Hemodynamic Characteristics of a Tortuous In Vivo Microvessel Using Red Blood Cell Resolved Simulations*

Tortuous microvessels are characteristic of microvascular remodeling associated with numerous physiological and pathological scenarios. These vessels have unique morphology compared to straight vessels, the latter being the subject of extensive flow modeling studies over the past few decades. Three-dimensional (3D) hemodynamics in tortuous microvessels influenced by red blood cells (RBCs), however, remain largely unknown and important questions remain. Is blood viscosity influenced by vessel tortuosity? Do RBC flow dynamics cause localized hematocrit variations in tortuous vessels? How do these dynamics affect wall shear stress (WSS) patterns and the near-wall cell-free layer (CFL)? Here we use high-fidelity 3D RBC-resolved simulations in a tortuous in vivo microvessel over a range of physiological flow conditions to elucidate novel hemodynamic characteristics unique to this vessel morphology. The findings show how curvature can increase apparent viscosity by upwards of 26% compared to a straight tube. Due to unique RBC flow patterns, curvature-dependent variations in the Fahraeus effect are quantified and observed. We further characterize dependencies of the CFL and WSS on flow conditions and demonstrate correlation patterns between these two quantities as influenced by tortuosity. Altogether, the results provide new information to better understand the role of vessel tortuosity in physiological and pathological processes, as well as help improve reduced-order models.