Experimental Determination of Dynamic Characteristics 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 consists of a shaftless impeller, which also acts as the rotor of the brushless DC motor. The impeller remains passively suspended in the pump cavity by hydrodynamic forces, which result from the small clearances between the outside surfaces of the impeller and the pump cavity. These small clearances range from approximately 50 microm to 230 microm in size in the version of pump reported here. This article presents experimental investigation into the dynamic characteristics of the impeller-bearing-pump housing system of the rotary blood pump for increasing pump speeds at different flow rates. The pump was mounted on a suspension system consisting of a platform and springs, where the natural frequency and damping ratio for the suspension system were determined. Real-time measurements of the impeller's displacement were performed using Hall effect sensors. A vertical disturbance force was exerted onto the pump housing, causing the impeller to be displaced in vertical direction from its dynamic equilibrium position within the pump cavity. The impeller displacement was represented by a decaying sine wave, which indicated the impeller restoring to its equilibrium position. From the decaying sine wave the natural frequency and stiffness coefficient of the system were determined. Furthermore, the logarithmic decrement method was used to determine the damping ratio and eventually the damping coefficient of the system. Results indicate that stiffness and damping coefficients increased as flow rate and pump speed increased, representing an increase in stability with these changing conditions. However, pump speed had a greater influence on the stiffness and damping coefficients than flow rate did, which was evident through dynamic analysis. Overall the experimental method presented in this article was successful in determining the dynamic characteristics of the system.

A Compact Highly Efficient and Low Hemolytic Centrifugal Blood Pump With a Magnetically Levitated Impeller

“…The damping effect of the impeller in water increased due to the rotation. However, it is not clear from this data whether the damping effect is due to the additional mass effect or the increase of both the damping coefficient and the spring stiffness produced by the hydrodynamic effect (18). A detailed analysis of the dynamic characteristics of the impeller in the axial Z direction should be carried out in future work.…”

Artificial Organs 2004: A Year in Review

“…Michael K.H. Chung et al (40) of the University of Technology (Sydney, Australia) evaluated the dynamic characteristics of their impeller‐bearing‐pump housing of their rotary blood pump for increasing pump speeds. The results indicated that stiffness and damping coefficients increased as flow rate and pump speed increased representing an increase in stability with these changing conditions.…”

Pulsatile driving of the helical flow pump

“…Therefore the risk to fall into sever suction can be reduced and also inlet pressure can be kept in physiological level. Highly sophisticated blood pumps for LVAD are centrifugal flow pump or axial flow pump [7][8][9]. Especially centrifugal pumps can obtain passively-created pulsatile flow which is induced by native heart beat.…”