T. Chinzei

In vitro and in vivo evaluation of a jellyfish valve for practical use.

A practical model (Model-1) of a jellyfish valve was developed, which was composed of a valve seat and a flexible membrane. The valve seat has 12 spokes to hold the membrane, and is made of solution-cast polyurethane coated with segmented polyurethane or Cardiothane. The flexible membrane is 200 microns thick, and made of segmented polyurethane or Cardiothane by a casting method. The valves were built into a sac type blood pump. In mock circulation tests, this jellyfish valve revealed performance superior to Bjork-Shiley (B-S) valves. No stagnation point was observed in the flow visualization study, and durability testing is ongoing beyond 7.5 months. The valves were used in animal artificial heart experiments for up to 112 days with good performance. No thrombi were formed on the valve membrane or around the spokes. Although a ring thrombus was observed behind the valve, it would be prevented by perfect adhesion of the valve seat to the blood pump. The plasma free hemoglobin level was less than 2 mg/dl during these experiments. These results suggest that a jellyfish valve (Model-1) is useful in ventricular assist devices, and in short-term bridge use of a total artificial heart.

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.

Converting algorithms for detecting physiological function changes from time sequential thermal images of skin surface

The temperature of the skin surface closely relates to physiological functions which control the body temperature constant. When we intend to analyze such physiological functions from thermal images of the skin surface which are obtained by a far infrared thermograph, we should prepare an algorithm to convert from thermal to other physiological information. The temperature of the skin surface is influenced many environmental, physiological and structural parameters. When we wish to detect a pathophysiological function, especially, changes of the parameter, we should develop some methods to eliminate the other parameters. The computed thermography system (CTS) developed in 1986 offers fundamental sequential image processing tools. Using this tool, we developed some algorithms to detect transient changes of some physiological functions when we applied thermal, physical hormonal and neural stress. We obtained images, i.e. therma-tomes, which are caused by changes of such physiological functions as skin blood flow rate, blood volume in subcutaneous vascular bed, sweat volume and activities of sympathetic nerve systems.

Implementation of the Natural Heartbeat Synchronize Control for the Undulation Pump Ventricular Assist Device Using the Inflow Pressure

The undulation pump ventricular assist device (UPVAD) is a small implantable ventricular assist device using an undulation pump. The UPVAD can produce not only continuous flow but also pulsatile flow by changing the motor rotational speed of the UPVAD. Because the undulation pump is a volume displacement type pump in which the inflow action and outflow action both start at the same phase, the inflow sucking occurs easily. The purpose of this study is to develop a suitable control method for the UPVAD. The UPVAD inflow cannula equipped with an implantable blood pressure sensor is inserted into the ventricular. Therefore, pressure fluctuation that synchronizes with the natural heartbeat is observed in the inflow cannula. By changing the motor rotational speed that responds to the inflow pressure, the UPVAD can synchronize with the natural heartbeat and the UPVAD can generate either aco-pulse assist flow or a counter pulse assist flow. The newly developed control method exhibited superior characteristics than existing ones due to high immunity against pressure sensor drift. The improved control method is implemented into the microcontroller. The UPVAD generated 5.3 l/min co-pulse assist flow without inflow cannula sucking using this control method. The assist flow can be increased more than 15% with this control method. This control was implemented one-chip microcontroller without extra peripheral device. It can reduce the UPVAD controller size. The UPVAD can generate the suitable assist flow with the developed control method.

Development of a database for medical infrared imaging

The object of the report is to describe concepts and methodologies for developing a database of medical infrared thermography. Infrared thermography is a typical noninvasive imaging modality to express thermal homeostatic functions of a body which include skin blood flow distribution and autonomic nerve functions. However, physiological functions such as skin surface temperature are easily and rapidly modified many in- and extrinsic factors. If there are no standards or guidelines to handling the thermographs, a clinician sometimes misreads pathophysiological meanings of his patient from infrared images. This is a system to supply standard techniques of handling infrared imaging modalities and to draw up guidelines for diagnosing some pathophysiological status using thermographic images through the Internet system.

Use of a Total Right Heart Bypass Model for Analyses of Abnormal Hemodynamics in Total Artificial Heart Animals, and the Function and Regulatory Mechanisms of a Natural Heart

By fixing the function of one ventricle, a total right heart bypass model can clarify the function and regulatory mechanism of the natural heart, and the etiology of abnormal hemodynamics in TAH animals such as increased CVP blood pressure and hepatic congestion. The pulmonary artery of a right heart bypass in a goat was clamped proximally; the pulmonary circulation was thus supplied entirely by the artificial heart and the systemic circulation by the natural heart. This model enabled studies of long-term effects of an artificial right heart on systemic circulation at a right heart output of 80-100 ml/kg/min; the response of the natural left heart to changes in output of the right heart; and the response of the natural left heart and artificial right heart to treadmill exercise. It was found that only slight increase in CVP or no increase in blood pressure was observed during the experiment (112 days); a rapid increase in output of the RAH resulted in an increase in left atrial pressure, stroke volume and output of the left ventricle, and a decrease in its heart rate at rest; and significant increase in both artificial right heart and natural left heart output and heart rates were observed during treadmill exercise, despite the marked decrease in left atrial pressure. The above results suggest that the increase in CVP and blood pressure in total artificial heart animals are not due to factors involving the artificial right heart, and that although left ventricular function acts in accordance with Starlings law at rest, this is no longer true during treadmill exercise.

Analysis of chronically recorded autonomic nerve signals for the control of artificial heart systems

In order to realize an artificial heart system capable of being controlled by autonomic nervous signals, we have studied the methods of long-term stable recording of autonomic nervous signals as well as methods to control an artificial heart by these signals. In this study, we have focused on algorithms to generate the control commands to an artificial heart system from recorded neural signals. We have chronically recorded signals from a goats cardiac sympathetic nerve and vagal nerve and circulation parameters such as aortic pressure, and results of the analysis of these signals showed the feasibility of the neural control of artificial heart systems.

Changes with Respect to Time in the In Vivo Adsorption of Plasma Proteins onto Artificial Heart Blood Pumps

The distribution of adsorbed plasma proteins (albumin, IgG, and fibrinogen) on 10 artificial heart blood pumps coated with 2 segmented polyurethanes was evaluated quantitatively after long-term in vivo experiments with goats to determine how the adsorption of plasma proteins on the pumps was affected by the kinds of biomaterials used, and by the pumping duration. The adsorbed plasma proteins on the materials were determined quantitatively using the iodine-125 conjugated antibody method. Microscopically, the adsorbed plasma proteins were marked by the gold colloid conjugated antibody method, and analyzed using a field emission scanning electron microscope. The macroscopic results showed that: 1) the adsorbed plasma proteins on KP-13 were more evenly and finely distributed than those on Cardiothane; 2) with KP-13, the adsorption of IgG and albumin at the center of the pumps was significantly less than in the peripheral areas, and the adsorbed IgG and albumin decreased significantly as the pumping duration increased; 3) in contrast, the adsorbed fibrinogen increased significantly with time; and 4) with Cardiothane, the tendencies for adsorbed IgG and albumin to decrease, and for adsorbed fibrinogen to increase, were less significant than with KP-13. Microscopically, the gold colloids marking plasma proteins were found to not cover the whole of the surface, but were found scattered randomly or in clusters, with no relationship observed between the distributions of the three plasma proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Simulation of dynamic behavior of heart rate for TAH control

It is desirable that the dynamic behavior of the drive rate of the total artificial heart (TAH) can be as similar as possible to that of the recipients heart rate (HR) before implantation. This requires a model which can simulate the behavior of HR on the basis of only information measured with the limited number of approvable sensors. The present study aims at deriving the model for simulating the dynamic behavior of HR from a few measurements in order to apply the model to TAH control.