Control of externally induced current in implantable medical devices

• US 6,198,972 B1
• Filed: 04/30/1997
• Issued: 03/06/2001
• Est. Priority Date: 04/30/1997
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Stein, Marc T., Hartlaub, Jerome T.
• Primary Examiner(s): Getzow, Scott M.
• Application Number:
  US08/847,642
• Time in Patent Office: 1,406 Days
• Field of Search: 607/2, 607/63, 607/64
• US Class Current: 607/63
• CPC Class Codes: A61N 1/32 alternating or intermittent currents applying electric fields by inductive or capacitive coupling A61N1/40; microwave apparatus A61N5/02

Abstract

A current limiting apparatus that is adapted to be operatively connected as part of a conductive loop formed by a medical device implanted within a living organism having electrically excitable tissue. This apparatus limits unwanted current in the conductive loop that may be induced by a significant level of an external signal such as a time-alternating electromagnetic field. This apparatus includes a switch for introducing a high impedance into the conductive loop when the switch is turned off. The apparatus also includes a control circuit that controls the switch to be turned on when the conductive loop should be closed to stimulate the electrically excitable tissue for a therapeutic effect. The control circuit turns the switch off whenever the living organism enters an area having a significant level of external signal that may induce unwanted current in the conductive loop to limit the unwanted current. The living organism can manually initiate turning off the switch when the living organism is about to enter an area having such an external signal. Alternatively, such an external signal is sensed to turn the switch off automatically when such an external signal is sensed.

Claims

1. A method for limiting unwanted current, induced when the level of an external signal is greater than an external signal threshold level, in a conductive loop formed by a medical device implanted within a living organism having electrically excitable tissue, the method including the steps of:

A. closing said conductive loop when said medical device is stimulating said electrically excitable tissue for achieving a therapeutic effect if the level of said external signal is less than said external signal threshold level; and

B. opening said conductive loop by generating and maintaining a high impedance within said conductive loop whenever the level of said external signal is greater than said external signal threshold level,

wherein said living organism manually initiates said opening of said conductive loop when said living organism is about to enter an area where the level of said external signal is greater than said external signal threshold level.

2. A method for limiting unwanted current, induced when the level of an external signal is greater than an external signal threshold level, in a conductive loop formed by a medical device implanted within a living organism having electrically excitable tissue, said method including the steps of:

A. closing said conductive loop when said medical device is stimulating said electrically excitable tissue for achieving a therapeutic effect if the level of said external signal is less than said external signal threshold level;

B. opening said conductive loop by generating and maintaining a high impedance within said conductive loop whenever the level of said external signal is greater than said external signal threshold level,

wherein said living organism manually initiates said opening of said conductive loop when said living organism is about to enter an area where the level of said external signal is greater than said external signal threshold level; and

C. sensing said external signal to automatically perform step B, wherein said step C includes the step of sensing the level of said unwanted current induced in said conductive loop, wherein a significant level of said unwanted current in said conductive loop indicates that the level of said external signal is greater than said external signal threshold level.

3. A current limiting apparatus that is adapted to be operatively connected as part of a conductive loop formed by a medical device implanted within a living organism having electrically excitable tissue, said current limiting apparatus comprising:

a switch, adapted to be operatively connected within said conductive loop, that turns on to close said conductive loop and that turn off to open said conductive loop; and

means for controlling said switch to turn said switch on when said medical device is stimulating said electrically extitable tissue to achieve a therapeutic effect if the level of an external signal is less than an external signal threshold level, and to turn said switch off whenever the level of said external signal is greater than said external signal threshold level,

wherein said switch further comprises;

a first switch device, operatively connected within said conductive loop, that turns on when said means for controlling turns said switch on and that turns off when said means for controlling turns said switch off;

a second switch device, operatively connected within said conductive loop, that turns on when said means for controlling turns said switch on and that turns off when said means for controlling turns said switch off,

wherein the first switch device and the second switch device are operatively coupled in series such that the first switch device prevents parasitic current flow through said second switch device when the external signal causes voltage build-up to a positive polarity within the conductive loop, and such that said second switch device prevents parasitic current flow through said first switch device when the external signal causes voltage build-up to a negative polarity within the conductive loop; and

a control terminal, operatively coupled to the means for controlling, that receives a control signal sent by said living organism, wherein said living organism manually initiates turning off said switch by sending said control signal to said control terminal when said living organism is about to enter an area where the level of said external signal is greater than said external signal threshold level, and wherein said means for controlling turns said switch off when said control terminal receives said control signal sent by said living organism.

4. A current limiting apparatus that is adapted to be operatively connected as part of a conductive loop formed by a medical device implanted within a living organism having electrically excitable tissue, said current limiting apparatus comprising:

a switch, adapted to be operatively connected within said conductive loop, that turns on to close said conductive loop and that turns off to open said conductive loop;

means for controlling said switch to turn said switch on when said medical device is stimulating said electrically excitable tissue to achieve a therapeutic effect if the level of an external signal is less than an external signal threshold level, and to turn said switch off when the level of said external signal is greater than said external signal threshold level,

a control terminal, operatively coupled to the means for controlling, that receives a control signal sent by said living organism, wherein said living organism manually initiates turning off said switch by sending said control signal to said control terminal when said living organism is about to enter an area where the level of said external signal is greater than said external signal threshold level, and wherein said means for controlling turns said switch off when said control terminal receives said control signal sent by said living organism; and

an external signal sensor for sensing said external signal, wherein said means for controlling turns said switch off when said sensor senses that the level of said external signal is greater than said external signal threshold level, wherein said external signal sensor senses the level of said unwanted current induced in said conductive loop, wherein a significant level of said unwanted current in said conductive loop indicates that the level of said external signal is greater than said external signal threshold level.

5. A current limiting apparatus that is adapted to be operatively connected as part of a conductive loop formed by a medical device implanted within a living organism having eletrically excitable tissue, said current limiting apparatus comprising:

means for switching said conductive loop between being closed and being open; and

a control circuit, operatively connected to said means for switching, that controls said means for switching to close said conductive loop when said medical device is stimulating said electrically excitable tissue to achieve a therapeutic effect if the level of an external signal is less than an external signal threshold level, and the controls said means for switching to open said conductive loop whenever the level of said external signal is greater than said external signal threshold level

where said means for switching further comprises;

a first switch device, operatively connected within said conductive loop, that turns on when said control circuit closes said conductive loop and than turns off when said control circuit opens said conductive loop;

an

a second switch device, operatively connected within said conductive loop, that turns on when said control circuit closes said conductive loop and that turns off when said control circuit opens said conductive loop,

wherein the first switch device and the second switch device are operatively coupled in series that the first switch device prevents parasitic current flow through said second switch device when the external signal causes voltage build-up to a positive polarity within the conductive loop, and such that said second switch device prevents parasitic current flow through said first switch device when the external signal causes voltage build-up to a negative polarity within the conductive loop;

a control terminal, operatively coupled to the means for controlling, that receives a control signal sent by said living organism, wherein said living organism manually initiates opening said conductive loop by sending said control signal to said control terminal when said living organism is about to enter an area where the level of said external signal is greater than said external signal threshold level, and wherein said means for controlling turns said switch off when said control terminal receives said control signal sent by said living organism; and

means for sensing said external signal, wherein said control circuit controls said means for switching to open said conductive loop when said means for sensing senses that the level of said external signal is greater than the external signal threshold level.

6. A current limiting apparatus that is adapted to be operatively connected as part of a conductive loop formed by a medical device implanted within a living organism having electrically excitable tissue, said current limiting apparatus comprising:

means for switching said conductive loop between being closed and being open;

a control circuit, operatively connected to said means for switching, that controls said means for switching to close said conductive loop when said medical device is stimulating said electrically excitable tissue to achieve a therapeutic effect if the level of an external signal is less than an external signal threshold level, and that controls said means for switching to open said conductive loop whenever the level of said external signal is greater than said external signal threshold level,

a control terminal, operatively coupled to the means for controlling, that receives a control signal sent by said living organism, wherein said living organism manually initiates opening of said conductive loop by sending said control signal to said control terminal when said living organism is about to enter an area where the level of said external signal is greater than said external signal threshold level, and wherein said means for controlling turns said switch off when said control terminal receives said control signal sent by said living organism; and

means for sensing said external signal, wherein said control circuit controls said means for switching to open said conductive loop when said means for sensing senses that the level of said external signal is greater than the external signal threshold level.

7. A method for limiting unwanted current, induced when the level of a magnetic field generated by an external magnetic system is greater than a threshold level, in a conductive loop formed by a medical device implanted within a living organism having electrically excitable tissue, the method including the steps of:

A. detecting the level of said magnetic field when said living organism is substantially near the external magnetic system;

B. closing said conductive loop when said medical device is stimulating said electrically excitable tissue for achieving a therapeutic effect if the level of said magnetic field that is detected is less than said threshold level; and

C. opening said conductive loop by generating and maintaining a high impedance within said conductive loop whenever the level of said magnetic field that is detected is greater than said threshold level.

8. A current limiting apparatus that is adapted to be operatively connected as part of a conductive loop formed by a medical device implanted within a living organism having electrically excitable tissue, said current limiting apparatus comprising:

a sensor for detecting the level of a magnetic field generated by an external magnetic system;

a switch, adapted to be operatively connected within said conductive loop, that turns on to close said conductive loop and that turns off to open said conductive loop; and

a control circuit, operatively coupled to the sensor and the switch, for controlling said switch to turn said switch on when said medical device is stimulating said electrically excitable tissue to achieve a therapeutic effect if the level of the magnetic field that is detected by the sensor is less than a threshold level, and to turn said switch off whenever the level of the magnetic field that is detected by the sensor is greater than said threshold level.