Role of pulmonary vascular disorder in determining exercise capacity in patients with severe chronic obstructive pulmonary disease.

Abstract

In patients with chronic obstructive pulmonary disease (COPD), the primary cardiovascular complication is the development of pulmonary hypertension, especially during exercise. The purpose of this study was to determine whether pulmonary vascular disorder plays an important role in determining exercise capacity in patients with severe COPD. Twenty-one male patients with severe COPD (mean FEV1 = 0.91 +/- 0.26 1) performed a progressive incremental exercise test, until symptom-limited maximum, to determine maximal exercise capacity, and then a constant-load exercise test for 5 min at a workload (20-60 W) corresponding to 60% of maximal workload during right heart catheterization to characterize the haemodynamic behavior of pulmonary circulation during exercise. The severity of the pulmonary vascular disorder was assessed using the slope of the mean pulmonary arterial pressure (PAP) - cardiac index (CI) relationship during constant-load exercise (P-Q slope). A significant inverse correlation was found between the maximal oxygen consumption (VO2max) and P-Q slope (r = -0.669), but not between VO2max and indices of expiratory airflow obstruction. In addition, the P-Q slope was inversely correlated with mixed venous oxygen tension (PvO2) at the end of constant-load exercise (r = -0.679) and with the change in oxygen delivery relative to oxygen consumption (delta DO2/delta VO2) during constant-load exercise (r = -0.671). These findings suggest that in patients with COPD, the functional impairment of the pulmonary vasculature is associated with disturbance in oxygen transport to the peripheral muscle during exercise, resulting in reduction of exercise capacity. We conclude that pulmonary vascular disorder may be an important factor in determining the exercise capacity of patients with severe COPD.