[Pulmonary arterial hypertension. Part I: pathobiologic, pathophysiologic, clinical and diagnostic aspects].

Pulmonary hypertension is a pathophysiologic condition characterized by the increase of mean pulmonary arterial pressure > or =25 mmHg. A concomitant increase of pulmonary wedge pressure >15 mmHg may be present (post-capillary pulmonary hypertension) or not (precapillary pulmonary hypertension). The increase of pulmonary arterial pressure and of pulmonary vascular resistance and consequent elevation of the right ventricular afterload lead to right ventricular failure after variable periods of time. Pulmonary hypertension is present in multiple clinical conditions which have been classified in five groups. Pulmonary arterial hypertension (group 1) includes the familial and the idiopathic form and the forms associated with anorexigen drug use, connective tissue diseases, congenital heart diseases, HIV infection and portal hypertension. Group 2 includes all left heart diseases characterized by the increase of left atrial pressure and pulmonary wedge pressure (post-capillary pulmonary hypertension). Group 3 includes parenchymal lung diseases (chronic obstructive lung disease, lung fibrosis, ecc). Chronic thromboembolic pulmonary hypertension (group 4) is characterized by the obstruction of elastic pulmonary arteries at different levels by organized thromboembolism. Group 5 includes heterogeneous conditions such as sarcoidosis and histiocytosis X. These clinical groups are characterized by different pathobiologic and pathophysiologic mechanisms and therapeutic strategies. The exact pathobiologic mechanisms leading to pulmonary arterial hypertension (group 1) are unknown. Genetic factors (inheritable forms), predisposing factors (female gender) and exogenous factors (drugs, antibodies, viruses, congenital heart disease, etc). Endothelial dysfunction of lung microcirculation is invariably present and is characterized by the reduction of vasodilator and antiproliferative substances (prostacyclin, nitric oxide) and by the increase of vasoconstrictor and mitogenic factors (endothelin, thromboxane A2). Current approved therapies are targeted to the correction of this imbalance, which leads to the progressive increase of pulmonary vascular resistance. Different therapeutic strategies that are effective in diverse groups require an appropriate diagnostic algorithm in order to identify the precise group and specific conditions within the group. Evaluation of vasoreactivity and assessment of the severity of functional and hemodynamic changes are also required in pulmonary arterial hypertension for an appropriate therapeutic decision-making and estimate of results.