DETECTING CUTANEOUS ELECTRODE PEELING USING ELECTRODE-SKIN IMPEDANCE

• US 20140296934A1
• Filed: 03/31/2014
• Published: 10/02/2014
• Est. Priority Date: 03/29/2013
• Status: Active Grant

• Current Assignee: Neurometrix, Inc.
• Original Assignee: Neurometrix, Inc.
• Inventors: Gozani, Shai, Kong, Xuan, Aguirre, Andres, Ferree, Tom
• Granted Patent: US 9,474,898 B2
• Time in Patent Office: Days
• US Class Current: 607/46
• CPC Class Codes: A61B 2560/0276 Determining malfunction
• CPC Class Codes: A61B 5/0531 Measuring skin impedance
• CPC Class Codes: A61B 5/486 Bio-feedback A61B5/375 takes precedence
• CPC Class Codes: A61B 5/6828 Leg
• CPC Class Codes: A61N 1/0456 Specially adapted for transcutaneous electrical nerve stimulation [TENS]
• CPC Class Codes: A61N 1/0492 Patch electrodes A61N1/0412, A61N1/0428 take precedence
• CPC Class Codes: A61N 1/36021 for treatment of pain
• CPC Class Codes: A61N 1/3603 Control systems

Abstract

Apparatus for transcutaneous electrical nerve stimulation in a user, the apparatus comprising:

• • stimulation means for electrically stimulating at least one nerve;
  • an electrode array connectable to said stimulation means, said electrode array comprising a plurality of electrodes for electrical stimulation of the at least one nerve, said electrodes having a pre-formed geometry and known electrode-skin contact area size when in complete contact with the user'"'"'s skin;
  • monitoring means electrically connected to said stimulation means for monitoring the impedance of the electrical stimulation through said electrode array; and
  • analysis means for analyzing said impedance to estimate a change in the electrode-skin contact area.

Claims

1. Apparatus for transcutaneous electrical nerve stimulation in a user, the apparatus comprising:

stimulation means for electrically stimulating at least one nerve;

an electrode array connectable to said stimulation means, said electrode array comprising a plurality of electrodes for electrical stimulation of the at least one nerve, said electrodes having a pre-formed geometry and known electrode-skin contact area size when in complete contact with the user'"'"'s skin;

monitoring means electrically connected to said stimulation means for monitoring the impedance of the electrical stimulation through said electrode array; and

analysis means for analyzing said impedance to estimate a change in the electrode-skin contact area.

2. Apparatus according to claim 1 wherein said monitoring of the impedance is accomplished with the same electrical stimulation as that used to stimulate said at least one nerve.

3. Apparatus according to claim 1 wherein said monitoring of the impedance is accomplished with different electrical stimulation than that used to stimulate said at least one nerve.

4. Apparatus according to claim 3 wherein the electrical stimulation used for monitoring of the impedance has an intensity that is below the electrotactile sensation threshold of the user.

5. Apparatus according to claim 1 wherein said impedance is defined as the anode-cathode voltage difference divided by the stimulation current of the electrical stimulation of said monitoring means at a particular time in the electrical stimulation.

6. Apparatus according to claim 1 wherein a history of the electrode-skin impedance values is stored by said monitoring means.

7. Apparatus according to claim 1 wherein said stimulation means alters the electrical stimulation of said stimulation means when said analysis means determines that the monitored electrode-skin impedance value has changed significantly.

8. Apparatus according to claim 7 wherein the change in the impedance value at a given time is quantified by an impedance ratio between the impedance value at that time and a baseline impedance value.

9. Apparatus according to claim 8 wherein the baseline impedance value is the first available impedance value from the impedance history.

10. Apparatus according to claim 8 wherein the baseline impedance value is the minimum among all available impedance values.

11. Apparatus according to claim 7 wherein said significant change is defined as that where the impedance ratio exceeds an impedance ratio threshold.

12. Apparatus according to claim 7 wherein the alteration to the electrical stimulation is to terminate stimulation.

13. Apparatus according to claim 7 wherein the alteration to the electrical stimulation is to inversely scale the electrical stimulation intensity by the impedance ratio.

14. Apparatus according to claim 1 wherein the geometry and size of said electrodes can be identified by said monitoring means.

15. Apparatus according to claim 11 wherein the impedance ratio threshold depends upon the identified electrode geometry and size.

16. A method for monitoring electrode-skin contact area while delivering transcutaneous electrical nerve stimulation to at least one nerve of a user through an electrode array comprising a plurality of electrodes, wherein each electrode has a known geometry and size, the method comprising the steps of:

applying the electrode array to the surface of the user'"'"'s skin to allow a complete contact between the plurality of electrodes and the skin;

electrically stimulating said at least one nerve of the user with an electrical stimulator connected to the electrode array;

monitoring the impedance of the electrode-skin interface; and

analyzing the monitored impedance to estimate electrode-skin contact area size.

17. A method according to claim 16 wherein monitoring of the impedance is accomplished with the same electrical stimulation as that used to stimulate the at least one nerve of the user.

18. A method according to claim 16 wherein monitoring of the impedance is accomplished with different electrical stimulation than that used to stimulate the at least one nerve.

19. A method according to claim 18 wherein the electrical stimulation used for monitoring of the impedance has an intensity that is below the electrotactile sensation threshold of the user.

20. A method according to claim 18 wherein the electrical stimulation used for monitoring of the impedance is continuously active regardless the status of the electrical stimulation used to stimulate the at least one nerve.

21. A method according to claim 16 wherein the impedance is monitored by dividing the anode-cathode voltage difference by the stimulation current of the electrical stimulation used for monitoring at a particular time in the electrical stimulation.

22. A method according to claim 16 wherein the impedance is derived by fitting the anode-cathode voltage difference curve using a parametric model of electrode-skin interface impedance.

23. A method according to claim 22 wherein the model is a capacitor-resistor network.

24. A method according to claim 16 wherein a history of monitored electrode-skin impedance values is stored for analysis.

25. A method according to claim 16 wherein the electrical stimulation applied to the at least one nerve is altered when the electrode-skin contact area size is estimated to be reduced significantly.

26. A method according to claim 25 wherein changes in the electrode-skin contact area size is quantified by an impedance ratio between a currently monitored impedance value and a baseline impedance value.

27. A method according to claim 26 wherein the baseline impedance value is the first available impedance value from the impedance history.

28. A method according to claim 26 wherein the baseline impedance value is a percentile of all available impedance values from the impedance history.

29. A method according to claim 28 wherein the percentile is zero-th percentile.

30. A method according to claim 25 wherein a significant reduction in electrode-skin contact area size is defined to occur when the impedance ratio exceeds an impedance ratio threshold.

31. A method according to claim 25 wherein the alteration to the electrical stimulation applied to the at least one nerve is to terminate stimulation.

32. A method according to claim 25 wherein the alteration to the electrical stimulation applied to the at least one nerve is to inversely scale the stimulation intensity by the impedance ratio.

33. A method according to claim 30 wherein the impedance ratio threshold depends upon the geometry and size of the electrodes in the electrode array.

34. A method according to claim 30 wherein the impedance ratio threshold is a function of the targeted minimum electrode-skin contact area expressed as a fraction of the total electrode-skin contact area created with a compete contact between the electrodes and skin of the user.

35. Apparatus for transcutaneous electrical nerve stimulation in a user, said apparatus comprising:

an electrode array comprising a plurality of electrodes, said plurality of electrodes having a pre-formed geometry and known electrode-skin contact area when said plurality of electrodes are in complete contact with the skin of a user;

stimulation means connectable to said electrode array for providing electrical stimulation to the skin of the user so as to stimulate at least one nerve of the user;

monitoring means electrically connectable to said electrode array for monitoring the electrode-skin impedance value; and

control means for controlling the electrical stimulation provided to the skin of the user when the monitoring means determines that the electrode-skin impedance value has changed by a predetermined value.

36. A method for applying transcutaneous electrical nerve stimulation to a user, said method comprising:

applying a stimulation current to a user through an anode having an electrode-skin interface and a cathode having an electrode-skin interface;

measuring (i) the stimulation current through, and (ii) the voltage difference between, the anode and the cathode so as to determine electrode-skin impedance; and

modifying the stimulation current when the electrode-skin impedance changes in a predetermined manner.