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Biomedical subjects

K Imachi

Publications and source records attributed to K Imachi.

At least 55 records · Page 3Linked to original sources
PubMed1984

How can the total artificial heart (TAH) patient be mobile and enjoy his life with an air driven system?

Two air driven VAD and TAH driving and control units were developed for clinical use, one to be installed at the bedside and the other to be installed in an electric wheelchair. The reliability and safety of the bedside unit were shown by long-term TAH experiments using animal models and by clinical application in conjunction with VAD. A TAH goat was safety taken on a 12 hr trip to a destination 550 km away while attached to a bedside unit. The driving and control functions of the wheelchair unit were found to be practically identical to those of the bedside unit.

Animals↗
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↗
PubMedDate not supplied

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.

Animals↗