Vasoconstriction and Medial Hypertrophy in Pulmonary Hypertension

To determine whether thickening of the media of pulmonary muscular arteries in cases of pulmonary hypertension is the result of vasoconstriction or of hypertrophy or of both, a method for calculating the amount of arterial muscular tissue per unit of pulmonary tissue was devised. Comparison of the mean medial thickness, expressed as a percentage of the diameters of the arteries, with the amount of arterial muscular tissue per unit of lung, will give an impression as to whether vasoconstriction or hypertrophy prevails in a certain case. This method was applied to sections of pulmonary tissue from 10 normal controls and 17 patients with congenital cardiac disease with pulmonary hypertension. Medial hypertrophy was present in all cases of congenital heart disease studied as compared with controls, and was more pronounced in severe than in moderate pulmonary hypertension. In some cases also vasoconstriction appeared to play an important or even a dominant role in the thickening of the medial layer. In 2 cases of atrial septal defect with large pulmonary flow, hypertrophy was masked by dilatation of the vessels resulting in a relatively thin media.