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 D7: Biofluids: Cardiac Flows |
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Chair: Iman Borazjani, Buffalo University Room: 3012 |
Sunday, November 23, 2014 2:15PM - 2:28PM |
D7.00001: Quantification of avian embryonic cardiac outflow hemodynamics through 3D-0D coupling Stephanie Lindsey, Irene Vignon-Clementel, Jonathan Butcher Outflow malformations account for over 20{\%} of CHDs in the US. While the etiology of these malformations is poorly understood, most can be traced back to perturbations in the patterning of the pharyngeal arch arteries (PAAs), the precursors to the great vessels. Here, we examine the effects of normal and aberrant PAA flow, through the use of two computational models. A 0D electric analog model allows for rapid computation and global tuning of the embryo's vasculature relative to the arches. A second 3D-0D model replaces the electric analog representation of the arches with a 3D reconstruction, thereby leading to more extensive pressure and flow characterization. We obtain 3D arch artery reconstructions from nano-CT stacks and couple them to 0D outlets. In contrast to standard boundary conditions, such coupling maintains the physiologically desired cranial-caudal flow split in control embryos and predicts how this will change with vessel occlusion. We use flow inputs from Doppler velocity tracings to compute 0D and 3D-0D pulsatile hemodynamic simulations in HH18 (day 3), HH24 (day 4), and HH26 (day 5) geometries. We then calculate flow distributions and wall shear stress maps for control embryos. From here, we modify HH18 geometries to simulate varying levels of PAA occlusion. Pulsatile simulations are run in each geometry and results compared to that of controls. Results serve as a basis for examining flow-mediated growth and adaptation in cardiac outflow morphogenesis. [Preview Abstract] |
Sunday, November 23, 2014 2:28PM - 2:41PM |
D7.00002: A New Parameter for Cardiac Efficiency Analysis Iman Borazjani, Navaneetha Krishnan Rajan, Zeying Song, Kenneth Hoffmann, Eileen MacMahon, Marek Belohlavek Detecting and evaluating a heart with suboptimal pumping efficiency is a significant clinical goal. However, the routine parameters such as ejection fraction, quantified with current non-invasive techniques are not predictive of heart disease prognosis. Furthermore, they only represent left-ventricular (LV) ejection function and not the efficiency, which might be affected before apparent changes in the function. We propose a new parameter, called the hemodynamic efficiency (H-efficiency) and defined as the ratio of the useful to total power, for cardiac efficiency analysis. Our results indicate that the change in the shape/motion of the LV will change the pumping efficiency of the LV even if the ejection fraction is kept constant at 55\% (normal value), i.e., H-efficiency can be used for suboptimal cardiac performance diagnosis. To apply H-efficiency on a patient-specific basis, we are developing a system that combines echocardiography (echo) and computational fluid dynamics (CFD) to provide the 3D pressure and velocity field to directly calculate the H-efficiency parameter. Because the method is based on clinically used 2D echo, which has faster acquisition time and lower cost relative to other imaging techniques, it can have a significant impact on a large number of patients. [Preview Abstract] |
Sunday, November 23, 2014 2:41PM - 2:54PM |
D7.00003: In-vivo characterization of 2D residence time maps in the left ventricle Lorenzo Rossini, Pablo Martinez-Legazpi, Javier Bermejo, Yolanda Benito, Marta Alhama, Raquel Yotti, Candelas Perez del Villar, Ana Gonzalez-Mansilla, Alicia Barrio, Francisco Fernandez-Aviles, Shawn Shadden, Juan Carlos del Alamo Thrombus formation is a multifactorial process involving biology and hemodynamics. Blood stagnation and wall shear stress are linked to thrombus formation. The quantification of residence time of blood in the left ventricle (LV) is relevant for patients affected by ventricular contractility dysfunction. We use a continuum formulation to compute 2D blood residence time ($T_R$) maps in the LV using in-vivo 2D velocity fields in the apical long axis plane obtained from Doppler-echocardiography images of healthy and dilated hearts. The $T_R$ maps are generated integrating in time an advection-diffusion equation of a passive scalar with a time-source term. This equation represents the Eulerian translation of $D\ T_R/D\ t=1$ and is solved numerically with a finite volume method on a Cartesian grid using an immersed boundary for the LV wall. Changing the source term and the boundary conditions allows us to track blood transport (direct and retained flow) in the LV and the topology of early (E) and atrial (A) filling waves. This method has been validated against a Lagrangian Coherent Structures analysis, is computationally inexpensive and observer independent, making it a potential diagnostic tool in clinical settings. [Preview Abstract] |
Sunday, November 23, 2014 2:54PM - 3:07PM |
D7.00004: Clinical characterization of 2D pressure field in human left ventricles Maria Borja, Lorenzo Rossini, Pablo Martinez-Legazpi, Yolanda Benito, Marta Alhama, Raquel Yotti, Candelas Perez del Villar, Ana Gonzalez-Mansilla, Alicia Barrio, Francisco Fernandez-Aviles, Javier Bermejo, Andrew Khan, Juan Carlos del Alamo The evaluation of left ventricle (LV) function in the clinical setting remains a challenge. Pressure gradient is a reliable and reproducible indicator of the LV function. We obtain 2D relative pressure field in the LV using in-vivo measurements obtained by processing Doppler-echocardiography images of healthy and dilated hearts. Exploiting mass conservation, we solve the Poisson pressure equation (PPE) dropping the time derivatives and viscous terms. The flow acceleration appears only in the boundary conditions, making our method weakly sensible to the time resolution of in-vivo acquisitions. To ensure continuity with respect to the discrete operator and grid used, a potential flow correction is applied beforehand, which gives another Poisson equation. The new incompressible velocity field ensures that the compatibility equation for the PPE is satisfied. Both Poisson equations are efficiently solved on a Cartesian grid using a multi-grid method and immersed boundary for the LV wall. The whole process is computationally inexpensive and could play a diagnostic role in the clinical assessment of LV function. [Preview Abstract] |
Sunday, November 23, 2014 3:07PM - 3:20PM |
D7.00005: Image-based flow modeling in a two-chamber model of the left heart Vijay Vedula, Jung-Hee Seo, Kourosh Shoele, Richard George, Laurent Younes, Rajat Mittal Computational modeling of cardiac flows has been an active topic of discussion over the past decade. Modeling approaches have been consistently improved by inclusion of additional complexities and these continue to provide new insights into the dynamics of blood flow in health and disease. The vast majority of cardiac models have been single-chamber models, which have typically focused on the left or right ventricles, and in these models, the atria are modeled in highly simplistic ways. However, the left atrium acts as a mixing chamber and works with the left ventricle in a highly coordinated fashion to move the blood from the pulmonary veins to the aorta. The flow dynamics associated with this two-chamber interaction is not well understood. In addition, the flow in the left atrium has by itself significant clinical implications and our understanding of this is far less than that of the left ventricle. In the current study, we use 4D CT to create a physiological heart model that is functionally normal and use an experimentally validated sharp-interface immersed boundary flow solver to explore the atrio-ventricular interaction and develop insights into some of the questions addressed above. [Preview Abstract] |
Sunday, November 23, 2014 3:20PM - 3:33PM |
D7.00006: Intrinsic Frequency Method for Noninvasive Diagnosis of Left Ventricular Systolic Dysfunction Niema Pahlevan, Derek Rinderknecht, Peyman Tavallali, Danny Petrasek, Ray Matthews, Morteza Gharib We have recently developed a new mathematical method, intrinsic frequency (IF) method, that views the left ventricle-arterial system as a coupled dynamic pumping system which is decoupled upon the closure of the aortic valve. Utilizing this method, given an arterial blood pressure waveform we are able to extract two intrinsic frequencies ($\omega_{1}$ and $\omega_{2})$ correlating to systole when the left ventricle (LV) and aorta (vasculature) act as a coupled dynamic pumping system and diastole where the dynamics of the LV is removed. Each of these dynamical pumping states has an inherent frequency of operation ($\omega _{1}$ and $\omega_{2})$ which gives information about LV systolic function ($\omega_{1})$ as well as arterial dynamics ($\omega_{2})$. IF methodology extracts $\omega_{1}$ and $\omega_{2}$ from the pressure wave. This method was applied to invasive aortic pressure waveforms and noninvasively measured carotid pressure waveforms. Our results shows that $\omega_{1}$ is elevated in patients with LV systolic dysfunction (LVSD). However, $\omega _{1}$ remains relatively constant under healthy conditions as age advances. Our results indicate that IF methodology can be used to detect LVSD from a single pressure waveform. One unique advantage of the IF method is only the shape of the waveform is required. Therefore, $\omega _{1}$ can be easily derived from noninvasive measurements and monitored continuously. [Preview Abstract] |
Sunday, November 23, 2014 3:33PM - 3:46PM |
D7.00007: Comparative study of diastolic filling under varying left ventricular wall stiffness Pritam Mekala, Arvind Santhanakrishnan Pathological remodeling of the human cardiac left ventricle (LV) is observed in hypertensive heart failure as a result of pressure overload. Myocardial stiffening occurs in these patients prior to chronic maladaptive changes, resulting in increased LV wall stiffness. The goal of this study was to investigate the change in intraventricular filling fluid dynamics inside a physical model of the LV as a function of wall stiffness. Three LV models of varying wall stiffness were incorporated into an in vitro flow circuit driven by a programmable piston pump. Windkessel elements were used to tune the inflow and systemic pressure in the model with least stiffness to match healthy conditions. Models with stiffer walls were comparatively tested maintaining circuit compliance, resistance and pump amplitude constant. 2D phase-locked PIV measurements along the central plane showed that with increase in wall stiffness, the peak velocity and cardiac output inside the LV decreased. Further, inflow vortex ring propagation toward the LV apex was reduced with increasing stiffness. The above findings indicate the importance of considering LV wall relaxation characteristics in pathological studies of filling fluid dynamics. [Preview Abstract] |
Sunday, November 23, 2014 3:46PM - 3:59PM |
D7.00008: Right Heart Vortex Entrainment Volume and Right Ventricular Diastolic Dysfunction James Browning, Jean Hertzberg, Brett Fenster, Joyce Schroeder Recent advances in cardiac magnetic resonance imaging (CMR) have allowed for the 3-dimensional characterization of blood flow in the right ventricle (RV) and right atrium (RA). In this study, we investigate and quantify differences in the characteristics of coherent rotating flow structures (vortices) in the RA and RV between subjects with right ventricular diastolic dysfunction (RVDD) and normal controls. Fifteen RVDD subjects and 10 age-matched controls underwent same day 3D time resolved CMR and echocardiography. Echocardiography was used to determine RVDD stage as well as pulmonary artery systolic pressure (PASP). CMR data was used for RA and RV vortex quantification and visualization during early and late ventricular diastole. RA and RV vortex entrainment volume is quantified and visualized using the Lambda-2 criterion, and the results are compared between healthy subjects and those with RVDD. The resulting trends are discussed and hypotheses are presented regarding differences in vortex characteristics between healthy and RVDD subjects cohorts. [Preview Abstract] |
Sunday, November 23, 2014 3:59PM - 4:12PM |
D7.00009: In vivo quantification of intraventricular flow during left ventricular assist device support Vi Vu, Kin Wong, Juan del Alamo, Pablo M.L. Aguilo, Karen May-Newman Left ventricular assist devices (LVADs) are mechanical pumps that are surgically connected to the left ventricle (LV) and aorta to increase aortic flow and end-organ perfusion. Clinical studies have demonstrated that LVADs improve patient health and quality of life and significantly reduce the mortality of cardiac failure. However, In the presence of left ventricular assisted devices (LVAD), abnormal flow patterns and stagnation regions are often linked to thrombosis. The aim of our study is to evaluate the flow patterns in the left ventricle of the LVAD-assisted heart, with a focus on alterations in vortex development and blood stasis. To this aim, we applied color Doppler echocardiography to measure 2D, time resolved velocity fields in patients before and after implantation of LVADs. In agreement with our previous in vitro studies (Wong et al, Journal of Biomechanics 47, 2014), LVAD implantation resulted in decreased flow velocities and increased blood residence time near the outflow tract. The variation of residence time changes with LVAD operational speed was characterized for each patient. [Preview Abstract] |
Sunday, November 23, 2014 4:12PM - 4:25PM |
D7.00010: Bumps and Ridges: Trabeculation Effects in Embryonic Heart Development Nicholas Battista, Andrea Lane, Laura Miller Trabeculae form in developing zebrafish hearts for Re on the order of 0.1; effects of trabeculae in this flow is not well understood. Dynamic processes, such as vortex formation, are important in the generation of shear at the endothelial surface layer and strains at the epithelial layer, which aid in proper morphology and functionality. In this study, CFD is used to quantify the effects of Re and idealized trabeculae height on the resulting flows. [Preview Abstract] |
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