Experimental study of pathological and cardiovascular device hemodynamics
Abstract
Experimental studies of various pathological and cardiovascular device flows are performed to assess their hemodynamic pathologic basis and to better understand the potential mechanisms which can be developed to improve them. A Viscous Impeller Pump (VIP) based on the Von Karman viscous pump is specifically designed to provide cavopulmonary assist in a univentricular Fontan circulation. The technology will make it possible to biventricularize the univentricular Fontan circulation. Ideally, it will reduce the number of surgeries required for Fontan conversion from three to one early in life, while simultaneously improving physiologic conditions. Later in life, it will provide a currently unavailable means of chronic support for adolescent and adult patients with failing Fontan circulations. Computational Fluid Dynamics (CFD) simulations demonstrate that the VIP can satisfactorily augment cavopulmonary blood flow in an idealized total cavopulmonary connection (TCPC). When the VIP is deployed at the TCPC intersection as a static device, it stabilizes the four-way flow pattern, and is not obstructive to flow. As a rotational device, it will augment the flow. Experimental studies are carried out to assess performance, hemodynamic characteristics and flow structures of the VIP in an idealized TCPC model. Stereoscopic Particle Image Velocimetry (SPIV) is applied using index-matched blood analog. Results show excellent performance of the VIP, without cavitation and with reduction of energy losses. The non-rotating VIP smooths and accelerates flow, and decreases stresses and turbulence in the TCPC. The rotating VIP generates the desired low-pressure Fontan flow augmentation (0-10 mmHg) while maintaining acceptable stress thresholds. Dynamic Mode Decomposition is applied to SPIV data for unpowered Fontan hemodynamics to extract underlying coherent flow features of the flow problem. This shows that unpowered Fontan flow is unstable with alternation of one and two counter-rotating vortex rings along the pulmonary arteries. Ultrasound measurements are performed on the in vitro experimental setup to show that this technique can be used as a means to optimize the placement of the temporary VIP in the TCPC of patients and maximize the univentricular function. In addition to the above study, this work also examines flows associated with thoracic aortic aneurysms, a defect induced by the acquired cardiovascular disease atherosclerosis. Atherosclerosis is known to be responsible for aneurysms (weakening of the vascular walls leading to outward bulging of the vessel with eventual rupture). Experimental techniques to assess the hemodynamics related to these pathological geometries are presented. 2D Particle Image Velocimetry (PIV) is applied to an in vitro circulatory loop with index-matched blood analog fluid and patient-specific geometries of a Thoracic Aortic Aneurysm before and after surgical repair. Results show that more recircultions, back-flow and small scale as well as large scale vortical structures exist in the TAA before surgical repair than in the TAA after surgical repair. This is accompanied by slowing down of the flow in the aneurysm portion and increased residence time of the blood that may lead to platelet activation.
Degree
Ph.D.
Advisors
Chen, Purdue University.
Subject Area
Biomedical engineering|Mechanical engineering
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