Continuous flow blood pumps, such as axial flow and centrifugal pumps, have been gaining interest as circulatory devices for total artificial hearts (TAHs) because of their smaller size and simpler structure compared to pulsatile pumps. However, continuous flow pumps are more prone to atrial wall suction than pulsatile pumps are. Sudden increases in flow rate to meet changes in physiological demand, especially in the left pump, often cause atrial wall suction. In this study, a control algorithm to prevent atrial wall suction from occurring in the left atrium by controlling the rotational speed of the right pump, instead of reducing the cardiac output of the left pump, was developed and investigated. The method was tested in a mock circulatory system and in acute animal experiments with adult goats. Two centrifugal pumps were used to totally replace the circulatory function of the natural heart. The cardiac output of each pump was determined independently by a control algorithm running on a computer connected through a serial interface to the pump driving units. Results showed that left atrial wall suction could be prevented using this method, and that the method could be performed simultaneously with physiological control of the artificial heart.

Continuous flow blood pumps, such as axial flow and centrifugal pumps, have been gaining interest as circulatory devices for total artificial hearts (TAHs) and a biventricular assist device (BVAD) because of their smaller size and simpler structure compared to pulsatile pumps. However, continuous flow pumps are more prone to suction of the left ventricle than pulsatile pumps are. Sudden increases in flow rate to meet changes in physiological demand, especially in the left pump, often cause ventricle suction. In this study, a control algorithm to prevent suction from occurring in the left ventricle by controlling the rotational speed of the right pump, instead of reducing the cardiac output of the left pump, was developed and investigated. The method was tested in acute animal experiments with calves. The results indicate that this proposed method is capable of preventing suction and could simultaneously maintain circulatory control. A key advantage of this control system is that flow rates can be maximized while avoiding ventricle suction conditions particularly when the circulatory system is unstable such as in a the first few days after operation.

The authors have been developing a newly-designed totally-implantable artificial myocardium using a covalent shape-memory alloy fibre (Biometal®, Toki Corporation), which is attached onto the ventricular wall and is also capable of supporting the natural ventricular contraction. This mechanical system consists of a contraction assistive device, which is made of Ti-Ni alloy. And the phenomenon of the martensitic transformation of the alloy was employed to achieve the physiologic motion of the device. The diameter of the alloy wire could be selected from 45 to 250μm. In this study, the basic characteristics of the fiber of 150μm was examined to design the sophisticated mechano-electric myocardium. The stress generated by the fiber was 400gf under the pulsatile driving condition (0.4W, 1Hz). Therefore it was indicated that the effective assistance might be achieved by using the Biometal shape-memory alloy fiber.

In totally implantable ventricular assist device systems, measuring flow rate of the pump is necessary to ensure proper operation of the pump in response to the recipient's condition or pump malfunction. To avoid problems associated with the use of flow probes, several methods for estimating flow rate of a rotary blood pump used as a ventricular assist device have been studied. In the present study, we have performed a chronic animal experiment with two NEDO PI gyro pumps as the biventricular assist device for 63 days to evaluate our estimation method by comparing the estimated flow rate with the measured one every 2 days. Up to 15 days after identification of the parameters, our estimations were accurate. Errors increased during postoperation days 20 to 30. Meanwhile, their correlation coefficient r was higher than 0.9 in all the acquired data, and estimated flow rate could simulate the profile of the measured one.

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