Abstract: A method and apparatus for measuring impedance of heart tissue or the leads associated with a cardiac stimulation apparatus involves charging a capacitor, storing the value of the voltage across the capacitor when charged, discharging the capacitor into said lead/heart system and storing the voltage on said capacitor when discharged. The two voltages may then be used to determine the combined impedance of the lead and the heart tissue. This may be advantageously accomplished by using separate circuits to measure each of the voltages of the capacitor and storing those voltages. These voltages then may be applied to an analog-to-digital converter which converts the ratio of said voltages to digital form. This value can then be used to calculate the combined impedance of the heart tissue or the lead. If one of the two impedances is known the other can then be easily determined.

Abstract: A data communication system for control of transcutaneous energy transmission to an implantable medical device is disclosed having an implantable medical device with rechargeable batteries and a single coil that is employed both for energy transmission and data telemetry. Control circuitry in the implantable device senses battery voltage and current through the battery, encodes those values by use of a multiplexer, and transmits the sensed and encoded values through the coil to an external energy transmission device. The external device includes a coil that is electromagnetically coupled to the coil in the implantable device for receiving the encoded signals and for transmitting energy to the implantable device. The external device decodes the transmitted values and transmits those to a controller for controlling energy transmission.

Abstract: An improved hermetically-sealed automatic implantable cardioverter-defibrillator (AICD) or any other bioimplantable device which may be operated on a single rechargeable cell, or a dual power source system, the rechargeable component being recharged by magnetic induction. Included in the implantable devices are new lithium rechargeable chemistries designed to sense the state-of-charge or discharge of the battery; a battery charge controller specifically designed to recharge a lithium battery rapidly to less than 100% full charge, and preferably 90%, more preferably 80%, of full rated charge capacity; and charging means for multi-step charging. The batteries are based on lithium chemistries specially designed to yield higher currents than conventional primary lithium chemistries and to permit long-term performance despite sub-capacity recharging.