Porth's Essentials of Pathophysiology, 4e

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Disorders of Blood Flow and Blood Pressure

C h a p t e r 1 8

Arterial Disease of the Extremities Disorders of the circulation in the extremities often are referred to as peripheral vascular disorders. 17 In many respects, the disorders that affect arteries in the extremi- ties are the same as those affecting the coronary and cerebral arteries in that they produce ischemia, pain, impaired function, and in some cases infarction and tis- sue necrosis. Not only are the effects similar, but the pathologic conditions that impair circulation in the extremities are also identical. This section focuses on peripheral arterial disease, thromboangiitis obliterans, and Raynaud phenomenon. Peripheral Arterial Disease Peripheral artery disease (PAD) refers to the obstruc- tion of large arteries that supply the body’s peripheral structures rather than its central structures such as the heart or brain. Often PAD is a term used to refer to ath- erosclerotic blockages found in the lower extremities. Peripheral artery disease can result from atherosclerosis, inflammatory processes leading to stenosis, embolism, or thrombus formation. It causes either acute or chronic ischemia. The disease is seen most commonly in men in their 60s and 70s. The risk factors for PAD are similar to those for coronary artery disease. Cigarette smoking and diabetes mellitus are the strongest risk factors, with more than 80% of persons with the disorder being cur- rent or former smokers. 17 As with atherosclerosis in other locations, the signs and symptoms of vessel occlusion are gradual. The pri- mary symptom of chronic obstructive arterial disease is pain with walking or claudication (from the Latin verb claudicare, “to limp”). 18 Typically, persons with the dis- order complain of calf pain because the gastrocnemius muscle has the highest oxygen consumption of any mus- cle group in the leg during walking. Some persons may complain of a vague aching feeling or numbness, rather than pain. Other activities such as swimming, bicycling, and climbing stairs use other muscle groups and may not incite the same degree of discomfort as walking. Other signs of ischemia include atrophic changes and thinning of the skin and subcutaneous tissues of the lower leg and diminution in the size of the leg muscles. The foot often is cool, and the popliteal and pedal pulses are weak or absent. Limb color blanches with elevation of the leg because of the effects of gravity on perfusion pressure and becomes deep red when the leg is in the dependent position because of an autoregulatory increase in blood flow and a gravitational increase in perfusion pressure. When blood flow is reduced to the extent that it no lon- ger meets the minimal needs of resting muscle and nerves, ischemic pain at rest, ulceration, and gangrene develop. As tissue necrosis develops there typically is severe pain in the region of skin breakdown, which is worse at night with limb elevation and is improved with standing. Diagnostic methods include inspection of the limbs for signs of chronic low-grade ischemia such as subcuta- neous atrophy, brittle toenails, hair loss, pallor, coolness, or dependent rubor. Palpation of the femoral, popliteal,

posterior tibial, and dorsalis pedis pulses allows for an estimation of the level and degree of obstruction. The ratio of ankle to arm (i.e., tibial and brachial arter- ies) systolic blood pressure is used to detect significant obstruction, with a ratio of less than 0.9 indicating occlusion. Blood pressures may be taken at various lev- els on the leg to determine the level of obstruction. A Doppler ultrasound stethoscope may be used for detect- ing pulses and measuring blood pressure. Ultrasound imaging, magnetic resonance imaging (MRI) arteriogra- phy, spiral computed tomographic (CT) arteriography, and invasive contrast angiography also may be used as diagnostic methods. 17,18 Treatment includes measures directed at protection of the affected tissues and preservation of functional capacity. Walking (slowly) to the point of claudica- tion usually is encouraged because it increases col- lateral circulation. Avoidance of injury is important because tissues of extremities affected by atherosclero- sis are easily injured and slow to heal. It is important to address other cardiovascular risk factors such as smoking, hypertension, hyperlipidemia, and diabetes. Drug therapy includes antiplatelet therapy (e.g., aspi- rin or clopidogrel). Other medications that are useful include statins, cilostazol (a vasodilator with antiplate- let properties), and pentoxifylline (an antiplatelet agent that decreases blood viscosity and improves erythrocyte flexibility). Percutaneous or surgical intervention is typi- cally reserved for the patient with disabling claudication or limb-threatening ischemia. Surgery (i.e., femoropop- liteal bypass grafting using a section of saphenous vein) may be indicated in severe cases. Percutaneous translu- minal angioplasty and stent placement, in which a bal- loon catheter is inserted into the area of stenosis and the balloon inflated to increase vessel diameter, is another form of treatment. 17,18 Thromboangiitis Obliterans Thromboangiitis obliterans, also known as Buerger disease , is a recurring progressive, nonatherosclerotic inflammation and thrombosis of small and medium- sized arteries and veins, usually the plantar and digital vessels in the foot and lower leg. 1,2,19,20 Arteries in the arm and hand also may be affected. Although primar- ily an arterial disorder, the inflammatory process often extends to involve adjacent veins and nerves. Usually it is a disease of young, heavy cigarette smokers, occurring before the age of 35. The pathogenesis of Buerger disease remains elusive, though cigarette smoking and in some instances tobacco chewing seem to be involved. It has been suggested that the tobacco may trigger an immune response in susceptible persons or it may unmask a clot- ting defect, either of which could incite an inflammatory reaction of the vessel wall. 19 It is more common in the Mediterranean region, Middle East, and Asia. 1,2 Pain is the predominant symptom of the disorder. It usually is related to distal arterial ischemia. During the early stages of the disease, there is intermittent claudi- cation in the arch of the foot and the digits. In severe cases, pain is present even when the person is at rest.