Comparison of different exercise tests in assessing outcomes of pulmonary rehabilitation

Common modalities of clinical exercise testing for outcome measurement after pulmonary rehabilitation (PR) include walk tests, progressive cycle ergometry, and cycle endurance testing. We hypothesized that patients' responses to PR, as measured by those 3 tests, are differentially correlated, and we designed a study to investigate the tests' capacity to detect changes after PR.

We prospectively tested 37 male patients with stable chronic obstructive pulmonary disease who completed a comprehensive 6-week PR program that included supervised exercise training that emphasized steady-state lower-limb aerobic exercise. Before and after the PR program the patients underwent 6-minute walk test, progressive cycle ergometry, and cycle endurance testing (at 80% of the peak work rate achieved during progressive cycle ergometry). The exercise performance indices of interest were the peak oxygen uptake (VO2max) and maximum work-rate (Wmax) during progressive cycle ergometry, the cycling endurance time, and the 6-minute walk distance (6MWD).

After PR there were statistically significant improvements in 6MWD (16%, p <0.001), VO2max (53%, p=0.004), Wmax (30%, p=0.001), and cycling endurance time (144%, p <0.001). The changes in VO2max and Wmax were significantly correlated (r=0.362, p=0.027), as were the changes in endurance time and Wmax (r=0.406, p=0.013). There was no significant correlation between changes in any other exercise index.

Among the frequently used exercise tests in PR, the most responsive index is the endurance time. The correlation between the post-PR changes in the various exercise indices is poor.