as % of predicted and sensitivity and specificity for diagnosis of asthma were established. A relationship between dabs and initial FEVl was not found in asthma (dabs vs. % initial FEV1. r= 0.07) or COPD (I = 0.02). A%pred did not show a correlation in asthma (v=O.lO) or COPD (u= 0.06). A?/oinit was dependent on the baseline value in asthma (r=0.38 , Pi 0,001 ) but not in COPD (r=O.lS , P=n.s.). dmax was dependent in both. The combination of best sensitivity and specificity to separate asthma and COPD was obtaiced with dabs (70.4 or 70.6%). The worst specificity for asthma diagnosis was obtained with A% init (50%). The best likelihood ratios were obtained with dabs and A%pred and the worst likelihood ratio with A%init A%init is not recommended as an index for differential diagnosis between asthma and COPD; 2) A%init overscores bronchodilator response in patients with low FEV,. The independence of each bronchodilator response index should be verified in clinical trials for each selected sample.

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