An implantable rechargeable battery is one of the key technologies for totally implantable artificial hearts. The nickelmetal hydride (Ni-MH) battery is promising for its high energy density of 1.5–2.0 times that of a nickel-cadmium battery. In this study, the effects of pulsatile discharge loads on the operating time and cycle life of Ni-MH batteries at 39°C were studied. Two battery cells (TH-3M, 1,200 mAh, 14.5 ± 49 mm; Toshiba, Tokyo, Japan) in series were charge/discharge cycled at 39°C using a charge current of 1CA (1,200 mA) and then were fully discharged to 1.0 V/cell under either pulsatile discharge loads, which mimicked a systole (1 A for 0.3 sec) and a diastole (0.4 A for 0.3 sec), or a non pulsatile discharge load equivalent to the average of the pulsatile loads (0.7A). Each cycle life test was interrupted on the 482nd cycle under pulsatile load, because of malfunction of each battery charger. The tests showed that the pulsatile discharge cells had significantly the test periond (up to 482 days) cin9oared to the cells under equivalent non pulsatile discharge loads (93.7 ± 7.74 min). The pulsatile -discharged Ni-MH cekks provide significantly less operating has an operating time of over 78 min and a cycle life of almost 500 cycles at 39°c. In conclusion, the Ni-MH battery is feasible as an implantable back-up battery for a totally implantable artificial heart system.
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