Pulmonary arterial hypertension--the primary pulmonary hypertension syndromes.

There is a broad range of diseases that can cause an elevation in pulmonary pressures. Pulmonary hypertension is the focal point and cause of significant morbidity and mortality in some of these disorders but plays a secondary, less clinically central role in others. Pulmonary arterial hypertension is a subclass of pulmonary hypertension that includes the former type of disorders in which progressive elevation in pulmonary pressures and right heart failure are often the cause of death. The classic example of this group is primary pulmonary hypertension. This review will focus on the various forms of pulmonary arterial hypertension, their pathophysiology, and recent advances in treatment of this life-threatening disorder. Pulmonary hypertension is a hemodynamic abnormality with multiple causes and clinical presentations. The World Health Organization classification of PH is detailed in Table 1 [1]. This system breaks the classification of PH into five major categories: a) pulmonary arterial hypertension, b) pulmonary venous hypertension, c) PH associated with disorders of the respiratory system and/ or hypoxemia, d) embolic disorders, and e) disorders directly affecting the vasculature. It is important to distinguish the various diseases included under the WHO classification because the various forms of PH are quite separate in their natural history and treatment. For example, treatment of PH related to congestive heart failure with pulmonary venous hypertension is aimed at improving the primary abnormalities of left ventricular dysfunction and volume overload rather than attempting to dilate pulmonary vessels. PH due to primary respiratory disease such as emphysema is not treated by vasodilators other than oxygen. These examples are in contrast to the treatment of PAH in which lowering pulmonary vascular resistance is a primary and effective treatment. The current review will focus on the first group in the WHO classification.