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The EMG Signal






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The EMG Signal The EMG Signal Presentation Transcript

  • The EMG Signal H-reflexes
  • H-reflex
    • Originally described by Piper in 1912
    • More clearly elucidated by Hoffman in 1922
      • Studied the gastrocnemius by electrically stimulating the main trunk of the tibial nerve
    • Magladery and McDougal (1950) credited with designating the reflex response the Hoffman reflex
      • Shortened to the H-reflex
  • H-reflex Theory.1
    • The electrical equivalent of the deep tendon reflex for testing a monosynaptic loop
    Group Ia fiber Spindle Gross muscle Reflex hammer Alpha motoneuron Spinal cord View slide
  • H-reflex Theory.2
    • The electrical equivalent of the deep tendon reflex for testing a monosynaptic loop 1
    Group Ia fiber Spindle Gross muscle Alpha motoneuron Spinal cord EMG Recording Electrodes Galvanic Stimulator Stimulating Electrodes 1 Hugon, 1971 View slide
  • H-reflex Theory.3
    • Confirms the integrity of the afferent - efferent nerve connections
    • Amplitudes (mV) provide an index of alpha motoneuron excitability at the spinal cord level
  • H-reflex Uses.1
    • First used as a clinical/diagnostic tool
      • Most frequently used to study the tibial nerve in the posterior compartment of the thigh
        • Gastrocnemius usually studied
        • Compare latencies between M-waves and H-reflex bilaterally
          • Correlates with leg length - range = 22.64 - 40.14 msec (tibial nerve)
  • H-reflex Uses.2
    • Examples - Clinical/Diagnostic Use
      • Assess the integrity of the S 1-2 nerve roots with suspected foraminal encroachment (Braddom & Johnson, 1974)
      • Takamori (in Braddom & Johnson, 1974) studied patients with spasticity and Parkinson’s disease
      • Magladery & McDougal (1950) studied nerve disorders secondary to ischemia
  • H-reflex Uses.3
    • More recently the H-reflex has been used in clinical and basic research
    • Tibial, common peroneal, femoral, median and ulnar nerves have been studied with varying degrees of success
  • H-reflex - Uses.4
    • Mongia (1972) studied the femoral nerve and quadriceps
    • Bulbulian & Bowles (1992) studied eccentric contractions in downhill running
    • Kennedy et al. (1982); Spencer et al. (1984); and McDonough & Weir (1996) studied reflex inhibition in the quadriceps secondary to knee joint capsular swelling
  • Neurophysiological Overview.1
    • After the nerve (e.g., femoral, tibial, etc.) has been identified and stimulating electrodes are applied over the nerve, and after recording EMG electrodes are applied over the muscle’s motor point…
    • A galvanic stimulator simulates the nerve (group Ia afferents) directly thereby by-passing the spindle
  • Neurophysiological Overview.2
    • Group Ia fibers monosynaptically connect with alpha motoneurons in the anterior horn of the spinal cord
    • The alpha motoneurons activate extrafusal (somatic) fibers in the homonymous muscle
      • Recording EMG electrodes pick-up electrical activity in the muscle
    • A twitch contraction is elicited
      • Similar is appearance to a DTR response
  • EMG Response - Vastus Medialis Stimulus artifact M-wave H-reflex Volts Latency msec
  • Potential Confounding Influences
    • Head/neck position
    • Mental/emotional/alertness state
    • Cognitive state
    • Ambient temperature
    • The specific nerve being studied
    • Stimulating electrode conditions
  • Procedure.1 - Femoral Nerve
    • Using a galvanic stimulator with a probe electrode identify the motor points of VM and VL
      • Apply EMG electrodes in the standard way with standard skin prep
        • Reference electrode over ASIS
      • Confirm signal using Scope1.vi
    • Palpate the femoral artery pulse in the femoral triangle - mark the skin
  • Procedure.2 - Femoral Nerve
    • Using a galvanic stimulator with a probe electrode locate the femoral nerve 1-2 cm lateral to the femoral artery - mark skin
      • Confirm with Scope1.vi
    • Apply a pre-gelled, self-adhesive electrode over the femoral nerve
      • Large dispersal electrode on back of thigh
  • Procedure.3 - Femoral Nerve
    • Stimulator settings
      • Rate: 0.30 - 0.40 Hz
      • Duration: 0.50 - 1.0 msec
      • Intensity: 40 - 110 volts
    • Collect data using Bincolct.vi
      • Saves data in binary format
    • ~10 seconds of rest between trials
  • Procedure.4 - Femoral Nerve
    • Using Scope1a.vi bring intensity (voltage) up gradually until an M-wave and H-reflex are visualized
    • Decrease intensity in ~5 volt increments until the M-wave decreases in amplitude but the H-reflex remains constant
  • Procedure.5 - Femoral Nerve
    • Run Bincolct.vi
      • Will continue to collect data until Stop button is pushed
      • Every 10 seconds press stimulator switch “On” to elicit H-reflexes
  • Bincolct.vi
  • Procedure.6 - Femoral Nerve
    • Analyze data using Hread.vi (reads binary format data)
      • Run the VI
      • Each time the SHOW NEXT button is pushed 1000 data points will be advanced
      • Approximately every 10 seconds a triplex of signals will appear
        • Stimulus artifact
        • M-wave
        • H-reflex
  • Hread.vi
  • EMG Response - Vastus Medialis Stimulus artifact M-wave H-reflex Volts Latency msec
  • Procedure.7 - Femoral Nerve
    • To “stretch-out” the triplex of waves adjust (re-scale) the ‘x-axis’ values
    • Measure waveform amplitudes (V; mV) and latencies (msec) using Cursor Display
  • References
    • Braddom, R.L., & Johnson, E.W. (1974) H-reflex: Review and classification with clinical uses. Archives of Physical Medicine and Rehabilitation , 55 , 412
    • Enoka, R.M. (1994). Neuromechanical basis of kinesiology (2nd ed.). Champaign, IL: Human Kinetics, pp. 177-179.
    • Enoka, R.M., Hutton, R.S., & Eldred, E. (1980). Changes in excitability of tendon tap and Hoffman reflexes following voluntary contractions. Electroencephalography and Clinical Neurophysiology , 18 , 664-672.
  • References
    • Garland, S., Gerilovsky, L, & Enoka, R.M. (1994). Association between muscle architecture and quadriceps femoris H-reflex. Muscle & Nerve , 17 , 581-592.
    • Hugon, M. (1973). Methodology of the Hoffman reflex in man. In J.E. Desmedt (Ed.). New developments in electromyography and clinical neurophysiology. Basel: Karger, pp. 277-293.
    • Kennedy, J.C., Alexander, I.J., & Hayes, K.C. (1982). Nerve supply o f the human knee and its functional importance. The American Journal of Sports Medicine , 10 , 187-194.
  • References
    • Magladery, J.W., & McDougal, D.B. (1950). Electrophysiological studies of nerve and reflex activity in normal man: Identification of certain reflexes in electromyogram and conduction velocity of peripheral nerves. Bulletin of Johns Hopkins Hospital , 86 , 265-290.
    • McDonough, A.L., & Weir, J.P. (1996). The effect of post-surgical edema of the knee on reflex inhibition of the quadriceps femoris - a case study. Journal of Sport Rehabilitation , 5 , 172-181.
  • References
    • Mongia, S.K. (1972). H-reflex from quadriceps and gastrocnemius muscle. Electromyography and Clinical Neurophysiology , 12 , 179-190.
    • Spencer, J.D., Hayes, K.C., & Alexander, I.J. (1984). Knee joint effusion and quadricepsreflex inhibition in man. Archives of Physical Medicine and Rehabilitation , 65 , 171-177.