Causes
Most embolisms happen to people who have risk factors for blood clot
formation, like smoking, high blood pressure, high cholesterol, and heart disease.
The primary cause of most pulmonary embolisms is deep vein thrombosis
(DVT). This is a condition in which the veins of the legs develop clots.
Natural agents in the blood often dissolve small clots. Some clots are too big
to dissolve and are big enough to block major blood vessels in the lungs or
in the brain.
Factors that slow blood flow in the legs may promote clotting. People can
develop a DVT or pulmonary emboli after sitting still on long flights or after
immobilization of the leg in a cast, or after prolonged bedrest without moving
the legs. Other factors associated with DVT or pulmonary embolism include cancer,
previous surgery, a broken leg or hip, and genetic conditions affecting the
blood cells that increase the chance of blood clot formation.