In vivo implantable medical device with battery monitoring circu

Details In vivo implantable medical device with battery monitoring circu In vivo implantable medical device with battery monitoring circu

1992-01-09

1993-03-16

Howell, Kyle L.

Surgery

Truss

Pad

128419PG, 128419PS, A61N 1378

Patent

active

051935384

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

In a living body implantable electromedical device The present invention relates to an electromedical device implantable in a living body and comprising stimulating means for the stimulation of a physiological function in the living body, stimulating mode selector means connected to said stimulating means to enable modification of said stimulation by selecting one or more out of a plurality of available&imulating modes, a power source in the form of a battery for powering said stimulating means and stimulating mode selector means, sensing means connected to said battery to enable sensing of the instantaneous battery capacity and evaluating means connected to said sensing means to establish whether said battery capacity, on a sensing event, is higher or lower than a predetermined first threshold value adapted to guarantee, in an assumed standard operation of the device, its function within a predetermined time interval during which said battery capacity shall exceed a lower second threshold value.
The invention is primarily intended for use with an electromedical device such as a pacemaker, which is intended to stimulate the cardiac function of the living body by means of generated electrical pulses different in time when said cardiac function deviates from normal.
A device of the type initially cited is disclosed by U.S. Pat. No. 390 020. This device relates to a programmable pacemaker capable of operating in several stimulating modes, having battery powered stimulating means and stimulating mode selector means. Sensing and evaluating means, which can be activated externally by means of a magnet, for example at a medical examination, monitor the terminal voltage of the battery and cause the pacemaker via the stimulating selector means to change operation from a first stimulating mode with a programmed stimulation rate to said mode with a fixed stimulation rate, when the terminal voltage decreases below a first threshold value, and to operate in a second predetermined stimulating mode at a fixed stimulation rate when the terminal voltage decreases below the first and a lower second threshold value. The limitation to a predetermined stimulating mode at a fixed rate decreases the current demand from the battery and indicates to the patient or an observing physician that the pacemaker should be replaced.
U.S. Pat. No. 4,416,282 discloses a similar pacemaker, which also includes sensing and evaluating means for monitoring of the battery capacity with regard to two battery depletion levels. The stimulation rate automatically decreases with the decreasing of the battery capacity below the depletion levels.
As is known from U.S. Pat. No. 4,606,350 or U.S. Pat. No. 4,290,429, the battery monitoring can be performed by cutting off all current flow from the battery to the pacemaker circuitry, which, however, is still powered by a by-pass capacitor, whereby a test capacitor is connected to the battery and the time period needed for the voltage across the test capacitor to reach a predetermined value gives a measure of the internal resistance of the battery.
From U.S. Pat. No. 4,481,950, another method to monitor the battery capacity is known, where the battery is loaded with a predetermined load and the battery terminal voltage is sensed. The sensed voltage gives a measure of the internal resistance of the battery, the value of which has a certain unambiguous relation to the instantantaneous battery capacity. As is known from U.S. Pat. No. 4,120,306, the internal resistance value of lithium-type batteries usually used for pacemakers is lower, the higher the battery capacity and vice versa.
When the monitoring of the battery capacity is activated as described in connection with the above mentioned U.S. Pat. No. 4,390,020, the battery capacity must be sufficiently high to guarantee operation of the pacemaker under definite conditions during a predetermined time interval up to the next medical examination; otherwise the approaching of the end of life (EOL) of the battery must be indicated, so

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