Pathophysiology of obstructive arterial disease

Intermittent claudication is due to ischemia of working muscles in patients with stenoses or obstructions of large or medium sized arteries. Arteriosclerosis obliterans is by far the most common etiology. As an arterial stenosis develops, the distal blood flow and blood pressure are not affected until a critical diameter occurs. Then, blood flow and blood pressure fall precipitously with further narrowing of the lumen area. The most important factors that influence blood flow and the blood pressure drop across a stenosis are the radius of the stenosis and of the artery, and the velocity of blood flow. The velocity of blood flow varies inversely with the peripheral resistance. A decrease in peripheral resistance which occurs with exercise, vasodilator drugs, or sympathectomy leads to an increased blood flow velocity and an increased pressure drop across a stenosis. Thus, a non-critical stenosis at rest can become critical and limit blood flow during exercise. In arterial occlusions and critical arterial stenoses, the distal perfusion pressure is decreased due to the high resistance of the small collateral vessels but blood flow may be normal at rest. With exercise, the distal perfusion pressure decreases to a lower level due to the fall in peripheral resistance. Then, the external pressure of muscle contraction may close the arterial bed and stop blood flow. The stimulus to collateral blood vessel development is not known but may involve the pressure differential across the involved vascular bed and metabolic products produced during the ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)