The Ultrasonic Flowmeter as an Adjunct to Femoral Arteriography

Abstract

Evaluation of blood flow through the intact human skin has been made possible through the development of the transcutaneous Doppler flowmeter (2). Clinical investigation has shown that this unit can aid in the evaluation of patients with arterial disease (3). We are evaluating the use of this instrument in the performance and interpretation of femoral arteriography. The device consists of a piezoelectric crystal which produces an ultrasound beam at an angle through the skin (Fig. 1). A second crystal, slightly separated from the first, detects the reflected sound. Backscattered sound from moving intravascular components is changed in frequency by an amount proportional to the velocity of the particles. Stationary objects reflect sound at the same frequency as their origin. A sudden increase in frequency indicates vascular stenosis, and cessation of sound indicates occlusion. Distal to an occlusion the characteristic flow patterns are altered, indicating either a patent vessel supplied by collateral flow or the presence of only collateral vessels. Patients are examined with the Doppler flowmeter prior to femoral arteriography. Since tracing the entire length of the vessel is time-consuming and not practical, readings are made only over the areas for palpation of the femoral, popliteal, and anterior and posterior tibial pulses. The pulses are graded as to intensity, and a verbal description and a tape-recording of the sound produced by the flow are made. Arteriography is performed through a percutaneous needle in the femoral artery. The flowmeter recordings are compared to the arteriographic findings. Injection of contrast material into the femoral artery distal to an iliac artery occlusion demonstrates the distal vessels more clearly than injection into the aorta or contralateral femoral artery. We use the Doppler flowmeter to determine the patency of the femoral artery when a pulse is not palpable. If flow is detected, the injection is made on the involved side. The distal femoral artery, its outflow, and collateral vascular supply are better visualized than by other means (Fig. 2). Pre-arteriographic evaluation of occlusions aids in performing the roentgenographic vascular study. Where popliteal artery flow is not discernible by ultrasound the filming period is lengthened to demonstrate the distal vessels. When the superficial femoral artery is occluded, the distal popliteal artery branches may fill incompletely during arteriography. The flowmeter may indicate patent vessels despite lack of arteriographic filling. Following transluminal femoral artery dilatation (1), the Doppler flowmeter is used to determine patency of the peripheral vessels over the following months. We have performed transluminal dilatation in several patients in whom the popliteal artery branches were severely diseased and no pedal pulses were palpable. Comparison of recordings before and after dilatation indicated improvement in flow even though the pedal pulses were never palpable.