Role of ventilatory response to exercise in determining exercise capacity in COPD

The progression of chronic obstructive pulmonary disease (COPD) is generally associated with decreased exercise capacity. Differences in forced expired volume in 1 s (FEV1) among patients account for only a fraction of the variability in maximal oxygen consumption (VO2max). We hypothesized that variability in ventilatory response to exercise and in inspiratory mechanics and body mass index contributes importantly to variability in VO2max in this disease. We analyzed the files of 53 patients with established diagnosis of COPD who underwent a recent symptom-limited exercise test. We used inspiratory capacity and maximum inspiratory flow as measures of variability in inspiratory mechanics. The minute ventilation (VE) at the subject's VO2max was divided by the predicted in a normal subject at the same VO2 to obtain a ratio (VE,max/VE,pred). The ventilatory response during exercise provided the best correlation with peak VO2 (r = 0.62). FEV1 and inspiratory capacity also correlated with peak oxygen consumption but not as well as the ventilatory response (r = 0.49 and r = 0.46, respectively). Maximum inspiratory flow and body mass index showed only weak positive correlations (r = 0.23, not significant). The stepwise analysis generated the following equation: VO2max (%predicted) = (77.26 x VE,pred/VE,max) + 0.45 x FEV1 (%predicted) - 23.66; r = 0.76, P < 0.001. We conclude that variability in the ventilatory response during exercise is one of the main determinants of variability in exercise capacity in COPD patients.