Pulmonary resistance in acquired heart disease.

Disproportionately high pulmonary artery pressures and pulmonary vascular resistance in acquired heart disease, particularly mitral stenosis, have been repeatedly observed. Seventeen patients with pulmonary hypertension secondary to elevated left atrial pressure have been studied by the method of temporary unilateral pulmonary artery occlusion: Resistances calculated before and after occlusion showed no change in most cases. The data show that despite very high initial resistance, increase in flow in the lung can occur with rapid reduction in resistance. It is suggested that "tone" of the pulmonary vasculature is operative even at very high pressure levels.