The effect of celiac and renal artery outflows on near-wall velocities in the porcine iliac arteries.

The effects of the outflow of aortic blood through the celiac and renal arteries on the flow field in the external iliac arteries were studied under steady and physiologically realistic pulsatile flow conditions. Laser Doppler velocimetry (LDV) measurements were made close to the medial, lateral, ventral, and dorsal walls of the external iliac branches of a clear, flow-through replica of a porcine aorta and its daughter vessels. The outflow from each branch of the replica was controlled so that the infrarenal aortic flow rate and the flow partition at the aortic trifurcation were the same for all experiments. LDV measurements were made with flow exiting through both the renal and celiac artery ostia, only the celiac ostium, and neither ostium. The steady flow results indicate that while the outflow through the renal arteries did not have a significant effect on near wall shear rate in the external iliac arteries, the flow through the celiac artery did. However, in pulsatile flow, three indices of near wall velocity in the iliac arteries were unaffected by celiac artery outflow, while a fourth showed a small effect that can be attributed to differences in minimum velocity. These results indicate that reliable simulations of blood flow in the external iliac arteries can be carried out without including the renal and celiac vessels, provided that the correct infrarenal flow wave is used. They also demonstrate that the flow field downstream of a region, such as a branch, that strongly alters the flow, can be nearly independent of the velocity field entering the region.

Effect of periodic alterations in shear on vascular macromolecular uptake.

Experiments were carried out in swine to test the hypothesis that changes in the fluid dynamic environment of the arterial wall, with time constants of several minutes to perhaps a few hours, prompt adaptive responses that transiently increase endothelial permeability. After parenteral Evans Blue Dye (EBD) administration, the hemodynamics of the external iliac arteries of the experimental animals were altered using a reversible arteriovenous femoral shunt. For 3 h, the shunt was opened and closed with a period (tau) between 1-180 min. Subsequently, the animal was euthanized and the iliac vessels were photographed en face to obtain the distribution of EBD-bound albumin uptake by the tissue during its exposure to the dye. Albumin uptake increases with tau in a fashion that can be explained by an a priori model of the adaptive permeability response, with a time constant of about an hour.

Effect of alterations in femoral artery flow on abdominal vessel hemodynamics in swine.

In support of an in vivo investigation in swine of the influence of changes in fluid dynamic wall shear on arterial macromolecular permeability, a procedure has been developed to alter the flows in the porcine posterior arterial vasculature by opening and closing a reversible arteriovenous shunt placed on one of the femoral arteries. Laparoscopic techniques were used to place appropriately modified Transonic Systems ultrasonic flow probes on both external and circumflex iliac arteries, and on the terminal aorta. Flow measurements were made prior to shunt placement, and with the shunt open and closed, to measure the influence of altered external iliac artery flow on the distribution to the infrarenal abdominal vessels. Similar experiments were carried out to relate the flow rates in the external iliac arteries to those in the femoral arteries, which are more accessible. Based on the relationships among the measured flow rates, rules have been developed to estimate the major infrarenal flows in the pig, at baseline and with the shunt opened and closed, from only the flow rates measured at the two femoral arteries.