Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-05-14
2001-02-20
Getzow, Scott M. (Department: 3737)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06192272
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an implant including an electric power consuming device connected to an electric power source with an anode and a cathode. This invention also relates to such an implant which consumes electric power itself and/or which is coupled to a separate, implanted device which consumes electric power.
2. Description of Related Art
In currently available implants which require an electric power source for operation, for example, cardiac pacemakers, hearing aids, stimulation devices and the like, either primary cells or secondary cells are used as the electric power source. A drop in the efficiency of the electric power source which endangers implant operation can be prevented by replacing or recharging the cell before the expected service life of the electric power source expires. However, because any replacement of the electric power source requires surgery on the implant wearer, achieving a long service life of the electric power source is very important and is of the highest priority in the field of implant technology.
In order to be able to predict the efficiency of the electric power source provided in the implant, whether it be a primary or secondary source, and to also prevent processes that damage the individual electrodes which can occur especially in charging processes of an electric power source made as a secondary cell, the electrodes should be monitored with respect to certain characteristics such as current and voltage.
In an implant equipped with a conventional electric power source, the electrodes of the electric power source cannot be observed and monitored independently from the other electrode. Rather, the characteristics of current and voltage which can be measured outside the power source, are always referenced to the entire combination of the electrodes provided in the electric power source. When these characteristics are measured, they are generally dependent on the fact that these electrodes have predictable properties during discharge, at rest and optionally, during charging. However, this measurement can be adulterated by simultaneous processes which polarize the electrodes differently. Thus, this measurement allows conclusions regarding the instantaneous state of the electric power source only under current conditions and only with accurate knowledge of the simultaneous processes under the boundary conditions prevailing at the time.
For example, when charging a secondary electrochemical cell, the equilibrium potentials of the two active electrodes are shifted to more negative (negative electrode) and more positive (positive electrode) potentials due to the existing internal resistances. The internal resistances are thus composed of ohmic and non-ohmic portions. The ohmic portions generally relate to contact and electrolytic resistors. The non-ohmic portions are dictated by the electrode composition and geometry and the electrochemical processes which take place on the electrodes.
Overall, there is a very complex network of resistive, capacitive and inductive components which can no longer be broken down especially when there is loading, i.e. when the electric power source supplies the implant with electrical energy. Therefore, a simple current/voltage measurement cannot provide the basis for concluding which of the electrodes involved behaves as desired and which does not.
Only by extensive experience with a given system under clearly defined boundary conditions (for example, “discharging at C/2 rate to an end discharge voltage of 1.5 V”; “charging at C/10 rate for 14 h”) can one skilled in the art assess whether the electric power source being tested is “good” or “bad” from simply measuring current and voltage values. In addition, even if the discharging behavior is known for a certain current load with a certain cut off criterion for a given electric power source, one skilled in the art still cannot exactly predict the behavior of the electric power source under different conditions, for example, at {fraction (1/10)} or {fraction (1/100)} of the current load at the known boundary conditions. At best, one skilled in the art can only give an estimate.
SUMMARY OF THE INVENTION
In view of the foregoing, the primary object of the present invention is to devise an implant which allows more accurate and more reliable measurement of the electrode characteristics.
Another object of the present invention is to devise an implant which allows more accurate and more reliable monitoring of the electrode characteristics.
These objects are achieved by providing an implant of the initially mentioned type in which the electric power source has at least one potential probe which is independent of an anode or a cathode. In this manner, a reference potential is provided which is independent of the anode and cathode of the electric power source and by which unwanted secondary reactions or undesirably intense secondary reactions on the electrodes under consideration can be detected and prevented by controlled monitoring and/or control of individual electrode potentials relative to the reference potential.
Thus, when the respective electrode properties are known, the electrodes can be prevented from being irreversibly damaged, which can lead to premature failure of the electric power source. In an implant in accordance with the present invention, it is no longer necessary to combine extensive technical knowledge based on years of experience with tedious series of tests as required in the present implant designs. Rather, with the present invention, definitive and generally valid conclusions are possible with respect to the pertinent electrodes after performing a few, relatively non-time critical, measurements. Processes which damage electrodes can thus be easily avoided without the need for an analysis of the entire respective current/voltage curves based on numerous assumptions. By practicing the present invention, longer service lives of the electrodes used in the electric power source will result and premature access to the implant which would require surgery on the implant wearer is thereby avoided.
More specifically, in one embodiment of the present invention, the electric power source may be an electrochemical power source or a super-capacitor. Such an electrochemical power source may be made as a galvanic element, especially as a primary element, secondary element or as a fuel cell. The electric power source of the implant can be provided with an electrically conductive housing which has a tap which is used as the potential probe. For reasons of production engineering, this embodiment is the simplest to build since a tap from the outside may be attached to the housing of the electric power source, for example, by soldering, without requiring penetration into the housing. In this embodiment, the housing can have several sections electrically insulated from one another, at least two of the housing sections having a tap which are used as potential probes. For example, the housing of the electric power source provided in the implant can have a first housing section which surrounds the anode and a second housing section which surrounds the cathode, the second housing section being electrically insulated relative to the first housing section and the first and the second housing section each having a tap used as potential probes. In this embodiment of the present invention, the taps serve another function in addition to providing reference potentials for measurements of the anode and the cathode in that the taps also provide information on the state of the interior of the electric power source of the implant on various areas within the housing of the electric power source.
In yet another embodiment of the present invention, a third housing section may be provided between the first housing section and the second housing section which is electrically insulated relative to the first and the second housing sections. The first, second, and third housing sections may each include a tap which are used as poten
Getzow Scott M.
Implex Aktiengesellschaft Hearing Technology
Nixon & Peabody LLP
Safran David S.
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