Optimizing baseline constant work rate exercise test duration for COPD bronchodilator studies

Constant work rate (CWR) cycle ergometer testing has been used to evaluate long acting bronchodilator effects (BD) on exercise tolerance. It is recommended that baseline CWR duration be restricted to between 3 and 8 min. We evaluated this recommendation using a database assembled by the COPD Biomarker Qualification Consortium (CBQC). 8 published studies yielded 1349 COPD patient (FEV1=49±14 %pred.) responses studying effects of ~6 wks of BD on CWR duration in tests performed at 75-80% of peak incremental WR. Figure shows a wide range of baseline durations (left); for tests >11 min, duration increase (center) declines and SD (right) increases. Table shows responses for all subjects, those restricted to 3-8 min and to 2-11 min. Also shown is sample size needed in a trial for a cohort with these characteristics and % of subjects requiring re-testing at an altered WR to achieve the desired range. Restricting baseline duration range greatly decreases sample size required. The 2-11 min limit, compared to the 3-8 min limit, yields a much lower fraction of subjects needing repeat tests. A 2-11 min baseline duration limit is proposed for future BD studies.