Estimation of pump flow rate and abnormal condition of implantable rotary blood pumps during long-term in vivo study.

Abstract

The control system for an implantable rotary blood pump is not clearly defined. A detection system is considered to be necessary for pump flow monitoring and abnormal conditions such as back flow or a sucking phenomenon where the septum or left ventricle wall is sucked into the cannula, etc. The ultrasound flowmeter is durable and reliable but the control system should not be totally dependent on the flowmeter. If the flowmeter breaks, the rotary blood pumps have no control mechanism. Therefore, the authors suggest controlling the pumps by an intrinsic parameter. One left ventricular assist device (LVAD) calf model was studied where the flow rate and waveform of the pump flow proved to identify the sucking phenomenon. Thus, the pump flow rate was calculated from the required power, motor speed, and heart rate. The value of the coefficient of determination (R2) between the measured and estimated pump flow rate was 0.796. To estimate this abnormal phenomenon, 2 methods were evaluated. One method was the total pressure head in which the pump flow rate and motor speed were estimated. During normal conditions the total pressure head is 79.5 +/- 7.0 mm Hg whereas in the abnormal condition, it is 180.0 +/- 2.8 mm Hg. There was a statistical difference (p < 0.01). Another method is using a current waveform. There is an association between the current and pump flow waves. The current was differentiated and squared to calculate the power of the differentiated current. The normal range of this value was 0.025 +/- 0.029; the abnormal condition was 11.25 +/- 15.13. There was a statistical difference (p < 0.01). The predicted flow estimation method and a sucking detection method were available from intrinsic parameters of the pump and need no sensors. These 2 methods are simple, yet effective and reliable control methods for a rotary blood pump.