Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session H7: Biofluids: Cardiovascular Fluid Mechanics I |
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Chair: Alison Marsden, University of California, San Diego Room: 3012 |
Monday, November 24, 2014 10:30AM - 10:43AM |
H7.00001: Coupling 1D Navier Stokes equation with autoregulation lumped parameter networks for accurate cerebral blood flow modeling Jaiyoung Ryu, Xiao Hu, Shawn C. Shadden The cerebral circulation is unique in its ability to maintain blood flow to the brain under widely varying physiologic conditions. Incorporating this autoregulatory response is critical to cerebral blood flow modeling, as well as investigations into pathological conditions. We discuss a one-dimensional nonlinear model of blood flow in the cerebral arteries that includes coupling of autoregulatory lumped parameter networks. The model is tested to reproduce a common clinical test to assess autoregulatory function - the carotid artery compression test. The change in the flow velocity at the middle cerebral artery (MCA) during carotid compression and release demonstrated strong agreement with published measurements. The model is then used to investigate vasospasm of the MCA, a common clinical concern following subarachnoid hemorrhage. Vasospasm was modeled by prescribing vessel area reduction in the middle portion of the MCA. Our model showed similar increases in velocity for moderate vasospasms, however, for serious vasospasm ($\sim$ 90{\%} area reduction), the blood flow velocity demonstrated decrease due to blood flow rerouting. This demonstrates a potentially important phenomenon, which otherwise would lead to false-negative decisions on clinical vasospasm if not properly anticipated. [Preview Abstract] |
Monday, November 24, 2014 10:43AM - 10:56AM |
H7.00002: Automated tuning for parameter identification in multiscale coronary simulations Justin Tran, Daniele Schiavazzi, Abhay Ramachandra, Andrew Kahn, Alison Marsden Computational simulations of coronary flow can provide non-invasively obtained information on hemodynamics and wall mechanics that can aid in treatment planning and improve understanding of disease progression. In this study, patient-specific geometry of the aorta and coronary arteries is constructed from CT scans and combined with finite element flow simulations. Lumped parameter networks are coupled as boundary conditions at the inlet and outlets and calculate global hemodynamic quantities. These tools have potential for clinical impact in identifying optimal geometries for Coronary Artery Bypass Grafts, in determining the risk of re-stenosis in saphenous vein grafts, or for studying other coronary diseases. Despite advances in simulation methods, clinical adoption of these tools is currently hindered by the lack of tools for uncertainty quantification. In current simulations, results are reported as single values without confidence intervals. These simulations also do not account for uncertainties in modeling assumptions, nor the uncertainties in the clinical measurements. This study will take the first step in quantifying these uncertainties. Distributions of the modeling parameters will be inferred through inverse Bayesian estimation and propagated through the model to determine parameter sensitivity and quantify confidence in simulation results. Quantification of these uncertainties is a crucial step towards acceptance of coronary flow simulations in the clinical community. [Preview Abstract] |
Monday, November 24, 2014 10:56AM - 11:09AM |
H7.00003: A patient-specific CFD-based study of embolic particle transport for stroke Debanjan Mukherjee, Shawn C. Shadden Roughly 1/3 of all strokes are caused by an embolus traveling to a cerebral artery and blocking blood flow in the brain. A detailed understanding of the dynamics of embolic particles within arteries is the basis for this study. Blood flow velocities and emboli trajectories are resolved using a coupled Euler-Lagrange approach. Computer model of the major arteries is extracted from patient image data. Blood is modeled as a Newtonian fluid, discretized using the Finite Volume method, with physiologically appropriate inflow and outflow boundary conditions. The embolus trajectory is modeled using Lagrangian particle equations accounting for embolus interaction with blood as well as vessel wall. Both one and two way fluid-particle coupling are considered, the latter being implemented using momentum sources augmented to the discretized flow equations. The study determines individual embolus path up to arteries supplying the brain, and compares the size-dependent distribution of emboli amongst vessels superior to the aortic-arch, and the role of fully coupled blood-embolus interactions in modifying both trajectory and distribution when compared with one-way coupling. Specifically for intermediate particle sizes the model developed will better characterize the risks for embolic stroke. [Preview Abstract] |
Monday, November 24, 2014 11:09AM - 11:22AM |
H7.00004: Novel Non-invasive Estimation of Coronary Blood Flow using Contrast Advection in Computed Tomography Angiography Parastou Eslami, Jung-Hee Seo, Amirali Rahsepar, Richard George, Albert Lardo, Rajat Mittal Coronary computed tomography angiography (CTA) is a promising tool for assessment of coronary stenosis and plaque burden. Recent studies have shown the presence of axial contrast concentration gradients in obstructed arteries, but the mechanism responsible for this phenomenon is not well understood. We use computational fluid dynamics to study intracoronary contrast dispersion and the correlation of concentration gradients with intracoronary blood flow and stenotic severity. Data from our CFD patient-specific simulations reveals that contrast dispersions are generated by intracoronary advection effects, and therefore, encode the coronary flow velocity. This novel method- Transluminal Attenuation Flow Encoding (TAFE) - is used to estimate the flowrate in phantom studies as well as preclinical experiments. Our results indicate a strong correlation between the values estimated from TAFE and the values measured in these experiments. The flow physics of contrast dispersion associated with TAFE will be discussed. This work is funded by grants from Coulter Foundation and Maryland Innovation Initiative. The authors have pending patents in this technology and RM and ACL have other financial interests associated with TAFE. [Preview Abstract] |
Monday, November 24, 2014 11:22AM - 11:35AM |
H7.00005: Numerical study of blood flow and bruits from a realistic arterial stenosis Jaeyong Jeong, Donghyun You The arterial stenosis is a major cause of fatal cardiovascular diseases in developed countries. It is well known that a stenosed artery generates distinct sounds called bruits. Many researchers have been trying to use bruits to diagnose how severely an artery is stenosed without using an invasive method. The previous research revealed that more intensified acoustic fluctuations with higher frequency contents are induced by blood flow for more severely constricted arteries. However, most previous research has been conducted on two-dimensional configurations of artery with a variety of simplifications, which may exclude some of the crucial aspects in real stenosed arteries. In the present study, the generation and propagation of bruits from a realistic stenosed artery is simulated and analyzed in detail using a hydrodynamic/acoustic splitting method, where the flow field in a lumen is predicted by solving the incompressible Navier-Stokes equations using an immersed boundary method, while the acoustic field is predicted by linearized perturbed compressible equations. [Preview Abstract] |
Monday, November 24, 2014 11:35AM - 11:48AM |
H7.00006: Direct numerical simulation of a pulsatile flow in a coronary artery Jorge Bailon-Cuba, Heather Hayenga, Stefano Leonardi A direct numerical simulation of the blood flow in a coronary artery has been performed. A pulsatile, turbulent flow, inside a branchless, rigid cylindrical artery with non-slip conditions has been considered. The blood is assumed to be a Newtonian fluid. As a fundamental component of the coronary geometry, several cross-sectional shapes of the arterial lumen, as a function of the streamwise coordinate-z, are being included using the immersed boundary method, with a simple transversal wavy wall, as the most simple case. A preliminary set of simulations has being run, with two time varying flow rate functions. Results include flow velocities, pressure gradients and wall shear stress (WSS) distribution, and their comparison with other CFD and experimental results. In particular, WSS is important due to the significant role that it plays in the early formation of coronary artery disease (CAD). It has been found that waviness on the wall increases the instantaneous streamwise velocity, $w(y)$, and its fluctuations, $\langle w'^2 \rangle (y)$, and more drastically the WSS. [Preview Abstract] |
Monday, November 24, 2014 11:48AM - 12:01PM |
H7.00007: A Numerical Multiscale Framework for Modeling Patient-Specific Coronary Artery Bypass Surgeries Abhay B. Ramachandra, Andrew Kahn, Alison Marsden Coronary artery bypass graft (CABG) surgery is performed to revascularize diseased coronary arteries, using arterial, venous or synthetic grafts. Vein grafts, used in more than 70{\%} of procedures, have failure rates as high as 50{\%} in less than 10 years. Hemodynamics is known to play a key role in the mechano-biological response of vein grafts, but current non-invasive imaging techniques cannot fully characterize the hemodynamic and biomechanical environment. We numerically compute hemodynamics and wall mechanics in patient-specific 3D CABG geometries using stabilized finite element methods. The 3D patient-specific domain is coupled to a 0D lumped parameter circulatory model and parameters are tuned to match patient-specific blood pressures, stroke volumes, heart rates and heuristic flow-split values. We quantify differences in hemodynamics between arterial and venous grafts and discuss possible correlations to graft failure. Extension to a deformable wall approximation will also be discussed. The quantification of wall mechanics and hemodynamics is a necessary step towards coupling continuum models in solid and fluid mechanics with the cellular and sub-cellular responses of grafts, which in turn, should lead to a more accurate prediction of the long term outcome of CABG surgeries, including predictions of growth and remodeling. [Preview Abstract] |
Monday, November 24, 2014 12:01PM - 12:14PM |
H7.00008: Modelling Brain Temperature and Cerebral Cooling Methods Stephen Blowers, Prashant Valluri, Ian Marshall, Peter Andrews, Bridget Harris, Michael Thrippleton Direct measurement of cerebral temperature is invasive and impractical meaning treatments for reduction of core brain temperature rely on predictive mathematical models. Current models rely on continuum equations which heavily simplify thermal interactions between blood and tissue. A novel~two-phase 3D porous-fluid model is developed to address these limitations. The model solves porous flow equations in 3D along with energy transport equation in both the blood and tissue phases including metabolic generation. By incorporating geometry data extracted from MRI scans, 3D vasculature can be inserted into a porous brain structure to realistically represent blood distribution within the brain. Therefore, thermal transport and convective heat transfer of blood are solved by means of direct numerical simulations. In application, results show that external scalp cooling has a higher impact on both maximum and average core brain temperatures than previously predicted. Additionally, the extent of alternative treatment methods such as pharyngeal cooling and carotid infusion can be investigated using this model. [Preview Abstract] |
Monday, November 24, 2014 12:14PM - 12:27PM |
H7.00009: Determining an Effective Shear Modulus in Tubular Organs for Fluid-Structure Interaction Robert Chisena, James Brasseur, Francesco Costanzo, Hans Gregersen, Jingbo Zhao Fluid-structure interaction (FSI) is central to the mechanics of fluid-filled tubular organs such as the intestine and esophagus. The motions of fluid chyme are driven by a muscularis wall layer of circular and longitudinal muscle fibers. The coupled motions of the fluid and elastic solid phases result from a local balance between active and passive muscle stress components, fluid pressure, and fluid viscous stresses. Model predictions depend on the passive elastic response of the muscularis layer, which is typically parameterized with an average isotropic elastic modulus (EM), currently measured \textit{in vivo} and \textit{in vitro} with estimates for total hoop stress within a distension experiment. We have shown that this approach contains serious error due to the overwhelming influence of incompressibility on the hydrostatic component. We present a new approach in which an effective shear modulus, containing only deviatoric contributions, is measured to overcome this serious error. Using \textit{in vitro} measurements from pig intestines, we compare our new approach to the current method, showing vastly different predictions. We will also report on our current analysis which aims to determine the influence of residual stress on the EM measurements and comment on it use in FSI simulations. [Preview Abstract] |
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