Critical Velocity Determined by a Non-Exhaustive Method in Subjects With COPD

Exercise training is an effective and low-cost tool for COPD rehabilitation. Thus, validating a non-exhaustive method to determine a patient's anaerobic threshold would be a very interesting tool in practical settings. We aimed to test the reproducibility of critical velocity values determined in a non-exhaustive manner (CV_NE) and tolerance for exercise performed at this physiological marker in subjects with COPD.

Twelve subjects with COPD were evaluated in this cross-sectional study. The study was divided into 2 phases: Phase A consisted of reproducibility of CV_NE for subjects with COPD, and Phase B determined the tolerance for exercise tests performed at this physiological marker.

The proposed protocol for determining CV_NE presented fair reproducibility according to blood lactate concentrations (intraclass correlation coefficient = 0.58). However, we cannot consider that the tests were reproducible due to the wide CI (0.03-0.85). Furthermore, moderate and strong correlations were observed between the CV_NE determined by lactate concentration, by oxygen consumption (V̇_O ) (r = 0.66), and by heart rate (r = 0.88). However, a high limit of agreement was observed ±1.45 km/h and ±1.55 km/h, respectively. In the tolerance for exercise test, none of the subjects presented lactate destabilization, whereas 3 tests were interrupted by oxygen saturation decline and 1 test was interrupted by hemodynamic instability.

Although most of the subjects presented good tolerance for exercise at CV_NE, fair levels of reproducibility were observed in subjects with COPD, even using lactate. Thus, the use of CV_NE determined through double 3-min efforts should be considered with caution.