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Biomedical subjects

K Imachi

Publications and source records attributed to K Imachi.

At least 19 recordsLinked to original sources
PubMed1991

[Artificial hearts--toward future technologies].

What are the most essential technologies for developing the implantable artificial heart in future? The first is the development of autonomic and dispersed micro actuators for acting as sarcomeres of the heart muscle. An electric motor driven artificial heart transmitted the power with belts had been developed as a preliminary mechanism. A micro actuation using noise energy has been developed for simulating the structure and the function of striate-muscle sarcomeres. The chemical energy conversion mechanism must be applied instead of the conventional electro-mechanical mechanisms, when we implant the total artificial heart permanently. As a implantable assisted artificial heart using tentatively, we have developed an axial flow pump system. The pump system acts as a systemic and a pulmonary pump produced pulsatile flow switching an axial pump output. The second is the search of biocompatible materials, which do not only mean blood compatibility but also tissue compatibility. The great masses in chest cavity have inevitably occurred infection. The autonomic and dispersed control system is the third item. We have developed a jellyfish valve with low fluid dynamical resistances for improving the pump dynamic characteristics.

Heart, Artificial↗
PubMed1990

The system and procedures of percutaneous intradiscal laser nucleotomy.

Since 1986, percutaneous intradiscal laser nucleotomy (PILN) has been studied in the authors' laser laboratory. The purpose of this report is to develop PILN as an alternative to chemonucleolysis and percutaneous discectomy, which are currently applied, and to establish a safe, easy, accurate and short-time therapy method for lumbar disc herniation. After laser irradiation, intradiscal pressures (IDP) decreased and the nucleus pulposus was gradually replaced with cartilaginous fibrous tissue. The evaluation of heat distribution with thermocouples and thermography was done to determine safe optimum irradiating conditions and to develop a new double-lumen needle and a bare quartz fiber. Neodymium-yttrium-aluminum-garnet (Nd-YAG) laser devices have been improved for easy and safe use, and a new tip type pressure transducer has been made for improved therapeutic results using this new method.

Animals↗
PubMed1989

[Automatic control of total artificial heart to simulate the hemodynamics under natural heart circulation].

We developed control system of total artificial heart (TAH) during exercise simulating the circulatory response of natural heart. The following procedures were taken to develop this system. 1) Measurement of hemodynamics and physical activity rate (PAR) of natural heart goats during treadmill exercise. 2) Estimation of cardiac output from PAR using a non-linear model. 3) Development of a pneumatic artificial heart (AH) driver with high speed controllability and a control unit to deliver CO calculated from PAR beat by beat. 4) Evaluation of the physiological condition of the TAH goat during exercise controlled by this system. Using this control method, CO of TAH goats was similar to that of natural heart goats during treadmill exercise. Hypertension was observed during exercise. This hypertension was considered to be derived from two causes. One was high inflow and outflow resistance of cannulae between AH pump and living body. The other was the disorder of peripheral circulatory control mechanism in TAH animal. Such as increased sympathetic activity, insufficient secretion of atrial natriuretic polypeptide (ANP) and decreased sensitivity of peripheral circulatory system with ANP.

Animals↗
PubMed1987

Research and development on total artificial heart in University of Tokyo.

The research and development on the total artificial heart (TAH) in the University of Tokyo can be divided chronologically into the three stages, i.e., the first stage (1959-1970); trial and error stage to find appropriate hardwares, the second stage (1970-1985); software stage to find how to control pneumatic TAH and to manage the animals, and the third stage (1985- ); final goal to develop implantable TAH for animal and human. This paper reviews the process of research and development in each stage.

Animals↗
PubMed1986

Quantitative surface analysis of Cardiothane 51 by FT-IR-ATR spectroscopy.

Surface analysis has been carried out for Cardiothane 51 samples as commercially available balloon pumps and cast films prepared from the solution. Silicone contents on surfaces have been quantitatively determined by FT-IR-ATR spectroscopy coupled with a subtraction technique. The contents on the air-facing surface vary from 0.7 to 5.3% among six balloon pumps examined; three of them contain less silicone on the air-facing surface than on the substrate-facing surface, whereas just the opposite is true for one, and the other two have nearly and quite an equal content of it between the two surfaces. Silicone contents on surfaces of cast films vary also from a sample to another even when sample films were prepared from the same Cardiothane solution, indicating difficulty in quality control of Cardiothane surfaces. An appreciable fraction of silicone was found not to be covalently bonded to polyurethane in Cardiothane 51 for the cast film samples.

Biocompatible Materials↗
PubMed1976

Pathological studies of the animals replaced totally with the artificial heart. Part I. Concerning lungs, natural heart, and brain.

Pathological studies using routine pathological technics, microangiography and electron microscopy were performed on the 28 goats with an artificial heart (including 2 goats which survived for 30 and 37 days). In this paper, the brain, natural heart, and lungs of the goats were discussed. No special findings were seen in the brain except for rare infarcted areas. The natural heart almost always showed infarction-like lesions in the sub-endocardium and myocardium at the cut surface. The longer the animal survive, these findings became the more serious. The light microscopic findings on the lungs were classified into 6 groups. The most important findings of them are massive, diffuse exsudation with hemorrhage and its changes to chronic status. The main pathophysiological status, causing the pulmonary lesions, seemed to be peripheral circulatory insufficiency with increased permeability of peripheral vessels, especially of venulae. Thrombi were detected more frequently in the kidneys and lungs than in any other organs. The vascular walls where the thrombi were attached to, where often seen to be damaged, so that almost all thrombi were thought to be formed in the local vessels in situ, but not in the artificial heart. The main clinical causes to the pulmonary insufficiency were thought to be surgical operation including anesthesia, functional incompleteness of the artificial heart, etc.

Angiography↗
PubMed1976

Pathological studies of the animals replaced totally with the artificial heart. Part II Concerning liver, gastrointestinal tract, kidney, and general discussion.

Twenty-eight goats with an artificial heart (AH) were studied pathologically. Being continued from the previous report, the liver, gastrointestinal tract, and kidneys were taken up in this paper and finally, general discussion was done to get our ideas in shape concerning the pathophysiological status of the goat. Central necrosis of the liver was always observed in the goats which survived for over 140 hours. This finding seemed to be caused mainly by circulatory insufficiency of the portal vein at the latter half of the survival time. Microscopic findings of degeneration, necrosis, and edema were commonly observed at the walls of gastrointestinal tracts, when goats showed poor apetite, mucous feces and constipation. But these problems have been improved by application of a new control method to regulate the output of AH system within a goat's physiological range since October 1974. The lesions seen in the kidneys are classified into 5 groups. The most important findings of them are lower nephron nephrosis and cortical necrosis, both of which indicate the occurrence of long standing vasoconstriction of proximal renal arteries. By means of microangiographic method and others, thrombi were detected frequently in the kidneys. The vascular walls, where thrombi were attached to, were often damaged. Therefore, these thrombi were thought to be formed in the local vessels in situ through renal circulatory insufficiency. The renal pathological lesions have been also improved and severe renal failure from which the previous goats could not escape, has been lessened since the application of a new AH control method. As a whole, the main pathophysiological status of the animals replaced by the AH are thought conclusively to be peripheral circulatory insufficiency. This would be caused by abnormal hemodynamics, so that, the essential clinical etiology is thought to be AH function itself.

Animals↗
PubMed1975

Hemodynamic analysis on prolonged survival cases (30 days and 20 days) of artificial total heart replacement.

High output AH pumping causes a marked decrease in hematocrit, as well as peripheral circulatory insufficiency. By the application of a new control method, based on our hypothesis of regulating the output of the pump, maintenance of normal outputs, long term survival, after total heart replacement, has improved from 10 days to 37 days, with the average survival of 18 days. In addition, the experimentsl animals' general condition has been markeldy improved.

Animals↗
PubMedDate not supplied

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.

Animals↗
PubMedDate not supplied

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 Starling's law at rest, this is no longer true during treadmill exercise.

Animals↗
PubMedDate not supplied

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.

Animals↗