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The 1/R control was developed to provide control over the output of a total artificial heart (TAH) by the central nervous system by using the peripheral vascular conductance (1/R) the vasodilatation in for the control signal. The physiologic stability of the 1/R control algorithm was tested by using goats with TAH. To apply the 1/R control equation to TAH in goats, real-time and continuous measurements of cardiac output, aortic pressure, and right atrial pressure were performed throughout the survival period. Left atrial pressure was also measured, to prevent lung edema. Under the 1/R control, 532 days’ survival was obtained in a goat with a TAH. Findings over the course of the experiment showed no hemodynamic or metabolic abnormality. Autopsy findings showed macroscopically no congestion in the liver. The experiment demonstrated the physiologic stability of the 1/R control algorithm for an extended period. Improvement of methods for measurement, such as the development of feasible techniques for the noninvasive measurement of the required hemodynamic parameters, will make it possible to use 1/R control in practice, especially for a totally implantable TAH system.

The spectral profile of fluctuations of hemodynamic parameters was investigated in the natural heart, the total artificial heart (TAH) with fixed drive condition, and in the TAH with automatic (1/R) control. The inverse frequency (1/f) fluctuations were found in the heart rate (HR) and peripheral conductance (1/TPR) in the natural heart, and in the pulse rate (PR) and 1/TPR in the TAH with 1/R control. The PR of the TAH with 1/R control is considered to have some compatibility with the HR of the natural heart, although the control loop is completely different.

A new prototype model of a flow-transformed pulsatile total artificial heart (FTPTAH), which consists of one undulation pump (UP; formerly known as a precessional displacement pump; PDP), four jellyfish valves, and a flexible membrane has been developed. Flow transformation between pulmonary and systemic circulation is brought about by the switching direction of motor rotation, so that no electrical flow switching valve is needed. The undulation pump is a continuous flow pump, and it can also be driven as a reversible pump. A prototype model perfused 3.01/min alternately in the pulmonary and systemic circulations with pulsatile flow in a mock circulatory system. A compensatory chamber has been designed, with the objective of preventing deoxygenated blood from being sent to the systemic circulation. The chamber is formed by a flexible membrane located between immediately in front of the mitral valve and immediately behind the tricuspid valve. Its volume is nearly equal to the priming volume of the undulation pump. Deoxygenated blood present in the undulation pump at the end of pulmonary circulation is stored in the compensatory chamber by shifting the flexible membrane to the direction of the left atrium, thus preventing the deoxygenated blood from being sent to the systemic circulation.

Antithrombogenic regimens for pneumatic ventricular assist devices (VADs) were evaluated in 77 VADs used clinically in a total of 70 patients. Macroscopic thrombus formation in the devices was assessed in relation to potential risk factors, including hematological and hemodynamic derangements, during use of the VAD. Effects of varions antithrombogenic regimens were assessed on the basis of this risk analysis. A thrombus score was used to quatititate the grade of thrombosis. As a linear increase in the thrombus score was noted in accordance with increase in support duration, a time-adjusted thrombus score was calculated to compare scores in anticoagulant groups with different pumping duration. The scores appeared to be high in patients in those groups which received gabexate mesilate (GM, a protease inhibitor). Heparin was not demonstrated to be effective in this study. Univariate risk analysis showed that the use of GM, low-flow pumping, prolonged pumping, and semi-normal platelet count were significantly correlated with the incidence and grade of thrombosis. A multivariate regression analysis also indicated that the use of GM, low-flow, and prolonged pumping were detrimental to anti-thrombogenicity. As the use of GM was demonstrated to be predominantly detrimental, its withdrawal from use should lead to a substantial reduction in the incidence and grade of thrombosis.

The artificial heart (AH) is already being used clinically as a bridge to heart transplantation or a circulatory assist for post-cardiotomy. However, there are, as yet, no established control methods for the AH, except for some that are very primitive. Consequently, such problems as elevation of the central venous pressure (CVP) and poor response of cardiac output to exercise still remain to be overcome.

The development of a polymer membrane valve for artificial heart blood pumps is very much required, since the mechanical valves, such as the Bjork-Shiley (BS) and Hall valves, used in the present artificial heart (AH) blood pumps have the following problems: 1. A ring thrombus is often formed at the interface between the valve ring and pump housing, because these cannot be fixed seamlessly. 2. Valve failure sometimes occurs at the disc and stent due to a water-hammer effect. 3. Regurgitant and leakage flow generated in the mechanical valve induces hemolysis and the AH patient becomes mildly anemic. 4. The valves are too expensive to popularize the AH as a therapeutic method.

The compliance chamber which is required for a totally implantable artificial heart, to compensate the volume change generated in a blood pump, makes it harder to implant the whole system inside a human body, for several reasons. To eliminate the compliance chamber from the totally implantable artificial heart, a new blood pump, in which no compliance chamber was required, has been designed by our group and was reported elsewhere. In this study, an actuator to drive this blood pump was developed. The mechanism of the actuator converts the rotation of the d.c. motor to linear motion of the pump diaphragm by permanent magnets without any connection. A prototype system was made and tested in a mock circulatory system. The results clarified the controversial points of the present system. However, the future feasibility of this mechanism was also exhibited.

To establish a total artificial heart (TAH) control method during exercise, we developed a predictive control method in which cardiac output (CO) is controlled predictively based on the objective function curve obtained from natural heart (NH) goats subjected to various grades of exercise. During treadmill exercise, CO of the TAH was controlled to follow the objective function curve by changing the driving parameters, such as positive and negative pressures, S/D ratio, and pulse rate of both artificial heart (AH) pumps under the control algorithm installed in a computer.

A transcutaneous energy transmission system (TETS) was composed of a couple of coils, which formed a transformer across the skin, a driving circuit, and a rectifying circuit. By using coreless coils and a high driving frequency (100–160 kHz), more than 25 W of electric power could be transmitted with 78.5% of maximum efficiency (dc to dc). In animal experiments, the primary coil temperature during operation was under 39°C on thermograms. After 10 months of implantation of a secondary coil coated with epoxy resin, it was wrapped by a thin capsule of connecting tissue. No obvious tissue reaction was recognized.

It is desirable to use the adult goat as an experimental animal for the TAH with an implantable pneumatic driven blood pump since the calf has the problem of growth during the study period. Adult animals are also much more similar to adult human patients in physiological terms than immature animals such as the calf. However, it has not yet been possible to design a blood pump that fits well into the narrow space of the goat chest cavity. To solve this problem, a new design of the blood pump fitted to the goat chest cavity was investigated in this study. A bullet-shaped blood pump, which has two sack-type ventricles, was designed and fabricated together with a low-profile atrial cuff. The pump fitted well into goats weighing 47–67 kg and easily produced normal pump output. The results show the promise of future success in obtaining long survival with goats using this blood pump.

A fully automatic pneumatically driven total artificial heart (TAH) system was developed with the following objectives: (a) Analysis of the circulatory mechanism under normal and abnormal conditions; (b) clarification of the required performance of the TAH pump under various conditions such as rest and exercise; (c) establishing the data acquisition of biochemical factors, neurological factors, exercise, and their feedback to the TAH system.