Pulmonary precapillary hypertension in mitral valve disease.

Pulmonary hypertension in mitral stenosis is caused by a blockade of the mitral orifice. The haemodynamic examinations of 302 patients with mitral stenosis (MS) revealed that the increase in pulmonary vascular resistance significantly depended on the degree of stenosis. This increase is of functional and of anatomic origin; the acetylcholine infusion test makes possible to differentiate both these causal components. In mitral defects, the blood flow distribution in the lungs is altered, too. During exercise, pulmonary vascular resistance increases mainly in patients with elevated left intraatrial pressure. The pulmonary vascular bed, whose distensibility in mitral disease is diminished, is able to resist higher intravascular pressures without increasing its capacity.