Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session A16: Biofluids: Valves, Stents and Devices |
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Chair: Marija Vukicevic, Clemson University Room: 28B |
Sunday, November 18, 2012 8:00AM - 8:13AM |
A16.00001: Transcatheter valve implantation can alter fluid flow fields in aortic sinuses and ascending aorta Neelakantan Saikrishnan, Ajit Yoganathan Transcatheter aortic valves (TAVs) are valve replacements used to treat aortic stenosis. Currently, these have been used in elderly patients at high-risk for open-heart procedures. Since these devices are implanted under fluoroscopic guidance, the implantation position of the valve can vary with respect to the native aortic valve annulus. The current study characterizes the altered hemodynamics in the aortic sinus and ascending aorta under different implantation (high and low) and cardiac output (2.5 and 5.0 L/min) conditions. Two commonly used TAV designs are studied using 2-D Particle Image Velocimetry (PIV). 200 phase locked images are obtained at every 25ms in the cardiac cycle, and the resulting vector fields are ensemble averaged. High implantation of the TAV with respect to the annulus causes weaker sinus washout and weaker sinus vortex formation. Additionally, the longer TAV leaflets can also result in a weaker sinus vortex. The level of turbulent fluctuations in the ascending aorta did not appear to be affected by axial positioning of the valve, but varied with cardiac output. The results of this study indicates that TAV positioning is important to be considered clinically, since this can affect coronary perfusion and potential flow stagnation near the valve. [Preview Abstract] |
Sunday, November 18, 2012 8:13AM - 8:26AM |
A16.00002: Integrating bio-prosthetic valves in the Fontan operation - Novel treatment to control retrograde flow in caval veins Marija Vukicevic, Timothy Conover, Jian Zhou, Tain-Yen Hsia, Richard Figliola For a child born with only one functional heart ventricle, the sequence of palliative surgeries typically culminates in the Fontan operation. This procedure is usually successful initially, but leads to later complications, for reasons not fully understood. Examples are respiratory-dependent retrograde flows in the caval and hepatic veins, and increased pulmonary vascular resistance (PVR), hypothesized to be responsible for elevated pressure in the liver and disease of the liver and intestines. Here we study the parameters responsible for retrograde flows in the inferior vena cava (IVC) and hepatic vein (HV), and investigate two novel interventions to control retrograde flow: implanting either a Medtronic Contegra valved conduit or an Edwards lifescience pericardial aortic valve in the IVC or HV. We performed the experiments in a multi-scale, patient specific mock circuit, with normal and elevated PVR, towards the optimization of the Fontan circulation. The results show that both valves can significantly reduce retrograde flows in the veins, suggesting potential advantages in the treatment of the patients with congenital heart diseases. [Preview Abstract] |
Sunday, November 18, 2012 8:26AM - 8:39AM |
A16.00003: Finite Element CURVIB method for fluid-structure interaction simulations of tissue heart valves Anvar Gilmanov, Henryk Stolarski, Trung Le, Fotis Sotiropoulos A new fluid-structure interaction (FSI) model is developed for solving the three-dimensional unsteady Navier-Stokes equations in domains with arbitrarily complex tissues undergoing large deformation. The method employs the sharp-interface CURVIB method [L. Ge, F. Sotiropoulos, JCP, 225 (2007) 1782-1809] for handling complex moving boundaries, with a finite element (FE) model, which can handle large structural/tissue deformations using the nonlinear Kirckhhoff thin shells theory. A new treatment of the flexible immersed body is introduced to handle the thin body surfaces. A version of Aitken's acceleration for strong fluid-structure coupling is used to calculate the responses of the flexible bodies to the applied fluid load. The new, rotation-free finite element formulation for large deformations of thin shells has been extensively tested and validated for a range of relevant problems. The coupled FE-CURVIB FSI model is validated for vortex induced oscillations of a flexible cantilever and applied to simulate physiologic pulsatile flows through a tissue aortic heart valve in an anatomic artery geometry. The results show the good convergence property of the new FSI algorithm and demonstrate its promise for a broad range of biological applications. [Preview Abstract] |
Sunday, November 18, 2012 8:39AM - 8:52AM |
A16.00004: Experimental investigation of the effects of inserting a bovine venous valve in the inferior vena cava of Fontan circulation Arvind Santhanakrishnan, Jacob Johnson, Monica Kotz, Elaine Tang, Reza Khiabani, Ajit Yoganathan, Kevin Maher The Fontan procedure is a palliative surgery performed on patients with single ventricle (SV) congenital heart defects. The SV is used for systemic circulation and the venous return from the inferior vena cava (IVC) and superior vena cava (SVC) is routed to the pulmonary arteries (PA), resulting in a total cavopulmonary connection (TCPC). Hepatic venous hypertension is commonly manifested in the Fontan circulation, leading to long-term complications including liver congestion and cirrhosis. Respiratory intrathoracic pressure changes affect the venous return from the IVC to the PA. Using a physical model of an idealized TCPC, we examine placement of a unidirectional bovine venous valve within the IVC as a method of alleviating hepatic venous hypertension. A piston pump is used to provide pulsatility in the internal flow through the TCPC, while intrathoracic pressure fluctuations are imposed on the external walls of the model using a pair of linear actuators. When implanted in the extrathoracic position, the hepatic venous pressure is lowered from baseline condition. The effects of changing caval flow distribution and intrathoracic pressure on TCPC hemodynamics will be examined. [Preview Abstract] |
Sunday, November 18, 2012 8:52AM - 9:05AM |
A16.00005: Mitigation of Shear-Induced Blood Damage of Mechanical Bileaflet Heart Valves using Embedded Vortex Generators Pablo Hidalgo, Sivakkumar Arjunon, Neelakantan Saikrishnan, Ajit Yoganathan, Ari Glezer The strong transitory shear stress generated during the time-periodic closing of the mechanical prosthetic bileaflet aortic heart valve, is considered to be one of the main factors responsible for complications, associated with thrombosis and thromboembolism. These flow transients are investigated using phase and time-averaged PIV in a low-volume (about 150 ml) test setup that simulates the pulsatile physiological conditions associated with a 23 mm St. Jude Medical valve. The PIV measurements are accompanied by continuous monitoring of the ventricular and aortic pressures and valve flow rate. Following the valve closure, the leakage flow between the valve leaflets is caused by the pressure buildup across the leaflets, leading to the formation of a regurgitation jet starting from the BMHV B-datum line. As in a typical starting jet, a counter-rotating vortex pair is formed along each leaflet edge and the vorticity sheet is associated with high shear stress that may be result in blood platelet activation. The present investigation demonstrates that the placement of arrays of mm-scale vortex generators near the edges of the leaflets diffuses the vortex sheet and suppresses the formation of these vortices, weakening the local velocity gradients and small-scale vortical structures. [Preview Abstract] |
Sunday, November 18, 2012 9:05AM - 9:18AM |
A16.00006: Simulations of pulsatile suspension flow through bileaflet mechanical heart valves to quantify platelet damage Brian Yun, Cyrus Aidun, Ajit Yoganathan Studies have shown that high shear stress and long exposure times on platelets have a strong impact on thromboembolic complications in bileaflet mechanical heart valves (BMHVs). This numerical study quantifies the platelet damage incurred in pulsatile flow through various BMHV designs. The lattice-Boltzmann method with external boundary force (LBM-EBF) was implemented to simulate pulsatile flow and capture the dynamics and surface shear stresses of modeled platelets with realistic geometry. The platelets are released in key regions of interest in the geometry as well as at various times of the cardiac cycle. The platelet damage is quantified using a linear shear stress-exposure time blood damage index (BDI) model. The multiscale computational method used to quantitatively measure the BDI during the pulsatile flow has been validated as being able to accurately capture bulk BMHV fluid flow and for accurately quantifying platelet damage in BMHV flows. These simulations will further knowledge of the geometric features and cardiac cycle times that most affect platelet damage. This study will ultimately lead to optimization of BMHV design in order to minimize thromboembolic complications. [Preview Abstract] |
Sunday, November 18, 2012 9:18AM - 9:31AM |
A16.00007: Bio-inspired, low-cost, self-regulating valves for drip irrigation in developing countries Pawel Zimoch, Eliott Tixier, Anette Hosoi, Amos Winter We use nonlinear behavior of thin-walled structures - an approach inspired by biological systems (the human airway, for example) - to address one of the most important problems facing subsistence farmers in developing countries : lack of access to inexpensive, water-efficient irrigation systems. An effective way of delivering water to crops is through a network of drippers, with up to 85{\%} of the water delivered being absorbed by plants. However, of the 140m hectares of cropped land in India, only 61m are irrigated and just 5m through drip irrigation. This is, in part, due to the relatively high cost of drip irrigation. The main cost comes from the requirement to pump the water at relatively high pressure ($>$1bar), to minimize the effect of uneven terrain and viscous losses in the network, and ensure that each plant receives the same amount of water. We demonstrate that the pressure required to drive the system can be reduced significantly by using thin-walled structures to design drippers with completely passive self-regulation that activates at approximately 0.1bar. We also report on our work towards reducing the overall price of drip irrigation systems by as much as 90{\%}, and making them more affordable for 800 million subsistence farmers worldwide. [Preview Abstract] |
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