The goal of this study is to develop an effective control system for cardiac output regulation based upon the preload and afterload conditions without any transducers and compliance chambers in the moving actuator type total artificial heart.
Motor
current waveforms during the actuator movement are used as an input to the automatic control algorithm. While the current waveform analysis is performed, the stroke length and velocity of the actuator are gradually increased up to the maximum
pump
output level. If the diastolic filling rate of either right or left pump begins to exceed the venous return, atrial collapse will occur. Since the diastolic suction acts as a load to the motor, this critical condition can be detected by analyzing
the
motor current waveforms. Every time this detection criterion is met, the control algorithm decreases the stroke velocity and length of the actuator step by step just below the critical detection level. Then, they start to increase. In this way
the
maximum pump output under given venous return can be achieved. Additionally the control algorithm provides some degree of after load sensitivity. If the aortic pressure is detected to exceed 120 mmHg, the stroke length and velocity decrease in
the
same
way as the response to the preload. Left-right pump output balance is maintained by proper adjustment of the asymmetry of the stroke angle.
In the mock circulatory test, this control system worked well and there was a corsiderable range of stroke volume difference with adjustment of the asymmetry value. Two ovine experiments were performed. It was confirmed that the required cardiac
output
regulation according to the venous return coul d be achieved with adequate detection of diastolic suction, at least in the in vivo short-term survival cases (2-3 days). We conclude that this control algorithm is a promising method to regulate
cardiac
output in the moving actuator type total artificial heart.
(Korean J Thorac Cardiovasc Surg 1995;28:542-8)
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