Profiles of velocity in coronary arteries of dogs indicate lower shear rate along inner arterial curvature.

Abstract

Multiple-range, gate-pulsed Doppler veloclmetry was used to examine the velocity profile within the lumen of the left circumflex and toft anterior descending coronary arteries of 10 anesthetized, open-chest dogs at rest and after administration of propranolol and Intracoronary adenoslne. The peak dlastollc and mean profiles of velocity were skewed away from the Inner walls of the vessels (p<0.01). The extent of skewness was not affected by propranolol or adenoslne. The shear rates were significantly lower along the Inner wall In comparison to the outer wall under all conditions In both the left circumflex and the left anterior descending coronary arteries (p<0.017). Irrespective of the levels of flow, therefore, the velocity profiles were skewed away from the Inner wall of the coronary arteries. Consequently, the shear rates were lower along the Inner walls of the coronary arteries. (Arteriosclerosis 9:167-175, March/April 1989) C urvature of arteries alters the shear stress at the wall from that which would occur in straight vessels. The magnitude and location of high-and low-shear stress may be important because shear stress may contribute to atherogenesis. Theories that implicate either low-shear stresses or high-shear stresses in the pathogenesis of atherosclerosis have been proposed.1 -6 Subsequent investigations have shown an influence of shear upon endothelial structure, function, and intimal thickening. 9 -22 In the coronary vasculature, the large epicardial vessels display a significant curvature as they course over the surface of the heart. In flow through curved tubes, the profile of velocity is skewed away from the inner wall, resulting in lower shear stresses near the inner curvature of the tube. 23 In curved tubes, the effects of increased flow on wall shear are not easily predicted. Increased flow in a curved tube may increase the skewness of the velocity profile, altering the relative magnitude of shear at the inner and outer walls. 23 In addition, high flows can introduce secondary flows in the velocity profile. 24 This factor may tend to reverse the skewness of the velocity profile in a curved tube. 23 Although several investigators have reported the profile of velocity in the coronary arteries of animals, 26 -29 there is no general agreement as to the configuration of the velocity profiles in the coronary arteries.The shear stress at the wall of arteries caused by the flowing blood is defined as the product of the effective blood viscosity and the shear rate. 3031 The shear rate at the wall is the velocity gradient at the wall (du/dy, where u From the Henry Ford Heart and Vascular Institute, Detroit, Michigan.This work was supported in part by Grant HL23669-08 from the U.S. Public Health Sendee, National Heart, Lung, and Blood Institute.Address for reprints: Paul D. Stein, M.D., Henry Ford Heart and Vascular Institute, 2799 West Grand Boulevard, Detroit, Ml 48202.Received December 21, 1987; revision accepted September 29, 1988. is velocity in the axial direction and y is the distanc...

Collagen Induced Thrombus Formation at the Apex of Eccentric Stenoses - A Time Course Study with Non-Anticoagulated Human Blood

“…The corresponding shear rates at the apex of the stenoses where thrombus formation was triggered by im mobilized collagen fibrils, were 2600,10,500 and 32,000 s_1. The wall shear rate proximal and distal to the respective stenoses was 420 s_1, which is within the range of shear reported in average-sized healthy epicardial coronary arteries (23,27).…”

Effect of aspirin and epinephrine on experimentally induced thrombogenesis in dogs. A parallelism between in vivo and ex vivo thrombosis models.

“…Indeed, shrinkage may reduce the vessel lumen by 16%, and when this factor is taken into account would have decreased the calculated stenotic shear rate from 15,000-64,000 to 9,000-40,000 sec" 1 . With such a correction the average nonstenotic shear rate would be decreased from 400 to 260 sec" 1 , a value that is within the range of experimentally measured shear rates in the circumflex coronary artery of normal dogs 32 or in moderately stenosed human coronary arteries. 33 While wall shear rates (and concomitantly, shear stresses) have been studied extensively over the physiological range (up to 10,000 sec" 1 ), few perfusion studies have been conducted at these high-shear conditions or perhaps, more importantly, in flow situations in which high shear and complex recirculation patterns (lower shear) are encountered in close proximity, such as might occur in advanced stenosis.…”

Estimation of coronary flow reserve by intracoronary doppler flow probes and digital angiography

“…For peak velocity determination, the Doppler crystal sample volume must intercept the maximum portion of the velocity profile. The spatial velocity profile is not uniform cross coronary vessels, as has been reported by Bell and co-workers in normal animals [34]. Higher velocities at rest and after a hyperemic stimulus are skewed away from the inner curvature of the vessel.…”