In shear flow, red blood cells (RBCs) exhibit a variety of dynamic behaviors such as translation, tumbling, swinging, and tank-treading. The physiological consequences of these dynamic behaviors, however, are unknown. For example, how different cell dynamics, be it translation, tumbling, or tank-treading relate to ATP release and how these dynamics are altered by pathological geometries such as constrictions and plaque formations at asymmetric bifurcations are not known. Using microfluidic channels to mimic pathological geometries and RBCs with attached carboxylate beads, to follow any relevant motion, we are able to quantify the dynamical response of red cells to specific pathological geometries with in vitro models. Further, by using an ATP-luciferase enzymatic reaction we set out to determine if there is a functional difference, via chemical release, in cell behaviors. Previously, we correlated RBC deformation and ATP release (Wan et al, PNAS 2008) which in vivo is known to stimulate nitric oxide production, leading to vasodilation. High-speed video and a probability-based cell tracking algorithm make it possible to study large numbers of cells. Preliminary experiments have shown that when cells enter a constriction, there are increased instances of tumbling along constriction wall, while cells more central in the constriction are aligned and deformed by the entrance flow. The relation between the observed cell behaviors and resulting ATP release will be reported.

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