FLOW CHARACTERISTICS AND REQUIRED CONTROL ALGORITHM OF AN IMPLANTABLECENTRIFUGAL LEFT-VENTRICULAR ASSIST DEVICE

As the clinical application of LVADs has increased, attempts have been made to develop smaller, less expensive, more durable and efficient i mplantable devices using rotary blood pumps. Since chronic circulatory support with implantable continuous-flow LVADs will be established in the near future, we need to determine the flow characteristics throug h an implantable continuous-flow LVAD. This study describes the flow c haracteristics through an implantable centrifugal blood pump as a left ventricular assist device (LVAD) to obtain a simple non-invasive algo rithm to control its assist flow rate adequately. A prototype of the c ompletely seal-less and pivot bearing-supported centrifugal blood pump was implanted into two calves, bypassing from the left ventricle to t he descending aorta. Device motor speed, voltage, current, flow rate, and aortic blood pressure were monitored continuously. The how pattern s revealed forward how in ventricular systole and backward flow in dia stole. As the pump speed increased, an end-diastolic notch became evid ent in the flow profile. Although the flow rate (Q [l/min]) and rotati onal speed (R [rpm]) had a linear correlation (Q = 0.0042R - 5.159; r = 0.96), this linearity was altered after the end-diastolic notch was evident. The end-diastolic notch is considered to be a sign of the suc king phenomenon of the centrifugal pump. Also, although the consumed c urrent (I [A]) and how rate had a linear correlation (I = 0.212Q + 0.2 9; r = 0.97), this linearity also changed after the end-diastolic notc h was evident. Based upon the above findings, we propose a simple algo rithm to maintain submaximal flow without inducing sucking. To maintai n the submaximal flow rate without measuring flow rate, the sucking po int is determined by monitoring consumed current according to gradual increases in voltage.