PHYSIOLOGY_LC4_ELECTROMYOGRAPHY.pdf

C.2. INTRAMUSCULAR (Needle) COURSE OUTLINE ELECTROMYOGRAPHY (nEMG) Invasive electrode I. ELECTROMYOGRAPHY...

C.2. INTRAMUSCULAR (Needle) COURSE OUTLINE ELECTROMYOGRAPHY (nEMG) Invasive electrode I. ELECTROMYOGRAPHY A needle electrode inserted directly into a A. Definition muscle record the electrical activity in that B. Uses muscle C. Types C.1. Surface Electromyography C.3. NERVE CONDUCTION STUDY (NCS) (sEMG) uses electrode stickers applied to the skin C.2. Intramuscular (Needle) (surface electrodes) to measure the speed and Electromyography (nEMG) strength of signals traveling between two or C.3. Nerve Conduction Study more points (NCS) most helpful in classifying a neuropathy as due D. Procedures to axonal degeneration or segmental E. Parameters demyelination F. Clinical Correlation F.1. Neuropathy vs. Myopathy D. PROCEDURES 1. Needle electrode inserted into muscle I. ELECTROMYOGRAPHY 2. Neurologist tells you when to contract and rest muscle 3. Needle records muscle activity during rest and A. DEFINITION movement Figure 1: Electromyography Figure 2: EMG records and analyzes the electrical activity in your muscles. It is used to learn more about the functioning of nerves in the arms and legs. For Example, a fracture of the upper arm bone Measures muscle response or electrical activity (Humerus) may tear or pinch the radial nerve. An EMG can be in response to a nerve's stimulation of the used to identify the damage if nerve function doesn’t return within 4 muscle months of the injury. Refers to the collective electric signal from muscles, which is controlled by the nervous Note: Electrical activity detected during rest is system and produced during muscle abnormal contraction Neurophysiological technique for examining the electrical activity of skeletal muscles Signal represents the anatomical and physiological properties of muscles The electrical activity of a muscle's motor units. B. USES To detect neuromuscular abnormalities Evaluate patients with suspected peripheral neuropathy C. TYPES C.1. SURFACE ELECTROMYOGRAPHY (sEMG) Figure 3: Expectation during nerve conduction study. Non-invasive electrode Obtain information about the time or intensity of 1. Stimulating electrodes placed over nerve superficial muscle activation 2. Recording electrode place over muscle the Advantage: More coverage compared to nerve controls nEMG 3. Low-level electrical shock applied through Disadvantage: More prone to artifacts in stimulating electrodes reading BATCH 2028 1B 1 PHYSIOLOGY LC 4: ELECTROMYOGRAPHY Dr. UJANO, S. 08/05/2024 4. Recording electrodes measures speed of impulse 5. Impulses appear as waves on the monitor. E. PARAMETERS IN EMG/NCS REPORT These are the things that must be recorded: Amplitude: The electrical signal is represented as a wave, and the amplitude is its height. Conduction velocity (CV): The conduction velocity describes the speed at which the electrical impulse travels along the nerve. Duration: This describes the width of an electrical wave. Conduction block: This is the reduction of a signal across an anatomical region. F reflex: The F wave is a kind of electrical echo in which the impulse travels up the spine and then back down along the same fiber. It thereby gives a sense of the conduction along the entire length of a motor nerve. H reflex: The H wave is the electrical Figure 5. (A) Normal triphasic potential, (B) Long-duration, high-amplitude. Polyphasic potential (neuropathic potential), (C) equivalent of a reflex in the leg. An impulse Short-duration, low-amplitude, Polyphasic potential (myopathic travels to the spinal cord via a sensory nerve, potential) then back along a motor nerve. F. CLINICAL CORRELATIONS F.1. MYOPATHY Decrease number of muscle fibers in individual motor units (muscle fibers + neurons), number of motor units is normal Full recruitment in weak muscles because individual motor units generate less tension than normal, increase number is recruited for any given voluntary activity (rapid recruitment) Recruitment density is normal Short-duration, low-amplitude polyphasic potential (myopathic potential) Short duration is due to few muscle fibers, all Figure 4. Parameters of a Motor Unit Action Potential are reached in a short time Low amplitude is due to decreased muscle Normal MUAPs are biphasic or triphasic fiber recruited Duration 2-15 msec. Amplitude 200 uV - 3 mV Polyphasic potentials (>4 phases) are nonspecific findings ○ occur in both neurogenic and myogenic diseases ○ also are found in small numbers (10-15%) in all normal muscles Figure 6. Motor Unit Figure 7. Myopathic EMG F.2. NEUROPATHY decreased number of motor units; decreased recruitment density, decreased recruitment overall due to low action potential transmission during voluntary activity, there is compensatory increase in rates, at which individual remaining units begin firing and at which they fire before additional units are recruited BATCH 2028 1B 2 PHYSIOLOGY LC 4: ELECTROMYOGRAPHY Dr. UJANO, S. 08/05/2024 after reinnervation, surviving axons branch to innervate adjacent muscle fibers, thus enlarging number of muscle fibers per unit One(1) axon will have a lot of muscles to supply( increased excitation, increased amplitude) Figure 6. Motor Unit Figure 8. Neuropathic EMG Long-duration, high-amplitude, polyphasic potential (neuropathic potential) Long duration is due to difficulty in transmission of impulse to muscle or motor unit High amplitude is due to increased motor unit recruitment after reinnervation Reference(s): Dr. Stephen A. Ujano lecture and Powerpoint presentation. BATCH 2028 1B 3