The effects of exercise on ventilation-perfusion relationship in patients with mitral stenosis.

Exercise limitation is common in patients with chronic pulmonary venous hypertension. One postulated mechanism is ventilation-perfusion inequality secondary to vascular congestion and edema formation. To investigate this possibility, five patients with symptomatic, chronic mitral stenosis were studied at rest, during 10 min of steady-state exercise and during recovery from exercise. Both conventional indices of gas exchange and the multiple inert gas elimination method were used. Hypoxemia was not present in patients at any stage in the study and negligible shunt or low VA/Q lung units were demonstrated by the inert gas method. Instead, regions with high VA/Q ratio appeared toward the end of exercise and immediately after exercise. We postulate that this was the result of a marked redistribution of pulmonary blood flow, possibly due to an accumulation of interstitial edema fluid. It is concluded that the excessive ventilatory response to exercise observed in patients with mitral stenosis may, in part, be explained by an unequal distribution of ventilation and perfusion.