FLUID DYNAMIC ANALYSIS USING FLOW VISUALIZATION OF THE BAYLOR NASA IMPLANTABLE AXIAL-FLOW BLOOD PUMP FOR DESIGN IMPROVEMENT/

The Baylor/NASA Axial Blood Flow Pump has been developed for use as an implantable left ventricular assist device (LVAD). The pump is intend ed as an assist device for either pulmonary or systemic circulatory su pport for more than 3-months' duration. To date the pump provides acce ptable results in terms of thrombus formation and hemolysis (IH of 0.0 18 g/100 L). A fluid dynamics analysis using flow visualization was pe rformed to investigate the flow fields and to determine areas within t he pump that could be improved. These studies focused upon the inflow area in front of the pump. A prototype axial flow pump assembly was co nstructed to facilitate the flow visualization studies. Particle image tracking velocimetry techniques were used to measure Amberlite partic les suspended in a blood analog fluid composed of 63% water and 37% gl ycerin. This method used a pulsed (612 Hz) laser light to determine fl ow velocity profiles, shear stress, Reynolds numbers, and stagnant are as within the axial pump. These studies showed that the flow straighte ner (a vaned assembly in the pump inflow) reduced Reynolds numbers fro m 4,640 to 2,540 (at 8.5 L/min) and that the flow straightener exacerb ates a discontinuity found between it and the impeller. Within the inf low area, a maximum of 80 N/m(2) shear stress was measured, which is w ell below published blood damage thresholds. Design variations were in vestigated resulting in a smoother flow transition between flow straig htener and impeller. These variations must be investigated further to establish a correlation with hemolysis and thrombus formation.