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Abstract

A method and apparatus for measuring lead impedance during preselected test mode operation of an implantable body tissue stimulator. The analysis circuitry is periodically triggered into operation, such as on each reprogramming by the physician or periodically as a function of elapsed time or number of stimulation events counted from the preceding measurement. The actual lead impedance, measured from the output circuit from the body tissue-stimulator pulse generator, and taking into account impedance of the interconnection between the lead connector pin and the pulse generator connector block, the lead electrical conductor and its connections with the electrode and the connector pin and the electrode-tissue interface, is calculated as a function of the ratio of the elapsed times that it takes to discharge a capacitor from a first reference voltage to a second reference voltage through a precision resistor and through the lead impedance itself The calculated lead impedance may be stored in memory with a suitable time tag, employed to automatically effect a change in operating modes or change a lead and electrode selection, if measured lead impedance falls outside normal high and low impedance boundary values. In the pacing context, calculated lead impedance may be employed to adjust sense amplifier sensitivity and pacing output pulse parameters. The method and apparatus may also be employed to calculate cardioversion/defibrillation lead impedance through selective partial discharge of high voltage output capacitors.

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