Assessing the impact of pulmonary rehabilitation on functional status in COPD

Background: The optimal way of assessing the impact of pulmonary rehabilitation on functional status in chronic obstructive pulmonary disease (COPD) is currently unknown. The minimal clinically important difference for the constant work rate cycling exercise test also needs to be investigated to facilitate its interpretation. A study was undertaken to evaluate the changes in the 6-min walking test and in the constant work rate cycle endurance test immediately following and 1 year after pulmonary rehabilitation, together with the importance of these changes in terms of health status in patients with COPD. Methods: Patients with COPD of mean (SD) age 65 (8) years and mean (SD) forced expiratory volume in 1 s (FEV1) 45 (15)% predicted were recruited from a multicentre prospective cohort study and evaluated at baseline, immediately after a pulmonary rehabilitation programme (n= 157) and at 1 year (n= 106). The 6-min walking test and the cycle endurance test were performed at each evaluation. Health status was evaluated with the St George Respiratory Questionnaire. Results: Following pulmonary rehabilitation, cycle endurance time increased (198 (352) s, p<0.001) and stayed over baseline values at 1 year (p<0.001). The 6-min walking distance also showed improvements following rehabilitation (25 (52) m, p<0.001) but returned to baseline values at the 1-year follow-up. Changes in cycle endurance time were more closely associated with changes in health status than with the 6-min walking test. An improvement of 100-200 s in the cycle endurance time was associated with clinically meaningful changes in the St George Respiratory Questionnaire scores. Conclusions: The cycle endurance test was more responsive than the 6-min walking test in detecting improvement in exercise tolerance following pulmonary rehabilitation, and was also better correlated with improvements in health status. An improvement in the cycle endurance time of 100-200 s appeared to be clinically meaningful.