LAUSR

Introduction: The constant workrate test (CWRT) can be used to estimate improvement after pulmonary rehabilitation (PR) in patients with COPD. The initial endurance time (Tlim) should be within 180 and 480 seconds, but the consequences of a Tlim outside this range on the prognostic value of the CWRT have not been studied. We aimed at evaluating the effect of the initial Tlim on the predictive value of the CWRT. Methods: We studied COPD patients that had completed an 8-week PR program in our centre in 2014. All patients performed a pre- and post-PR CWRT on ergocycle at 80% of the maximal workrate reached on a previous incremental exercise test. Physiological characteristics and changes in COPD Assessment Test scores (ΔCAT) and endurance time (ΔTlim) after PR were compared in patients with an initial Tlim in the recommended range and those that did not. Results: 92 patients were included (52 males). Mean forced expiratory volume in 1 second (FEV1) was 50±16 percent predicted. 28 patients (30%) had initial Tlim outside the recommended range. Age, sex, FEV1, diffusion capacity, ΔCAT, ΔTlim and exacerbation rates pre- and post-RP were similar between the two groups (all p>0.05). However, there was a significant correlation between ΔTlim and ΔCAT in patients that had an initial Tlim in the recommended range (r=-0.44, p=0.01), but not in those that did not (r=0.27, p=0.20). Conclusion: Tlim values outside of the recommended range are frequent, and impair the ability of the CWRT to predict improvement in disease activity / quality of life following PR. This strengthens the recommendation of aiming at an initial Tlim value of 180-480 seconds.