Characteristics and determinants of endurance cycle ergometry and six-minute walk distance in patients with COPD

Background: Exercise tolerance can be assessed by the cycle endurance test (CET) and six-minute walk test (6MWT) in patients with Chronic Obstructive Pulmonary Disease (COPD). We sought to investigate the characteristics of functional exercise performance and determinants of the CET and 6MWT in a large clinical cohort of COPD patients. Methods: A dataset of 2053 COPD patients (43% female, age: 66.9 +/- 9.5 years, FEV1% predicted: 48.2 +/- 23.2) was analyzed retrospectively. Patients underwent, amongst others, respiratory function evaluation; medical tests and questionnaires, one maximal incremental cycle test where peak work rate was determined and two functional exercise tests: a CET at 75% of peak work rate and 6MWT. A stepwise multiple linear regression was used to assess determinants. Results: On average, patients had impaired exercise tolerance (peak work rate: 56 +/- 27% predicted, 6MWT: 69 +/- 17% predicted). A total of 2002 patients had CET time of duration (CET-T-end) less than 20 min while only 51 (2.5%) of the patients achieved 20 min of CET-T-end. In former patients, the percent of predicted peak work rate achieved differed significantly between men (48 +/- 21% predicted) and women (67 +/- 31% predicted). In contrast, CET-T-end was longer in men (286 +/- 174 s vs 250 +/- 153 s, p < 0.001). Also, six minute walking distance (6MWD) was higher in men compared to women, both in absolute terms as in percent of predicted (443 m, 67% predicted vs 431 m, 72% predicted, p < 0.05). Gender was associated with the CET-T-end but BMI, FEV1 and FRC were related to the 6MWD highlighting the different determinants of exercise performance between CET and 6MWT. Conclusions: CET-T-end is a valuable outcome of CET as it is related to multiple clinical aspects of disease severity in COPD. Gender difference should temper the interpretation of CET.