Biomedical subjects

Akimasa Kouno

Publications and source records attributed to Akimasa Kouno.

7 recordsLinked to original sources

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

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

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↗

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↗

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↗