[Pulmonary hypertension].

Depending on their size pulmonary emboli are responsible for an abrupt rise in pulmonary artery pressure. Not only mechanical obstruction, but also liberation of vasoactive substances from platelets trapped within the emboli represent the underlying mechanism. Intrapulmonary shunts, caused by vaso- and bronchoconstriction, may result in arterial hypoxemia. Although this clinical finding is encountered in most cases, normal arterial blood gases do not rule out significant pulmonary embolism. Even a small rise in pulmonary artery pressure causes significant reduction of right ventricular stroke volume and a decrease in left ventricular filling pressure. Impaired left ventricular filling is aggravated by biventricular interdependence. Elevated pulmonary artery pressures during rest and exercise are normalized by effective fibrinolytic therapy.