Decreased amplitude of the pulse denotes proximal stenosis and arterial insufficiency . It is unusual for collateral flow to be sufficient to produce a pulse distal to an occluded artery. The surgeons generally use the right common carotid as “normal” for that patient and the 4+ denominator in the traditional 4+ grading system.
Grading of pulses.
3+ Slightly reduced
2+ Markedly reduced
1+ Barely palpable
A bruit is the sound produced by dissipation of energy as blood flows through a stenotic arterial segment. It is heard loudest during systole and, with greater stenosis, may extend into diastole. The bruit is transmitted distally along the course of the artery. Thus, when a bruit is heard through a stethoscope placed over a peripheral artery, stenosis is present at or proximal to that level. The pitch of the bruit rises as the stenosis becomes more marked, until a critical stenosis is reached or the vessel becomes occluded, when the bruit may disappear. Thus, absence of a bruit does not indicate insignificant disease.
Pallor of the foot on elevation of the extremity indicates advanced ischemia. Pallor on elevation does not occur unless advanced ischemia is present.
The ischemia produced by elevation results in maximum cutaneous vasodilation. When the extremity is returned to a dependent position, blood returning to the dilated vascular bed produces an intense red color in the foot, called reactive hyperemia, and denotes advanced disease. Reactive hyperemia occurs only if ischemia is provoked. The rate of return of skin color when the extremities return to a dependent position is proportionate to the efficiency of the collateral circulation; the more delayed the reactive hyperemia, the more severe the impairment in circulation.
In advanced atherosclerotic disease and arterial insufficiency, the skin of the foot displays a characteristic dark red cyanosis on dependency. Because of reduced inflow, the blood in the capillary network of the foot is relatively stagnant, oxygen extraction is high, and the capillary blood becomes the color of the venous blood. The concurrent vasodilation due to ischemia causes blood to suffuse the cutaneous plexus, imparting a purple color to the skin. The purple discoloration due to chronic congestion from venous insufficiency does not become pallid on elevation.
Response to Exercise
Exercise in a normal individual increases the pulse rate without producing arterial bruits or changes in pulse amplitude. In an individual who complains of claudication but who has minimal findings at rest, exercise will sometimes produce an audible bruit and a decrease in pulse strength and distal arterial pressure, unmasking a significant stenosis. This is best used in vascular testing.
With chronic ischemia, the temperature of the skin of the foot decreases. Coolness can best be detected by palpation.
Ischemic ulcers are usually very painful and accompanied by rest pain in the foot. They occur in toes or at a site where trauma from a shoe or bedding causes additional ischemia or infection. The margin of the ulcer is sharply demarcated or punched-out, and the base is devoid of healthy granulation tissue. The surrounding skin is pale and mottled, and signs of chronic ischemia are invariably present.
Tissue necrosis first becomes apparent in the most distal portions of the extremity, often at an ulcer site. Necrosis halts proximally at a line where the blood supply is sufficient to maintain viability and results in dry gangrene. If the necrotic portion is infected (wet gangrene), necrosis may extend into tissues that would normally remain viable.
Moderate to severe degrees of chronic ischemia produce gradual soft tissue and muscle atrophy and loss of strength in the ischemic zone. Joint mobility may be reduced in the forefeet as atrophy of the muscles produces increasing prominence of the interosseous spaces. Subsequent changes in foot structure and gait increase the possibility of developing foot ulceration.
Noninvasive Vascular Tests
Noninvasive assessment is helpful to determine the severity of hypoperfusion and the sites of hemodynamically significant stenoses or occlusions.
The ankle-brachial index (ABI) is a quick screening test and the cornerstone of diagnosis. The ABI is determined by dividing the systolic pressure obtained by Doppler insonation at the ankle by the brachial arterial pressure. Normally, the ABI is 1.0 or greater; a value below 1.0 indicates occlusive disease proximal to the point of measurement. ABIs correlate roughly with the degree of ischemia; eg, rest pain usually appears when the ratio is 0.3 or lower.
In elderly patients or diabetics, the tibial artery wall may be calcified. Since such a vessel cannot be compressed, an elevated pressure is recorded even though the intraluminal pressure may be low, leading to a false-negative examination. Wall calcification should be suspected whenever the ABI is above 1.2 or when the value is out of proportion to the patient’s clinical status. This pitfall can be avoided by listening to the quality of the Doppler signal, ie, a monophasic signal indicates significant disease, or by obtaining toe pressures by plethysmography.
Additional noninvasive studies are useful in localizing disease or determining its severity. Segmental limb pressure measurement using both Doppler and plethysmography accurately detects and segmentally localizes hemodynamically significant occlusive lesions by determining pressures and pulse volume changes at the high thigh, low thigh, upper calf, and lower calf levels in addition to ankle pressures. The location of the occlusive lesions and their relative severity can be ascertained from these measurements.
Blood pressures can also be measured at rest and after exercise in the ankle and the effect of exercise can be monitored. This type of functional testing confirms and quantitates the diagnosis of claudication. To perform exercise testing the patient walks on a treadmill at a standard speed and grade until claudication pain is experienced or a time limit is reached. A graded treadmill with a slowly rising walking platform is often used. With significant arterial occlusive disease there will be a decrease in the ABI between the resting and postexercise time, usually measured 1 minute after cessation of walking. If the pain is not due to arterial stenosis, no fall in pressure will occur. This test is particularly useful in differentiating neurogenic pain with walking from vascular insufficiency.
Color duplex imaging is a mainstay of vascular imaging. It is a painless, relatively inexpensive, and (in experienced hands) accurate method for developing anatomic and functional information about arterial insufficiency and arterial aneurysms. Although the accuracy of this study is operator-dependent, it can supply sufficient information to permit intervention in selected cases.
Arteriography provides detailed anatomic information about peripheral arterial disease. It is reserved for patients warranting invasive intervention such as percutaneous transluminal angioplasty or vascular surgery. Complications of angiography are related to technique and contrast media. Technical complications such as puncture site hematomas, arteriovenous fistulas, and false aneurysms are rare (about 1% risk). Contrast agents may precipitate allergic reactions (about 0.1% risk). Use of nonionic agents, carbon dioxide instead of contrast, and digital subtraction angiography lessens symptoms and the risk of adverse outcomes. Both standard and nonionic agents cause a transient decrease in renal blood flow and increased vascular resistance. In a small proportion of patients, angiography induces acute renal insufficiency. Patients with renal failure, proteinuria, diabetes, and dehydration are at increased risk for contrast-induced renal failure. Adequate hydration of patients before and after angiography, acetylcysteine, and periprocedural infusions of sodium bicarbonate infusions have dramatically reduced the incidence of this complication.
Magnetic resonance angiography can delineate arteries without using contrast agents. The basic principle of MRA is that the vector of the proton spin becomes aligned with the brief application of a magnetic field. The MRA signal is generated as the protons return to a nonexcited or random alignment. The use of gadolinium as a contrast agent has dramatically improved MRA resolution and reduced imaging time. Recent studies using a gadolinium contrast agent that is attached to albumin shows that MRA compares favorably to arteriography in the identification of aortoiliac stenoses. This coupled with the fact that MRA has reduced toxicity compared to angiography has led to MRA replacing angiography as the first-line imaging technique.
The introduction of multiplanar CT scanners has allowed high-resolution images of the arterial tree. Although CT-angiography (CTA) still requires the administration of contrast material, it avoids an arterial puncture, and 3D reconstructions are an excellent alternative to arteriography. Current management and surgery of aortic aneurysms is done with CT alone, with arteriography rarely needed.
Calcification in the walls of atherosclerotic arteries is often visible on standard x-ray films and may occur without narrowing of the arterial lumen; for this reason, it is not an index of the functional status of the artery.