Impedance measurement for an implantable device

• US 20060025828A1
• Filed: 07/28/2004
• Published: 02/02/2006
• Est. Priority Date: 07/28/2004
• Status: Abandoned Application

• Current Assignee: LivaNova USA, Inc. (LivaNova Plc)
• Original Assignee: LivaNova USA, Inc. (LivaNova Plc)
• Inventors: Armstrong, Randolph K., Armstrong, Scott A.
• Application Number:
  US10/900,573
• Publication Number:
  US 20060025828A1
• Time in Patent Office: Days
• US Class Current: 607/28
• CPC Class Codes: A61N 1/3708 for power depletion
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables

Abstract

A method and an apparatus for determining an impedance experienced by a lead associated with the implantable device. A substantially constant current signal is provided through a first terminal and a second terminal of the lead. A voltage across the first and second terminals is measured. An impedance across the first and second terminals is determined based upon the constant current signal and the measured voltage.

Claims

1. A method for determining an impedance associated with a lead assembly in an implantable medical device, said lead assembly comprising a first terminal and a second terminal, said method comprising:

providing a controlled current signal through said first terminal and said second terminal;

measuring a voltage across said first and second terminals; and

determining the impedance across said first and second terminals based upon said constant current signal and said voltage.

2. The method of claim 1, wherein said controlled current is a substantially constant current.

3. The method of claim 2, wherein providing a substantially constant current signal comprises providing a current signal that is independent of the impedance across said lead terminals.

4. The method of claim 2, wherein measuring said voltage across said first and second terminals comprises measuring said voltage that results from said constant current signal.

5. The method of claim 2, wherein determining an impedance across said first and second terminals of said lead assembly further comprises dividing said measured voltage by the magnitude of said constant current signal.

6. The method of claim 2, wherein determining an impedance across said first and second terminals of said lead assembly comprises dividing said measured voltage by the magnitude of said constant current signal, and then subtracting an impedance associated with said first and second terminals.

7. The method of claim 2, wherein measuring said voltage across said first and second terminals comprises converting said voltage signal from analog to digital using an analog-to-digital converter.

8. The method of claim 2, further comprising calibrating said analog-to-digital converter using a known impedance and driving a known current signal across said known impedance to calibrate said analog-to-digital converter based upon a resultant theoretical voltage.

9. An implantable medical device, comprising:

an amplifier circuit for providing a substantially constant current signal through a first terminal and a second terminal of a lead assembly;

a voltage measurement unit to measure a voltage across said first and second terminals; and

an impedance measurement unit to determine an impedance between said first and second terminals based upon said constant current signal and said measured voltage.

10. The implantable medical device of claim 9, wherein said implantable medical device is a vagus nerve stimulator device.

11. The implantable medical device of claim 9, further comprising an analog-to-digital converter to convert said voltage from an analog signal to a digital signal for measurement.

12. The implantable medical device of claim 9, wherein said voltage measurement unit is adapted to measure the voltage resulting from an application of said constant current signal across said first and second terminals of said lead assembly.

13. The implantable medical device of claim 9, wherein said impedance measurement unit is adapted to divide the magnitude of said voltage by the magnitude of said constant current signal.

14. The implantable medical device of claim 9, wherein said impedance measurement unit is adapted to divide the magnitude of said voltage by the magnitude of said constant current signal and subtract an impedance value associated with said first and second terminals.

15. A system for measuring the impedance of a lead assembly in an implantable medical device, said lead assembly comprising first and second terminals, comprising:

an external device for performing remote communications with an implantable medical device;

an implantable medical device adapted to communicate with said external device and to deliver a stimulation signal to a patient via a lead assembly, said implantable device comprising;

an amplifier circuit for providing a substantially constant current signal through said first terminal and said second terminal of said lead assembly;

a voltage measurement unit to measure a voltage across said first and second terminals;

an impedance measurement unit to determine an impedance between said first and second terminals based upon said constant current signal and said voltage; and

a communications unit for providing said impedance determination to said external device.

16. The system of claim 15, wherein said implantable device is a vagus nerve stimulator.

17. The system of claim 15, wherein said communications unit is capable of providing wireless communications with said external device.

18. The system of claim 17, wherein said external device comprises a computer system capable of executing at least one of a communication program and a data acquisition program.

19. The system of claim 18, wherein said external device is capable of transmitting software code to said implantable device, and said implantable medical device is capable of receiving and executing said code.

20. The system of claim 15, wherein said implantable medical device further comprises an analog-to-digital converter to convert said voltage from an analog signal to a digital signal for measurement.

21. The system of claim 15, wherein said voltage measurement unit is adapted to measure the voltage that resulting from an application of said constant current signal across said first and second terminals of said lead assembly.

22. The system of claim 15, wherein said impedance measurement unit is adapted to divide said voltage by the magnitude of said constant current signal.

23. The system of claim 15, wherein said impedance measurement unit is adapted to divide said voltage by the magnitude of said constant current signal, and subtract an impedance value associated with said first and second terminals.

24. An apparatus for determining an impedance associated with a lead medical assembly of an implantable medical device, comprising:

means for providing a substantially constant current signal through a first terminal and a second terminal of said lead assembly; and

means for measuring a voltage across said first and second terminals; and

means for determining an impedance across said first and second terminals based upon said constant current signal and said measured voltage.

25. A computer readable program storage device encoded with instructions that, when executed by a computer, performs a method for determining an impedance associated with a lead assembly having first and second terminals and comprising a component of an implantable medical device, comprising:

providing a substantially constant current signal through said first terminal and said second terminal of said lead assembly;

measuring a voltage across said first and second terminals while said constant current is provided; and

determining an impedance across said first and second terminals based upon said constant current signal and said measured voltage.

26. The computer readable program storage device of claim 25, wherein providing a constant current signal comprises providing a current signal that is independent of the impedance across said first and second terminals of said lead assembly.

27. The computer readable program storage device of claim 25, wherein measuring said voltage across said first and second terminals comprises measuring said voltage resulting from said constant current signal.

28. The computer readable program storage device of claim 25, wherein determining an impedance across said first and second terminals comprises dividing said measured voltage by the magnitude of said constant current signal.

29. The computer readable program storage device of claim 25, wherein said lead assembly further comprises first and second lead wires coupled to tissue of a patient, and wherein said step of determining an impedance across said first and second terminals comprises dividing the magnitude of said voltage by the magnitude of said constant current signal, and subtracting an impedance associated with said first and second lead wires.

30. The computer readable program storage device of claim 25, wherein measuring said voltage across said first and second terminals further comprises converting said voltage signal from analog to digital using an analog-to-digital converter.

31. The computer readable program storage device of claim 25, further comprising calibrating said analog-to-digital converter using a known impedance and driving a known current signal across said known impedance to calibrate said analog-to-digital converter based upon a resultant theoretical voltage.