Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session L24: Biofluids: Cardiovascular Fluid Dynamics II |
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Chair: Jung-Hee Seo, Johns Hopkins University Room: 302 |
Monday, November 23, 2015 4:05PM - 4:18PM |
L24.00001: Fluid Dynamics of the Generation and Transmission of Heart Sounds: (2): Direct Simulation using a Coupled Hemo-Elastodynamic Method Jung-Hee Seo, Hani Bakhshaee, Chi Zhu, Rajat Mittal Patterns of blood flow associated with abnormal heart conditions generate characteristic sounds that can be measured on the chest surface using a stethoscope. This technique of `cardiac auscultation' has been used effectively for over a hundred years to diagnose heart conditions, but the mechanisms that generate heart sounds, as well as the physics of sound transmission through the thorax, are not well understood. Here we present a new computational method for simulating the physics of heart murmur generation and transmission and use it to simulate the murmurs associated with a modeled aortic stenosis. The flow in the model aorta is simulated by the incompressible Navier-Stokes equations and the three-dimensional elastic wave generation and propagation on the surrounding viscoelastic structure are solved with a high-order finite difference method in the time domain. The simulation results are compared with experimental measurements and show good agreement. The present study confirms that the pressure fluctuations on the vessel wall are the source of these heart murmurs, and both compression and shear waves likely plan an important role in cardiac auscultation. [Preview Abstract] |
Monday, November 23, 2015 4:18PM - 4:31PM |
L24.00002: Computational 3D fluid-structure interaction for the aortic valve Haoxiang Luo, Ye Chen, Wei Sun Three-dimensional fluid--structure interaction (FSI) involving large deformations of flexible bodies is common in biological systems. A typical example is the heart valves. Accurate and efficient numerical approaches for modeling such systems are still lacking. In this work, we report a successful case of combining an immersed-boundary flow solver with a nonlinear finite-element solid-dynamics solver, both in-house programs, specifically for three-dimensional simulations. Based on the Cartesian grid, the viscous incompressible flow solver can handle boundaries of large displacements with simple mesh generation. The solid-dynamics solver has separate subroutines for analyzing general three-dimensional bodies and thin-walled structures composed of frames, membranes, and plates. Both geometric nonlinearity associated with large displacements and material nonlinearity associated with large strains are incorporated in the solver. The FSI is achieved through a strong coupling and partitioned approach. We have performed several benchmarking cases to validate the FSI solver. Application to the native aortic valve will be demonstrated. [Preview Abstract] |
Monday, November 23, 2015 4:31PM - 4:44PM |
L24.00003: Calibration of Blood Flow in Simulations via Multi-fidelity Bayesian Optimization Paris Perdikaris, George Karniadakis We present a mathematical and computational framework for model inversion based on multi-fidelity information fusion and Bayesian optimization. The proposed methodology targets the accurate construction of high-dimensional response surfaces, and the effective identification of global optima while keeping the number of expensive function evaluations at a minimum. We train families of correlated surrogates on available variable fidelity data using auto-regressive stochastic models via recursive co-kriging, and exploit the resulting predictive inference schemes within a Bayesian optimization setting. The effectiveness of the proposed framework is illustrated through examples involving the calibration of outflow boundary conditions in blood flow simulations using multi-fidelity information from 3D and 1D models. [Preview Abstract] |
Monday, November 23, 2015 4:44PM - 4:57PM |
L24.00004: Time-resolved X-ray PIV measurements of hemodynamic information of real pulsatile blood flows Hanwook Park, Eunseop Yeom, Sang Joon Lee X-ray imaging technique has been used to visualize various bio-fluid flow phenomena as a nondestructive manner. To obtain hemodynamic information related with circulatory vascular diseases, a time-resolved X-ray PIV technique with high temporal resolution was developed. In this study, to embody actual pulsatile blood flows in a circular conduit without changes in hemorheological properties, a bypass loop is established by connecting a microtube between the jugular vein and femoral artery of a rat. Biocompatible CO$_{2}$ microbubbles are used as tracer particles. After mixing with whole blood, CO$_{2}$ microbubbles are injected into the bypass loop. Particle images of the pulsatile blood flows in the bypass loop are consecutively captured by the time-resolved X-ray PIV system. The velocity field information are obtained with varying flow rate and pulsataility. To verify the feasibility of the use of CO$_{2}$ microbubbles under \textit{in vivo} conditions, the effects of the surrounding-tissues are also investigated, because these effects are crucial for deteriorating the image contrast of CO$_{2}$ microbubbles. Therefore, the velocity information of blood flows in the abdominal aorta are obtained to demonstrate the visibility and usefulness of CO$_{2}$ microbubbles under \textit{ex vivo} conditions. [Preview Abstract] |
Monday, November 23, 2015 4:57PM - 5:10PM |
L24.00005: Effects of a protein glycocalyx in the hemodynamics of small blood vessels Yiannis Dimakopoulos, George Delidakis, John Tsamopoulos Glycocalyx is a protein layer of approximate thickness 0.5$\mu $m that lines vessel walls. We study the effects this layer has on the blood flow inside arterioles and venules, where the relative size of the glycocalyx is significant. To properly describe phenomena that naturally occur in blood flow, such as the inhomogeneous distribution of red blood cells and their aggregation, we use an improved viscoelastic constitutive model. The glycocalyx layer is modeled as fixed porous media. Cells cannot penetrate inside it, since its hydraulic permeability is very low, and the flow inside this layer is described by the equations for a viscous fluid with an extra Brinkman term to account for the effects the porous medium has on the flow. The closed set of equations is solved using the Finite Element method, assuming steady-state with dependence only in the r-direction. Our results are favorably compared with the in vivo velocity profiles in venules of mice produced by Damiano et al., (2004) and the formation of cell-free layer near glycocalyx. Flow inside the glycocalyx layer is found to be severely attenuated due to the low hydraulic permeability, which can have interesting implications in the transport of various substances form the blood to the tissues or in the use of shear stresses as signals for the endothelial surface cells. Finally, we simulate the transient blood flow under pulsatile conditions. [Preview Abstract] |
Monday, November 23, 2015 5:10PM - 5:23PM |
L24.00006: Particle tracking velocimetry using echocardiographic data resolves flow in the left ventricle Kaushik Sampath, Thura T. Abd, Richard T. George, Joseph Katz Two dimensional contrast echocardiography was performed on patients with a history of left ventricular (LV) thrombus. The 636 x 434 pixels electrocardiograms were recorded using a GE Vivid 9E system with (M5S-D and 4V-D) probes in a 2-D mode at a magnification of 0.3 mm/pix. The concentration of 2-4.5 micron seed bubbles was adjusted to obtain individually discernable traces, and a data acquisition rate of 60-90 fps kept the inter-frame displacements suitable for matching traces, and calculating vectors, but yet low enough to allow a scanning depth and width of upto 13 cm and 60 degrees respectively. Particle tracking velocimetry (PTV) guided by initial particle image velocimetry (PIV) was used to obtain the velocity distributions inside the LV with vector spacing of 3-5 mm. The data quality was greatly enhanced by implementing an iterative particle specific enhancement and tracking algorithm. Data covering 20 heart beats facilitated phase averaging. The results elucidated blood flow in the intra-ventricular septal region, lateral wall region, the apex of the LV and the mitral valve region. [Preview Abstract] |
Monday, November 23, 2015 5:23PM - 5:36PM |
L24.00007: Data Assimilation and Propagation of Uncertainty in Multiscale Cardiovascular Simulation Daniele Schiavazzi, Alison Marsden Cardiovascular modeling is the application of computational tools to predict hemodynamics. State-of-the-art techniques couple a 3D incompressible Navier-Stokes solver with a boundary circulation model and can predict local and peripheral hemodynamics, analyze the post-operative performance of surgical designs and complement clinical data collection minimizing invasive and risky measurement practices. The ability of these tools to make useful predictions is directly related to their accuracy in representing measured physiologies. Tuning of model parameters is therefore a topic of paramount importance and should include clinical data uncertainty, revealing how this uncertainty will affect the predictions. We propose a fully Bayesian, multi-level approach to data assimilation of uncertain clinical data in multiscale circulation models. To reduce the computational cost, we use a stable, condensed approximation of the 3D model build by linear sparse regression of the pressure/flow rate relationship at the outlets. Finally, we consider the problem of non-invasively propagating the uncertainty in model parameters to the resulting hemodynamics and compare Monte Carlo simulation with Stochastic Collocation approaches based on Polynomial or Multi-resolution Chaos expansions. [Preview Abstract] |
Monday, November 23, 2015 5:36PM - 5:49PM |
L24.00008: Decoding Hemodynamics of Large Vessels via Dispersion of Contrast Agent in Cardiac Computed Tomography Parastou Eslami, Jung-Hee Seo, Thura T. Abd, Richard George, Albert C. Lardo, Marcus Y. Chen, Rajat Mittal Computed tomography angiography (CTA) has emerged as a powerful tool for the assessment of coronary artery disease and other cardiac conditions. Continuous improvements in the spatial and temporal resolution of CT scanners are revealing details regarding the spatially and temporally varying contrast concentration in the vasculature, that were not evident before. These contrast dispersion patterns offer the possibility of extracting useful information about the hemodynamics from the scans. In the current presentation, we will describe experimental studies carried out with CT compatible phantoms of coronary vessels that provide insights into the effect of imaging artifacts on the observed intracoronary contrast gradients. In addition, we will describe a series of computational fluid dynamics studies that explore the dispersion of contrast through the ascending-descending aorta with particular focus on the effect of the aortic curvature on the dispersion patterns. [Preview Abstract] |
Monday, November 23, 2015 5:49PM - 6:02PM |
L24.00009: Multiple equilibrium states for blood flow in microvascular networks Halley Pollock-Muskin, Cecilia Diehl, Nora Mohamed, Nathan Karst, John Geddes, Brian Storey When blood flows through a vessel bifurcation at the microvascular scale, the hematocrits in the downstream daughter vessels are generally not equal. This phenomenon, known as plasma skimming, can cause heterogeneity in the distribution of red blood cells inside a vessel network. Using established models for plasma skimming, we investigate the equilibrium states in a microvascular network with simple topologies. We find that even simple networks can have multiple equilibrium states for the flow rates and distributions of red blood cells inside the network for fixed inlet conditions. In a ladder network, we find that for certain inlet conditions the network can have $2^N$ observable equilibrium states where N is the number of rungs in the ladder. For ladders with even just a few rungs, the complex equilibrium curves make it seemingly impossible to set the internal state of the network by controlling the inlet flows. Microfluidic experiments are being used to confirm the model predictions. [Preview Abstract] |
Monday, November 23, 2015 6:02PM - 6:15PM |
L24.00010: Fluid-Structure interaction modeling in deformable porous arteries Rana Zakerzadeh, Paolo Zunino A computational framework is developed to study the coupling of blood flow in arteries interacting with a poroelastic arterial wall featuring possibly large deformations. Blood is modeled as an incompressible, viscous, Newtonian fluid using the Navier-Stokes equations and the arterial wall consists of a thick material which is modeled as a Biot system that describes the mechanical behavior of a homogeneous and isotropic elastic skeleton, and connecting pores filled with fluid. Discretization via finite element method leads to the system of nonlinear equations and a Newton-Raphson scheme is adopted to solve the resulting nonlinear system through consistent linearization. Moreover, interface conditions are imposed on the discrete level via mortar finite elements or Nitsche's coupling. The discrete linearized coupled FSI system is solved by means of a splitting strategy, which allows solving the Navier-Stokes and Biot equations separately. The numerical results investigate the effects of proroelastic parameters on the pressure wave propagation in arteries, filtration of incompressible fluids through the porous media, and the structure displacement. [Preview Abstract] |
Monday, November 23, 2015 6:15PM - 6:28PM |
L24.00011: Fluid Dynamics of the Generation and Transmission of Heart Sounds: (1) A Cardiothoracic Phantom Based Study of Aortic Stenosis Murmurs Hani Bakhshaee, Jung-Hee Seo, Chi Zhu, Nathaniel Welsh, Guillaume Garreau, Gaspar Tognetti, Andreas Andreou, Rajat Mittal A novel and versatile cardiothoracic phantom has been designed to study the biophysics of heart murmurs associated with aortic stenosis. The key features of the cardiothoracic phantom include the use of tissue-mimetic gel to model the sound transmission through the thorax and the embedded fluid circuit that is designed to mimic the heart sound mechanisms in large vessels with obstructions. The effect of the lungs on heart murmur propagation can also be studied through the insertion of lung-mimicking material into gel. Sounds on the surface of the phantom are measured using a variety of sensors and the spectrum of the recorded signal and the streamwise variation in total signal strength is recorded. Based on these results, we provide insights into the biophysics of heart murmurs and the effect of lungs on sound propagation through the thorax. Data from these experiments is also used to validate the results of a companion computational study. [Preview Abstract] |
Monday, November 23, 2015 6:28PM - 6:41PM |
L24.00012: A universal number for wave reflection optimization of the mammalian cardiovascular system. Niema Pahlevan, Morteza Gharib Quantifying the optimum arterial wave reflection and systemic arterial function is essential to the evaluation of optimal cardiovascular system (CVS) operation. The CVS function depends on both the dynamics of the heart and wave dynamics of the arterial network. Here, we are introducing a universal dimensionless number, called wave condition number ($\alpha )$ that quantifies the arterial wave reflection. An in-vitro experimental approach, utilizing a unique hydraulic model was used to quantify $\alpha $ in human aortas with a wide range of aortic rigidities. Our results indicate that the optimum value of the wave condition number is 0.1 at each level of aortic rigidity. Looking into mammals of various size (from mice to elephant), our results show that the optimum wave condition number remains 0.1 and is universal among all mammals. Clinical applications and the relevancy of the wave condition number will also be discussed. [Preview Abstract] |
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