Pulmonary hypertension: a cellular basis for understanding the pathophysiology and treatment.

Much of the understanding of hypertensive pulmonary vascular disease comes from studies of primary pulmonary hypertension. The three subtypes of primary pulmonary hypertension, plexogenic pulmonary arteriopathy, thromboembolic pulmonary hypertension and venoocclusive disease, have served as a basis to understand the mechanisms and to develop treatments of all forms of pulmonary hypertension. However, many inconsistencies regarding presumed pulmonary vasoconstriction and recurrent embolization remain. With newer data on the influence of the endothelium on vascular responsiveness and thrombosis, it appears that older concepts regarding the pathophysiology of pulmonary hypertension need to be revised. Recent studies have shown that plexogenic pulmonary arteriopathy is associated with abnormalities of endothelial structure and function that could result in impaired release of endothelial derived relaxing factors. Thromboembolic pulmonary arteriopathy, or more properly thrombotic pulmonary hypertension, appears to be the result of endothelial cell injury that creates a procoagulant environment in the pulmonary vascular bed with the development of widespread eccentric intimal proliferation and thrombosis in situ. It is possible that the effectiveness of vasodilator or anticoagulant therapy depends on the nature of the endothelial injury. Secondary pulmonary hypertension without endothelial injury, such as that which occurs with hypoxic lung disease or mitral stenosis, appears more satisfactorily treated when the primary cause is reversed.