Biofeedback

2. Biofeedback

3. Biofeedback • A therapeutic procedure which uses electronic or electromechanical instruments to accurately measure, process, and feedback reinforcing information via auditory or visual signals • Used to help patient develop greater voluntary control of either neuromuscular relaxation or muscle re-education following injury

4. Role of Biofeedback • Feedback includes information related to the sensations associated with movement itself as well as information related to the result of the action relative to some goal or objective

5. Role of Biofeedback • Feedback refers to intrinsic information inherent to movement including kinesthetic, visual, cutaneous, vestibular, and auditory signals collectively termed as response produced feedback • Also refers to extrinsic information or some knowledge of results presented verbally, mechanically, or electronically to indicate the outcome of some movement performance

6. Role of Biofeedback • Feedback is ongoing, in a temporal sense, occuring before, during, and after any motor or movement task • Feedback from some measuring instrument which provides moment to moment information about a biologic function is referred to as biofeedback

7. Role of Biofeedback • Provides patient with a chance to make correct small changes in performance which are immediately noted and rewarded so that eventually larger changes or improvements in performance can be accomplished • Goal is to train patient to perceive changes without the use of a measuring instrument so that they can practice by themselves

8. Biofeedback Instrumentation • Designed to monitor some physiologic event, objectively quantify these monitorings, and interpret the measurements • Biofeedback units cannot directly measure a physiologic event but they record some aspect which is highly correlated with the physiologic event

9. Biofeedback Instrumentation • Biofeedback reading gives an indication of a physiological process but should not be confused with the physiological process itself

10. Biofeedback Instruments • Peripheral skin temperatures measures the extent of vasoconstriction or vasodilation • Finger phototransmission units (photoplethysmograph) measures vasoconstriction and vasodilation • Units that record skin conductance activity indicating sweat gland activity • Units that measure electromyographic activity (EMG)indicating amount of electrical activity during muscle contraction

11. EMG Biofeedback • Nerve fiber conducts an impulse to the neuro- muscular junction where acetylcholine binds to receptor sites on the sarcolemma inducing a depolarization of the muscle fiber which creates movement of ions and thus an electrochemical gradient around the muscle fiber • Changes in potential difference or voltage associated with depolarization can be detected by an electrode placed in close proximity

12. Measuring Electrical Activity • EMG does not measure muscle contraction directly • EMG measures electrical activity associated with muscle contraction • Electrical activity of muscle measured in microvolts (1 volt=1,000,000 µV) • EMG readings can be compared only when the same equipment is used for all readings

13. Measuring Electrical Activity • EMG biofeedback unit receives small amounts of electrical energy generated during muscle contraction through electrode • Separates or filters electrical energy from other extraneous electrical activity on skin and amplifies the EMG electrical energy • Amplified EMG activity is then converted to some type of information which has meaning to the patient

14. Anatomy of EMG Biofeedback

15. EMG Electrodes • Skin surface electrodes most common while indwelling electrodes are not practical • Electrodes made of stainless steel or nickel- platted brass recessed in a plastic holder • Some electrodes permanently attach to cable wires while others may snap onto the wire • Some units include a set of three electrodes preplaced on a velcro band which attachesto the skin

16. EMG Electrodes • Size of electrodes ranges between 4mm in diameter for recording small muscle activity and 12.5 mm for larger muscles • Increasing the size of the electrode will not cause an increase in the amplitude of the signal • Electrodes may be disposable or non-disposable and require some type of conducting gel

17. EMG Electrode Placement • Skin must be appropriately prepared by scrubbing with an alcohol-soaked prep pad • Electrodes should be placed as near to the muscle being monitored as possible • Electrodes should be parallel to the direction of the muscle fibers • Spacing of the electrodes is critical to reduce extraneous electrical activity (noise)

18. Separation and Amplification of EMG Activity • Electrode arrangement must eliminate noise • 2 active electrodes and 1 reference electrode • Active electrodes pick up electrical activity from motor units firing in the muscles beneath the electrodes

19. Separation and Amplification of EMG Activity • Magnitude of the small voltages detected by each active electrode will differ with respect to the reference electrode creating two separate signals

20. Separation and Amplification of EMG Activity • Two signals are fed to a differential amplifierwhich subtracts the signal from one active electrode from the other active electrode • Differential amplifier uses reference electrode to compare the signals of the two active electrodes

21. Separation and Amplification of EMG Activity • This in effect cancels out or rejects any components that the two signals coming from the active electrodes have in common thus amplifying the difference between the signals

22. Separation and Amplification of EMG Activity • Ability of the differential amplifier to eliminate the common noise between active electrodes is called the common mode rejection ratio (CMRR)

23. Separation and Amplification of EMG Activity • External noise can be reduced by using filterswhich make amplifier sensitive to some incoming frequencies and less sensitive to others • Amplifier will pick up signals only at bandwidth produced by electrical activity in the muscle

24. Converting EMG Activity to Meaningful Information • After amplification and filtering the EMG signal indicates true electrical or raw EMG activity in muscle • Raw EMG is an alternating voltage - direction or polarity is constantly reversing

25. Converting EMG Activity to Meaningful Information • To determine the overall increase and decrease in electrical activity deflection toward the negative pole must be flipped upward toward the positive pole • This summation of electrical activity is referred to asrectification

26. Converting EMG Activity to Meaningful Information • Once rectified EMG signal can be smoothed to eliminate the peaks and valleys or high frequency fluctuations which are produced with a changing electrical signal

27. Converting EMG Activity to Meaningful Information • Once smoothed the signal may be integrated by measuring the area under the curve for a specified period of time • Integration forms the basis for quantification of EMG activity.

28. Converting EMG Activity to Meaningful Information • Biofeedback units generally provide either visual or auditory feedback relative to the quantity of electrical activity • Visual feedback uses lights, bars, or analogue or digital meters • Auditory feedback uses increasing or decreasing tones, buzzing, beeping or clicking.

29. Setting Sensitivity • Signal sensitivity orsignal gain may be set • Sensitivity may be set at 1 µV, 10 µV, or 100 µV • A high signal gain means the biofeedback unit is sensitive enough to detect the smallest amounts of electrical activity • High sensitivity levels should be used during relaxation training

30. Setting Sensitivity • Low sensitivity gain should be used in muscle-reeducation during which the athlete may produce several hundred µV of EMG activity • When adjusting the sensitivity range it should be set at the lowest level that does not elicit feedback at rest

31. Clinical Applications • Muscle Re-education • Involves regaining neuromuscular control and/or increasing strength of a muscle • Relaxation of muscle spasm or muscle guarding • Pain reduction