Eimei Shu

A transcutaneous energy transmission system with rechargeable internal back-up battery for a totally implantable total artificial heart

We have been developing an externally coupled transcutaneous energy transmission system (ECTETS) for a totally implantable total artificial heart (TITAH). When the ECTETS is unable to supply the energy to drive the TITAH from outside the body, a rechargeable internal back-up battery (RIBB) implanted inside the body is used as a back-up to supply the required energy. This paper reports on the performance characteristics of our ECTETS with an RIBB. In this study, a lithium-ion (Li+) secondary battery was used as the RIBB. The transcutaneous energy transmission and the charging control characteristics of the ECTETS, while simultaneously supplying energy to the TITAH and the RIBB, were evaluated in an in vitro experiment. The output power and transmission efficiency of the ECTETS operating in this mode were found to vary from 20 W to 34 W and from 84% to 71%, respectively. It was also found that a sufficient power of more than 20 W could be supplied to the TITAH. The time needed to fully charge the RIBB was 117 minutes, and a fully charged RIBB could drive the TITAH, consuming 20 W for 62 minutes. It may, therefore, reasonably be concluded that the ECTETS with the RIBB is sufficient to drive the TITAH.

Transcutaneous optical telemetry system with infrared laser diode

A transcutaneous telemetry system is indispensable when monitoring and controlling the operation of an artificial heart totally implanted inside the body. A telemetry system using light is more useful than radio waves from the viewpoint of electromagnetic interference and power consumption. In this report, a transcutaneous optical coupler consisting of an infrared laser diode (LD) and a PIN photodiode (PINPD) was evaluated, and the transcutaneous optical coupling and information transmission characteristics were evaluated in in vitro experiments. The wavelength and directional angle of the LD used were 830 nm and 9.5 degrees, respectively. With regard to the directional angle of PINPD, the authors found that a PINPD with a larger directional angle allowed for more deviation between the axes optical axes of the LD and the PINPD. It was also found that the transcutaneous coupler had an optimum distance for the permissible deviation to be maximized. The information signals modulated by the phase shift keying (PSK) were transmitted at a rate of 9,600 bps through goat skin 4 mm thick, and demodulated by the phase locked loop (PLL) on the receiving side. As a result, the information signals were demodulated without any errors in deviation within 10.5 mm at a distance of 11 mm. In conclusion, the transcutaneous optical telemetry system using an infrared LD has sufficient characteristics to monitor and control the operation of an artificial heart totally implanted inside the body.

Efficiency improvement and in vivo estimation of externally-coupled transcutaneous energy transmission system for a totally implantable artificial heart

In order to enhance the implantability of the externally-coupled transcutaneous energy transmission system (ECTETS), efficiencies in various parts of the circuit system were improved to reduce heat dissipation. As a result, a DC-to-DC energy transmission efficiency of 85% or more was obtained in an in vitro experiment conducted at a power output of 19 W. In the in vivo measurement of this improved ECTETS with the internal coil and the rectifier circuit implanted under the skin of a living goad, a DC-to-DC energy transmission efficiency of 82% or more was obtained. Fluctuation of efficiency due to movement of the body was found to be less than 0.5%. When this improved ECTETS is used with the totally implantable electrohydraulic artificial heart with an overflow mock circulatory system connected as a load, the pump output flow at a changing heart rate was found to be 4.4-7.0 L/min (50-110 bpm). For continuous operation at 70 bpm, the DC-to-DC energy transmission efficiency was 81% or more, the pump output flow was 6.2 L/min, and the temperature in the part of implantation was lower than 41/spl deg/C, a temperature that can hardly affect a living body.

Selection of a rechargeable internal back-up battery for a totally implantable artificial heart.

Three kinds of rechargeable batteries, NiCd, NiMH, and Li+, were compared for the purpose of selecting the most appropriate battery for use in a Rechargeable Internal Back-up Battery (RIBB) unit for a Totally Implantable Artificial Heart. Batteries of each kind were connected in series to obtain the required driving voltage of 24 V. The NiCd and NiMH batteries were charged by a constant current of 1 C, and the Li+ batteries were charged first by a constant current of 1 C and later by a constant voltage of 28.7 V. All three types of batteries were discharged using a dummy electronic pulsatile load consuming 20 W of power. The tests showed that the Li+ batteries were capable of supplying the required energy for more than 60 minutes. The Li+ batteries had a specific energy of 121.5 Wh/kg, which was more than 3x that of the NiCd and NiMH, and an energy density of 282.5 Wh/L more than double that of the other two. In addition, the Li+ batteries recorded the least temperature rise during charging and discharging. The results of our tests conclusively showed that the Li+ battery is the best among the three for use in an RIBB from the viewpoint of energy density and temperature rise.

Study on lithium-ion secondary battery for implantable artificial heart

In the totally implantable artificial heart system now being developed by the authors, seven lithium-ion secondary batteries connected in series are used as the backup secondary battery. In this paper are reported the results of investigations made on the charging and discharging characteristics of four kinds of lithium-ion secondary batteries using different cathode active materials and electrolytes. It is found that, of the four kinds of batteries under examination, one that uses LiNi/sub 0.8/Co/sub 0.2/O/sub 2/ as cathode active material and electrolyte B is most suitable, because with this battery the charging time is shortest and the temperature rise at the time of discharging is least. When these lithium-ion secondary batteries are used to drive a totally implantable electrohydraulic artificial heart, it is found that the system is capable of continuous operation for about an hour with a pump output flow of 7.6 L/min and a power consumption of 17.8 W.

Transcutaneous optical telemetry system-investigation on deviation characteristics

As a means of sending signals from the interior of a living body to the exterior, or vice versa, we have proposed a transcutaneous optical telemetry system (TOTS). As there is the skin between the transmitter and the receiver, light will be attenuated in it and the signal will be deteriorated. Therefore, careful examinations are necessary on the performances of the transcutaneous optical coupler, wavelength of the light used, directivities of the light-emitting element and light-receiving element. In this report, a light emitting diode (LED) and a laser diode (LD) are used as the light-emitting element. Transcutaneous transmission characteristics of these two elements are measured and compared. As a result, it is found that, in the transcutaneous telemetry system used, the LD shows better transmission characteristics.

Development of an Electrohydraulic Total Artificial Heart System

An electrohydraulic total artificial heart (EHTAH) system is being developed in our institute. Components of the EHTAH system were evaluated in in vitro and in vivo studies. The system comprises a blood pump system with diaphragm-type ellipsoidal ventricles, an energy converter system consisting of a regenerative pumpbrushless DC motor assembly, and an electronics system with transcutaneous energy transfer (TET) and optical telemetry (TOT) systems. Excellent anatomic fit of the ventricles to the human chest cavity was confirmed by computer graphics based on magnetic resonance imaging. The durability and antithrombogenicity of the blood pump were examined in a series of air-driven chronic implantations into calves for up to 16 weeks. The energy converter is connected to alternate ventricles through flexible conduits, and is placed separately in the abdominal region to minimize anatomic constraints. Maximum output of the pumping unit (the integrated blood pump and energy converter systems) was 10.71/min in a mock circulation at 2500 rpm motor speed. The TET and TOT systems were evaluated in chronic animal studies. The TET system, consisting of a pair of annular coils, demonstrated around 80% DC/DC efficiency for 40 days when 20 W of energy was finally transferred into a simulated load. The TOT system, at a signal transmission rate of 19 200 bits per second (bps) allowed up to 12mm misalignment. These favorable characteristics of the components indicate that the EHTAH system has the capacity to be used as a totally implantable cardiac replacement.

Automatic control of a totally implantable artificial heart using impedance cardiography

Since the physical position or motion of the body affects its condition, and this in turn affects the heart-rate and amount of blood being pumped, an artificial heart must be controlled according to the change in the physical condition caused by physical position or motion. For automatic control of the actuator in a totally implantable artificial heart (TIAH), a great deal of information concerning the physical condition of the body is required. Part of the necessary information can be obtained by measuring the impedance of various parts on the body surface with an impedance cardiograph. The information thus obtained can be transmitted into the body through a transcutaneous optical telemetry system (TOTS), and is used for controlling the actuator which is driven by a transcutaneous energy transmission system (TETS). This paper describes the scheme of such an automatic control system for an artificial heart.