Nerve proximity and status detection system and method

• US 20030045808A1
• Filed: 10/16/2002
• Published: 03/06/2003
• Est. Priority Date: 11/24/1999
• Status: Active Grant

• Current Assignee: Nuvasive Incorporated
• Original Assignee: Nuvasive Incorporated
• Inventors: Marino, James F., Kaula, Norbert F., Blewett, Jeffrey J.
• Granted Patent: US 7,177,677 B2
• Time in Patent Office: Days
• US Class Current: 600/546
• CPC Class Codes: A61B 2017/00039 Electric or electromagnetic phenomena other than conductivity, e.g. capacity, inductivity, Hall effect
• CPC Class Codes: A61B 5/24 Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
• CPC Class Codes: A61B 5/296 for electromyography [EMG]
• CPC Class Codes: A61B 5/389 Electromyography [EMG]
• CPC Class Codes: A61B 5/4893 Nerves

Abstract

A method and system is disclosed for detecting proximity of a nerve to a proximity electrode and status of nerve. The method of detecting the proximity of the nerve to the proximity electrode applies a first electrical signal with multiple current levels to a calibration electrode. The method applies a second electrical signal with multiple current levels to the proximity electrode. Based on the response of the nerve to the first and second electrical signals, the method determines the proximity of the proximity electrode to the nerve. The method determines the status of the nerve by applying the first electrical signal with multiple signal levels to the calibration electrode.

Claims

1. A method of determining nerve status comprising the steps of:

(a) applying an electrical signal having a plurality of predetermined current levels to a conductive element located near the nerve;

(b) measuring the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels; and

(c) determining the nerve status based on the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels.

2. The method of claim 1, wherein step c) includes:

(a) mapping the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels for a fixed latency; and

(b) determining the nerve status based on the mapping of the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels for the fixed latency.

3. The method of claim 2, wherein step a) includes:

(a) placing a conductive element near the nerve; and

(b) applying an electrical signal having a plurality of predetermined current levels to the conductive element.

4. The method of claim 2, wherein each response is an EMG.

5. The method of claim 2, wherein each response is an EMG measured at a muscle physiologically coupled to the nerve.

6. The method of claim 2, further comprising the step of determining the fixed latency as a function of peaks in each response of the nerve to the applied electrical signal for the plurality of predetermined current levels.

7. The method of claim 2, wherein the fixed latency is selected by performing the steps of:

(a) determining the peaks in the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels; and

(b) selecting the latency having the largest number of peaks located thereabout.

8. The method of claim 2, wherein the fixed latency is selected by performing the steps of:

(a) determining the peaks in the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels;

(b) determining the number of peaks located about each latency having a peak located thereabout; and

(c) selecting the latency having the largest number of peaks located thereabout.

9. The method of claim 2, wherein the fixed latency is selected by performing the steps of:

(a) determining the peaks in the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels;

(b) determining the ratio of the peak level to corresponding current level for each peak;

(c) determining the sum of the ratio of peak level to current level for peaks located about each latency having a peak located thereabout; and

(d) selecting the latency having the largest sum of ratios.

10. The method of claim 9, wherein each response is an EMG.

11. The method of claim 9, wherein each response is an EMG measured at a muscle physiologically coupled to the nerve.

63. The apparatus for determining proximity of a nerve to a second conductive element of claim 64, wherein the second fixed latency is equal to the first fixed latency.

64. The method of claim 3, wherein step a) includes placing a conductive element in the epidural space above the dura of the spinal column in which the nerve is located.

12. An article of manufacture for use in determining nerve status, the article of manufacture comprising computer readable storage media including program logic embedded therein that causes control circuitry to perform the steps of:

(a) applying an electrical signal having a plurality of predetermined current levels to a conductive element located near the nerve;

(b) measuring the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels; and

(c) determining the nerve status based on the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels.

13. The article of manufacture for use in determining nerve status of claim 12, wherein step c) includes:

(a) mapping the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels for a fixed latency; and

(b) determining the nerve status based on the mapping of the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels for the fixed latency.

14. The article of manufacture for use in determining nerve status of claim 13, wherein each response is an EMG.

15. The article of manufacture for use in determining nerve status of claim 13, wherein each response is an EMG measured at a muscle physiologically coupled to the nerve.

16. The article of manufacture for use in determining nerve status of claim 13, further performing the step of determining the fixed latency as a function of peaks in each response of the nerve to the applied electrical signal for the plurality of predetermined current levels.

17. The article of manufacture for use in determining nerve status of claim 13, wherein the fixed latency is selected by performing the steps of:

(a) determining the peaks in the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels; and

(b) selecting the latency having the largest number of peaks located thereabout.

18. The article of manufacture for use in determining nerve status of claim 13, wherein the fixed latency is selected by performing the steps of:

(a) determining the peaks in the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels;

(b) determining the number of peaks located about each latency having a peak located thereabout; and

(c) selecting the latency having the largest number of peaks located thereabout.

19. The article of manufacture for use in determining nerve status of claim 13, wherein the fixed latency is selected by performing the steps of:

(a) determining the peaks in the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels;

(b) determining the ratio of the peak level to corresponding current level for each peak;

(c) determining the sum of the ratio of peak level to current level for peaks located about each latency having a peak located thereabout; and

(d) selecting the latency having the largest sum of ratios.

20. An apparatus for determining nerve status, the apparatus comprising:

(a) means for applying an electrical signal having a plurality of predetermined current levels to a conductive element located near the nerve;

(b) means for measuring the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels; and

(c) means for determining the nerve status based on the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels.

23. The apparatus of claim 23, wherein each response is an EMG measured at a muscle physiologically coupled to the nerve.

21. The apparatus of claim 22, wherein the means for determining the nerve status based on the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels includes:

(a) means for mapping the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels for a fixed latency; and

(b) means for determining the nerve status based on the mapping of the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels for the fixed latency.

22. The apparatus of claim 23, wherein each response is an EMG.

24. The apparatus of claim 23, further including means for determining the fixed latency as a function of peaks in each response of the nerve to the applied electrical signal for the plurality of predetermined current levels.

25. The apparatus of claim 23, further comprising:

(a) means for determining the peaks in the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels; and

(b) means for selecting the latency having the largest number of peaks located thereabout as the fixed latency.

26. The apparatus of claim 23, further comprising:

(a) means for determining the peaks in the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels;

(b) means for determining the number of peaks located about each latency having a peak located thereabout; and

(c) means for selecting the latency having the largest number of peaks located thereabout as the fixed latency.

27. The apparatus of claim 23, further comprising:

(a) means for determining the peaks in the responses of the nerve to the applied electrical signal for the plurality of predetermined current levels;

(b) means for determining the ratio of the peak level to corresponding current level for each peak;

(c) means for determining the sum of the ratio of peak level to current level for peaks located about each latency having a peak located thereabout; and

(d) means for selecting the latency having the largest sum of ratios as the fixed latency.

29. The apparatus of claim 29, wherein each response is an EMG measured at a muscle physiologically coupled to the nerve.

28. The apparatus of claim 29, wherein each response is an EMG.

30. A method of determining proximity of a nerve to a second conductive element comprising the steps of:

(a) applying a first electrical signal having a plurality of predetermined current levels to a first conductive element located near the nerve;

(b) measuring the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels;

(c) applying a second electrical signal having the plurality of predetermined current levels to the second conductive element;

(d) measuring the responses of the nerve to the second applied electrical signal for the plurality of predetermined current levels; and

(e) determining the nerve proximity to the second conductive element based on the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels and the responses of the nerve to the second applied electrical signal for the plurality of predetermined current levels.

33. The method of claim 33, wherein each response is an EMG.

31. The method of claim 32, wherein step e) includes:

(a) mapping the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels for a first fixed latency;

(b) mapping of the responses of the nerve to the second applied electrical signal for the plurality of predetermined current levels for a second fixed latency and

(c) determining the nerve proximity to the second conductive element based on the mapping of the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels for the first fixed latency and the mapping of the responses of the nerve to the second applied electrical signal for the plurality of predetermined current levels for the second fixed latency.

32. The method of claim 33, wherein step a) includes:

(a) placing a first conductive element near the nerve; and

(b) applying a first electrical signal having a plurality of predetermined current levels to the first conductive element.

34. The method of claim 33, wherein each response is an EMG measured at a muscle physiologically coupled to the nerve.

35. The method of claim 33, further comprising the step of determining the first fixed latency as a function of peaks in each response of the nerve to the first applied electrical signal for the plurality of predetermined current levels.

36. The method of claim 33, wherein the first fixed latency is selected by performing the steps of:

(a) determining the peaks in the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels; and

(b) selecting the latency having the largest number of peaks located thereabout as the first fixed latency.

37. The method of claim 33, wherein the first fixed latency is selected by performing the steps of:

(a) determining the peaks in the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels;

(b) determining the number of peaks located about each latency having a peak located thereabout; and

(c) selecting the latency having the largest number of peaks located thereabout as the first fixed latency.

38. The method of claim 33, wherein the first fixed latency is selected by performing the steps of:

(a) determining the peaks in the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels;

(b) determining the ratio of the peak level to corresponding current level for each peak;

(c) determining the sum of the ratio of peak level to current level for peaks located about each latency having a peak located thereabout; and

(d) selecting the latency having the largest sum of ratios as the first fixed latency.

40. The method of claim 40, wherein each response is an EMG measured at a muscle physiologically coupled to the nerve.

39. The method of claim 40, wherein each response is an EMG.

42. An article of manufacture for use in determining proximity of a nerve to a second conductive element, the article of manufacture comprising computer readable storage media including program logic embedded therein that causes control circuitry to perform the steps of:

(a) applying a first electrical signal having a plurality of predetermined current levels to a first conductive element located near the nerve;

(b) measuring the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels;

(c) applying a second electrical signal having the plurality of predetermined current levels to the second conductive element;

(d) measuring the responses of the nerve to the second applied electrical signal for the plurality of predetermined current levels; and

(e) determining the nerve proximity to the second conductive element based on the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels and the responses of the nerve to the second applied electrical signal for the plurality of predetermined current levels.

41. The method of claim 42, wherein the second fixed latency is equal to the first fixed latency.

45. The article of manufacture for use in determining proximity of a nerve to a second conductive element of claim 45, wherein each response is an EMG measured at a muscle physiologically coupled to the nerve.

43. The article of manufacture for use in determining proximity of a nerve to a second conductive element of claim 44, wherein step e) includes:

(a) mapping the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels for a first fixed latency;

(b) mapping the responses of the nerve to the second applied electrical signal for the plurality of predetermined current levels for a second fixed latency and

(c) determining the nerve proximity to the second conductive element based on the mapping of the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels for the first fixed latency and the mapping of the responses of the nerve to the second applied electrical signal for the plurality of predetermined current levels for the second fixed latency.

44. The article of manufacture for use in determining proximity of a nerve to a second conductive element of claim 45, wherein each response is an EMG.

46. The article of manufacture for use in determining proximity of a nerve to a second conductive element of claim 45, further comprising the step of determining the first fixed latency as a function of peaks in each response of the nerve to the first applied electrical signal for the plurality of predetermined current levels.

47. The article of manufacture for use in determining proximity of a nerve to a second conductive element of claim 45, wherein the first fixed latency is selected by performing the steps of:

(a) determining the peaks in the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels; and

(b) selecting the latency having the largest number of peaks located thereabout as the first fixed latency.

48. The article of manufacture for use in determining proximity of a nerve to a second conductive element of claim 45, wherein the first fixed latency is selected by performing the steps of:

(a) determining the peaks in the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels;

(b) determining the number of peaks located about each latency having a peak located thereabout; and

(c) selecting the latency having the largest number of peaks located thereabout as the first fixed latency.

49. The article of manufacture for use in determining proximity of a nerve to a second conductive element of claim 45, wherein the first fixed latency is selected by performing the steps of:

(a) determining the peaks in the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels;

(b) determining the ratio of the peak level to corresponding current level for each peak;

(c) determining the sum of the ratio of peak level to current level for peaks located about each latency having a peak located thereabout; and

(d) selecting the latency having the largest sum of ratios as the first fixed latency.

51. The article of manufacture for use in determining proximity of a nerve to a second conductive element of claim 51, wherein each response is an EMG measured at a muscle physiologically coupled to the nerve.

50. The article of manufacture for use in determining proximity of a nerve to a second conductive element of claim 51, wherein each response is an EMG.

53. An apparatus for determining proximity of a nerve to a second conductive element, the apparatus comprising:

(a) means for applying a first electrical signal having a plurality of predetermined current levels to a first conductive element located near the nerve;

(b) means for measuring the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels;

(c) means for applying a second electrical signal having the plurality of predetermined current levels to the second conductive element;

(d) means for measuring the responses of the nerve to the second applied electrical signal for the plurality of predetermined current levels; and

(e) means for determining the nerve proximity to the second conductive element based on the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels and the responses of the nerve to the second applied electrical signal for the plurality of predetermined current levels.

52. The article of manufacture for use in determining proximity of a nerve to a second conductive element of claim 53, wherein the second fixed latency is equal to the first fixed latency.

56. The apparatus for determining proximity of a nerve to a second conductive element of claim 56, wherein each response is an EMG measured at a muscle physiologically coupled to the nerve.

54. The apparatus for determining proximity of a nerve to a second conductive element of claim 55, wherein the means for determining the nerve proximity to the second conductive element includes:

(a) means for mapping the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels for a first fixed latency;

(b) means for mapping the responses of the nerve to the second applied electrical signal for the plurality of predetermined current levels for a second fixed latency and

(c) means for determining the nerve proximity to the second conductive element based on the mapping of the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels for the first fixed latency and the mapping of the responses of the nerve to the second applied electrical signal for the plurality of predetermined current levels for the second fixed latency.

55. The apparatus for determining proximity of a nerve to a second conductive element of claim 56, wherein each response is an EMG.

57. The apparatus for determining proximity of a nerve to a second conductive element of claim 56, further comprising means for determining the first fixed latency as a function of peaks in each response of the nerve to the first applied electrical signal for the plurality of predetermined current levels.

58. The apparatus for determining proximity of a nerve to a second conductive element of claim 56, further comprising:

(a) means for determining the peaks in the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels; and

(b) means for selecting the latency having the largest number of peaks located thereabout as the first fixed latency.

59. The apparatus for determining proximity of a nerve to a second conductive element of claim 56, further comprising:

(a) means for determining the peaks in the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels;

(b) means for determining the number of peaks located about each latency having a peak located thereabout; and

(c) means for selecting the latency having the largest number of peaks located thereabout as the first fixed latency.

60. The apparatus for determining proximity of a nerve to a second conductive element of claim 56, further comprising:

(a) means for determining the peaks in the responses of the nerve to the first applied electrical signal for the plurality of predetermined current levels;

(b) means for determining the ratio of the peak level to corresponding current level for each peak;

(c) means for determining the sum of the ratio of peak level to current level for peaks located about each latency having a peak located thereabout; and

(d) means for selecting the latency having the largest sum of ratios as the first fixed latency.

62. The apparatus for determining proximity of a nerve to a second conductive element of claim 62, wherein each response is an EMG measured at a muscle physiologically coupled to the nerve.

61. The apparatus for determining proximity of a nerve to a second conductive element of claim 62, wherein each response is an EMG.