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Peripheral Vascular Disease (cont.)

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How does atherosclerosis cause disease?

There are two ways atherosclerosis causes disease; 1) atherosclerosis can limit the ability of the narrowed arteries to increase delivery of blood and oxygen to tissues during periods of increased oxygen demand such as during exertion, or 2) complete obstruction of an artery by a thrombus or embolus (thrombus and embolus are forms of blood clots; see below) resulting in tissue necrosis (death of tissue). Exertional angina and intermittent claudication are two examples of insufficient delivery of blood and oxygen to meet tissue demand; whereas strokes and heart attacks are examples of death of tissue caused by complete artery obstruction by blood clots.

There are many similarities between coronary artery diseases (atherosclerosis involving the arteries of the heart) and peripheral artery disease, and the two conditions may coexist in the same individual. For example, patients with exertional angina typically have no symptoms at rest. But during exertion the critically narrowed coronary arteries are incapable of increasing blood and oxygen delivery to meet the increased oxygen needs of the heart muscles. Lack of blood and oxygen causes chest pain (exertional angina). Exertional angina typically subsides when the patient rests. In patients with intermittent claudication, the narrowed arteries in the lower extremities (for example, a narrowed artery at the groin) cannot increase blood and oxygen delivery to the calf muscles during walking. These patients experience pain in the calf muscles that will only subside after resting.

Patients with unstable angina have critically narrowed coronary arteries that cannot deliver enough blood and oxygen to the heart muscle even at rest. These patients have chest pain at rest and are at imminent risk of developing heart attacks. Patients with severe artery occlusion in the legs can develop rest pain (usually in the feet). Rest pain represents such severe occlusion that there is insufficient blood supply to the feet even at rest. They are at risk of developing foot ulcers and gangrene.

When the arteries are narrowed as a result of atherosclerosis, blood tends to clot in the narrowed areas, forming a so-called thrombus (plural thrombi). Sometimes pieces of the thrombi break off and travel in the bloodstream until they are trapped in a narrower point in the artery beyond which they cannot pass. A thrombus or piece of thrombus that travels to another point is called an embolus. Thrombi and emboli can cause sudden and complete artery blockage, leading to tissue necrosis (death of tissue).

For example, complete blockage of a coronary artery by a thrombus causes heart attack, while complete blockage of a carotid or cerebral artery causes ischemic stroke. Emboli originating form atherosclerosis in the aorta (the main artery delivering blood to the body) can obstruct small arteries in the feet, resulting in painful and blue (cyanotic) toes, foot ulcers, and even gangrene.

What are collaterals?

Sometimes, despite the presence of a severe blockage in an artery, the involved area does not become painful or ischemic due to the presence of collateral vessels. Collateral circulation means that the particular area is supplied by more than one artery to an extent that blockage of a single vessel does not result in a severe degree of ischemia. Collateral circulation can develop over time to help provide oxygenated blood to an area where an artery is narrowed. Doctors believe that regular supervised exercise can stimulate the growth and development of collateral circulation and relieve symptoms of intermittent claudication.

Medically Reviewed by a Doctor on 7/16/2014

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Source: MedicineNet.com
http://www.medicinenet.com/peripheral_vascular_disease/article.htm

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