Abstract
Small pulmonary arteries, arterioles, venules, and small veins were studied in 105 cases of mitral stenosis and compared with those of 67 controls. Diffuse muscular hypertrophy of pulmonary arterioles with medial hypertrophy of the small arteries in some, occurred in 40% of cases of mitral stenosis, and in none of the controls. The development of decrescent changes in the pulmonary vessels in the venous side was accelerated by mitral stenosis. In some cases of mitral stenosis the small pulmonary vessels were normal. Intimal thickening of the small pulmonary vessels probably is not a factor in maintaining pulmonary hypertension.