Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session P30: Biological Fluid Dynamics : Medical Devices |
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Chair: Wesley Harris, MIT Room: 612 |
Monday, November 25, 2019 5:16PM - 5:29PM |
P30.00001: The impact of cervical geometry and suture material on cerclage integrity Alexa Baumer, Alexis Gimovsky, Megan C Leftwich Cervical insufficiency is a medical condition during pregnancy in which the uterine cervix softens, shortens and dilates before reaching full term, usually between 18 and 22 weeks gestation, such that a preterm birth occurs. It is a common cause of second trimester pregnancy loss. Part of the clinical treatment of this condition is the cervical cerclage, a procedure to close the cervix with a purse-string stitch. There are conflicting findings on the efficacy of the cerclage, with most studies relying on statistical evidence. The purpose of this investigation is to examine the mechanical limitations of the cerclage. Working with physicians from The George Washington University Hospital, we create generalized, synthetic models of the cervix and fabricate them with silicone to mimic physiological, softening cervical tissue. Aspects of the cervical geometry (length of cervix, shape and width of dilatation) and suture material used in the cerclage are varied. The synthetic cervices are stitched by physicians according to clinical techniques. The maximum force required for the synthetic tissue to rupture through the cerclage stitch is recorded. The results of this study provide insight into the most effective clinical interventions and the mechanism of their success. [Preview Abstract] |
Monday, November 25, 2019 5:29PM - 5:42PM |
P30.00002: A Magnetorheological Hemostatic Agent Yonatan Tekleab, Nikolaos Kokoroskos, George Velmahos, Gareth McKinley, Wesley Harris Magnetorheological (MR) suspensions are used in systems requiring responsive fluids with fast-acting, tunable properties. MR valves, have been effective in rapidly and locally arresting pressure-driven flows in mechanical systems. Motivated by these applications, we developed a magnetically-actuated valve for use in the human body, to reduce or halt hemorrhage. 80{\%} of trauma related deaths in the first hour of hospital admission are due to hemorrhagic shock. Such a hemostat would provide a prehospital intervention opportunity to stem bleeding, giving physicians more time to resuscitate patients upon trauma facility admission. The valve comprises an injectable, biocompatible MR suspension with externally-placed permanent magnets. To trigger the MR effect near the injury site in bleeding patients, the fluid was designed for biocompatibility, rapid injectability, and local actuation within blood vessels. We have synthesized, characterized, and demonstrated efficacy, through benchtop and \textit{in vivo} rat tests, a novel, minimally invasive, MR hemostatic agent. Using magnets in 3D printed holders that can be worn by field surgeons, we demonstrate arrest of a major hemorrhagic event, dramatically reduced lost blood volume, sustained blood pressure, and significantly increased survival time. [Preview Abstract] |
Monday, November 25, 2019 5:42PM - 5:55PM |
P30.00003: Influence on the fluid mechanics of blood flow of heterogeneity and anisotropy of the coil mass deployed inside intracranial aneurysms Julia Romero Bhathal, Fanette Chassagne, Laurel Marsh, Mike Levitt, Christian Geindreau, Alberto Aliseda Cerebral aneurysms are often treated with coils to induce thrombosis. Flow in coiled aneurysms has been studied extensively through CFD simulations to predict the flow after endovascular treatment. Representing coil mass as a homogeneous porous medium represents a limitation to the understanding of flow in coiled aneurysms and inhibits clinically accurate predictions. We present the characterization of the spatial heterogeneity and anisotropy of the coil mass deployed inside the aneurysmal sac based on synchrotron X-ray tomography of aneurysm phantoms treated with real coils and describe the resulting flow based on a parametrization of coil's permeability that combines a theoretical model with the experimental results. The segmented images are used to compute the mean porosity, the porosity gradient along the inertial axis of the coil, the porosity map and the corresponding permeability map for different types of spatial discretization. The results show that the porosity varies between 0.6 to 0.95, leading to a factor 100 in permeability variations. CFD simulations results compare our results with standard homogeneous isotropic modeling. [Preview Abstract] |
Monday, November 25, 2019 5:55PM - 6:08PM |
P30.00004: Effect of varying inhalation durations in normal breathing and HFOV conditions Manikantam Gaddam, Yu Feng, Arvind Santhanakrishnan Experimental and computational studies in idealized and subject-specific airways at normal breathing conditions (Womersley number, Wo$=$2-4) and in high-frequency oscillatory ventilation (HFOV, Wo$=$4-25) have shown flow separation at bifurcations, secondary flows, and steady streaming at the end of inhalation. However, the effects of varying inhalation duration (relative to breathing time period) on the flow field remain unclear. We conducted 2D simulations on a Weibel airway model representing mouth to trachea with G2 to investigate the influence of inhalation time (IT) to breathing time (BT) in normal breathing and HFOV conditions. Oscillatory breathing patterns, with peak inhalation at Reynolds number (Re) of 1070 and peak exhalation at Re of 1100, were prescribed as inflow conditions for different Wo values. With increasing Wo for a given IT/BT ratio, residual flow region increased at the end of exhalation, affecting flow during inhalation in the next breathing cycle. With increasing IT/BT, residual flow region increased at the end of exhalation for Wo ranging from 2.4 to 7.5 in the oral region. [Preview Abstract] |
Monday, November 25, 2019 6:08PM - 6:21PM |
P30.00005: Steady streaming and conditional turbulence in high-frequency ventilation Justin Leontini, Chinthaka Jacob, David Tingay High-frequency ventilation (HFV) is a technique used to ventilate neonates and patients with critical respiratory distress syndrome. It uses very fast yet shallow inflations, resulting in small peak pressures, thereby protecting lungs from over-distension. There are several mechanisms proposed for the gas transport during HFV, and here we investigate two of the primary ones; turbulent mixing and mean streaming. We have conducted direct numerical simulations of these high-frequency reciprocating flows in 1:2 bifurcations with geometric proportions relevant to the first five generations of the neonatal airway. Conditional turbulence is observed in the first three generations of the airway, the turbulence occurring when the flow rate is near its maximum. The results suggest this turbulence is generated via an instability of the Dean vortices generated via the curvature of the bifurcation. This mechanism differs from that which leads to conditional turbulence in the reciprocating flow in a straight pipe. We also quantify the recirculating flow rate due to mean streaming and find it to be around $5\%$ of the maximum flow rate in the upper airway - this is enough to provide adequate gas exchange during HFV. [Preview Abstract] |
Monday, November 25, 2019 6:21PM - 6:34PM |
P30.00006: Effect of fluid properties and impact speed for ophthalmic drug delivery via droplet impact Idera Lawal, Pedro Mallet, Jeremy Marston Front-of-the-eye (FOTE) delivery is the most popular route for administering drugs to the eye (i.e. ophthalmic delivery), with dropper bottles constituting a vast majority of the current market. These are notoriously inefficient and dictate the need for innovative devices to deliver discrete volumes to the eyeball. In addition, to promote adhesion many novel formulations incorporate polymers, leading to complex fluid properties. However, the fluid dynamics of this process and the specific role of fluid rheology combined with the pre-existing tear film are not well understood. Here, we will present preliminary results on delivery of polymeric solution using droplets, and discuss the effect of rheology, impact speed, substrate curvature, and evaluate universal scaling laws to capture the dynamics. [Preview Abstract] |
Monday, November 25, 2019 6:34PM - 6:47PM |
P30.00007: Effect of applied load and jet dispersion on efficiency of needle-free injections Pankaj Rohilla, Jeremy Marston Intradermal delivery of vaccines with the jet injections is one of the leading alternatives to the needle injections for needle free drug delivery. However, effect of various parameters related to nozzle geometry, fluid properties and skin properties are still not well understood. In addition to design parameter such as the orifice diameter, jet speed, ampoule volume, and standoff distances, we must also consider applied load of the device on the skin, skin tension, and jet collimation. These three parameters are studied herein using an ex-vivo model (guinea pig and human skin), We investigate the effect of the skin support, viscosity of the liquid injected, ampoule volume, standoff distance and loading mechanism on the dispersion of the vaccine and the drug delivery efficiency into the skin. [Preview Abstract] |
Monday, November 25, 2019 6:47PM - 7:00PM |
P30.00008: Patient-specific analysis of esophageal transport using barium swallow fluoroscopy Sourav Halder, Shashank Acharya, Wenjun Kou, John Erik Pandolfino, Peter J. Kahrilas, Neelesh Ashok Patankar Barium swallow is an X-ray test for diagnosis of esophageal disorders such as achalasia, diverticula, dysphasia, gastroesophageal reflux disease (GERD) etc. This test gives a qualitative idea of how efficiently a bolus is transported through the esophagus. We have developed a technique by which we can analyze a barium swallow fluoroscopy and calculate the velocity and pressure distribution inside the esophagus. In this technique, we use a Convolutional Neural Network to perform segmentation of image sequences generated from a fluoroscopy, and use these segmented images as input to a reduced-order model to calculate the velocity and pressure in the fluid inside the esophagus. We have also used this method along with High Resolution Manometry (HRM) to identify and estimate biomarkers such as wall-relaxation that occurs ahead of the peristalsis wave in the esophagus wall. This reduced-order model can run very fast, and hence can be used in clinical applications to add more quantitative information to the barium swallow test, thus resulting in better diagnosis of esophageal disorders. [Preview Abstract] |
Monday, November 25, 2019 7:00PM - 7:13PM |
P30.00009: Flow in a cavity: fluid mechanics of kidney stone removal Jessica G. Williams, Sarah L. Waters, Derek E. Moulton, Ben W. Turney, Alfonso A. Castrejon-Pita Flexible uretero-renoscopy provides a minimally invasive treatment for kidney stone removal. The ureteroscope is passed to the kidney through a hollow cylinder (access sheath) and has a central lumen (working channel) for surgical tools, such as laser fibres which pulverise stones. Resulting stone dust can impede the view from a miniscule camera at the scope tip; this necessitates irrigation -- debris clearance by saline solution, which flows into the kidney through the working channel, and returns via the access sheath. Fast debris clearance allows for efficient ureteroscopy. We represent the renal pelvis of the kidney as a 2D rectangular cavity and investigate the effects of flow rate and cavity size on flow structure and subsequent clearance time. We model fluid flow with the steady Navier-Stokes equations, imposing a Poiseuille profile at the inlet boundary for the jet of saline, and zero-stress on the outlets, allowing for a parallel return flow. Resulting flow patterns in the cavity contain competing vortical structures. We demonstrate the existence of multiple solutions dependent on the Reynolds number of the flow and the aspect ratio of the cavity. We complement numerical predictions with PIV experiments. We model the clearance of an initial debris cloud via an advection-diffusion equation. We determine how the initial position of the debris cloud within the flow, and the Peclet number, affect clearance time, which is prolonged by entrapment of debris within closed streamlines. We discuss flow manipulation strategies to extract debris from vortices and decrease washout time. [Preview Abstract] |
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