Near wall concentration profiles of 1.0 and 2.5 microns beads during flow of blood suspensions.

A freeze-capture method was used to determine the concentration profiles of latex beads in the flow of blood suspensions at a wall shear rate of 400 s-1 in hollow fibers of 200 microns i.d. Bead diameters of 1.0 and 2.5 microns and suspension hematocrits from 15 to 80% were used. All profiles exhibited an excess of beads in the 20 microns closest to the wall and a uniform central concentration. Near-wall excesses greater than 2.5 times the central concentration occurred with suspensions having 2.5 microns beads when the hematocrit was 15-40%. Although large near-wall excesses sometimes occurred for the small beads and higher hematocrits, the usual event was a small near-wall excess. A Mann-Whitney-Wilcoxan test showed that the group of data for 2.5 microns beads in suspensions with hematocrits ranging from 15 to 40% was significantly different from all other data (p less than 0.0002). As the 2.5 microns beads approximate the average platelet, these data suggest that blood flows with physiologic hematocrits are associated with larger near-wall excesses of platelets than blood flows with elevated hematocrits.