JAMA patient page: Air travel-related deep vein thrombosis and pulmonary embolism.

Pulmonary embolism occurs when blood clots leave the veins where they developed, travel through the right side of the heart, and lodge in the small or large branches of the blood vessels going to the lung (pulmonary arteries). This can cause symptoms such as chest pain, difficulty breathing, or coughing up blood. In severe cases, it may result in collapse and sudden death. Long airplane flights or multiple flights in a short period can cause deep vein thrombosis and pulmonary embolism. Any situation in which the leg is bent at the knee for prolonged periods without much active motion may lead to a reduction of blood flow and increase the risk of blood clots. Other factors can increase this risk, such as recent surgery, taking oral contraceptives or hormone therapy, pregnancy, cancer, heart problems, and older age. Inherited genetic factors may also play a role.