Factors associated with improvement in breathing capacity during exercise in patients with chronic obstructive pulmonary disease.

Objectives: The aim of this study was to explore the relationship between resting pulmonary function indices and the ratio of minute ventilation at peak exercise to the maximal voluntary ventilation (VEmax/MVV) and to determine whether an improvement in breathing capacity during exercise (i.e. VEmax/MVV > 1) is associated with greater exercise capacity in patients with COPD.

Methodology: The results of pulmonary function tests and incremental, symptom-limited cardiopulmonary exercise testing in 84 patients with predominantly moderate to severe COPD were reviewed. Multiple linear regression analysis was applied to determine the relationship of VEmax/MVV with selected independent variables at rest. Multiple logistic regression was used to determine significant predictors of VEmax/MVV 1.

Results: FEV1/FVC and inspiratory capacity (IC) were the only variables among resting pulmonary function indices that were significant independent determinants of VEmax/MVV and the stepwise analysis generated the following equation: VEmax/MVV = (-1.05E-02 x FEV1/FVC) + (0.15 x IC) + 1.28; r= 0.701, P < 0.001. Using multiple logistic regression with VEmax/MVV 1 as a dependent categorical variable, FEV1/FVC was the only significant predictor among resting pulmonary indices of a VEmax/MVV ratio of > 1 (Odds ratio 0.93, 95%CI 0.89, 0.97). There was a significant association between VEmax/MVV and peak oxygen uptake (VO2max) after adjusting for FEV1 (r = 0.66, P < 0.001). If the categorical variable of VEmax/MVV ( 1) was used instead of a continuous variable, a significant association with VO2max remained after adjusting for FEV1 (r = 0.60, P < 0.001).

Conclusions: Among resting pulmonary function indices, the FEV1/FVC ratio is the best determinant of an improvement in breathing capacity during exercise in COPD patients. After adjusting for FEV1, an improvement in breathing capacity during exercise is associated with significantly higher exercise capacity.