Hemodynamic Characteristics of Tortuous Microvessels Using High-Fidelity Red Blood Cell Resolved Simulations
Authors: Hossain Mir Md Nasim , Hu Nien-Wen , Kazempour Ali , Murfee Walter L , Balogh Peter 
Published: May 2024

Introduction: 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 hemodynamics in tortuous microvessels influenced by red blood cell (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 patterns and the near-wall cell-free layer? Previous work has connected physiological function to tortuosity1, while other recent work has shown how RBC dynamics and vessel complexity can influence hemodynamics2. Such findings drive our hypothesis that unique hemodynamic characteristics exist in tortuous microvessels compared to straight vessels. Revealing such differences and answering the above questions requires 3D RBC-resolved simulations. The objective of this work is to investigate the hemodynamic characteristics of tortuous microvessels using high-fidelity red blood cell (RBC) resolved simulations and real image data. Methods: High fidelity RBC resolved simulations were performed using a 3D immersed boundary method (IBM) based fluid dynamic solver3. A tortuous microvessel is constructed in 3D based on imaging of a rat mesenteric microvascular network post angiogenic remodeling. The diameter and length of the vessel are 20 μm and 930 μm, respectively. Simulations were performed spanning a range of physiological shear rates (SR) and overall hematocrit levels (Ht). Output simulation data is used to parametrically quantify characteristics of apparent viscosity, local hematocrit variations, time-averaged wall shear stress (TAWSS) and cell free layer (CFL) patterns due to vessel tortuosity. Data and Results: The findings show how curvature can increase apparent viscosity to different degrees based on overall Ht & SR (max 236% increase), with local variations occurring over the vessel length at sites of curvature changes (max 2.25cP change). Because of RBC flow patterns, local variations in tube hematocrit are found to occur which result in local curvature-dependent variations in the Fahraeus effect. We further characterize dependencies of the CFL and TAWSS on Ht & SR and resultant lengthwise 3D spatial variations along the vessel, and demonstrate correlation patterns between these two quantities as influenced by tortuosity. Conclusions: New findings from this work reveal significant dependency of hemodynamic parameters and spatial variations on vessel tortuosity. 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. NSF CBET 2309559, NIH R21HL159501, and Expanse at the San Diego Supercomputer Center per NSF Accelerate Award BIO230073. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.