Takumi Yonezawa

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.

Fabrication of a jellyfish valve for use in an artificial heart

For a valve to be fabricated seamlessly into an artificial heart (AH) blood pump, a jellyfish valve has been developed, in which a thin membrane is fixed at the center of a valve seat having several spokes to protect against prolapse of the membrane. The valve is superior in performances to a Björk-Shiley valve, and reveals good blood compatibility. The valve would be very useful not only for AH animal study, but for future clinical use in infants to adults. Several institutions are already trying the valve. In this paper, the fabrication of the jellyfish valve is introduced, and in vitro and in vivo results summarized. A computer aided design (CAD) system was developed to cut a male wax mold of the valve seat. The input parameters to the CAD are diameter, height, thickness of rim, number of spokes, width and thickness of spokes, etc. Jellyfish valves with diameters of 4 to 27 mm have already been fabricated for many types of AHs and assist pumps.

The second and third model of the flow transformed pulsatile total artificial heart.

For the purpose of future total implantation, a new pulsatile total artificial heart, a flow transformed pulsatile total artificial heart (FTPTAH), in which the continuous flow from a single centrifugal pump (CFP) was converted to pulsatile flow by switching two three-way valves that could alternately perfuse the systemic and pulmonary circulation, was proposed, and the data from the prototype model were reported. As the next step, the second model, in which a CFP and a spool valve (SV) driven with a solenoid were fabricated in one piece, was made and tested in a mock circulatory system. The system could send 4.7 L/min of pulsatile output alternately to the pulmonary artery and aorta, with 30 and 100 mmHg afterload, respectively, at 3000 rpm CFP. However, three problems were encountered: the output was not enough, mixture or inversion of venous and arterial blood in the CFP would occur, and heat generation at the solenoid was very severe. To solve these problems, a third model was designed in the current study. To increase pump output, hydrodynamic analysis was performed. The SV was divided into inlet and outlet to control the blood mixture or inversion. To suppress heat generation, each SV was driven back and forth by two solenoids, one on each side of the SV. The model revealed satisfactory results in a mock circulatory system.

The Jellyfish Valve: A Polymer Membrane Valve for the Artificial Heart

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.

Development of multiparameter automatic control system of total artificial heart for analysis of circulation mechanism

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.

Reciprocal of the Peripheral Vascular Resistance (1/R) Control Method for the Total Artificial Heart

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.

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.

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)

Development of a Pulsatile Total Artificial Heart Using a Single Continuous Flow Pump: Development of the Third Model

To reduce the pump size of the total artificial heart for future implantation, a new mechanized pulsatile total artificial heart, the flow-transformed pulsatile total artificial heart (FTPTAH), was developed. This device consists of a single continuous flow pump and two three-way valves; it can perfuse the pulmonary and systemic circulation alternately by pulsatile flow. The prototype and secondary model revealed that the system worked well in terms of the mechanism [1,2]. However, low performance, heat generation at the solenoid to drive the spool valve, and blood mixture or inversion of arterial and venous blood were noted in the secondary model. In this study, the third model was developed to overcome these problems.

Development of an artificial heart actuator for a compliance chamberless blood pump

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.