The United States experience with the acute and chronic treatment of primary pulmonary hypertension.

Patients who clinically have primary or 'unexplained' pulmonary hypertension are found at autopsy or lung biopsy to have a variety of pulmonary vascular changes, including medial hypertrophy, thrombosis, intimal fibrosis and plexiform lesions. It is not surprising that the haemodynamic response to vasodilators varies widely. In general, the non-specific vasodilators used to treat pulmonary hypertension cause an acute fall in systemic arterial pressure, with an increase in cardiac output and a reduction in pulmonary vascular resistance. Pulmonary arterial pressure usually does not change much but occasionally drops dramatically. The risk of death in an acute trial of a vasodilator is less than 0.5% in experienced hands. The use of a short-acting vasodilator (e.g., prostacyclin) may indicate the presence or absence of vasoconstriction, the likelihood of fixed structural obstruction to flow and the risk of administering longer-acting vasodilators, and it may give a clue to prognosis. The risk-benefit ratio in the use of vasodilators in the long-term treatment of primary pulmonary hypertension needs to be evaluated by a controlled trial, conducted in those who respond acutely. The role of high-dose calcium channel blocker treatment and multiple drug therapy will also require further study.