The Use of Criteria for Reversibility and Obstruction to Define Patient Groups for Bronchodilator Trials

Abstract

Multiple criteria for obstruction and reversibility are being used at present to define patient populations for bronchodilator studies. In order to establish whether the use of different criteria would result in variation in results, we evaluated 4 criteria for obstruction and found that the outcome of a bronchodilator trial, mean response, will depend on the definition of obstruction used. The obstruction criteria evaluated were: (1) FEV < lower 95% confidence limit (CL) of predicted, (2) FEV1/FVC% < lower 95% CL, (3) FEV1 between 500 and 1,500 ml, and (4) FEV1 < 60% of predicted. Patients selected by criterion (1) had 8.9% FEV1 response, whereas those selected by criterion (3) had 14% FEV1 response. This difference resulted mostly from the difference in the degree of obstruction among the groups as well as the effect of regression to the mean compounded by calculating the results as percent of baseline. Also, it appears the use of obstruction criteria based on the absolute value of the FEV1 or on predic...