Impeller Behavior and Displacement of the VentrAssist Implantable Rotary Blood Pump

Abstract

The VentrAssist implantable rotary blood pump, intended for long-term ventricular assist, is under development and is currently being tested for its rotor-dynamic stability. The pump is of the centrifugal type and consists of a shaftless impeller, also acting as the rotor of the brushless DC motor. The impeller remains passively suspended in the pump cavity by hydrodynamic forces, resulting from the small clearances between the impeller outside surfaces and the pump cavity. In the older version of the pump tested, these small clearances range from approximately 50 microm to 230 microm; the displacement of the impeller relative to the pump cavity is unknown in use. This article presents two experiments: the first measured displacement of the impeller using eddy-current proximity sensors and laser proximity sensors. The second experiment used Hall-effect proximity sensors to measure the displacement of the impeller relative to the pump cavity. All transducers were calibrated prior to commencement of the experiments. Voltage output from the transducers was converted into impeller movement in five degrees of freedom (x, y, z, theta(x), and theta(y)). The sixth degree of freedom, the rotation about the impeller axis (theta(z)), was determined by the commutation performed by the motor controller. The impeller displacement was found to be within the acceptable range of 8 micro m to 222 microm, avoiding blood damage and contact between the impeller and cavity walls. Thus the impeller was hydrodynamically suspended within the pump cavity and results were typical of centrifugal pump behavior. This research will be the basis for further investigation into the stiffness and damping coefficient of the pump's hydrodynamic bearing.

Evaluation of Left Ventricular Assist Device Performance and Hydraulic Force in a Complete Mock Circulation Loop

“…Increased static force requires excessive power diversion to the bearing system, which reduces overall efficiency. Hydrodynamic bearing systems become more dynamically stable with the introduction of a static bias force (16), however, the suspension capacity is partially compromised in the direction of this force vector. Finally, the wear lifetime of mechanical type pivot bearing systems significantly benefit from a reduction in static thrust.…”

“…However, the stability of a hydrodynamic bearing system increases with the introduction of a static bias force (16). The weight of the impeller can be used; however, the bias may be increased in the desired direction with the correct impeller/volute selection.…”

Measurement of the Rotor Motion and Corresponding Hemolysis of a Centrifugal Blood Pump With a Magnetic and Hydrodynamic Hybrid Bearing

“…In terms of the measurement device, Chung (9) reported that the accuracy of the eddy current gap sensors could not be assured because of the interference of the electromagnetic noise from the motor coils. However, the motor of our pump was placed below the housing bottom, and far enough from the sensors, while the motor of Chung's pump was built in the rotor.…”

Artificial Organs 2004: A Year in Review

“…Michael K.C. Chung et al (57) of the University of Technology (Sydney, Australia) reported on impeller behavior and displacement of their implantable rotary blood pump. The impeller was hydrodynamically suspended within the pump cavity and results were typical of centrifugal pump behavior.…”