Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session G10: Biofluids: Medical Devices I |
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Chair: Ibrahim Yildiran, George Washington University Room: 140B |
Sunday, November 19, 2023 3:00PM - 3:13PM |
G10.00001: Computational investigation of the influence of LVAD inflow cannula on left ventricle hemodynamic in advanced heart failure Clément Leger, Angela Straccia, Claudius Mahr, Alberto Aliseda, Fanette Chassagne In the last three decades, LVADs have improved hemocompatibility, making them a viable long-term treatment option for individuals with advanced heart failure. Despite reduced complications, the rate of stroke remains high. The LVAD inflow cannula placement impacts the hemodynamics in the Left Ventricle (LV), potentially creating thrombogenic flow patterns. The objective of this research is to analyse, via CFD simulations, the performance of two LVAD cannulae: one deeply implanted into the LV (HeartMate3) and the other flushed with the myocardium wall (Evaheart2). Both cannulae were virtually implanted on the apex of a patient-specific LV. The aortic valve was closed, as is common in LVAD patients, so flow enters the ventricle at the mitral valve and exits through the cannula. Two operating conditions are explored: constant 5 l/min flow rate and pulsatile waveforms from a lumped parameter model that includes the pumps' characteristic curves. Analysis focuses on Eulerian metrics to estimate LV washout and quantify blood stasis. Favourable hemodynamics are associated with a flushed cannula design (Evaheart2) compared to a protruding cannula. This is coupled with the EH2 high flowrate amplitude, that improves LV washout and reduces recirculation at the LV apex. This Eulerian approach will be complemented by a Lagrangian platelet tracking approach, via massless flow tracers, which will compute actual residence time and shear stress history, and help model prothrombotic platelet behaviour. |
Sunday, November 19, 2023 3:13PM - 3:26PM |
G10.00002: Synchronous PIV analysis of a self-powered blood turbine- pump couple Kerem Pekkan, Kagan Ucak, Faruk Karatas A magnetically-coupled blood turbine and pump system (iATVA) that resembles a turbocharger can provide mechanical circulatory support without external power to right-heart failure patients[1]. In this study, the fluid dynamics of the turbine and turbine-pump coupling efficiency are studied for the first-time in the literature. Optically clear prototypes are 3D printed. A time-resolved particle image velocimetry set-up equipped with a beam splitter allowed simultaneous velocity field acquisition from both impellers. The system is triggered with impeller rotation and velocity data is acquired at 6 different impeller orientations. Background subtraction, and multi-pass cross correlation were utilized as a pre and post-processing. The experimental pipeline is first verified through experiments with the FDA pump prototype, where two recirculation regions are observed, and impeller orientations affect the nozzle flow (0.25 to 0.42 m/s +-3.5% error). Coupled impellers operated synchronously. The peak velocity of the turbine span ~25% of the inter blade passage is operating at impulse mode. Backflow at the turbine exit tip reached 3/5 of peak flow. While turbine flowrates increase from 1.6 to 2.4 LPM, the relative inlet flow angle and rotation speed of the turbine change from 38 to 55% and from 630 to 900 rpm. Tip clearance leakage is localized at impeller inlets. Another recirculation region is observed in the coupled pump. Results will be used in CFD validation and to optimize iATVA system. |
Sunday, November 19, 2023 3:26PM - 3:39PM |
G10.00003: A multiscale approach to modeling transport processes in the whole hemodialyzer: A step towards optimal design Ruhit Sinha, Anne E Staples Hemodialyzers, or artificial kidneys, consist of cylindrical modules housing about 10^4 hollow fibers carrying blood. Uremic toxins are cleared from the blood by diffusing and convecting through the fibers' semipermeable membranes into a dialysate solution surrounding the fibers flowing in a countercurrent manner. Experimental studies reveal a dialysate flow channeling phenomenon that is correlated with decreased dialyzer clearance efficiency. To understand the mechanics of dialysate channeling we developed a multiscale computational dialyzer model that divides the dialyzer cross-section into three annular rings. The model captures both the module- and fiber-scale flow physics and is able to predict, for the first time, the toxin concentration profile across the dialyzer cross section. For a high-flux commercial hemodialyzer (the Baxter CT190G) we found peak dialysate axial velocity values at the periphery of the dialyzer module and peak dialysate toxin concentrations upstream of the dialysate outlet, consistent with previous "in vitro" and numerical studies. The detailed model revealed that outlet blood urea concentration remained as high as 80% of the inlet values in fibers near the centerline of the dialyzer and fell to almost zero at the inner ring periphery. These results provide a clear link between dialysate channeling and dialyzer clearance performance and suggest that annular multiscale models can be used to resolve outstanding issues in dialyzer design and performance. |
Sunday, November 19, 2023 3:39PM - 3:52PM |
G10.00004: Effect of inflow on coherent structures in the U.S. Food and Drug Administration's (FDA) idealized benchmark nozzle device using Proper Orthogonal Decomposition Donnatella G Xavier, Saleh Rezaeiravesh, Philipp Schlatter The FDA proposed an idealized nozzle geometry for assessing the performance of Computational Fluid Dynamics (CFD) in blood carrying medical devices. While many CFD simulations and experiments have been performed on this nozzle flow, there is disagreement in the reported locations of jet breakdown, peak viscous stresses and statistics at the FDA-specified transitional and turbulent Reynolds numbers (Re). Hence, the reproducibility of statistics at these Re is questionable, making it difficult to establish a reliable reference case for validation. The crucial fact that the specified Re are too low to define a unique turbulent inflow is often overlooked in literature. We performed direct numerical simulations of the flow through the FDA nozzle at the throat Re of 7500, facilitating a well-defined turbulent inflow, due to self-sustained turbulence in the inlet. A proper orthogonal decomposition (POD) revealed that the throat section housed the most energetic low-wavenumber streak-like structures, potential triggers for the jet breakdown downstream. POD of parabolic inflow at the same Re confirmed that numerical noise led to the jet breakdown, affirming the impact of the inflow condition on the downstream flow and ensuing structures aiding the jet breakdown. Our study provides a reference for the validation of CFD simulations of a turbulent flow through the FDA nozzle and identifies the flow structures arising from the geometry orientation, offering insight into the mechanics of the jet breakdown. |
Sunday, November 19, 2023 3:52PM - 4:05PM |
G10.00005: Feasibility Study of Investigating Soft Embolic Particle Transport Using an In Vitro Benchtop Flow Loop Model Tandralee Chetia, Argudit Chauhan, Thomas Puhr, Debanjan Mukherjee Stroke continues to be a critical health issue of global concern. A significant mechanism of stroke is embolic. wherein a fragmented piece of blood clot (embolus) migrates from its source to occlude cerebral arteries. Hence, embolic stroke occurrence is highly dependent on embolic pathways in the bloodstream. Prior investigations have shown that embolus distribution does not necessarily follow flow distribution. However, most existing models assume emboli to be quasi-rigid, and limited insights are available on how embolus deformability influences distribution. Replicating physiologic soft embolus transport in pulsatile flow through anatomical vascular pathways is a challenging task. Here, we demonstrate the feasibility of a benchtop model of soft-particle transport in a flow-loop comprising 3D printed human anatomical vessel models. The particles are prepared in the form of calcium alginate beads fabricated using a drip-infusion setup. Particle sizing is characterized as a function of fabrication parameters. The particles are then introduced into the flow loop and their dynamics and distribution across pulsatile flow in a carotid bifurcation model is quantified using high-speed videography and particle counting. Comparing these variables against those obtained from experiments with rigid particles of same size and density, we discuss how deformability may influence embolus distribution across vascular bifurcations. |
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