Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session L16: Biofluids: Medical Devices |
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Chair: Kerem Pekkan, Carnegie Mellon University Room: 304 |
Monday, November 25, 2013 3:35PM - 3:48PM |
L16.00001: Computational Simulations of Inferior Vena Cava (IVC) Filter Placement and Hemodynamics in Patient-Specific Geometries Kenneth Aycock, Shankar Sastry, Jibum Kim, Suzanne Shontz, Robert Campbell, Keefe Manning, Frank Lynch, Brent Craven A computational methodology for simulating inferior vena cava (IVC) filter placement and IVC hemodynamics was developed and tested on two patient-specific IVC geometries: a left-sided IVC, and an IVC with a retroaortic left renal vein. Virtual IVC filter placement was performed with finite element analysis (FEA) using non-linear material models and contact modeling, yielding maximum vein displacements of approximately 10{\%} of the IVC diameters. Blood flow was then simulated using computational fluid dynamics (CFD) with four cases for each patient IVC: 1) an IVC only, 2) an IVC with a placed filter, 3) an IVC with a placed filter and a model embolus, all at resting flow conditions, and 4) an IVC with a placed filter and a model embolus at exercise flow conditions. Significant hemodynamic differences were observed between the two patient IVCs, with the development of a right-sided jet (all cases) and a larger stagnation region (cases 3-4) in the left-sided IVC. These results support further investigation of the effects of IVC filter placement on a patient-specific basis. [Preview Abstract] |
Monday, November 25, 2013 3:48PM - 4:01PM |
L16.00002: Hemodynamics of Central Venous Catheters: experiments and simulations Michael Barbour, Patrick McGah, Alicia Clark, Chin Hei Ng, Kenneth Gow, Alberto Aliseda Central venous catheters (CVC) are used to provide vascular access during hemodialysis in patients with end-stage kidney disease. Despite several advantages and widespread use, CVCs have a high incidence rate of clot formation during the interdialytic phase (48 hrs). In an attempt the prevent clot formation, hospitals routinely administer heparin, an anticoagulant, into the catheter after a dialysis session. It has been reported, however, that up to 40\% of the heparin solution will leak into the blood stream during the interdialytic phase, placing the patient at risk for systemic bleeding incidences. The aim of this study is to determine the role that advective-diffusive transport plays in the heparin leaking process. Numerical simulations of heparin convective mass transfer have been conducted, showing that while advective losses may be significant at the tip, previous studies may be overestimating the total amount of heparin leakage. To validate the quantitative prediction from the simulations, P.L.I.F. is used to experimentally measure heparin transport from CVCs placed in an idealized Superior Vena Cava with physically accurate pulsatile flow conditions. Improved understanding of flow near the catheter tip is applied to improve catheter design and heparin locking procedures. [Preview Abstract] |
Monday, November 25, 2013 4:01PM - 4:14PM |
L16.00003: A Novel Thin Film Nitinol Covered Neurovascular Stent Significantly Decreases Intra-Aneurysmal Flow In Vitro Youngjae Chun, Soojung Hur, Mahdis Shayan, Colin Kealey, Daniel Levi, KP Mohanchandra, Dino Di Carlo, Gregory Carman A novel thin film nitinol (TFN) stent has been developed to promote aneurysm quiescence by diminishing flow across the aneurysm's neck. Laboratory aneurysm models were used to assess the flow changes produced by stents covered with different patterns of TFN. Flow diversion stents were constructed by covering Wingspan stents (Boston Scientific, DxL:4x20mm) with TFNs (i.e., 77 and 82 percent porosity). The flow changes that occur after deployment of two different porous TFN covered stent in intracranial aneurysm models were evaluated in vitro. The 82 percent porous TFN covered stent reduced the intra-aneurysmal mean flow velocity by 86.42 percent, while a 77 percent porous TFN covered stent reduced to intra-aneurysmal mean flow velocity to 93.44 percent compared to a nonstented model. Local wall shear rates were also significantly reduced in wide-neck aneurysm model (i.e., 97.52 - 98.92 percent) with TFN stent placement. The results showed that TFN covered stents significantly reduced intra-aneurysmal flow velocity magnitudes and local wall shear rates. This suggests that TFN covered stents with both 77 and 82 percent porosity have great potential to promote thrombosis in both wide-necked and fusiform aneurysm sacs. [Preview Abstract] |
Monday, November 25, 2013 4:14PM - 4:27PM |
L16.00004: Validation of an open-source framework for the simulation of blood flow in biomedical devices Annalisa Quaini, Tiziano Passerini, Umberto Villa, Alessandro Veneziani, Suncica Canic We discuss the validation of an open source framework for the solution of problems arising in hemodynamics. The framework is assessed through experimental data for fluid flow in an idealized medical device with rigid boundaries. The core of the framework is an open source parallel finite element library that features several algorithms for fluid problems. The numerical results for the flow in the idealized medical device are in good quantitative agreement with the measured axial components of the velocity and pressures for flow rates corresponding to laminar, transitional, and turbulent regimes. A detailed account of the methods is provided. [Preview Abstract] |
Monday, November 25, 2013 4:27PM - 4:40PM |
L16.00005: Numerical simulations of the hemodynamics impact of stent-malapposition in a circular idealized coronary artery Eric Poon, Andrew Ooi, Wei Pan, Yun Liu, Yufei Ye, Yuan Xue, Peter Barlis, Stephen Moore Pulsatile flow past two circular cylinder rings in tandem inside a circular pipe is carried out numerically at resting blood flow rate (around 200mL/min) to study the effect of stent-malapposition (distance between cylinders surface and the circular pipe wall) on the hemodynamics impact inside a coronary artery. The corresponding Reynolds number based on pipe diameter for this blood flow rate is \textit{Re} $=$ 600. Stent-malappostion is chosen to be 0.25--1 diameter from the circular pipe wall and the two circular cylinders are 36 diameters apart. At 0.25 diameter stent-malapposition, the flow between the cylinders and the wall slows down significantly as the boundary layers from the cylinder and the wall meet. At 0.5 diameter stent-malapposition, the flow between the leading cylinder and the wall increases substantially, leading to unsteady vortices rolling away from the wall and a dramatic increase in wall shear stress. However, the vortices behind the trailing cylinder are stable even though the two cylinders in tandem are 36 diameters apart as flow pusatility affects the velocity recovery behind the leading cylinder. At 1 diameter stent-malapposition, the vortices behind the leading cylinder become stable again. [Preview Abstract] |
Monday, November 25, 2013 4:40PM - 4:53PM |
L16.00006: Measurements of flow past a bileaflet mechanical heart valve Laura Haya, Stavros Tavoularis A bileaflet mechanical heart valve has been inserted in an axisymmetric model of the aorta within a mock circulation apparatus with physiological pressure and flow variations. The velocity field behind the valve has been measured with laser Doppler velocimetry and particle image velocimetry. The results closely match those reported by similar studies. A triple jet emanated from the valve's orifices and regions of reverse flow formed in the sinus region. Velocity fluctuations were greatest in the shear layers of the jets. The average r.m.s. streamwise velocity fluctuation over the turbulent period was 0.22 m/s; its maximum value was 0.53 m/s and occurred at the onset of deceleration. Measurements with the valve inserted in an anatomical model of the aorta are planned for the near future. The present and future measurements will be compared to determine the effects of the aorta anatomy on the characteristics of flow through bileaflet valves. In particular, measurements of the viscous and turbulent shear stresses will be analyzed to identify possible locations of blood element damage, and regions of recirculation and stagnation will be identified as locations favourable to thrombus growth. The effects of flows in branching arteries and valve orientation will also be investigated. [Preview Abstract] |
Monday, November 25, 2013 4:53PM - 5:06PM |
L16.00007: On the open/close performance of prosthetic heart valves at high frequencies A. Beltran, R. Zenit We report experimental observations of the performance of mechanical and biological prosthetic heart valves. The valves are mounted in a test circular channel conected to a flow system that emulates accelerated human-like conditions. The flow is generated by a high frequencie pulsative pump (in the range of 7 to 18 Hz). The objective of the investigation is to find the treshold conditions for which the open/close performance fails. Preliminary results show that for the mechanical valve the failure starts at 436 pulses/min, while for the biological valve, it starts a failing performance is observed for frequencies higher that 462 pulses/min. Even though these values are far from the heart rate in the human body, we use these measurements to further understand the structure-fluid interaction mechanics of the flow through heart valves. [Preview Abstract] |
Monday, November 25, 2013 5:06PM - 5:19PM |
L16.00008: ABSTRACT WITHDRAWN |
Monday, November 25, 2013 5:19PM - 5:32PM |
L16.00009: Effects of Pannus Formation on the Flow around a Bileaflet Mechanical Heart Valve Woojin Kim, Haecheon Choi, Jihoon Kweon, Dong Hyun Yang, Namkug Kim, Young-Hak Kim A pannus, an abnormal layer of fibrovascular tissue observed on a bileaflet mechanical heart valve (BMHV), induces dysfunctions of BMHV such as the time delay and incomplete valve closing. We numerically simulate the flows around an intra-annular type BMHV model with and without pannus formation, respectively, and investigate the flow and bileaflet-movement modifications due to the pannus formation. Simulations are conducted at a physiological condition (mean flow rate of 5 l/min, cycle duration of 866 ms, and the Reynolds number of 7200 based on the inflow peak bulk velocity and inflow diameter). We model the pannus as an annulus with fixed outer radius and vary the inner radius of the pannus. Our preliminary results indicate that the flow field changes significantly and the bileaflet does not close properly due to the pannus formation. The detailed results will be given at the final presentation. [Preview Abstract] |
Monday, November 25, 2013 5:32PM - 5:45PM |
L16.00010: The role of intraventricular vortices in the left ventricular filling? Pablo Martinez-Legazpi, Javier Bermejo, Yolanda Benito, Marta Alhama, Raquel Yotti, Candelas Perez del Villar, Ana Gonzalez-Mansilla, Alicia Barrio, Francisco Fernandez-Aviles, Juan Carlos del Alamo The generation of vortices during early filling is a salient feature of left ventricular hemodynamics. Existing clinical data suggest that these intraventricular vortices may facilitate pulling flow from the left atrium. To test this hypothesis, we have quantitatively dissected the contribution of the vortex to intraventricular pressure gradients by isolating its induced flow in ultrasound--derived data in 20 patients with non-ischemic dilated cardiomyopathy (NIDCM), 20 age-matched healthy controls and 20 patients with hypertrophied cardiomyopathy. We have observed that, in patients with NIDCM, the hemodynamic forces were shown to be partially supported by the flow inertia whereas that effect was minimized in healthy hearts. In patients with hypertrophied cardiomiopathy such effect was not observed. [Preview Abstract] |
Monday, November 25, 2013 5:45PM - 5:58PM |
L16.00011: Is aspect ratio sufficient to classify intra-aneurysmal hemodynamics- a parametric approach Michael Durka, Anne Robertson Intracranial aneurysms are a vascular pathology in which a localized bulge is formed in the arterial wall, most often in a saccular shape. It is believed that the blood flow field within the aneurysm plays a critical role in the degradation of the wall. Aneurysm rupture has a high mortality risk. Since only a small fracture of aneurysms rupture, and common treatments have their own risks, it is desirable to identify a useful means of assessing rupture risk. Therefore, numerous groups have endeavored to identify a correlation between rupture risk and sac geometry or flow dynamics. However, no clinically useful parameters have been identified to date. Prior work has suggested that the aspect ratio (sac height/neck) could be useful for risk stratification due to its influence on the sac hemodynamics. In this work, we make of a previously developed parametric model of the aneurysm geometry to evaluate the influence of aspect ratio (sac height/sac neck) on flow dynamics, using computational fluid dynamics. In particular, we assess the influence of aspect ratio on the number of vortices in the aneurysm sac over a wide range of sac geometries. The conclusions obtained for the parametric model are then assessed in 20 clinical cases. [Preview Abstract] |
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