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Effect of outflow graft size on stroke risk in the aortic arch
Bhalla, AmneetBuono, Michael
Heart Failure affects approximately 2.4% of the population with about 500,000 new cases reported each year. Left Ventricular Assist Device (LVAD) is a mechanical pump that is surgically connected to the heart to boost blood flow for patients. One devastating complication that can occur when using a LVAD, is stroke. The aim of this study is to measure the flow field in the aorta and outflow cannula of the HeartMate II and 3 LVAD to assess flow stasis, pulsatility, and distribution of flow in the aortic arch branch vessels. Experimental studies were performed with a glass aorta, silicone model of the left ventricle (LV), Tygon tubing, outflow graft (10, 12, 14 mm), arterial filter, and an LVAD. Fluorescent particles were used to image the blood flow throughout the system. Pressure and flow rate were obtained using LabChart software. Distribution of particles captured using LaVision Digital Particle Imaging Velocimetry (DPIV) software, CCD image intense 3 CMOS camera, and a laser. The camera was positioned below the tank while the laser applied perpendicular/midplane to the glass aorta. Boundary conditions consist of a mean arterial pressure (MAP) no higher than 100±5 mmHg and an aorta flow speed of 3.6 L/min. Flow sensors placed at branch (brachiocephalic, carotid, and subclavian arteries) outlets and downstream from descending aorta. Pressure and flow were continuously measured as LVAD speed increased. Test occurred at three separate LVAD speeds. Clamps on the Tygon tubing were adjusted at medium speed to maintain a 1:3 branch to aorta flow ratio (25%,75%). Regions of Interest (ROI) method was used to restrain the analysis to only the middle region of each branch to obtain the average flow distribution during the cardiac cycle. Results indicate a reduction in particle distribution to the left subclavian artery when a narrower outflow graft size is used and a decrease in particle distribution to the right carotid when using a wider graft size. According to the PI calculation, the 14 mm provides the best pulsatility, thus hemodynamics during operation, with the 12 mm as a close second. This study may provide an insight to future LVAD design changes.
San Diego State University
Master of Science (M.S.) San Diego State University, 2020
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