ADDITIONAL PRESSURE-DROP AT A BIFURCATION DUE TO THE PASSAGE OF FLEXIBLE DISKS IN A LARGE-SCALE MODEL

The flow of red blood cells (RBC) through a microvascular capillary bi furcation was modeled in a large scale system in which rigid circular tubes and bifurcations (diameter=.95 cm) simulated capillaries and cap illary bifurcations, flexible disks (undeformed diameter=0.75 cm) simu lated RBC and glycerol simulated plasma. At low Reynolds numbers (0.01 to 0.1), pressure drop was measured in the tubes upstream and downstr eam from the bifurcation as well as across the bifurcation itself, for various flow splits at the bifurcation while the inflow in the upstre am tube was held constant. Pressure gradient across the bifurcation is taken to be the average of the upstream and downstream pressure gradi ents if the additional pressure drop at the bifurcation due to the par titioning of flow and disks is negligible. For the case of glycerol al one, the ratio of pressure gradient (G) at the bifurcation to the one at the upstream region was always greater than expected and reached 1. 14 when the flow in the side branch was zero. With introduction of fle xible disks into the system, G at the bifurcation was as much as 10 ti mes the G at the upstream region as disks came in contact with, or clo se to, the dividing line of the bifurcation and paused momentarily bef ore they entered one or the other side of the bifurcation. The largest G was for even flow split at the bifurcation and the smallest G was f or the case where the flow in the side branch was smallest. Therefore, for the range of tube hematocrits (0-30 percent) and flow splits test ed here, a significant additional pressure drop at the bifurcation is observed.