Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session M18: Biological fluid dynamics: Hemodynamics |
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Chair: Amirhossein Arzani, Northern Arizona University Room: Georgia World Congress Center B305 |
Tuesday, November 20, 2018 8:00AM - 8:13AM |
M18.00001: A novel residence-time based blood rheology model: Are we overestimating the non-Newtonian behavior of blood in patient-specific models? Amirhossein Arzani The choice of blood rheology is often considered an important assumption in patient-specific modeling of cardiovascular disease. Blood is known as a non-Newtonian fluid where red blood cell (RBC) aggregation and rouleaux formation contribute to the shear-thinning behavior of blood. Current non-Newtonian models prescribe viscosity as a function of shear rate. However, rouleaux formation requires not only low shear rates but also high residence-time. Herein, a novel hybrid blood rheology model is presented where the non-Newtonian effects are only activated in high residence-time regions where RBCs have enough time to form rouleaux structures. Patient-specific abdominal aortic and cerebral aneurysm models are considered. Highly resolved numerical simulations of blood flow are performed using Oasis, a minimally dissipative solver. Rouleaux formation likelihood is modeled using a backward particle residence-time measure. The hybrid residence-time based non-Newtonian model shows reduced shear-thinning effects and estimates hemodynamics qualitatively indistinguishable and quantitatively close to the Newtonian model. Our results suggest that current non-Newtonian models commonly used in the literature overestimate the non-Newtonian behavior of blood. |
Tuesday, November 20, 2018 8:13AM - 8:26AM |
M18.00002: Volumetric vs. Linear Reduction of Arterial Stenosis for Trans-stenotic Pressure Gradient in Image-based Computational Hemodynamics Monsurul Khan, Rou Chen, Alan P Sawchuk, Xin Fang, Raghu L. Motaganahalli, Huidan (Whitney) Yu Arteries, transport oxygenated blood, is essential for sustaining life functions. Lumen reduction of an artery, known as arterial stenosis, causes insufficient blood supply and may lead to a fatal consequence such as heart attack and ischemic stroke. While the linear (diameter) reduction of arterial lumen has been a practical measurement, trans-stenotic pressure gradient is a more accurate measurement for determining the severity of blood flow blockage therefore image-based computational hemodynamics has emerged as a unique and powerful tool to noninvasively quantify the trans-stenotic pressure gradient in human arteries. In this work, we use a developed and validated in-house computation package, named InVascular, to study the relationship between the lumen reduction and trans-stenotic pressure gradient, aiming to provide more appropriate measurement of the severity of a diagnosed arterial stenosis from CT or MRI imaging. Through the parametrization of an image-based renal stenosis, fixing volumetric reduction with varying linear reduction and fixing linear reduction with varying volumetric reduction, by deteriorating the 3-D shape of the stenosis, we demonstrate that volumetric reduction of the renal lumen is more accurate to reflect the trans-stenotic pressure gradient. |
Tuesday, November 20, 2018 8:26AM - 8:39AM |
M18.00003: The novel criterion of Reynolds resolution to assess the wall shear stress accuracy estimated by magnetic resonance velocimetry Byungkuen Yang, Seungbin Ko, Jee-Hyun Cho, Jeesoo Lee, Simon Song Magnetic resonance velocimetry (MRV) is a versatile tool to obtain hemodynamic information related to cardiovascular disease. The wall shear stress (WSS) is one of important hemodynamic parameters available with MRV for clinical applications, and is considered to play an important role in assessing the development of atherosclerosis or plague rupture. Nevertheless, the accuracy of WSS estimated by MRV is rarely evaluated or reported in literature, especially in in vivo studies. We propose a novel and facile criterion to assess the accuracy of WSS estimation in MRV studies based on dimensional analysis. To ensure the inclusion of diverse and extensive cases, we evaluated the accuracy of WSS obtained by various MRV setups such as different radio frequency coils, strengths of magnetic field, even numerical results simulating MR measurements in addition to various Reynolds numbers and spatial resolutions. As a result, we propose a novel and simple criterion of Reynolds resolution which is found to be related to closely to the WSS accuracy. |
Tuesday, November 20, 2018 8:39AM - 8:52AM |
M18.00004: Nanoparticle diffusion in sheared cellular blood flow Zixiang Liu, Jonathan R Clausen, Rekha R Rao, Cyrus K Aidun We apply a three-dimensional lattice-Boltzmann based multiscale and multicomponent blood flow solver to interrogate the mechanisms of enhanced nanoparticle (NP) diffusion in blood flow over a wide range of shear rate and hematocrit. Anomalous dispersive behavior is observed in the transient NP-red blood cell (RBC) interaction. In the long-time asymptotic regime, the cross-stream diffusivity exhibits sublinear scales, while the longitudinal diffusivity shows superlinear scale. The deviation from classical linear shear-rate scaling is attributed to the morphological change of RBC under shear. This work provides insight in the design of optimal nano-drug systems and creates a more precise constitutive link between the hemorheological properties and the NP diffusion due to interaction with RBC (RBC-enhance diffusion) and Brownian effects in blood flow. |
Tuesday, November 20, 2018 8:52AM - 9:05AM |
M18.00005: Reduced order coronary hemodynamics modeling Mehran Mirramezani, Shawn C Shadden Image-based computational fluid dynamic simulations have been widely employed to characterize the global and local blood flow features in the cardiovascular system. Although these 3D simulations enable comprehensive analysis of hemodynamics, they come at a high computational cost. Reduced-order modeling (ROM) of blood flow provides the ability to study hemodynamics of large cardiovascular networks with comparatively negligible computational cost. This is useful when multiple simulations are desirable, such as for data assimilation, optimization and uncertainty analysis. The goal of this study is to develop ROM to capture vessel-level pressure and flow dynamics in the coronary arteries. Here we developed a fully lumped parameter model to predict pressure and flow throughout patient-specific models of the coronary arteries. We test the ability of our ROM to compute fractional flow reserve (FFR) in stenotic coronary arteries, since such information is highly relevant to clinical diagnosis of coronary disease. Finally, we evaluated the robustness of the computed FFR by quantifying the uncertainties in our modeling. Our approach demonstrated strong agreement with fully 3D simulations for several patient-specific models including arteries with significant stenosis. |
Tuesday, November 20, 2018 9:05AM - 9:18AM |
M18.00006: Red blood cell partitioning at simulated bifurcations in physiologically realistic microvascular networks Prosenjit Bagchi, Peter Balogh Partitioning of red blood cells (RBCs) at vascular bifurcations is studied using direct numerical simulations of cellular-scale blood flow in physiologically realistic microvascular networks. The in silico networks are constructed following in vivo data, and are comprised of multiple bifurcations. Flow of deformable RBCs at physiological hematocrit is considered, and the dynamics of each individual cell are accurately resolved. The simulations predict the classic disproportionality in cell partitioning, as observed in vivo, where a daughter vessel with a higher flow fraction receives a disproportionately higher fraction of cells. We also observe a reverse partitioning where the branch receiving a higher flow fraction receives a lower fraction of cells. The cellular-scale mechanisms underlying the diverse types of partitioning are presented. The sequential nature of the bifurcations is shown to result in a positive or negatively skewed hematocrit profile leading to the classical or reverse partitioning. Two underlying mechanisms, namely the plasma skimming and cell screening mechanisms, are quantified. The plasma skimming mechanism is shown to under-predict cell partitioning, leaving the cell screening mechanism to make up for the difference. |
Tuesday, November 20, 2018 9:18AM - 9:31AM |
M18.00007: Analysis of nanoparticle transport in blood flow through microvascular bifurcations Jonathan R Clausen, Zixiang Liu, Dan S Bolintineanu, Jeremy B Lechman, Justin L Wagner, Kimberly S Butler, Rekha R Rao, Cyrus K Aidun Delivery of nanoparticle (NP)-mediated drugs to bio-targets requires transport of NPs through microvasculature with bifurcations. The NP interaction with red blood cells (RBCs) and transport mechanism in such complex geometries has remained largely unexplored. In current work, we use an efficient computational approach based on coupled lattice Boltzmann and Langevin Dynamics (LB-LD) for simulating NP transport through microvascular bifurcations. To validate this approach, the blood flow and NP distribution in a chicken embryo bifurcation are measured and reconstructed via the in silico tool. The simulation compares favorably with the in vivo measurements. The LB-LD computational approach is shown to well capture the Brownian and RBC-enhanced NP diffusion and the Fåhræus effect. The partition of the NP concentration in the daughter branches shows dependence on bifurcation angle and contraction ratio. |
Tuesday, November 20, 2018 9:31AM - 9:44AM |
M18.00008: The cell-free layer (CFL) in simulated microvascular networks Peter Balogh, Prosenjit Bagchi As blood flows in small vessels, a plasma layer forms near the vessel walls that is free of red blood cells (RBCs). This cell-free layer (CFL) plays important hemorheological and biophysical roles. Blood vessels are typically tortuous and they sequentially bifurcate in to smaller vessels or merge to form larger vessels. Because of this geometric complexity, the CFL in vivo is 3D and asymmetric, unlike in fully developed flow in straight tubes or channels. Using a high-fidelity model of cellular-scale blood flow in physiologically realistic microvascular networks, we provide the first simulation-based analysis of the 3D CFL, including hydrodynamic origins of the observed behavior. We show that the CFL significantly varies over the vascular networks. Along the vessel lengths, such variations are predominantly non-monotonic. We show that vessel tortuosity causes the CFL to become more asymmetric along the length, and identify a curvature-induced cross-flow migration of the RBCs as the underlying mechanism. The vascular bifurcations and mergers are also seen to change the CFL profiles, and in the majority of them the CFL becomes more asymmetric. For most mergers, the dominant mechanism by which such changes occur is identified as the geometric focusing. |
Tuesday, November 20, 2018 9:44AM - 9:57AM |
M18.00009: Uncertainty quantification for patient-specific cardiovascular simulations in high-performance computing Jongmin Seo, Daniele E. Schiavazzi, Alison L Marsden Cardiovascular blood flow simulations solve the incompressible Navier-Stokes equations in patient-specific geometries constructed from image data with physiologic boundary conditions. To assess variabilities of simulation predictions under uncertainties in clinical measurements, we perform uncertainty quantification. In our computational model, we account for fluid-structure interaction, coupling blood flow with deformable vessel walls via an Arbitrary-Lagrangian-Eulerian framework, and open-loop lumped parameter boundary conditions to model the peripheral circulation. We consider multiple sources of input uncertainty, including uncertainties in inflow waveform, material properties, and resistance boundary conditions. We introduce several strategies to reduce computational cost for forward uncertainty propagation using Kalhunen-Loeve expansion and a sub-modeling approach. We report statistics on quantities of interest including flow rate, pressure at the distal vessel branches, time-averaged wall shear stress, and wall displacement. Comparisons of several forward uncertainty propagation methodologies will be discussed including Monte Carlo and a recently proposed multiresolution framework. |
Tuesday, November 20, 2018 9:57AM - 10:10AM |
M18.00010: Study type B aortic dissection using a deconvolution-based nonlinear filter Huijuan Xu, Alessandro Veneziani Progressive false lumen aneurysmal degeneration in type B aortic dissection (TBAD) is a complex process with a multi-factorial etiology. Patient-specific computational fluid dynamics simulations provide spatial and temporal hemodynamics factors and registration methods quantify the morphological changes of the false lumen (FL). By considering both simultaneously, correlations can be established to potentially help understanding the intertwining between hemodynamics and false lumen progression. A deconvolution-based nonlinear filter is applied to Navier-Stokes equations with a specific calibration method for the boundary conditions. Correlations between hemodynamics and the deformation of the FL are investigated. Moreover, backflow stabilization effect of the filter and sensitivity of the filter parameter are studied. The model is able to capture the flow properties accurately with a large reduction in computational time. The time averaged wall shear stress is found to correlate positively with FL dilation (𝑟2 = 0.44). A mild negative correlation is found between oscillatory shear index and deformation (𝑟2 = 0.29). High relative residence time is suspected to be correlated with thrombose absorption. |
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