Miniaturization and Performance Enhancement of the Magnetically Levitated Centrifugal Pump as an Implantable Ventricular Assist Device

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The purpose of the present study is enhancement of the performances and the biocompatibility of the centrifugal pump with magnetically levitated impeller as a left ventricular assist device, with the final goal of development of an implantable ventricular assist system.The primary results obtained through this study are as follows;1. Miniaturization and Stability Enhancement of the Levitation Controlling CircuitThe electronic circuits which control both radial levitation and rotation of the rotor (impeller) were designed to be implemented in the compact centrifugal pump. Numerical Simulations were carried out to obtain the optimized values of the inner/outer diameters of the stator, and the number of turns. The test rig pump was designed based on the analyses results, and the sufficient hydrodynamic performances were realized as a left ventricular assist device.2. The zero-power control method was employed and implemented into the present levitation system. The zero-power system sets t … More he control target onto the position where the radial fluid forces are minimized, and consequently save the electric power required to the levitation system. We built the numerical modeling of the electromagnetic components and then obtained the optimized thickness of the permanent magnets, diameter of the stator, and the number of turns of electric coils. Finally the diameter of the stator was set to 55 mm and we have succeeded in reducing the total electric power to 11 watts.3. The smallest clearance of the blood passage was 0.5 mm at the gap between the stator and the rotor. The hemolysis tesing was carried out to confirm the mechanical damage exerted to the red blood cells are within tolerable range toward clinical application. The results showed that the mechanical blood damage caused by the pump are compatible to that by the commercially available pump (Medtronic BP-80) at the flow rate of 5.0 L/min against the pressure head of 100 mmHg.4. The method of estimating the flow rate of the pump are also investigated. As the result of the zero-power control, the impeller positions shift to the balanced position on each flow condition. We have found the displacement of the impeller from the geometrical center are proportional to the flow rate. This basic founding can be developed into the flow rate measurement system which does not require any flow meter in the system. Less