Pathophysiology

Clinical effects of PE depend on a variety of factors:

• degree of pulmonary vascular obstruction
• pre-existing cardiopulmonary function
• age and general health
• release of bronchoconstrictive and vasoactive humoral agents from activated platelets, e.g. thromboxane A2

There is a significant increase in right ventricular afterload when more than 25% of the pulmonary artery is obstructed.

With pulmonary vascular obstruction there is an increase in pulmonary artery pressure and a reduction in pulmonary blood flow. There is a dilating of the right ventricle and displacement of the interventricular septum into the the left ventricular cavity - thus impairing filling of the left ventricle. The dyspnoea of acute severe obstruction of the pulmonary circulation is helped by manoeuvres which improve venous return, e.g. head-down tilting, leg raising, infusion of intravenous colloid.