Automatic Regulation of Output of an Electrohydraulic Left Ventricular Assist Device Using the Polymer Bellows Water Pressure and Motor Current

Summary

An electrohydraulically driven left ventricular assist device (LVAD) has been developed in our laboratory. Over years of in vitro and in vivo testing, a “suction” problem has been pointed out as one of the major problems related to the device mechanism. The suction problem involves collapse of the left atrium, which can be caused by excessive negative pressure generated by the active blood-filling mechanism, and can lead to damage to the atrium or an air-embolism. We have developed methods for properly controlling the assistance output, depending upon the inlet pressure conditions. Algorithms have been developed for setting an absolute limit to negative pressure and for the regulation of the diastolic velocity of the device. The regulating system is based on the estimation of left atrial pressure (LAP), using the internal pressure of the polymer bellows and the motor current as raw information indicating the status of the left atrium. The estimation is based upon direct analysis of the signal wave form, coupled with the use of fuzzy logic in determining significant parameters such as the systolic peak, diastolic peak, and diastolic integral. Results of experiments using a mock-circulation system have shown that the new control system performs satisfactorily in detecting suction. An animal experiment was conducted to verify the feasibility of the methods. In a 17-day experiment using an adult sheep with a left ventricular assist device, there was no sign of damage or suction-related problems when we used the new method for controlling the diastolic velocity depending upon the bellows water pressure. In this paper, the methods are described and the results are documented.