Biomedical subjects

Kou Imachi

Publications and source records attributed to Kou Imachi.

At least 19 recordsLinked to original sources

PubMed2004

Open-loop analysis of transfer characteristics from blood pressure to heart rate using an effectively total artificial heart.

It is desirable for the dynamic behavior of the drive rate of the artificial heart to be as similar as possible to that of the recipient's heart rate (HR) before implantation. This requires a model which can simulate the behavior of HR on the basis of only the information measured with the limited number of approvable implanted sensors. This article provides a linear time series model for explaining the behavior of HR only with aortic pressure and right atrial pressure. This could be obtained from open-loop analysis using a total artificial heart, which was introduced for measuring HR in vivo and for eliminating its effect on blood pressure. The model was identified in a goat equipped with a special biventricular assist device called the effectively total artificial heart (ETAH). The ETAH was introduced to make an open loop and awake situation in the animal with almost intact autonomic nerves, which could enhance the accuracy and reliability of the identification of the model. The adequacy of the proposed model was ascertained in several data sets measured in two goats, which were different from the data set used for identification. Most of the mean estimation errors were less than 3 beats/min and auto-correlation analysis showed approvable statistical appropriateness. However, it was clarified through comparison with the 1/R control method that the proposed model has a few problems still to be solved before its future implementation as an automatic controller of the TAH.

Animals↗

PubMed2004

Development of an implantable undulation type ventricular assist device for control of organ circulation.

It is well known that a rotary blood pump (RP) is effective as a small ventricular assist device (VAD). It might be still more effective if pulsation was available. The undulation pump (UP), which is a type of small RP, can also produce pulsation. In Japan, a development project for an implantable type UP ventricular assist device (UPVAD) is now advanced. Six universities and some companies together have been in charge of the development project for 5 years. In this study, the influence which the UP under development has on circulation in internal organs was investigated. Goats with the same weight as an average Asian person were used for the experiment. The left chest cavity was opened after resection of the fourth rib and the heart was approached. A cannula was inserted in the left ventricle from the apex. An outflow cannula was inserted into the left descending aorta. Heart muscle was excised using a newly developed puncher. The UPVAD was implanted using a left-heart bypass system. The myocardial blood flow, carotid arterial blood flow, and the kidney blood flow were recorded together with an electrocardiogram, blood pressure, and the flow rate. In these animal experiments, the blood circulation dynamic state was stabilized and sufficient support of the left heart was observed. Myocardial blood flow, carotid arterial flow, and a kidney blood flow increase resulting from UPVAD support was observed. Often the problem of multiple organ failure is important at the time of clinical application of a ventricular assist device. Assisting circulation to internal organs is important for prevention of multiple organ failure. It was concluded that the UPVAD might be useful for prevention of multiple organ failure.

Animals↗

PubMed2004

Component engineering for an implantable system.

Component engineering is important for the development of implantable-type rotary blood pumps (RP). The authors are conducting elementary development of an implantable artificial heart. A sensor system detects information in the living body. An automatic control system performs the drive control. Energy is provided by a transcutaneous energy transmission system (TETS). Various artificial hearts are being created. Miniaturization resulting from an increase in operating frequency is planned. A vibrating flow pump (VFP) has a reduced size of pumping chamber because of the high-speed reciprocating movement. Undulation pump ventricular assist devices (UPVAD) are small, lightweight rotary pumps. VFPs are useful in the medical treatment of multiple organ failure (MOF). UPVADs are planned to be permanent-use RPs. The purposes of these two artificial hearts differ, although they have a common component. The authors are developing TETS by using amorphous fibers, making efficient power transmission possible. Control information input from a micro or nano sensor is realized. A control algorithm has been developed and baroreflex control has been successful. Artificial heart development, fully exploiting component engineering, continues.

Animals↗

PubMed2004

Development of an electro-stethoscope system and design of an optimum filter based on tissue sound transmission for noninvasive early diagnosis of malfunction of an implanted mechanical total artificial heart.

Early diagnosis of the malfunction of a mechanical artificial heart implanted in a patient who has been discharged from hospital is very important. We have developed an electro-stethoscope system that enables the malfunction of an artificial heart to be detected from the analysis of sound signals from the artificial heart. The sound data can be transmitted to a hospital via a mobile telephone or the Internet, so that doctors can examine the condition of the artificial heart. The optimum frequency characteristics of a low-pass filter for the elimination of ambient sound through the electro-stethoscope casing were obtained by simulating sound transmission through tissue. We evaluated the usefulness of the electro-stethoscope system using a goat in which an undulation pump total artificial heart had been implanted. A frequency analysis of the sound signal provided information on the degree of degradation of each mechanical component of the artificial heart. The results of this study showed that the electro-stethoscope system is useful for the early detection of the malfunction of an artificial heart at home, and that the use of the system contributes to improvement in the quality of life of patients.

Animals↗

PubMed2003

Preliminary study of a new type of energy transmission system for artificial hearts.

A transcutaneous energy transmission (TET) system is the most common way to power artificial hearts and ventricular assist devices. However, an external battery used with a TET system poses several problems, such as its heavy mass, small charge capacity, and long recharging time. The battery is indispensable when patients want to be ambulatory. This article proposes a new type of TET system that does not require an external battery because electrical energy is supplied remotely by using electromagnetic waves. For this system to operate, multiple transmitting antennas have to be mounted in a room or facility that has been shielded from electromagnetic waves, and a receiving antenna is attached to the patient. Electromagnetic waves transmit electrical power from the transmitting antennas to the receiving antenna. The received electrical power is sent to an implanted device through the TET system. The total power efficiency was plotted against the transmitter-receiver distance by measuring the power that was input to the transmitting antennas, and the final direct current (DC) power that was received by the receiving antenna. A 430-MHz frequency was applied in the experiments. The obtained efficiency was around 10% within a transmitter-receiver distance of 1 m when Yagi-Uda antennas were used for the transmitting antennas and two other types of antenna were used for the receiving antennas: a folded dipole with a reflector and a single loop with a reflector. The results suggested that the proposed system is worth considering. The proposed system would go a long way toward enhancing the patient's quality of life compared with the currently used conventional TET system.

Computer Simulation↗

PubMed2003

Evaluation of pulsatile and nonpulsatile flow in microvessels of the bulbar conjunctiva in the goat with an undulation pump artificial heart.

This study has three purposes, as follows. The first is to develop a microscopic system to observe the microcirculation of animals implanted with an artificial heart. The second is to investigate the influence of flow pattern change from pulsatile to nonpulsatile on the microcirculation. The third is to study the effects of pulsatility in blood flow on endothelium-derived nitric oxide release in the microvasculature. When the flow pattern was changed from pulsatile to nonpulsatile, the velocity of erythrocytes in many capillaries dropped and remained at a low level, and the number of perfused capillaries decreased. After the flow pattern was returned to pulsatile, the velocity of erythrocytes recovered to the initial level. In many cases, the flow of nonperfused capillaries recovered to the initial level as well. Also, the pulsatile flow enhances the basal and flow-stimulated endothelium-derived nitric oxide release in microvessels.

Animals↗

PubMed2003

Basic study to develop an electromagnetic drive method for the rotary undulation pump.

The rotary undulation pump, which is composed of a disk with a convex shape on both sides and a pump housing with one narrow side and one wide side, is a unique continuous flow pump with a new principle. The concept of the levitation drive method for this pump was proposed. The electromagnetic driver model and drive circuit were developed to examine the possibility and the difference among the delta wired, Y wired, and repulsion methods. In the repulsion method, the disk was driven by magnetic repulsion. The model could be driven with either method, and the repulsion method was demonstrated to also be possible. With either method, owing to the wide gap between the permanent magnets and coils, the output was not enough when the load was high. The efficiency was almost the same in the delta wired and Y wired methods. In the repulsion method, however, it was less than 50% of that in the other two methods. From the results, the delta wired and Y wired methods with an active control of the gap distance were considered to be better than the repulsion method, which required no active gap control.

Centrifugation↗

PubMed2003

Progress in the control system of the undulation pump total artificial heart.

The undulation pump total artificial heart (UPTAH) is a small implantable total artificial heart. As the UPTAH generates outflow and inflow at the same time, control of the UPTAH is very difficult. Therefore suitable control methods specifically for the UPTAH should be established. Various motor control, left-right flow balance control, and physiological control methods were examined and tried for the UPTAH control in this study. The control system is divided into seven categories. It has a hierarchical structure and all control modes work at the same time. The UPTAH with the newly developed control method has been implanted into the chest cavities of 48 goats. Until now, six goats survived for more than one month, including 63 days in the longest case. The good condition of the UPTAH implanted animal could be maintained with the newly developed control scheme, consisting of the 1/R control and several other additional controls.

Animals↗

PubMed2003

Development of a polymer bileaflet valve to realize a low-cost pulsatile blood pump.

The final goal of this study is to realize a low-cost pulsatile blood pump especially for patients with acute heart failure or postoperative low cardiac output syndrome. In support of the pump, two types of polymer bileaflet valves with different configuration of the valve seats were developed. Influence of the leaflet thickness on the hydrodynamics of the prototype was preliminarily investigated among 70 microm, 100 microm, and 150 microm. As to the valves with the thinner leaflets, buckling of the leaflets was observed, which induced a large amount of regurgitation at valve closure. However, by thickening the leaflet to 150 microm, the mean flow of the prototype and the second model could be successfully comparable to the Medtronic-Hall valve. Moreover, accelerated fatigue tests showed that reinforcement of the valve seat with the additional spokes in the second model extended the durability by four times as compared with the prototype, equivalent to an in vivo duration of over one month.

Cardiac Output, Low↗

PubMed2003

A study on an energy supply method for a transcutaneous energy transmission system.

This study proposes a new type of a transcutaneous energy transmission system (TETS) that can supply electrical power for an implanted device without an external battery. In this system, the power is supplied from the floor to the shoes of the patients through coils that are set beneath the floor and the bottom of the shoes. If the patients wear the special shoes, they will be able to move freely on the specially designed floor without an external battery. Direct current (DC)-DC power efficiency was measured in the experiments, and the results showed that it varies with relative positions between the shoe and the floor coils. The results suggested that three-layered floor coils would enable the system to meet the demand for providing the required power anywhere on the floor without intermission. DC-DC power efficiency could be kept over 60% under the practical condition. It can then be concluded that the proposed system has a potential to provide better quality of life for the patients using a TETS.

Electromagnetic Fields↗

PubMed2003

[Biomaterials essential to regenerative medicine].

Biomaterial is one of the most important factors to be developed in regenerative medicine. In this paper, the biomaterials essential to regenerative medicine were described. Biomaterials in regenerative medicine are classified into 5 categories; 1) Biomaterials for cell culture, 2) Biomaterials for cell inducement, 3) Biomaterials for scaffold, 4) Biomaterials for immuno-isolation, 5) Biomaterials assist to regenerative medicine. As for 1), temperature responsible gel that can take out the cultured cell sheet without use protein breakdown enzyme, is mainly introduced. Micro-photolithography to make a micro patterning for cell inducement, kinds of materials for scaffold, isolated membrane and micro capsules, carrier for cell growth factors are mentioned in 2) to 5).

Animals↗

PubMed2002

Visible-light-induced surface graft polymerization via camphorquinone impregnation technique.

A surface modification method that is particularly applicable to complexly shaped fabricated devices has long been awaited. In this article, we describe the visible-light-induced surface photograft polymerization technique by which an inner surface of the device is modified by visible-light irradiation through the external surface. Comphorquione, as a photoradical initiator, was impregnated on a segmented polyurethane surface by solvent soaking, followed by visible-light irradiation in the presence of monomers such as acrylamide and poly(ethylene glycol) methacrylate. The resultant surfaces were highly wettable with water, and surface chemical compositional analysis by X-ray photoelectron spectroscopy revealed that the surface was graft-polymerized with these monomers. The simple and widespread applicability of this surface modification technique to biomedical devices is discussed.

Biocompatible Materials↗

PubMed2002

Non-linear dynamic analysis of hemodynamic parameters in an undulation type artificial heart system.

Undulation pump total artificial heart (UPTAH) is a unique total artificial heart implant (TAH) using an undulation pump that is a continuous blood flow pump. To evaluate the autonomic nerve function mediating the circulation system, we analyzed the hemodynamic parameters during animal experiments with UPTAH using the non-linear mathematical analyzing technique, including chaos and fractal theory. Adult female goats were used for the implantation of UPTAH. The natural heart was replaced with UPTAH under extra-corporal circulation. The conductance- and arterial pressure-based control method (1/R control) was applied on the 5th to 7th post-operative day as the influences of the cardiopulmonary bypass circulation were diagnosed to be terminated. Hemodynamic parameters were recorded on the data recorder, and non-linear mathematical analysis was performed. For the quantitative evaluation of the strange attractor, which was the characteristics of the deterministic chaos, the fractal dimension analysis was carried out. As a result, hemodynamic parameters fluctuated on the time axis and showed fractal characteristics, which were thought to be the characteristics of the deterministic chaos. The reconstructed attractor of the hemodynamics showed various behaviors according to changes in the situation of the goats. These results suggest that non-linear dynamical analysis might be useful in monitoring the circulatory regulatory system in artificial heart circulation.

Animals↗

PubMed2002

Ripple reduction control of the undulation pump total artificial heart.

An undulation pump total artificial heart (UPTAH) in which the revolutions of the motor are converted to undulation motion of a disk has been developed. In an experiment, a goat using the UPTAH survived for 54 days. However, a large ripple was observed in the device's output pressure and flow waveform. In calculating the spectrum of the ripple, we found that the ripple mainly comprised 2 frequency sine waves: 1 having the same frequency as and 1 having double the frequency of the motor revolutions. To reduce the ripple, 2 sine waves, 1 having the same frequency as and 1 having double the frequency of the motor revolutions, were provided to the motor current to modulate the pulse width of the pulse width modulation controlling the motor revolutions. This ripple control method reduced the pressure ripple by 90% in a mock circulation and by 70% in animal experiments. These results revealed that the ripple generated in the UPTAH could be controlled through the use of motor control software.

Animals↗

PubMed2002

Implications for the establishment of accelerated fatigue test protocols for prosthetic heart valves.

The goal of this research is to establish a reliable methodology for accelerated fatigue tests of prosthetic heart valves. A polymer valve was the subject, and the influence of various drive parameters on durability was investigated in three different machines. Valve lifetime was notably shortened by increasing the cyclic rate or stroke even though the maximum pressure difference at valve closure was maintained at 120 mm Hg. These results demonstrate that adjustment of the maximum transvalvular pressure is not sufficient to ensure tests are conducted under the same conditions and indicate that measurement of the dynamic load would be more efficacious. Moreover, the locations of tears sustained in the accelerated tests differed from those encountered in an animal experiment although in both cases the locations were entirely consistent with the areas of strain concentration revealed by finite element analysis. These findings should be discussed during a revision of ISO 5840.

Animals↗

PubMedDate not supplied

The improved Jellyfish Valve: durability enhancement with sufficient blood compatibility.

The Jellyfish Valve is one of the most promising polymer valves for artificial hearts. The present problems to be solved are 1) how to prevent a membrane fracture and 2) how to eliminate a calcification, because both of these problems were observed in experiments with goats after 312 days and 414 days of pumping. Finite element analysis demonstrated that mechanical tensile strain induced in the membrane at valve closure was clearly consistent with the fracture location as well as calcification area in in vivo experiments. Based on this finding, a new valve seat with an additional concentric ring 14 mm in diameter and 0.5 mm in width was finally developed. The maximum strain was dramatically reduced to 52% by the design improvement. Moreover, accelerated fatigue tests demonstrated that the improved valve was 10 times more durable as compared with the original valve, which was equivalent to an in vivo duration of 8.3 years. In animal experiments, including 31 days and 46 days use in a total artificial heart (TAH), no thrombus was found despite the lack of anticoagulant or antiplatelet therapies. These results indicate that the improved Jellyfish Valve might be one of the most durable polymer valves, able to perform in artificial hearts for a long period of time.

Animals↗

PubMedDate not supplied

Third model of the undulation pump total artificial heart.

The undulation pump is a small, continuous flow displacement type blood pump, and the undulation pump total artificial heart (UPTAH) is a unique, implantable total artificial heart based on this pump. To improve the durability of the UPTAH for investigating long-term pathophysiology with UPTAH, a third model (UPTAH3) has been developed. UPTAH3 was designed to separate the left and right undulation shafts and to be more durable. The undulation pumps were also redesigned. UPTAH3 was implemented with a diameter of 76 mm, width of 78 or 79 mm, total volume of 292 ml, and weight of 620 g. The priming volumes of the left and right pumps are 26 and 21 ml, respectively. The atrial cuffs and outflow cannulae were also redesigned for UPTAH3. The maximum output against an arterial pressure load of 100 mm Hg is about 11 L/min. The maximum pump efficiency is about 15% in the left pump and 18% in the right pump, giving a maximum total efficiency for both of about 11%. To date, UPTAH3 has been tested in 17 goats, and the longest survival period was 46 days. This third model will be useful for investigating pathophysiology with UPTAH.

Animals↗

PubMedDate not supplied

Advance in animal experiments with the undulation pump total artificial heart: 50 and 54 day survival periods with 1/R control.

The undulation pump total artificial heart (UPTAH) is a unique, implantable, total artificial heart (TAH) that uses undulation pumps. To achieve long-term survival in animals with physiologic hemodynamic conditions, a control method based on conductance and arterial pressure was applied to UPTAH. With this control method, called 1/R control, survival periods of 50 days (No. 0016, 49.6 kg) and 54 days (No. 0030, 42.5 kg) were obtained in adult female goats. In No. 0016, 1/R control was applied to the left pump, whereas in No. 0030, it was applied to the right pump. Another pump was used for left-right balance control. The control stability was better in No. 0030 than in No. 0016. The sucking effect of the left atrium was remarkable in No. 0016, possibly because of a time delay when left-right balance control was performed with the right pump. In No. 0016, the cause of death was probably a thrombus flown from a panus in the left atrium. It is possible that the left atrial suction effect influenced the thrombus and panus formation in the left atrium. In No. 0030, the cause of death was a small rupture of the membrane in the right pump. The rupture may have been caused by excessive negative pressure inside the pump. This pressure resulted from suction of the right atrium because of an unexpected control excursion, which was probably caused by a software bug. It will be necessary to redesign the undulation pump and improve the software to achieve longer survival periods for animals with physiologic hemodynamic conditions.

Animals↗