2.1
Chronic thromboembolic pulmonary hypertension is a progressive disease. It is caused by obstruction of the pulmonary arteries (from main to subsegmental levels) by pulmonary emboli that have not resolved but which have become organised. This causes narrowing of the pulmonary arteries, an increase in the resistance to blood flow and a rise in pressure within the pulmonary arteries. Progression of pulmonary hypertension may occur because of gradual remodelling of unobstructed pulmonary vasculature in response to the haemodynamic changes.