Pulmonary vascular disease: pulmonary thromboembolism and pulmonary hypertension

The alveolar–capillary barrier, comprising capillary endothelium, extracellular matrix and alveolar epithelium, is a thin membrane that provides a large surface area for diffusive gas exchange. In human health, the pulmonary circulation is completely separate from the systemic circulation, which allows the maintenance of a high-flow, low-pressure circuit to ensure optimal gas exchange even with increasing physiological demands. Increases in pressure within this circulation either acutely, for example secondary to pulmonary embolism, or over time secondary to vascular remodelling, can detrimentally affect ventilatory efficiency and also lead to an excessive afterload being placed on the right ventricle. If unrecognized and untreated, this can lead to right heart failure and death. This article explores the epidemiology, pathophysiology, clinical presentation and management of the major diseases of the pulmonary circulation – pulmonary thromboembolism and pulmonary hypertension.