Method and apparatus for testing and measuring current perception threshold and motor nerve junction performance

• US 5,797,854 A
• Filed: 08/01/1995
• Issued: 08/25/1998
• Est. Priority Date: 08/01/1995
• Status: Expired due to Term

• Current Assignee: James L. Hedgecock
• Original Assignee: James L. Hedgecock
• Inventors: Hedgecock, James L.
• Primary Examiner(s): Hindenburg, Max
• Assistant Examiner(s): WINGOOD, PAMELA LYNN
• Application Number:
  US08/509,952
• Time in Patent Office: 1,120 Days
• Field of Search: 128/741, 128/731-4, 128/422, 604/20
• US Class Current: 600/554
• CPC Class Codes: A61B 5/24 Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
• CPC Class Codes: A61N 1/0502 Skin piercing electrodes
• CPC Class Codes: A61N 1/36034 specified by the stimulation parameters

Abstract

A system is provided for stimulating and measuring performance of nerves which utilizes a novel system of electrodes. A large moistened absorbent pad-type electrode is used to provide one electrical contact with the body. A small moistened absorbent pad-type electrode in a handheld pencil-like configuration is used to provide a second, more targeted electrical contact with the body. By placing the large electrode along or near the spine, the pencil-like electrode may be used to excite and measure nerves on opposite sides of the body. In this manner, the electrical contact made by the large electrode is a constant during the measurement, both as to distance from the tested nerve site, and as to electrical conduction to the body. This arrangement provides more reliable and repeatable measurements. It also avoids patient discomfort associated with needle-like probes, tape-on probes, and other probes which involve discomfort. In another aspect of the invention, a galvanic skin response measurement system is incorporated into the nerve performance measurement system and is used to determine threshold nerve sensing events, rather than relying upon oral input from the patient. In this way, actual events are detected which do not rely for their accuracy upon the truthfulness of the patient. In another aspect of the present invention, the 2000 Hz signal used to stimulate the type A-Beta nerves is amplitude modulated with an adjustable sine wave signal in the range of about 5 Hz to about 700 Hz in order to obtain increased patient sensitivity to the combined signal.

Claims

1. An apparatus for testing and measuring current perception threshold in selected nerve fiber groups of a patient, said apparatus comprising:

a waveform generator for generating a current-limited electrical signal;

means for varying an electrical current magnitude of said electrical signal among a plurality of values;

a single first electrode comprising an absorbent pad of at least about 4 square inches in surface area and capable of being moistened to enhance electrical contact with the skin of the patient;

a single second electrode adapted to be placed at a distance from said first electrode;

the apparatus adapted to cause said electrical signal to pass through said first electrode, the selected nerve fiber groups of the patient, and said second electrode;

threshold detection means for detecting a threshold current magnitude at which the selected nerve fiber groups of the patient first perceive said electrical signal; and

means for displaying an indication of said electrical current magnitude corresponding to the current perception threshold.

2. An apparatus according to claim 1 wherein said second electrode is a handheld electrode including a fibrous tip which may be moistened to enhance electrical contact with the skin of the patient.

3. An apparatus according to claim 1 wherein said electrical signal is a sine wave.

4. An apparatus according to claim 1 wherein said electrical signal is a sine wave amplitude modulated by another sine wave.

5. An apparatus for testing and measuring current perception threshold in selected type A-Beta nerve fiber groups of a patient, said apparatus comprising:

a waveform generator for generating a repeating current-limited electrical signal of approximately 2000 Hz in frequency;

means for amplitude modulating said electrical signal with a modulating signal having a frequency adjustable in the range of about 5 Hz to about 700 Hz;

means for varying an electrical current magnitude of said electrical signal among a plurality of values;

a single first electrode;

a single second electrode;

the apparatus adapted to cause said electrical signal to pass through said first electrode, the selected type A-Beta nerve fiber groups of the patient, and said second electrode;

threshold detection means for detecting a threshold current magnitude at which the selected type A-Beta nerve fiber groups of the patient first perceive said electrical signal; and

means for displaying an indication of said electrical current magnitude corresponding to the current perception threshold.

6. An apparatus according to claim 5 wherein said modulating signal is a sine wave.

7. An apparatus according to claim 5 wherein said first electrode is an absorbent pad of at least about 4 square inches in surface area.

8. An apparatus according to claim 6 wherein said first electrode is an absorbent pad of at least about 4 square inches in surface area.

9. An apparatus according to claim 7 wherein said second electrode is a handheld electrode including a fibrous tip which may be moistened to enhance electrical contact with the skin of the patient.

10. An apparatus according to claim 8 wherein said second electrode is a handheld electrode including a fibrous tip which may be moistened to enhance electrical contact with the skin of the patient.

11. An apparatus for testing and measuring current perception threshold in selected nerve fiber groups of a patient, said apparatus comprising:

a waveform generator for generating a repeating current-limited electrical signal having a selected frequency in the range of about 5 Hz to about 2000 Hz;

means for varying an electrical current magnitude of said electrical signal among a plurality of values;

a single first and a single second current perception threshold electrode;

a first and a second separate galvanic skin response electrode;

the apparatus adapted to cause said electrical signal to pass through said first current perception threshold electrode, the selected nerve fiber groups of the patient, and said second current perception threshold electrode;

threshold detection means for detecting a threshold current magnitude at which the selected nerve fiber groups of the patient first perceive said electric signal, said threshold detection means responsive to a change in patient skin resistance measured between said first and second galvanic skin response electrodes; and

means for displaying an indication of said electrical current magnitude corresponding to the current perception threshold.

13. An apparatus according to claim 11 wherein said second electrode is a handheld electrode including a fibrous tip which may be moistened to enhance electrical contact with the skin of the patient.

15. An apparatus according to claim 11 further comprising means for amplitude modulating said electrical signal with a modulating signal having a frequency adjustable in the range of about 5 Hz to about 700 Hz.

12. An apparatus for testing and measuring current perception threshold in selected nerve fiber groups of a patient, said apparatus comprising:

a waveform generator for generating a repeating current-limited electrical signal;

means for varying an electrical current magnitude of said electrical signal among a plurality of values;

a single first current perception threshold electrode comprising an absorbent pad of at least 4 square inches in surface area;

a single second current perception threshold electrode adapted to be placed at a distance from said first current perception threshold electrode;

a first and a second galvanic skin response electrode separate from said first and second current perception threshold electrodes;

the apparatus adapted to cause said electrical signal to pass through said first current perception threshold electrode, the selected nerve fiber groups of the patient, and said second current perception threshold electrode;

threshold detection means for detecting a threshold current magnitude at which the selected nerve fiber groups of the patient first perceive said electric signal, said threshold detection means responsive to a change in patient skin resistance measured between said first and second galvanic skin response electrodes; and

means for displaying an indication of said electrical current magnitude corresponding to the current perception threshold.

14. An apparatus according to claim 12 wherein said second electrode is a handheld electrode including a fibrous tip which may be moistened to enhance electrical contact with the skin of the patient.

16. An apparatus according to claim 12 further comprising means for amplitude modulating said electrical signal with a modulating signal having a frequency adjustable in the range of about 5 Hz to about 700 Hz.

17. A method for measuring a current perception threshold in a selected nerve fiber group of a patient, said method comprising:

(a) applying a single first electrode comprising an absorbent pad of at least about 4 square inches in surface area to the back of the patient along the patient'"'"'s spine;

(b) moistening said first electrode;

(c) applying a single second electrode to a first selected point on the skin of the patient, said point selected so as to measure the selected nerve fiber group;

(d) generating a repeating current-limited electrical signal with a waveform generator;

(e) causing said electrical signal to pass through said first electrode, the selected nerve fiber group, and said second electrode;

(f) adjusting the current of said electrical signal among a plurality of values and detecting a current magnitude at which the selected nerve fiber group of the patient first perceives said electrical signal;

(g) displaying said current magnitude at which the selected nerve fiber group of the patient first perceives said electrical signal.

20. A method according to claim 17 further comprising the steps of:

(h) applying said single second electrode to a second selected point on the skin of the patient, said second selected point selected so as to be at an opposite point of the patient'"'"'s body from said first selected point, so as to measure a nerve fiber group opposite said selected nerve fiber group;

(i) generating a repeating current-limited electrical signal with a waveform generator;

(j) causing said electrical signal to pass through said first electrode, the opposite selected nerve fiber group, and said second electrode;

(k) adjusting the current of said electrical signal among a plurality of values and detecting a current magnitude at which the opposite selected nerve fiber group of the patient first perceives said electrical signal; and

(l) displaying said current magnitude at which the opposite selected nerve fiber group of the patient first perceives said electrical signal.

18. A method for measuring a current perception threshold in a selected type A-Beta nerve fiber group of a patient, said method comprising:

(a) applying a single first electrode comprising an absorbent pad of at least about 4 square inches in surface area to the back of the patient along the patient'"'"'s spine;

(b) moistening said first electrode;

(c) applying a single second electrode to a first selected point on the skin of the patient, said point selected so as to measure the selected type A-Beta nerve fiber group;

(d) generating a repeating current-limited electrical signal with a waveform generator having a frequency of approximately 2000 Hz;

(e) amplitude modulating said electrical signal with a modulating signal having a frequency adjustable in the range of about 5 Hz to about 700 Hz;

(f) causing said electrical signal to pass through said first electrode, the selected type A-Beta nerve fiber group, and said second electrode;

(g) adjusting the current of said electrical signal among a plurality of values and detecting a current magnitude at which the selected nerve fiber group of the patient first perceives said electrical signal;

(h) displaying said current magnitude at which the selected nerve fiber group of the patient first perceives said electrical signal.

21. A method according to claim 18 further comprising the steps of:

(i) applying said single second electrode to a second selected point on the skin of the patient, said second selected point selected so as to be at an opposite point of the body from said first selected point, so as to measure a type A-Beta nerve fiber group opposite said selected type A-Beta nerve fiber group;

(j) generating a repeating current-limited electrical signal with a waveform generator having a frequency of approximately 2000 Hz;

(k) amplitude modulating said electrical signal with a modulating signal having a frequency adjustable in the range of about 5 Hz to about 700 Hz;

(l) causing said electrical signal to pass through said first electrode, the opposite selected type A-Beta nerve fiber group, and said second electrode;

(m) adjusting the current of said electrical signal among a plurality of values and detecting a current magnitude at which the opposite selected nerve fiber group of the patient first perceives said electrical signal; and

(n) displaying said current magnitude at which the opposite selected nerve fiber group of the patient first perceives said electrical signal.

19. A method for measuring a current perception threshold in a selected nerve fiber group of a patient, said method comprising:

(a) applying a single first electrode to the patient;

(b) applying a single second electrode to a first selected point on the skin of the patient, said point selected so as to measure the selected nerve fiber group;

(c) generating a repeating current-limited electrical signal with a waveform generator having a selected frequency in the range of about 5 Hz to about 2000 Hz;

(d) causing said electrical signal to pass through said first electrode, the selected nerve fiber group, and said second electrode;

(e) applying a separate pair of galvanic skin resistance electrodes to the skin of the patient and monitoring skin resistance values measured by said resistance electrodes;

(f) adjusting the current of said electrical signal among a plurality of values and detecting a current magnitude at which the selected nerve fiber group of the patient first achieves perception of said electrical signal, said perception determined to have occurred at a point in time when said skin resistance values change by more than a predetermined amount; and

(g) displaying said current magnitude at which the selected nerve fiber group of the patient first perceives said electrical signal.

22. A method according to claim 19 wherein said first electrode is applied to the back of the patient along the patient'"'"'s spine, said method further comprising the steps of:

(h) applying said single second electrode to a second selected point on the skin of the patient, said second selected point selected so as to be at an opposite point of the body from said first selected point, said second point selected so as to measure current perception threshold in a nerve fiber group opposite said selected nerve fiber group;

(i) generating a repeating current-limited electrical signal with a waveform generator having a selected frequency in the range of about 5 Hz to about 2000 Hz;

(j) causing said electrical signal to pass through said first electrode, the opposite selected nerve fiber group, and said second electrode;

(k) applying a pair of galvanic skin resistance electrodes to the skin of the patient and monitoring skin resistance values measured by said resistance electrodes;

(l) adjusting the current of said electrical signal among a plurality of values and detecting a current magnitude at which the opposite selected nerve fiber group of the patient first achieves perception of said electrical signal, said perception determined to have occurred at a point in time when said skin resistance values change by more than a predetermined amount; and

(m) displaying said current magnitude at which the opposite selected nerve fiber group of the patient first perceives said electrical signal.