An embolus is a particle that moves about in our blood vessels, either in the veins or arteries. Most emboli are composed of clotted blood cells. A blood clot is called a thrombus and a moving blood clot is called a thromboembolus.
As an embolus moves through the body's blood vessels, it's likely to come to a passage it can't fit through. It lodges there, backing up blood behind it. The cells that normally get their blood supply via this passage are starved of oxygen (ischemia) and die. This condition is called an embolism.
There are several types of embolism:
Most embolisms happen to people who have risk factors for blood clot formation, such as smoking and heart disease. Other risk factors for other types of emboli include high blood pressure, atherosclerosis (buildup of fatty plaque in the blood vessels), and high cholesterol.
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 without causing any effects of blockage. 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 bed rest 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.
The symptoms of pulmonary embolism can be mild or severe. Some people have many small emboli that can only be detected by special X-ray techniques. A serious blockage, however, can lead to severe breathing difficulty or death.
Symptoms of pulmonary embolism appear suddenly and include: