Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session P29: Biological Fluid Dynamics : Red Blood Cells and Hemodynamics |
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Chair: Michael Graham, U. Wisconsin Room: 611 |
Monday, November 25, 2019 5:16PM - 5:29PM |
P29.00001: Dynamics of RBCs under shear flow in sickle cell disease. A tool for monitoring the clinical state of patients. Emmanuele Helfer, Maxime Sahun, Scott Atwell, Alexander Hornung, Anne Charrier, Annie Viallat, Catherine Badens The regimes of motion of red blood cells (RBCs) under shear flow have been extensively studied because they directly relate to the cell mechanical properties. In addition to tumbling and tanktreading motions, other regimes were recently discovered, such as swinging, flip-flopping, and rolling. Computational studies provide complex phase diagrams of motion that depend on the ratio of RBC cytoplasm to external fluid viscosities and on the capillary number. Surprisingly, no experiments have been performed on RBCs from patients with sickle cell disease (SCD) which have altered mechanical properties. Here, we show that the dynamics of SCD-RBCs is modified and correlates with change in RBC density and state of hydration. Though the tumbling - flip-flopping -- rolling path observed by increasing shear rate is not changed for SCD, the rolling to tanktreading threshold occurs at higher shear stress. We use this feature to propose a mechanical marker, namely the fraction of tanktreading RBCs in a large cell population, to follow the clinical state of SCD patients and to predict the very handicapping vaso-occlusive crises. We show that this marker is patient-dependent and is stable over time in the ``out of crisis'' period while it strongly varies during the course of a crisis. [Preview Abstract] |
Monday, November 25, 2019 5:29PM - 5:42PM |
P29.00002: Flow-induced Segregation and Dynamics of Red Blood Cells in Sickle Cell Disease Xiao Zhang, Christina Caruso, Wilbur A. Lam, Michael D. Graham Blood flow in sickle cell disease (SCD) can substantially differ from the normal due to significant alterations in the physical properties of sickle red blood cells (RBCs). Chronic complications, such as endothelial dysfunction, are associated with SCD, for reasons that are unclear. Direct numerical simulations are performed to investigate the dynamics of a binary suspension of flexible biconcave discoids and stiff curved prolate spheroids that represent healthy and sickle RBCs, respectively, in plane Poiseuille flow. The key observation is that the sickles exhibit a strong margination towards the walls. The marginated sickle RBCs roll like rigid bodies and may poke and damage the walls due to their stiffness and ``spikiness''. A simplified drift-diffusion model, which incorporates hydrodynamic migration and pair collisions, predicts a greater margination in a binary suspension containing a small fraction of stiff cells than in a pure suspension of stiff cells, which may explain the experimental observation that a heterogeneous blood sample containing healthy (flexible) RBCs with a small fraction of stiffened RBCs causes more severe endothelial inflammation and dysfunction than a homogeneous sample of stiffened RBCs. [Preview Abstract] |
Monday, November 25, 2019 5:42PM - 5:55PM |
P29.00003: 3 D Classification of Red Blood Cells in microchannels Christian Wagner Red blood cells (RBCs) are very soft objects that can pass capillaries smaller than the cell's diameter. Due to their high deformability, they couple strongly with the flow and can adopt many different shapes. For their quantitative characterization we developed a new confocal 3D imaging technique for fluorescent stained RBCs. We found two equilibrium cell shapes under certain flow condition: the so called 'slipper' and the 'croissant' shape. Numerical simulations are in good agreement with experimental observations. In addition, high throughput data of classical 2-D microscopy combined with an adaptive neural network allow us to obtain the full phase diagram of red blood cell shapes as a function of the flow rate. In larger channels, we use the confocal technique to characterize the margination of single rigidified RBCs in a suspension of healthy RBCs. Margination of e.g. white blood cells or platelets at the vessel walls is a haemodynamic key mechanism of our immune system. Our confocal observation technique allows us to characterize the distribution of hard vs. soft cells in full time and space resolution for the first time. Again numerical simulations are in good agreement although some quantitative differences remain that need further investigations. [Preview Abstract] |
Monday, November 25, 2019 5:55PM - 6:08PM |
P29.00004: Reduced-order Models for Migration and Shear-induced Diffusion of Red Blood Cells in Simple Geometries Harry Wang, Joseph Sherwood, Omar Matar From a fluid dynamics perspective, blood can be treated as a suspension of highly-deformable red blood cells (RBCs). The RBCs migrate away from the walls of the confining vessel primarily due to their deformability, resulting in inhomogeneous distributions, distinctive in the microvasculature. Migration away from the walls is countered by shear-induced diffusion effects due to hydrodynamic particle-particle interactions. While mesoscale simulations can capture RBC dynamics well, there is a need for more efficient continuum models that can accurately model RBCs distributions in larger networks that describe the microvasculature. Here, we study the behaviour of RBC suspensions in simple flow configurations using reduced-order models. We use a drift-diffusion equation to describe the evolution of the RBC concentration, coupled to balance equations for the bulk mixture. Different forms for migration and shear-induced diffusion terms in the drift-diffusion equation are compared in rectangular and cylindrical geometries. The problem is reduced to two-dimensions using appropriate scaling, which exploits geometrical length-scale disparity, and asymptotic reduction. Velocity and concentration profiles predicted by our simulations are compared to experimental data in the literature. [Preview Abstract] |
Monday, November 25, 2019 6:08PM - 6:21PM |
P29.00005: Red cell-resolved blood flow modeling in in vivo-like microvascular networks: predicting hemodynamic changes due to loss of red cell deformability Saman Ebrahimi, Prosenjit Bagchi Microvascular networks in human body are made of the smallest blood vessels, and responsible for gas and nutrient transport to tissues, and regulation of blood flow in individual organs. The architecture of a microvascular network is complex and characterized by bifurcating, merging and tortuous vessels. Blood in such small vessels behaves as a concentrated suspension primarily made of red blood cells (RBC) which are extremely deformable. We developed a 3D simulation technique to model flow of deformable RBCs in physiologically realistic microvascular networks that are comprised of multiple bifurcating and merging vessels. The model is versatile, and can consider networks irrespective of topological/geometrical complexities. It provides fully 3D and detailed information of hemodynamic quantities, such as RBC partitioning at bifurcations, cell-free layer, and wall shear stress. Many diseases, such as sickle cell disease, malaria and diabetes mellitus, are associated with a loss of RBC deformability. A detailed quantification of changes in microvascular hemodynamics under such conditions is lacking. Using the model, we provide the first-ever simulation results on the changes in network-scale blood flow under varying RBC deformability. The specific focus is on retinal microcirculation which is known to be adversely affected due to loss of RBC deformability. [Preview Abstract] |
Monday, November 25, 2019 6:21PM - 6:34PM |
P29.00006: Non-monotonic blood viscosity and cell free layer dependence on cell aggregation Yeng-Long Chen, Chih-Tang Liao In blood flow, large proteins in the blood plasma induces attraction between red blood cells (RBCs) and form columnar aggregates. As inter-cell attraction increases due to increased protein concentration as result of physiological changes, aggregate size and shape change. Such structural changes could strongly affect blood flow in micro-vessels where aggregate size is comparable to vessel diameter. We employ hybrid lattice Boltzmann -- Langevin dynamics to investigate how increasing inter-cell attraction affect the aggregate structure, flow-induced cell free layer, and blood viscosity in micro-vessels. We find that the cell free layer thickness exhibits non-monotonic dependence on aggregation, leading to shear-thinning and shear-thickening dependence on inter-cell attraction. We identify the structure-dynamics coupling mechanisms responsible for the complex dependence. [Preview Abstract] |
Monday, November 25, 2019 6:34PM - 6:47PM |
P29.00007: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 6:47PM - 7:00PM |
P29.00008: Development of margination of platelet-sized particles suspended in red cell suspension flows through Y-shaped bifurcating microchannels Tenki Onozawa, Toma Kawauchi, Junji Seki, Tomoaki Itano, Masako Sugihara-Seki In the blood flow through microvessels, platelets are known to have enhanced concentrations near the vessel wall, which is called “margination” or “Near-Wall Excess (NWE)” of platelets. At a bifurcation of vessels this preferential distribution of platelets would be impaired and gradually reconstructed again in the daughter vessels. The present study was aimed at analyzing the process of the reconstruction of NWE in the daughter vessel by \textit{in vitro} experiments. We adopted platelet-sized fluorescent particles for platelet substitutes to measure the distribution of particles suspended in the red cell suspension flow through a microchannel of Y-shaped bifurcation, by use of a confocal laser scanning microscope -- high speed camera system. In the parent channel just upstream of the bifurcation, particles showed fully developed NWE. Reflecting this distribution, the particles were located mainly near the outer wall at the inlet of the daughter channel, and exhibited a lateral shift from the outer wall to the inner wall until NWE was developed. Since the development length of NWE from the bifurcation was almost independent of the flow rate through the channel, the velocity of the lateral shift was suggested to be nearly proportional to the main flow velocity. [Preview Abstract] |
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