Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session KF: Biofluids XI |
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Chair: Leopold Grinberg, Brown University Room: Salt Palace Convention Center 151 G |
Tuesday, November 20, 2007 8:00AM - 8:13AM |
KF.00001: A Mechanics-Based Framework Leading to Improved Diagnosis and Treatment of Hydrocephalus Benjamin Cohen, Vedels Soren, Mark Wagshul, Michael Egnor, Abram Voorhees, Timothy Wei Hydrocephalus is defined as an accumulation of cerebrospinal fluid (CSF) in the cranium, at the expense of brain tissue. The result is a disruption of the normal pressure and/or flow dynamics of the intracranial blood and CSF. We seek to introduce integral control volume analysis to the study of hydrocephalus. The goal is to provide a first principles framework to integrate a broad spectrum of sometimes disparate investigations into a highly complex, multidisciplinary problem. The general technique for the implementation of control volumes to hydrocephalus will be presented. This includes factors faced in choosing control volumes and making the required measurements to evaluate mass and momentum conservation. In addition, the use of our Digital Particle Image Velocimetry (DPIV) processing program has been extended to measure the displacement of the ventricles' walls from Magnetic Resonance (MR) images. This is done to determine the volume change of the intracranial fluid spaces. [Preview Abstract] |
Tuesday, November 20, 2007 8:13AM - 8:26AM |
KF.00002: Cyto-fluid dynamics: Clarification of the cascade structure from nitrogenous base to human brain Ken Naitoh Nucleic acids (DNA and RNA) are only with five nitrogenous bases: two types of purines (A, G) and three types of pyrimidines (C, T, U). The size ratios of purines and pyrimidines are asymmetric around 3:2, that is, 1.5. Fluid dynamics shows a possible answer to the question of why the size ratio of purines and pyrimidines is around 1.5, because life exists when biological molecules such as nitrogenous bases are surrounded by the flow of aqua. Then, the explanation on inevitability of five bases leads to that of twenty-types of amino acids and also of complex structures of RNAs. Finally, we will show computational fluid-dynamics based on the Navier-Stokes equation simulates cerebral morphogenesis, i.e., the convexoconcave inside brain and eye balls. \textbf{References} \begin{enumerate} \item K. Naitoh, Japan J. of Industrial and Applied Mathematics, \textbf{18-1,} 75 (2001). \item K. Naitoh, Artificial Life and Robotics, \textbf{6-1 {\&} 2, }82 (2002). \item K. Naitoh, Proc. of 1$^{st}$ European Workshop on Artificial Life and Robotics (2006). \end{enumerate} [Preview Abstract] |
Tuesday, November 20, 2007 8:26AM - 8:39AM |
KF.00003: A Multiscale Model for the Brain Vascular Network Leopold Grinberg, George Karniadakis Simulations of blood flow in arterial networks requires physiologicaly correct boundary condition at inlets and outlets. Outflow boundary conditions for the Macrovascular Network (MaN) can be imposed by solving a closure problem based on modeling the rest of the flow in ten millions arterioles (Mesovascular Network, MeN) and one billion capillaries (Microvascular Network, MiN). Numerical solution of the three-level MaN-MeN-MiN integration can be performed on the future generation of petaflop supercomputers. An alternative approach for the MaN simulation is to impose the clinically measured flow rates at outlets. We have developed a new method to incorporate such measurements at multiple outlets, it is based on imposing Neumann boundary condition for the velocity and time-dependent resistance boundary conditions for the pressure. The convergence of numerical solution for the outlet flow-rates is achieved immediately. The computational complexity of the method is comparable to the widely used constant pressure boundary condition. Our approach is verified on a model of Brain Vascular Network with tens of arterial segments and outlets. [Preview Abstract] |
Tuesday, November 20, 2007 8:39AM - 8:52AM |
KF.00004: Image based numerical simulation of hemodynamics in a intracranial aneurysm Trung Le, Liang Ge, Fotis Sotiropoulos, David Kallmes, Harry Cloft, Debra Lewis, Daying Dai, Yonghong Ding, Ramanathan Kadirvel Image-based numerical simulations of hemodynamics in a intracranial aneurysm are carried out. The numerical solver based on CURVIB (curvilinear grid/immersed boundary method) approach developed in Ge and Sotiropoulos, JCP 2007 is used to simulate the blood flow. A curvilinear grid system that gradually follows the curved geometry of artery wall and consists of approximately 5M grid nodes is constructed as the background grid system and the boundaries of the investigated artery and aneurysm are treated as immersed boundaries. The surface geometry of aneurysm wall is reconstructed from an angiography study of an aneurysm formed on the common carotid artery (CCA) of a rabbit and discretized with triangular meshes. At the inlet a physiological flow waveform is specified and direct numerical simulations are used to simulate the blood flow. Very rich vortical dynamics is observed within the aneurysm area, with a ring like vortex sheds from the proximal side of aneurysm, develops and impinge onto the distal side of the aneurysm as flow develops, and destructs into smaller vortices during later cardiac cycle. This work was supported in part by the University of Minnesota Supercomputing Institute. [Preview Abstract] |
Tuesday, November 20, 2007 8:52AM - 9:05AM |
KF.00005: Evaluation of wall shear stress in a patient-specific model of a cerebral aneurysm using stereo PIV Yoshinori Bando, Masamichi Oishi, Marie Oshima It is important to determine whether a particular cerebral aneurysm has a high risk of rupture or not so that it can be treated before subarachnoid hemorrhage occurs. Hemodynamic stresses, especially Wall Shear Stress (WSS), are considered to play an important role in formation, growth and rupture of the cerebral aneurysm. In this paper, we investigate WSS under the pulsatile inflow conditions in a realistic in vitro model of a cerebral aneurysm. The geometry model is constructed in a patient-specific manner using CT data. The stereo PIV measurement is conducted to obtain the velocity field in the model and to derive WSS distribution from PIV results and geometry data of lost model. The results show that overall WSS distribution in the model does not charge uniformly with time due to palsatile flow. [Preview Abstract] |
Tuesday, November 20, 2007 9:05AM - 9:18AM |
KF.00006: A cumulative shear mechanism for tissue injury initiation in shock-wave lithotripsy Jonathan Freund Considerable injury to renal tissue often accompanies treatment when shocks waves are delivered to break up kidney stones. The most severe injuries seem to involve cavitation damage, driven by the expansive portion of the lithotripor's wave. However, data from animal studies indicate that inverted shock waves, which should preclude cavitation, still cause local injury near the tip of the renal papilla, which seems particularly susceptible to injury in general. We develop a model of papilla tissue, which consists mostly of parallel fluid filled elastic 10 to 30$\mu$m diameter tubules, to assess whether or not the shear of repeated shocks can accumulate to cause injury. Material properties are estimated from reported measurements of renal basement membranes. A Stokes-flow boundary integral algorithm is used to estimate the net viscoelastic properties of the tissue. It is predicted that the particular microstructure of the tissue near the tip of the papilla is indeed susceptible to shear accumulation as consistent with several observations. [Preview Abstract] |
Tuesday, November 20, 2007 9:18AM - 9:31AM |
KF.00007: Rupture Risk Prediction of Abdominal Aortic Aneurysms (AAAs) Rubing Tang, Christian Geindreau, Juan Lasheras Currently there is no reliable method to predict the risk of rupture of AAAs. Our study seeks to improve the capabilities of biomedical techniques to better monitor the rupture risk of these aneurysms by quantifying the spatial and temporal distribution of mechanical stresses acting on the vessel walls. Specifically it aims at providing improved guidelines for surgical or endovascular intervention. Numerical simulations has been performed to calculate the wall stress distribution based on the peak blood pressure (static analysis) in both idealized and patient specific models of AAAs, using finite element method. Pulsatile blood flows were also simulated for idealized models with different parameters. Our results have shown that, in addition to the maximum AAA diameter, eccentricity and the presence of thrombus are also significant factors affecting the wall stress distribution, flow characteristics and hemodynamic forces in AAAs. Therefore, we confirmed that current criterion based solely on maximum diameter obtained from population-based statistics is not appropriate for the clinical management of AAA rupture, and other factors such as AAA shape and the presence of ILT should also be considered for a better assessment. [Preview Abstract] |
Tuesday, November 20, 2007 9:31AM - 9:44AM |
KF.00008: Development of a Comprehensive Model of the Apparent Viscosity of Blood for Simulations of the Microcirculation in Rat Spinotrapezius Muscle Fascia Frank Jacobitz, Colin Porterfield, Cheryn Engebrecht, Ian Metzger A more comprehensive model for the apparent viscosity of blood is proposed and applied to simulations of the microcirculation in rat spinotrapezius muscle fascia. At the microcirculatory level, the apparent viscosity of blood depends on the local vessel diameter, hematocrit, and shear rate. Starting with the apparent viscosity model proposed by Pries, Secomb, Gaehtgens, and Gross (Circulation Research, 67, 826-834, 1990), describing the effect of vessel diameter and hematocrit on the apparent viscosity, and using experimental data presented by Lipowsky, Usami, and Chien (Microvascular Research, 19, 297-319, 1980), describing the shear rate dependence of apparent viscosity, a more comprehensive model is developed. This model is applied to simulations of the microcirculation in rat spinotrapezius muscle fascia. The simulations use realistic vessel topology for the microvasculature, reconstructed from microscope images of tissue samples, and consider passive and active vessel properties. The numerical method is based on a Hagen-Poiseuille balance in the microvessels and a sparse matrix solver is used to obtain the solution. It was found, for example, that the distribution of vessel length follows a log-normal law. The distribution of hematocrit, however, was found to be approximately normal. [Preview Abstract] |
Tuesday, November 20, 2007 9:44AM - 9:57AM |
KF.00009: A Lightweight Particle Deposition System for Particle Resuspension Studies Jason DeGraw, John Cimbala Experimental studies of particle resuspension often require that particles be deposited in a localized area in a repeatable manner. A system has been designed for this purpose that is lightweight in both mass and complexity -- attributes which are both highly desirable. The low mass of the system allows for accurate determination of the mass of particulate matter placed inside the system (via tare weighing), and the low complexity of the system makes it easy to use. The device is a piston-cylinder apparatus made of plastic, and is therefore inexpensive to build, easy to clean, and readily disposable. Rapid upward movement of the piston draws air into the cylinder through small ports placed around the perimeter of the cylinder. The injected air aerosolizes particulate matter placed in the ports, and then the particles are allowed to settle onto the substrate. The device enables the localized deposition of particles without much lost material, allowing for more frugal and careful use of allergen- containing particulate matter (some of which require a great deal of time and effort to produce). Our previous system would deposit about 15-20\% of the particles in the desired location (typically a small region of a flooring sample), while the new system is able to deposit more than 25-30\% of the particles in the desired location with considerably less waste. [Preview Abstract] |
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