S Mochizuki

Over 500 Days’ Survival of a Goat with a Total Artificial Heart with 1/R Control

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.

Pathological Study of a Goat That Survived for 532 Days with a Total Artificial Heart Using the 1/R Control Method

A goat survived for 532 days with a pneumatically driven total artificial heart (TAH) that was controlled by the 1/R (reciprocal of peripheral resistance) method. Pathological observations were compared with those of long-surviving goats which had been fitted with TAHs that were operated with fixed driving parameters. The most striking pathological differences were observed in the liver. In the goat under study, congestion of the liver was not as severe as in the past cases in which the central venous pressure (CVP) was high, although fibrosis was prominent around the hepatic veins in many areas of the liver. In both kidneys, severe infarctions were prominent (as in the past cases), but a characteristic of this case was the existence of marked hemosiderosis at proximal tubules; however, this was not prominent in the spleen and liver. This suggested that the hemosiderosis was due to hemolysis in the blood pump rather than due to an increased destruction of erythrocytes in the spleen and liver. The pathological improvements in the liver are believed to have been due to a comparatively low CVP (approximately 5–10 mmHg) which was achieved by the use of the 1/R control method, even though the existence of pathological abnormalities in the kidneys and liver suggested that such long-term driving of the TAH may still cause hemolysis and some damage to the liver. This point requires further investigation.

The prospect of a small-sized vibrating flow pump for an artificial heart

A small-sized blood pump is required for a high-performance total artificial heart. From the viewpoint of the implantation, anatomical fitting into the cavity from which the heart has been removed is very important for the design of the total artificial heart. A small, high-performance blood pump is desired for a totally implantable artificial heart system. A miniaturized blood pump is not easy to achieve because of its driving mechanism and material endurance. The stroke volume is necessarily decreased by the downsizing of a volume-displacing pump, such as a sac-type blood pump. Similarly, the centrifugal force is decreased by the downsizing of a centrifugal pump. The vibrating flow pump (VFP) is one of the inertia-type pumps, but it can make a volume flow wave by its vibrating motion. The short stroke volume and high rate of driving may be notable characteristics for the minimization of the pump. In this study, a prototype VFP was made for a basic performance test. It showed adequate performance for left ventricular assistance and also showed potential for more downsizing. The estimation of the design and the driving stroke of the vibrating tube may be the next step for an advanced VFP system.