What Causes Blood Clots In The Lungs?

How Blood Clots Form

There are a number of causes of blood clots in the lungs. Before describing them, it helps to know about how blood clots form.

A blood clot can occur anywhere in the veins and arteries of the body. But even one that forms in the arms or legs can pose a danger to the lungs - and that danger can be life threatening.

The medical name for a blood clot is a "thrombus." When you're talking about more than one, the word is "thrombi."

What causes blood clots? When a blood vessel is injured, blood clots form around the damaged area. This protects the injury and helps it heal.

A blood clot can also form due to fatty deposits that accumulate on the walls of your blood vessels. These are generally due to high cholesterol.

Wherever a clot forms, it tends to obstruct or restrict the efficient flow of blood. Circulation near the clot slows down, and when it does, blood has a tendency to form clots even more. As these clots form, the danger level rises.

What is a pulmonary embolism? A pulmonary embolism is a blood clot that forms away from the lungs - often in an arm or leg. This clot can break loose and travel through the blood stream to the heart, which then pumps it to the lungs. Somewhere in this process, the clot can become "stuck" in a blood vessel. The clot blocks blood circulation, possibly leading to two potentially deadly outcomes:

1. Blood to the lungs is blocked, causing tissue to die. This is known as an infarction.
2. The clot causes the lungs to provide less oxygen to the rest of the body. This causes a condition known as hypoxia.

A pulmonary embolism sometimes results from a condition called deep venous thrombosis, which is also known as DVT. The clot itself is known as a deep vein thrombus.

Deep vein thrombosis often occurs in an arm or leg. It is dangerous for individuals who are immobilized or bedridden for long periods. But can also occur in a relatively short time, from sitting in one place on an intercontinental airplane flight, or driving long distances without a break.

In addition to the threat DVT causes to the lungs, it may permanently damage a vein, causing limited function along with localized pain and swelling. Paralysis of the limb may also occur.

A clot forming in a limb is known as chronic thrombophlebitis.

Arterial thrombosis and atrial fibrillation Sometimes a blood clot will form in an artery where "plaque" from high levels of cholesterol has built up and blocked blood flow. The artery becomes narrow, blood begins to stagnate and eventually the artery ruptures. A clot forms at the site of the rupture. This clot can travel through the blood stream to the heart, lungs, brain, or other organs.

Risk factors associated with arterial thrombosis and include high blood pressure (hypertension), high cholesterol, diabetes, smoking, and family history of circulatory problems in your family.

Atrial fibrillation occurs when small clots form in the heart. These clots are pumped by the heart into bloodstream, where they may block an artery, causing tissue death.

Atrial fibrillation is most likely to cause problems in the blood vessels leading to the brain and intestines. When it affects arteries near the brain, a stroke results. When it affects the intestines, it causes a condition called mesenteric ischemia, which can trigger severe abdominal pain and diarrhea.

Treatment for blood clots in the lungs - or anywhere else in the body - usually involves anti-coagulation medications like warfarin (Coumadin). This, however, usually takes about a week to work. If more urgent treatment is needed, your doctor may recommend injections of a medication called enoxaparin or Lovenox.

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