pulmonary embolism

Imagine a pipe carrying water to a sprinkler suddenly blocked by a wad of debris that floated downstream and jammed where the pipe narrows. A pulmonary embolism is much the same: a clot, usually formed in a leg vein, breaks loose, travels through the heart, and lodges in one of the pulmonary arteries, the vessels carrying blood from the right side of the heart to the lungs to pick up oxygen.

When a clot blocks a pulmonary artery, blood cannot reach part of the lung to be oxygenated, even though that lung region is still being ventilated with air. The result is a mismatch between airflow and blood flow, falling blood oxygen, and increased strain on the right side of the heart, which must now pump against a more obstructed circuit. Symptoms range from sudden breathlessness and chest pain that worsens with breathing, to a fast heartbeat, coughing up blood, or, in large clots, collapse.

Pulmonary embolism is common, sometimes silent, and potentially fatal, but it is also treatable. Diagnosis usually combines clinical probability scoring, a D-dimer blood test, and imaging such as CT pulmonary angiography. Because the clot most often originates in the deep veins of the legs, pulmonary embolism and deep vein thrombosis are viewed as two faces of one disease, venous thromboembolism.