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Biomedical subjects

I Fujimasa

Publications and source records attributed to I Fujimasa.

At least 19 recordsLinked to original sources
PubMed1998

Physiological control of a total artificial heart: conductance- and arterial pressure-based control.

To obtain a physiological response by a total artificial heart (TAH), while eliminating the hemodynamic abnormalities commonly observed with its use, we proposed the use of a conductance- and arterial pressure-based method (1/R control) to determine TAH cardiac output. In this study, we endeavored to make use of a variable more closely tied to central nervous system (CNS) efferents, systemic conductance, to provide the CNS with more direct control over the output of the TAH. The control equation that calculates the target cardiac output of the TAH was constructed on the basis of measurement of blood pressures and TAH flow. The 1/R control method was tested in TAH-recipient goats with an automatic method by using a microcomputer. In 1/R control animals, the typical TAH pathologies, such as mild arterial hypertension and substantial systemic venous hypertension, did not occur. Cardiac output varied according to daily activity level and exercise in a manner similar to that observed in natural heart goats. These results indicate that we have determined a control method for the TAH that avoids hemodynamic abnormalities exhibited by other TAH control systems and that exhibits physiological responses to exercise and daily activities under the conditions tested. The stability of the control and the complete lack of inappropriate excursions in cardiac output is suggestive of CNS involvement in stabilizing the system.

Animals↗
PubMed1997

Development of the undulation pump total artificial heart.

The undulation pump is a small size continuous flow displacement type blood pump that has been developed for an artificial heart. Using undulation pumps, 2 types of implantable total artificial hearts (TAHs), the undulation pump TAH (UPTAH) type 1 (UPTAH 1) and UPTAH type 2 (UPTAH 2) were developed. Both UPTAHs were designed to be small enough to implant into the chest of a goat, the experimental animal. UPTAH 1 could be reduced in size to 75 mm in diameter and 78 mm in length. The weight was 520 g. UPTAH 2 could be reduced in size to 75 mm in diameter and 80 mm in length. The weight was 650 g. UPTAH 2 could be tested in an animal experiment using an adult female goat weighing 52.3 kg. The UPTAH 2 could be implanted successfully into the goat's chest with a good fit. The goat stood after the surgery and extubation and survived for 3 h and 40 min; thus, the potential of the UPTAH for a practical implantable TAH was demonstrated.

Animals↗
PubMed1997

Use of a catecholamine sensor in the control of an artificial heart system.

An electrochemical sensor system to allow real-time measurement and feedback of catecholamine concentrations was developed for use in the control of artificial hearts. Electrochemical analyses were carried out using a carbon fiber working electrode, an Ag-AgCl reference electrode, and a potentiostat. The operating parameters of the pneumatically-driven artificial heart system were altered in accordance with the algorithm for changes in the catecholamine concentration. The minimum detectable concentrations of both adrenaline and noradrenaline in a mock circulatory system using a phosphate-buffered solution were approximately 1-2 ng/ml (10(-8) mol/L). An artificial heart control system utilizing this set-up performed satisfactorily without delay, although sensor sensitivity decreased when placed in goat plasma instead of a phosphate-buffered solution, due to the adsorption of various substances such as plasma proteins onto the electrodes. This study demonstrated the future feasibility of a feedback control system for artificial hearts using catecholamine concentrations.

Adsorption↗
PubMed1996

A percutaneously accessible pulsatile left ventricular assist device: modified assist device type 5.

To provide percutaneous access, a new circulatory assist system was developed. We call this newly developed system the modified assist device (MAD). The system is composed of a sac-type blood pump and cannula. Inflow and outflow valves are mounted in the apex and at the side wall 10 cm from the apex of the cannula, respectively. During systole, the blood is sucked from the left ventricle through the inflow valve of the cannula connected to the blood pump, and during diastole, the blood is ejected to the root of the aorta through the outflow valve. In vitro and in vivo evaluations of the pump performance were performed. The maximum flow rate of 1.9 L/min was obtained in the mock circulatory system. In our animal experiment, effective systolic unloading and diastolic augmentation were observed by activation of this system during regular sinus rhythm. In conclusion, the MAD-5 is thought to be percutaneously accessible and increases systemic and coronary flow.

Animals↗
PubMed1995

Basic study to develop the undulation pump for practical use: antithrombogenicity, hemolysis, and flow patterns inside the pump.

The undulation pump (formerly called the precessional displacement pump) is a continuous flow displacement-type blood pump that is being developed as an implantable total artificial heart. A new undulation pump was developed for chronic use and was examined with animal experiment and flow visualization studies. In the animal experiment using a left ventricular bypass in goats, severe hemolysis occurred. After driving for 12 h, thrombus formation inside the pump was found. In the flow visualization studies, the flow pattern showed that the flow inside the pump was a very complicated turbulent flow. Improvement of hemolysis and thrombus formation is important to realize implantable total artificial hearts using undulation pumps.

Animals↗
PubMed1995

New version of flow-transformed pulsatile total artificial heart with no electrical switching valve.

The flow-transformed pulsatile total artificial heart (FTPTAH) is a new pulsatile total artificial heart that consists of a single continuous flow rotary blood pump and blood flow switching valves. It can perfuse the pulmonary and the systemic circulation alternately with pulsatile flow. A new version of the FTPTAH, which consists of one undulation pump (UP), 4 jellyfish valves, and a compensatory chamber, has been proposed. The UP is a reversible continuous flow blood pump, and flow transformation is caused by switching the direction of the motor rotation so that no electrical flow switching valve is needed. A prototype model could perfuse alternately pulmonary and systemic circulation with 3.0 L/min in a mock circulation. Unoxygenated blood in the UP at the end of pulmonary circulation will be stored in the compensatory chamber by shifting a flexible membrane to the direction of the left atrium (LA); therefore, the blood is not sent to the systemic circulation.

Atrial Function↗
PubMed1994

Evaluation of the pulsatility of a new pulsatile left ventricular assist device--the integrated cardioassist catheter--in dogs.

A new pulsatile left ventricle-femoral artery bypass system (integrated cardioassist catheter system) has been developed for rapid, percutaneous insertion as a left ventricular assist device. Previous experiments revealed its superiority over the intraaortic balloon pump system in maintaining the peripheral circulation and in improving myocardial blood flow and afterload. Our objective was to determine whether the pulsatility of left ventricular bypass of this system would be preferable for maintaining the peripheral circulation and managing the ischemic myocardium as compared with nonpulsatile left ventricular bypass. Ten dogs with profound heart failure were supported by this system. Their hemodynamic status and myocardial blood flow were measured under control, nonpulsatile left ventricular bypass, or synchronous pulsatile left ventricular bypass. Significant differences between the nonpulsatile bypass group and the pulsatile bypass group were observed in the mean increase in aortic pressure (3.5% versus 22.2%, respectively; p < 0.001), total cardiac output (13.0% versus 21.7%; p = 0.004), and myocardial blood flow (9.5% versus 21.8%; p < 0.001). No differences were found between groups in the decrease in left atrial pressure (-20.2% versus -20.2%; p > 0.05). The ratio of diastolic time index/tension time index was shown to be improved significantly in the pulsatile bypass group compared with that of control and nonpulsatile bypass groups (p < 0.001). Thus, the pulsatility of the integrated cardioassist catheter system may support the peripheral circulation and improve the myocardial blood flow and oxygen supply/demand ratio.

Animals↗
PubMed1993

Micromachining technology and biomedical engineering.

Medical science and clinical medicine include many microscopic environments. Recent micromachining techniques fit the microscopic environments and are applied to microsurgery, fiberscopic operation, micromanipulation, artificial organs, and drug delivery systems. Microactuators, microsensors, and micro mechanical parts will be prepared for such medical devices and techniques. Virtual reality, stereovision, and fiber imaging support handling of cells and small targets of living body. The paper reports some perspectives of microtechnologies in biomedical engineering.

Angioplasty, Laser↗
PubMed1993

[Micromachine].

Explore the source record for details and available documents.

Biotechnology↗
PubMed1993

Multivariate analysis of risk factors for thrombus formation in University of Tokyo ventricular assist device.

Of 77 University of Tokyo ventricular assist devices used in a total of 70 patients at 21 institutions, 13 pumps were found to have macroscopic thrombus formations. Because 19 devices that were used for less than 24 hours showed no thrombus deposition, they were considered not to have been sufficiently exposed to the thrombogenic environment for macroscopic thrombus deposition and were removed from the subsequent multivariate study. A total of eight potential risk factors were assessed in relation to thrombosis. Prevalences of thrombus formation were compared between two groups with or without each of the risk factors. In a univariate analysis, the following categoric variables were demonstrated to be significantly associated with complications, in descending order of significance: use of gabexate mesilate (protease inhibitor) as an anticoagulant (p = 0.005), normal platelet count (p = 0.010), duration of support (p = 0.038), leukocytosis (p = 0.042), and minimum pumping flow (p = 0.042). Use of heparin and the consequent increase in activated clotting time showed no relationship. Multivariate discriminant analysis, which was done to identify risk factors rejecting cross correlation between each variable, demonstrated platelet count (p = 0.006), use of gabexate mesilate (p = 0.007), and minimum flow (p = 0.008) to have significant and independent risks. These results indicate the importance of maintaining pumping flow above a certain minimum level, addition of antiplatelet drugs to the antithrombogenic regimen, and nonuse of gabexate mesitate.

Adolescent↗
PubMed1992

Hemodynamic evaluation of a new left ventricular assist device: an integrated cardioassist catheter as a pulsatile left ventricle-femoral artery bypass.

We developed a new left ventricular (LV) assist catheter (transaortic valve from LV to femoral artery) that is implemented percutaneously and exerted as a synchronous pulsatile partial LV flow support with conventional intraaortic balloon pump (IABP) driving system and centrifugal pump system. We investigated whether this pulsatile LV-aorta bypass is superior to the IABP from a hemodynamic viewpoint. Ten dogs with profound heart failure were placed on this device, and hemodynamic measurements were performed under on-off study of this system. The results revealed a significant increase of mean aortic pressure, total cardiac output, and myocardial blood flow, and a significant reduction of left atrial (LA) pressure and LV afterload estimated by diastolic pressure-time index/tension-time index (DPTI/TTI) measurement compared with baseline values and also with IABP exertion alone. These findings suggest that this system is of clinical value for supporting an impaired LV that is intractable under IABP counterpulsation.

Animals↗
PubMed1992

Development of a flow-transformed pulsatile total artificial heart for total implantation.

To realize a totally implantable total artificial heart (TAH), a new pulsatile TAH, the flow-transformed pulsatile TAH (FTPTAH), was developed. The system was composed of a single centrifugal pump (CFP) and two three-way valves. One port of each three-way valve was connected to the inlet and outlet of a CFP. The other two ports of each valve were connected to the right and left atrium, and the pulmonary artery and aorta. The CFP can perfuse the pulmonary and systemic circulation alternately with pulsatile flow by switching the two three-way valves. A prototype and the secondary model in which the solenoid valves and a spool valve were included, respectively, were connected to a mock circulatory unit with the results that a pulsatile TAH with physiological flow wave form could be obtained from a single CFP, about 5 L/min of pulsatile output could be obtained alternately on the right and left side by switching the solenoid valves or a spool valve, and flow balance between the right and left could be easily controlled by the switching duration. The system is feasible for a totally implantable TAH because it does not need a compliance chamber and can be miniaturized.

Heart, Artificial↗
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↗
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↗
PubMed1989

[Clinical experience for ventricular assist device].

We began applying of our VAD system clinically in 1982 and have subsequently obtained good results. The first case treated with the VAD returned to normal life. In a total of 70 cases of clinical applications this system there has been instance of apparatus dysfunction. Confirming the reliability and safety promised by the results of biological experiments. Here, we report the results of clinical application of the system in a total of 61 cases between August, 1985 and March, 1989. The following conclusions were reached: 1) Satisfactory weaning and survival rates were obtained i.e. 18 cases out of 61 cases (30%) survived over one month and 13 cases (21%) are currently surviving, even in elderly patients of 60 years of age or older. 2) The weaning rate and survival rates were good after approximately 1 week of support. Detailed evaluation of the recovery of the heart and functions of other major organs has led to the conclusion that the results can be improved further when the weaning period is carefully determined. 3) With regard to surgical factors, good findings were obtained when the artificial heart-lung bypass time was less than 6 hours. The VAD can be used in the early stages without vainly attempting weaning from the artificial heart-lung bypass. 4) There were no mechanical problems with the hardware of the blood pump drive assembly, etc., or noteworthy side effects.

Aged↗