AUTOMATIC CONTROL OF TRI-POD SUPPORTED SEAL-LESS CENTRIFUGAL BLOOD PUMP USING MOTOR CURRENT WAVEFORM

A tri-pod supported, seal-less centrifugal blood pump has been developed as an implantable ventricular assist pump. The impeller is supported with a tri-pod made of 3mm ceramic balls attached to the bottom surface of the impeller and magnetically coupled to the driver magnet mounted on the motor shaft. As the motor turns, the impeller rotates with the tri-pod sliding in the polyethylene groove imbedded in the pump bottom casing. The dimension of the pump including the driver is 60mm x 80mm with its weight being 450g. The pump can deliver flow of 5L/min against the 100mmHg head pressure at 1800RPM. The pumping efficiency is around 10%. The pump RPM control consists of two phases; The initial phase is rough adjustment of the RPM based on the native heart rate. The target RPM is preset based on the relationship between the cardiac output and heart rate, and pump RPM and pump output. Fine turning of the pump RPM then follows by computing the waveform deformation index (WDI) through Fourier analysis of the motor current waveform. The threshold level of WDI for occurrence of suction is < 0.2 and if the WDI exceeds this number, the pump RPM is reduced in order to prevent the suction. The control system demonstrated a stable performance in response to a sudden change in the system parameter with the response time being around 3 seconds. The automatic control of the implantable centrifugal blood pump is feasible without relying on external sensors. The system is under evaluation in chronic animal models.