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The authors developed an implantable left ventricular assist system (LVAS) for bridge to transplant of rather small sized adults. The pump was made of segmented polyether polyurethane and was 86 mm in diameter, 50 mm in height, with a 70 ml nominal stroke volume. A percutaneous drive line was connected with an external pneumatic control drive unit (CDU). In chronic animal experiments using 11 adult goats, the pump was installed between the LV apex and the descending aorta and was placed in the abdominal wall. Five goats were killed after 4 to 14 weeks while in good physical condition, and one is ongoing. There were no prominent thromboembolic symptoms despite no anti-thrombogenic agent being used. The new electrical impedance-based monitoring and control system (Z system) was installed in the CDU. In this Z system, automatic calibration was performed periodically for several seconds while the drive condition was changed to ensure full-fill of the blood pump. The full-fill to full-empty drive was well controlled by this Z system. In conclusion, the new Z system is practical and useful for monitoring and control of an implantable pump, giving this LVAS a promising place in clinical use.

We have developed centrifugal pumps for long-term circulatory assistance, with the final goal of a completely implantable ventricular assist device or total artificial heart. The previous model, NCVC-0, was characterized by a nonseal design and few flow-stagnating parts and acquired high durability and antithrombogenicity. To improve its pumping performance, NCVC-0 was modified. In the new model, NCVC-1, the profile shape of the impeller was changed from flat to conical, the number of vanes from 4 to 6, and the vane entrance angle from 30 degrees to 60 degrees. A flow visualization study performed by means of a combination of the polystyrene tracer method and the light-cutting method indicated decreased flow turbulence between vanes in NCVC-1, which corresponded well with the increased pumping performance. Flow visualization is a useful method to evaluate the design elements that are closely related to the pumping performance of a centrifugal blood pump.

An implantable left ventricular assist system was developed for long-term use. The system includes an implantable blood pump, a portable control drive unit (CDU), and a monitoring system. The blood pump was designed to be positioned in the left abdominal wall and was made of segmented polyether polyurethane. A percutaneous drive line connected it to the external CDU. The CDU included a continuous pump performance monitoring system that measured electrical impedance between the two metal connectors of a blood pump. In animal experiments using six adult goats, the pump was installed between the left ventricular apex and the descending aorta, and it was placed in the abdominal wall. No antithrombogenic agents were administered during the course of the experiment. This LVAS was easy to use and provided stable hemodynamic conditions for > 8 weeks. Pump output (Op), estimated by impedance, was linearly related to Op measured with an electromagnetic flowmeter. Pump performance was effectively estimated, and the fill-empty drive was well controlled by impedance. There were no significant abnormal hematologic or blood chemistry values, no signs of infection around the pump pocket (except in one animal), and no obvious thromboembolic symptoms. Maximum flow was 6.7 L/min with use of a prototype portable CDU (dimensions, 500 x 168 x 435 mm; weight, 16 kg). In conclusion, this LVAS is promising for long-term clinical use.

The authors designed a totally implantable circulatory assist device consisting of a bioartificial ventricle composed of a skeletal muscle ventricle lined with a bioartificial endocardium. The bioartificial endocardium consists of a structural matrix made of a polyurethane porous membrane, fragmented blood vessels, and collagen gel. The authors prepared the polyurethane porous membrane by solvent cocasting with salt powder. They used collagen gel with fragmented goat carotid vein to perform in vitro construction of the bioartificial endocardium. For in vivo construction of the bioartificial endocardium, the authors used a modified version of the tissue fragment method for vascular prostheses. The authors prepared suspensions of tissue fragments using collagen gel with fragmented goat carotid artery. They used a highly porous fabric vascular prosthesis as a structural matrix; tissue fragments were entrapped on the outer surface of the prosthesis, and the prosthesis then was implanted into the carotid artery of four adult goats. In specimens 1 and 3 months postimplantation, cells from the fragmented tissue regenerated an endothelium-like monolayer sheet on the inner surface of the prostheses. Output of a prototype bioartificial ventricle reached 660 ml/min at an afterload of 60 mmHg and a preload of 20 mmHg. Based on these data, the authors conclude that the bioartificial ventricle is promising as an implantable device with excellent antithrombogenicity.

A chronic animal experiment was designed to examine the changes in blood components induced by the use of a centrifugal pump (CP). In the pump, an impeller spins in a blood chamber by magnetic coupling with a rotating magnet outside the blood chamber. A pulsatile ventricular assist device was implanted between the left atrium and the descending aorta in four goats weighing from 63 to 75 kg; the CP was installed to replace the assist device, without surgery and anesthesia, more than 2 weeks later when the influences of implantation surgery were diminished. Antithrombotic therapy was performed with oral administration of an antiplatelet agent, cilostazol, a cyclic adenosine monophosphate phosphodiesterase at a dose of 30 mg/kg/day. No significant differences were observed in any of the following parameters: 1) hematocrit, 2) plasma free hemoglobin, 3) lactic acid dehydrogenase, 4) adenosine diphosphate, 5) platelet count, 6) fibrinogen, and 7) antithrombin III, between the data before and after the use of the CP, nor were deformation or pseudopods of platelets seen. The CP developed in the authors' institute and evaluated in this study did not damage blood components, and it proved to be a promising device for long-term use.

The authors suggested that a mammal immediately accommodates well to nonpulsatile flow in the systemic circulation. In the current study, nonpulsatile pulmonary blood flow using a centrifugal pump was established in chronic models to analyze its influence on the pulmonary circulation. A pulsatile right ventricular assist device (RVAD) was implanted to draw blood from both the right atrium and ventricle and send blood to the pulmonary artery in six goats. After 2 weeks, the pulsatile pump was quickly replaced with a centrifugal pump without anesthesia, and a 100% non-pulsatile pulmonary blood flow was obtained. Cardiac output was kept at 80-120 ml/kg/min during the experiments. No changes were observed in hemodynamic parameters, including pulmonary arterial pressure, pulmonary vascular resistance index, and blood gas data, after the immediate depulsation of the pulmonary blood flow. There was also no significant change in the ventral to dorsal tissue blood flow ratio of the lower lobe of the right lung, which was calculated by a colored microsphere method, between pulsatile and non-pulsatile pulmonary blood perfusion. These results suggest that pulmonary function, including blood flow distribution, is not affected by non-pulsatile pulmonary circulation for periods up to 14 days.

This study was designed to investigate the permeation of silicone oil through a pump diaphragm made of Pellethane in the authors' electrohydraulic ventricular assist system (EHVAS) and to evaluate influences on organ function. The permeability of the diaphragm to silicone oil was investigated by in vitro experiments. Influences on organ function were evaluated in five goats with an EHVAS by monitoring serum silicon levels (SSi), blood chemical parameters, and histologic findings. Elevation of silicone oil levels in Pellethane sheets immersed in silicone oil demonstrated that the Pellethane diaphragm was, in fact, permeable to silicone oil. The permeation rate of silicone oil was calculated to be 1.75 ml/year in the authors' EHVAS from the data of a diffusion apparatus test. Serum silicon levels did not increase during the EHVAS pumping, and renal and hepatic function were not affected. No abnormality or deposit suggestive of silicone oil was observed. However, the problem of permeation of silicone oil through the pump diaphragm must be solved to allow for a circulatory assist device for long-term use.

An integrated artificial heart-lung device (IAHLD) is being developed as a novel system for simultaneous long-term support of heart and lung. The IAHLD consists of an artificial lung component (LC) and two blood pumps. The LC is made with a special composite hollow fiber membrane that prevents serum leakage. The fibers are arranged as piled-up lattices and potted in a cylindrical housing made of polyurethane. The blood pump with a single port is of a pneumatic pusher-plate type, and a Björk-Shiley valve is mounted in the port. The LC is sandwiched between the inlet and outlet pumps, and all components are integrated. This special structure provides high gas exchange efficiency, prevention of flow channeling and stagnation, and reduction of blood contacting surfaces. The prototype IAHLD had exchange rates of up to 170 ml/min of O2 and CO2 and up to 5.5 L/min of pump output. A flow visualization analysis with cineroentgenography revealed that the flow distribution within the IAHLD was uniform, without any stasis. It was concluded that the IAHLD is a promising system for long-term heart and lung support, and can be used without systemic heparinization given thromboresistant surface treatment as the next step of development.

Peripheral circulation (PC) during nonpulsatile (NP) perfusion is not satisfactorily understood, although it is known that animals can survive with chronic NP flow. In awake goats, PC was analyzed by hemodynamic and hormonal parameters, tissue blood flow of the ear measured by a noninvasive laser Doppler flowmeter, and distribution of the body surface temperature monitored by thermography. An NP systemic circulation was established in five 40-64 kg goats with a centrifugal pump (MD-10, Iwaki Pump, Japan) that replaced a pulsatile ventricular assist device 2 weeks postoperatively; this was done without anesthesia. Nonpulsatile total left heart bypass was obtained, with flow rates of 78-165 ml/kg/min. Systemic vascular resistance and blood adrenalin and noradrenalin levels were not affected by the depulsation. Tissue blood flow during NP perfusion was well maintained and showed comparable values to those during pulsatile systemic circulation. Vasomotion of 10-20 cycles/min was obvious in the tissue blood flow pattern, indicating adequate PC at each sampling point. Thermography before and after depulsation indicated no change of temperature distribution, and displayed warm peripheral areas. In conclusion, PC of animals on chronic NP systemic perfusion is adequately maintained.

In a previous article, a left ventricular assist system (LVAS) with a percutaneous transseptal cannulation technique for easy application was described. This system was safe and efficient (maximum output greater than 3 L/min) and fitted between the intraaortic balloon pumping and LVAS with thoracotomy. But technical skill for placement was slightly complicated. The cannulation system has been improved. In the new system, the inlet cannula is initially used as a sheath introducer and is quickly inserted into the left atrium after transseptal puncture. The new inlet cannula is made of polyvinyl chloride (TM100, Toyobo, Co., Ltd., Osaka, Japan), which has excellent antithrombogenicity and low friction using a polyester plasticizer. The distal part is designed to be flexible with a spiral wire for easy manipulation. A sealing hub was installed to prevent bleeding at the proximal The simplicity and safety of the new system were examined in chronic animal experiments. The inlet cannula was placed into the left atrium within a few seconds after transseptal puncture. During 20 days of activation, there were no episodes of systemic or pulmonary embolism, although no anticoagulant was used. Under fluoroscopy, there was no thrombus formation around the cannula at removal. On the 14th day after removal, the puncture site of the septum had healed. This system is ready for clinical use and shows promise of satisfactory safety and manageability.