Control of FNS via pattern variations of response EMG

• US 5,016,635 A
• Filed: 11/29/1988
• Issued: 05/21/1991
• Est. Priority Date: 11/29/1988
• Status: Expired due to Fees

• Current Assignee: Sigmedics, Inc.
• Original Assignee: Sigmedics Incorporated of Delaware
• Inventors: Graupe, Daniel
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): Getzow, Scott M.
• Application Number:
  US07/277,323
• Time in Patent Office: 903 Days
• Field of Search: 128/421, 128/422, 128/423 R, 128/423 W, 128/733, 128/741, 128/419 S
• US Class Current: 607/49
• CPC Class Codes: A61B 5/389 Electromyography [EMG]
• CPC Class Codes: A61B 5/395 Details of stimulation, e.g. nerve stimulation to elicit EMG response
• CPC Class Codes: A61N 1/36003 of motor muscles, e.g. for walking assistance

Abstract

Paraplegic patients and cetain other paralyzed patients who suffer from an upper motor unit spinal cord injury and undergo FNS (Functional Neuromuscular Stimulation) experience muscle fatigue within a time span that is usually shorter than is normal, but have no sensation of this fatigue due to paralysis. When FNS is used functionally, as is its implied purpose, to stand and walk, the patients need the support of a walker or canes or elbow crutches, and are unable to manually adjust FNS levels or pulse widths to compensate for that fatigue, since the time for this adjustment is exactly when the patients cannot divert attention and hands to anything else. Under FNS, the stimulated muscles produce an EMG (electromyographic) signal at the stimulated site, in response to that stimulation. This response-EMG undergoes pattern changes with the progression of fatigue. The present invention employs pattern recognition of the response-EMG where pattern parameters are identified whose variation with time is a function of the progression of muscle fatigue. This time variation is employed to adjust FNS pulse width and/or pulse level to compensate for that fatigue in an automatic manner that does not require the patient'"'"'s attention. The present invention also provides for diagnostic uses of this pattern recognition, and for muscle contractions other than for standing or walking.

Claims

1. A functional neuromuscular stimulation system comprising:

FNS electrodes for coupling to the skin at the vicinity of a muscle to be stimulated;

FNS stimulation means for selectively outputting FNS stimulus signals coupled to said FNS electrodes;

Stimulus-Response-EMG electrodes for coupling in the vicinity of said muscle to be stimulated, for sensing Response-EMG signals responsive to said FNS stimulation means;

EMG pattern recognition means for recognition of fatigue patterns for selectively analyzing multiple Response-EMG signals and for selectively providing FNS control signals responsive to recognized deviations beyond a predefined threshhold level of change in patterns of said Response-EMG signals wherein said changes of said pattern over time are changes relative to an EMG reference pattern which is the pattern of the response EMG within a specified small time interval after initial application of the FNS stimuli, and after each successive readjustment of FNS stimuli wherein pattern recognition is in terms of measuring the point wise difference over a given fixed number of points in the Response-EMG voltage vs. time signals as obtained at the Response-EMG electrodes between their voltage values at discrete time points immediately after any adjustment of stimulus level vs. the corresponding value at any time later when fatigue may have started to take an effect, wherein the time scales are all with respect to the time instant of the initiation of each stimulus in a train of FNS stimuli, and wherein each point considered in the two patterns that are compared is the same distance from the time instant of initiation point for each pattern; and

,

FNS adjustment means for automatically adjusting the FNS stimulus signals responsive to the pattern recognition means responsive to changes over time in the EMG pattern as recognized by said EMG pattern recognition means, so as to prevent fatigue.

2. The system as in claim 1 wherein said FNS electrodes are further characterized as being of the type for coupling to the surface of the skin.

3. The system as in claim 1 wherein said FNS and EMG electrodes are further characterized as being of the type for implantation beneath the surface of the skin.

4. The system as in claim 1 wherein said EMG electrodes are further characterized as being of the type for coupling to the surface of the skin.

5. The system as in claim 1 wherein said EMG electrodes are further characterized as being of the type for implantation beneath the surface of the skin.

6. The system as in claim 1 wherein said adjustment means provides for adjustment of FNS signals by adjusting FNS stimuli pulse width.

7. The system as in claim 1 wherein said adjustment means provides for adjustment of FNS signals by adjusting FNS stimuli amplitudes.

8. The system as in claim 1 wherein pattern recognition is in terms of measuring said point wide difference and where a function of the absolute value of said point wide difference is summed up to comprise a function of area differences over a given fixed number of points in the Response-EMG voltage vs. time signals as obtained at the Response-EMG electrodes between their voltage values at discrete time points immediately after any adjustment of stimulus level vs. the corresponding value at any time later when fatigue may have started to take an effect, wherein the time scales are all with respect to the time instant of the initiation of each stimulus in a train of FNS stimuli, and wherein each point considered in the two patterns that are compared is the same distance from the time instant of initiation point for each pattern.

9. A method of functional neuromuscular stimulation comprising the steps of:

Electrically stimulating selected muscles;

Sensing Response-EMG signals from said stimulated muscles;

Repeatedly monitoring over time and analyzing the dynamic pattern of the Response-EMG signals;

Identifying a finite set of parameters associated with said pattern, wherein said finite set of parameters is determined in terms of a transfer function fit to the Response-EMG, where the Response-EMG is considered as an impulse response, such that the transfer function becomes the inverse Laplace transform calculated for that impulse response which is the Response-EMG pattern of EMG voltage vs. time, starting at the time instant at which the stimulus impulse is being applied by the stimulator;

Detecting when at least one of said parameters has a significant change beyond a predetermined minimum threshold value; and

Adjusting said electrical stimulation responsive to said detecting.

10. The method as in claim 9 wherein said finite set of parameters is determined by analysis of deviation of the Response-EMG pattern from its mean over time.

11. A functional neuromuscular stimulation system comprising:

means for selectively and adjustably electrically stimulating selected muscles;

means for sensing Response-EMG signals from said stimulated muscles;

means for repeatedly monitoring over time and analyzing the dynamic pattern of the Response-EMG signals;

means for identifying a finite set of parameters associated with said pattern wherein said finite set of parameters is determined in terms of a transfer function fit to the Response-EMG, where the Response-EMG is considered as an impulse response, such that the transfer function becomes the inverse Laplace transform calculated for that impulse response which is the Response-EMG pattern of EMG voltage vs. time, starting at the time instant at which the stimulus impulse is being applied by the stimulator;

means for detecting when at least one of said parameters has a significant change beyond a predetermined threshold minimum value; and

;

means for automatically modifying said electrical stimulation so as to prevent fatigue in said stimulated muscle, responsive to said means for detecting.

12. The system as in claim 11 wherein said electrical stimulation is comprised of a plurality of pulses having definable electrical characteristics of voltage level, duration and time spacing, wherein said means for modifying is further comprised of:

means for varying at least one of said electrical characteristics responsive to said means for detecting.

13. The system as in claim 11 wherein said means for identifying is further comprised of:

means for selecting a voltage versus time varying signal characteristic as a selected parameter of said Response-EMG signal, which characteristic changes in a detectable manner indicating the propensity for muscle fatigue conditions in said stimulated muscle, said system further characterized wherein said means for detecting is responsive to said selected parameter.

14. A diagnostic neuromuscular system for diagnosing rate and degree of muscle fatigue comprising:

EMG electrodes for coupling in the vicinity of a muscle, for sensing Response-EMG signals from said muscle;

EMG pattern recognition means including means for recognizing Response-EMG deviations for selectively analyzing multiple Response-EMG signals and for selectively providing output signals indicative of degree and rate of fatigue responsive to recognized deviations beyond a predefined threshold level of change in patterns of said Response-EMG signals wherein said changes of said pattern over time are changes relative to the Response-EMG pattern within a specified small time interval after an initial time.

15. The system as in claim 14 wherein pattern recognition is in terms of measuring the point wise difference over a given fixed number of points in the Response-EMG voltage vs. time signals as obtained at the Response-EMG electrodes between their voltage values at discrete time points immediately after any said initial time reference vs. the corresponding value at any time later when fatigue may have started to take an effect, wherein the time scales are all with respect to, said initial time reference and wherein each point considered in the two patterns that are compared is the same distance from the time instant of initiation point for each pattern.

16. The system as in claim 14 wherein pattern recognition is in terms of measuring the area difference over a given fixed number of points in the Response-EMG voltage vs. time signals as obtained at the Response-EMG electrodes between their voltage values at discrete time points immediately after any said initial time reference vs. the corresponding value at any time later when fatigue may have started to take an effect, wherein the time scales are all with respect to said initial time reference, and wherein each point considered in the two patterns that are compared is the same distance from the time instant of initiation point for each pattern.