Pulmonary gas exchange and exercise performance in pulmonary hypertension.

Patients with pulmonary hypertension have disordered pulmonary gas exchange and impaired exercise tolerance. The hypoxemia is due to mild ventilation-perfusion (VA/Q) inequality exaggerated by the presence of a low mixed venous PO2 (PvO2) and is accentuated during exercise due to a further fall in PvO2. This in turn may be worsened by vasodilators which increase the degree of VA/Q inequality. Decreased exercise tolerance is due predominantly to cardiac limitation, and thus an improvement in cardiac function subsequent to successful vasodilation can be assessed by improved exercise performance.