Poster U4 - Revealing Hemodynamic Characteristics of a Tortuous Microvessel Using High-Fidelity Red Blood Cell Resolved Simulations

Introduction: Tortuous microvessels are characteristic of microvascular remodeling observed is various physiological and pathological conditions. These vessels exhibit distinctive morphology compared to straight vessels, the latter being 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, leaving significant questions unanswered. 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 tortuosity(1), while other recent work has shown how RBC dynamics and vessel complexity can influence hemodynamics(2). These findings support our hypothesis that distinct hemodynamic characteristics exist in tortuous microvessel compared to straight vessels. Revealing such differences and addressing the above questions requires 3D RBC-resolved simulations. The objective of this work is to investigate the hemodynamic characteristics of a real tortuous microvessel using high-fidelity red blood cell (RBC) resolved simulations.

Materials and

Methods: High fidelity RBC resolved simulations were performed using a 3D immersed boundary method (IBM) based fluid dynamic solver(3). A tortuous microvessel is constructed in 3D, assuming a constant vessel diameter based on imaging of a rat mesenteric microvascular network post angiogenic remodelling, as shown in Fig 1A. 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.

Results, Conclusions, and Discussions: Results & Discussion :
The findings show how curvature can increase apparent viscosity to different degrees based on overall HT & SR up to 26% compared to straight tube, with local variations occurring over the vessel length at sites of curvature changes as shown in Fig 1D. Wall shear stress(WSS) sectional hotspots are observed to fluctuate by up to 3 dyne/cm2 because of curvature variation, as illustrated in Fig 1E. Due to 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 the resultant lengthwise 3D spatial variations along the vessel, and demonstrate correlation patterns between these two quantities as influenced by tortuosity.

Conclusions:
Novel findings from this work reveal a significant dependency of hemodynamic parameters and spatial variations on vessel tortuosity for a range of physiological conditions. The results provide new insights to better understand the role of vessel tortuosity in physiological and pathological processes, as well as contribute to improve reduced-order models.

Acknowledgements (Optional): Support or Funding Information:
NSF CBET 2309559, NIH R21HL159501, and Expanse at the San Diego Supercomputer Center per NSF Accelerate Award BIO230073.

References:
(1)Han et. al, J. Vasc. Res., 2012.
(2)Hossain et. al, FUNCTION, 2023.
(3)Balogh et. al, JCP., 2017.