Doppler techniques for lower extremity arterial diagnosis

Doppler ultrasonic methods are based on a frequency shift incurred in the reflected sound from moving objects, for example, red blood cells. According to the desired depth of penetration, ultrasonic frequencies between 2 and 10 MHz are used. Continuous-wave Doppler detects all blood flow through the path of the ultrasound beam and pulsed-wave Doppler ultrasound permits detection of flow at specific sites in the arterial lumen. Through measurement of the systolic blood pressure, the extent of hemodynamically-significant arterial occlusive disease can be assessed. With the use of the ankle-arm index, which is normally greater than 1.0, compensation is enabled for variations in systemic pressure. Localization of the occlusive lesion can be obtained by measuring the systolic pressure at various levels in the limb. Normally, the ratio of high-thigh to brachial artery systolic pressure is greater than 1.2 and the difference in systolic pressure between any two adjacent levels in the leg should be less than 20 mm Hg. Measurement of toe pressure may be helpful when the ankle pressure is falsely elevated due to arterial calcification; in normal limbs, the systolic toe pressure is about 80 to 90% of the brachial systolic pressure. The use of small cuffs on large limbs can result in spuriously high pressure and medial calcification in the arterial wall can also lead to falsely high pressures. Treadmill exercise testing with determination of the immediate drop in ankle systolic pressure and the time for recovery to resting pressure is valuable to confirm or rule out intermittent claudication as the cause of leg pain and to detect severe multiple level arterial disease.(ABSTRACT TRUNCATED AT 250 WORDS)