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We have developed internal battery systems for driving an undulation pump ventricular assist device using two kinds of lithium ion rechargeable batteries. The lithium ion rechargeable batteries have high energy density, long life, and no memory effect; however, rise in temperature of the lithium ion rechargeable battery is a critical issue. Evaluation of temperature rise by means of numerical estimation is required to develop an internal battery system. Temperature of the lithium ion rechargeable batteries is determined by ohmic loss due to internal resistance, chemical loss due to chemical reaction, and heat release. Measurement results of internal resistance (R(cell)) at an ambient temperature of 37 degrees C were 0.1 Omega in the lithium ion (Li-ion) battery and 0.03 Omega in the lithium polymer (Li-po) battery. Entropy change (DeltaS) of each battery, which leads to chemical loss, was -1.6 to -61.1 J/(mol.K) in the Li-ion battery and -9.6 to -67.5 J/(mol.K) in the Li-po battery depending on state of charge (SOC). Temperature of each lithium ion rechargeable battery under a discharge current of 1 A was estimated by finite element method heat transfer analysis at an ambient temperature of 37 degrees C configuring with measured R(cell) and measured DeltaS in each SOC. Results of estimation of time-course change in the surface temperature of each battery coincided with results of measurement results, and the success of the estimation will greatly contribute to the development of an internal battery system using lithium ion rechargeable batteries.

In this study, we have developed an implantable electronics unit (IEU) for driving an undulation pump-left ventricular assist device (UP-LVAD). The IEU consists of a pump driver, three series-connected lithium ion batteries (1800 mAh), a charger, and a transcutaneous information transmission system. These electronic subunits were encapsulated in a case (110 x approximately 80 x approximately 30 mm) made of epoxy resin. The IEU was evaluated in two animal experiments using goats implanted with the UP-LVAD. The lithium ion batteries in the IEU provided 30-min energy supply daily to the UP-LVAD. The transcutaneous information transmission system transmitted data bidirectionally between the IEU and the personal computer at the data transmission ratio of 56 kbps without any transmission error. We could obtain survival days of 27 and 28 days supporting cardiac function with the UP-LVAD system. The temperature inside the IEU case was maintained under 45 degrees C, and there was evidence of a burn on the surrounding tissue in autopsies in each experiment. Based on the results, the IEU is promising to be suitable for drive and control of an implantable UP-LVAD.

We have been developing an implantable battery system using three series-connected lithium ion batteries having an energy capacity of 1,800 mAh to drive an undulation pump left ventricular assist device. However, the lithium ion battery undergoes an exothermic reaction during the discharge phase, and the temperature rise of the lithium ion battery is a critical issue for implantation usage. Heat generation in the lithium ion battery depends on the intensity of the discharge current, and we obtained a relationship between the heat flow from the lithium ion battery q(c)(I) and the intensity of the discharge current I as q(c)(I) = 0.63 x I (W) in in vitro experiments. The temperature distribution of the implantable battery system was estimated by means of three-dimentional finite-element method (FEM) heat transfer analysis using the heat flow function q(c)(I), and we also measured the temperature rise of the implantable battery system in in vitro experiments to conduct verification of the estimation. The maximum temperatures of the lithium ion battery and the implantable battery case were measured as 52.2 degrees C and 41.1 degrees C, respectively. The estimated result of temperature distribution of the implantable battery system agreed well with the measured results using thermography. In conclusion, FEM heat transfer analysis is promising as a tool to estimate the temperature of the implantable lithium ion battery system under any pump current without the need for animal experiments, and it is a convenient tool for optimization of heat transfer characteristics of the implantable battery system.

A transcutaneous energy transmission system (TETS) for artificial hearts and ventricular assist devices uses electrical coupling of power between external and implanted coils. If the position of coils changes relative to each other, the TETS cannot feed the required power of the implanted device. During activity or sleep, the coils may move accidentally. TETS users and the people around them have to pay attention to this because the range of the position where the required power can be fed efficiently is not wide. Therefore, we added functions for the position changes of the coils to the TETS. Regular, cautious, and irregular positions were introduced, and the ranges of them were decided upon in our experiments. The cautious position was determined by the area where the change of the relative position of the coils was relatively small. When the coils were in the cautious position, the circuit was tuned by way of changing the resonant point. This modulation could give good power efficiency in the cautious position. When the coils were in the irregular position, an alarm switch was turned on. These functions ease the restriction of the coil position and give better quality of life (QOL) than do the conventional TETS.

The purpose of this study was to demonstrate the feasibility of the use of an implantable, high-energy, and compact battery system for an undulation pump total artificial heart (UPTAH). The implantable battery system tested consists of six lithium-ion batteries in series, a charge unit, and a charge/discharge control unit. A lithium-ion battery is currently the best energy-storage device because it has more energy density, a better life cycle, and a smaller temperature rise than those of other secondary batteries. The performance of the implantable battery system was evaluated in an in vitro experiment using an electric load that simulated the UPTAH. Also, sufficiently reliable operation of a system for supplying energy to a UPTAH consisting of a transcutaneous energy transmission system (TETS) and an implantable battery system was confirmed in three experiments using goats. The results of the in vitro and in vivo experiments showed that the implantable battery system supplied sufficient current to the UPTAH for maintenance of physiological conditions in the goat with maximum rise in temperature to less than 43 degrees C.

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.