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Medtronic of Minneapolis has found a clever way to make the batteries in
pacemakers and defibrillators last indefinitely (WO 00/09201). Batteries in
conventional implants go flat after a few years, but the new ones will be
powered by a thermocouple, which generates electricity when its two contact
leads are at different temperatures. Medtronic found unexpected gradients within
the human body, such as a difference of 2 °C between leads inside and
outside the lung or liver. Useful gradients also exist across blood vessels.