Fluid Dynamic Studies for Performance of Centrifugal Blood Pump with Magnetically Suspended Impeller

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Centrifugal blood pumps are simple, compact, easy to handle, and cheap compared with the displacement ventricular type of artificial hearts. It is promised as an artificial heart of next generation. At present, commercially available centrifugal blood pumps have some drawbacks ; the shear stress and friction heat produced on bearing and seal cause degeneration of blood. Therefore these pumps are clinically used for short term. To overcome these drawbacks, the authors have been developing a centrifugal blood pump with magnetically suspended impeller.(1) To improve pump efficiency, we have investigated the pump performances of many kinds of impeller's blades and diffusers, and the flow in the gap between the impeller's disc and the pump housing. We could find two kinds of blades with high efficiency. One is the 16-blades with outlet angle beta=90ﾟ and the other 7-blades with beta=40ﾟ. The hemolysis of these pumps is less than that of Bio-Pump. Further investigation will be necessary to determine which type is better.(2) Good washout flow is the gap between the impeller disc and the pump casing is observed by visualization. However, animal cxperiments show that white thrombus adheres to the polycarbonate surface of the impeller disc. But this problem is solved by surface polishing and coating with silicon.(3) The pump operation under the constant motor current shows the pressure-flow characteristics similar to Stirling's law. So the constant current mode is recommended hereafter.(4) Hemolysis test in the blood circuits with various kinds of orifices proves that the severe hemolysis is observed in case of the orifice with sharp corner faced upstream. This fact is verified by numerical analysis of shear stress.In conclusion, this pump proves to be very promising as blood pump for long-term use.