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 bifurcation was modeled in a large scale system in which rigid circular tubes and bifurcations (diameter = .95 cm) simulated capillaries and capillary bifurcations, flexible disks (undeformed diameter = 0.75 cm) simulated RBC and glycerol simulated plasma. At low Reynolds numbers (0.01 to 0.1), pressure drop was measured in the tubes upstream and downstream from the bifurcation as well as across the bifurcation itself, for various flow splits at the bifurcation while the inflow in the upstream tube was held constant. Pressure gradient across the bifurcation is taken to be the average of the upstream and downstream pressure gradients if the additional pressure drop at the bifurcation due to the partitioning of flow and disks is negligible. For the case of glycerol alone, 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 flexible disks into the system, G at the bifurcation was as much as 10 times the G at the upstream region as disks came in contact with, or close to, the dividing line of the bifurcation and paused momentarily before 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 for the case where the flow in the side branch was smallest. Therefore, for the range of tube hematocrits (0-30 percent) and flow splits tested here, a significant additional pressure drop at the bifurcation is observed.