Kaoru Imanishi

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.

Can total artificial heart animals control their TAH by themselves? One year survival of a TAH goat using a new automatic control method (1/R control).

A total artificial heart (TAH) goat survived for 360 days on the new automatic control method (1/R control), in which the cardiac output of the TAH can be controlled through the cardiovascular center by making it function by reflecting the beta-adrenergic reaction in peripheral vascular resistance. This is thought to be the only long-term, real-time, measurable parameter by which information on the activity of the cardiovascular center can be received directly by the TAH system. In this goat, the hemodynamic parameters (RAP, AoP, and so forth) were kept within physiologic limits when control was stable, and the cardiac output was automatically increased in response to exercise, not unlike that in the natural heart. There were no abnormal blood chemical or hormone data except at end stage. Based on these results 1/R can be considered a physiologic control method for a TAH.

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.

Calcification and Thrombus Formation on Polymer Surfaces of an Artificial Heart

Calcification and thrombus formation are still important problems in artificial heart research. The calcification and thrombus formation generated in artificial heart blood pumps, driven without anticoagulant for 312 days as the left side and 414 days as the right side, were analyzed in this study. A thrombus was observed at the circumference of the sac in the 312-day pump, but it was not associated with calcification. Several phenomena were observed on the polymer membrane valves (jellyfish valves) incorporated into the blood pump: plastic deformation of the valve membrane by creep fatigue; no calcification of stationary parts such as spokes and the center of the membrane; calcification of the particular portion which received repeated stretching stress; and no association of calcification with thrombus. The calcification of the valve area which received repeated stretching force might be explained as follows. Repeated stretching forces extend the polymer membrane, causing some loosening between polymer molecules and generating microgaps. Blood proteins and phospholipids invade these microgaps, which then attract Ca2+ ions followed by phosphate ions(PO4 2-) leading to the formation of calcium phosphate complexes.

Development of a New Circulatory Assist Method with the Combined Effects of Intra-Aortic Balloon Pumping and Counter Pulsation-First Report

Current circulatory assist methods, such as intra-aortic balloon pumping (IABP), are not always adequate to save acute circulatory failure patients. Therefore, a stronger, percutaneously accessible method is required. We found that the combination of IABP and CP generated a profound circulatory assist effect, and we have consequently developed a new assist system in this study. A sac type blood pump with a volume of 20 ml and a single port without a valve, was developed for CP. In the mock circulatory test, a 20 ml stroke volume was obtained using a cannula with a 5 mm diameter under the following driving conditions: air pressure = 200/-100 mmHg; S/D = 50%; pulse rate = 100 bpm. In vivo experiments were performed using four mongrel dogs with body weights of 12-20 kg. A cannula for CP was inserted via the brachial artery or subclavian artery into the aortic root. The pump flow (PF), coronary artery flow (CF), renal arterial flow (RF), and aortic pressure (AP) were measured, and the combined effects of IABP and CP were compared with their individual effects. In the most effective case, a marked increase in diastolic AP (60%), cardiac output (40%), and CF (100%) was obtained by the combination of IABP and CP, which produced a remarkable effect compared with the single use of IABP and CP. There was no negative effect on RF by this assist method. As this new circulatory support system has many circulatory assist effects, and is percutaneously accessible, it will be available for clinical use.

Predictive control of total artificial heart during exercise

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 New Method for the Chronic Evaluation of the Microcirculation During Artificial Heart Pumping

We developed a new miniature probe which does not require the use of a microscope for observing the microcirculation; the probe can be implanted chronically into the body with minimal invasion. The principle of the probe is quite new. A thin layer of living tissue is placed directly on a highly integrated charge coupled device (CCD) and illuminated with a very weak light source, i.e., a light-emitting diode. The vascular nets in the tissue are projected on the CCD like a contact photograph, and this is sent to a television monitor; the motion and function of the microvasculature can then be analyzed. A 1/2 inch CCD with 250 K pixels was used in this study. The CCD was molded with epoxy resin for electrical insulation. The probe was implanted into a rabbit for 18 h. The configuration of arterioles and venules 20–30μm in diameter and their motion in subcutaneous tissue could be observed. This method should be of great help in artificial heart studies, especially for the evaluation of control methods and for the evaluation of differences between pulsatile and non-pulsatile pumping.

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.