Final Flashcards
Clinical Electromyography (EMG)
used to evaluate the scope of neuromuscular disease or trauma as well as assist with establishing anticipated goals and expected outcomes
Forms of clinical EMG:
Nerve conduction velocity (NCV)
Electromyography (needle EMG)
Kinesiological EMG
used to study muscle activity and establish the role of various muscles in specific activities
Electromyography (primarily surface EMG)
Biofeedback
describes the use of instrumentation to make covert physiological processes more apparent to the patient
Best and most widely used electrodes:
silver silver chloride
How many electrodes:
2 active
1 isolation
What do the 2 active electrodes do?
primarily sense the activity of the muscle
What does the isolation electrode do?
make sure the two active electrodes only pickup electricity that is coming from the patient
Where are the active electrodes placed?
both active electrodes are generally placed at the midpoint of the muscle being recorded in line with the muscle fibers
Considerations for placing electrodes:
Place electrodes in position of movement
Consider how skin may shift over the underlying muscle during movement
What does closer spacing of the electrodes give?
smaller sampling are and lower amplitude of signals
What does wider spacing of the electrodes give?
larger sampling area and higher amplitude of signals
What is volume conduction?
the salt water conducts electricity through its volume and allows us to record from the surface of the skin
What is cross talk?
when the electrodes are far apart you can get recordings from other muscles
What is an artifact?
an excess or erroneous signal that is detected and displayed but does not come from the electrical activity of motor neurons or muscle tissue
What are the different types of artifact?
movement
power line interference
EMG
Movement artifact:
shift on the screen that is from the movement of wires not electrical activity
Power line interference:
if the reference ground isn’t on the pt and eliminating electrical interference
What happens during the processing phase?
filtering rectification and integration time constant amplification goal/threshold
What is filtering:
generally, the electrical signal from the pt is filtered to only allow frequency components of 80-250 Hz to pass
What is rectification and integration:
so that it makes more sense for us to look at and appreciate change
Time constant:
we can determine how fast the display on the screen follows changes in electrical activity of muscle
Low time constant (low smoothing)
screen displays changes very quickly to follow changes in muscle activity (see moment to moment changes)
High time constant (high smoothing)
Screen display does not change quickly to follow changes in muscle activity (seeing overall effect)
Screen does not change with every step
Amplification (gain/sensitivity)
Can be used to adjust the size of an EMG signal on a given display
Goal/threshold:
some level of EMG that a pt can be prompted to contract up to or relax down to, gives the pt something to shoot for
Display Phase
display mode
audio feedback to patient
Types of display mode
continuous
work/rest
Continuous:
the unit continuously displays the pts electrical activity along with any goals or other feedback
Work/rest:
The unit prompts the pt to contract toward the goal for a specific period of time and then prompts the pt to relax for a specific period of time
Turns on the display when you are likely to contract and turns it off when you’re likely to be resting
Electrode spacing for shaping up:
wide over target muscle or group to permit sampling of large number of motor units)
Gain/sensitivity for shaping up:
high, to pick up even very weak signals
Time constant/smoothing for shaping up:
low, so that even small, transient increases in muscle activity are reflected on the screen)
Threshold or goal for shaping up:
relatively low (just over voluntary EMG)
As facilitation occurs (amplitude of EMG signal increases)
Raise threshold/goal setting (requiring greater depolarization to hit target)
Decrease sensitivity setting (to keep the whole signal on the display)
Narrow electrode spacing (to focus more on a muscle and less on a group)
Electrode spacing for shaping down:
relatively narrow over target muscle or group
Gain/sensitivity for shaping down:
relatively low
Time constant for shaping down:
high (so that display on screen does not follow changes in activity very quickly- small, transient changes in activity are not reflected on display)
Threshold or goal for shaping down:
relatively high (but just under resting levels of EMG
As relaxation occurs (amplitude of EMG signal decreases)
Lower threshold/goal setting (requiring more relaxation to hit target)
Increase sensitivity setting (to keep signal on display)
Widen electrode placing (to broaden relaxation from one muscle to a muscle group or area)
Motor Copy
Contraction of the stronger (unaffected) limb/muscle provides a template for amplitude and timing of EMG activity
Pt contracts weaker (affected) limb/muscle and tries to “copy” amplitude and timing of stronger limb
Who are not good candidates for CAMA?
pts with cognitive impairment, receptive aphasia, or visual and/or auditory impairments are not good candidates for sEMG (biofeedback)
CAMA
targeted muscle training and “motor copy”, the output of the sEMG unit is directed to the pt, who is asked to respond appropriately and modify his or her performance
Fourier analysis:
Detect fatigue (reduction of higher frequency components of CMUAP and increase in lower frequency components of CMUAP)
Muscle fatigue index:
(decrease in median frequency)
less large neurons firing and you’re left with only small ones
Normalization:
Express EMG values as a percent of MVIC
can compare one person to another
Averaging:
For some tasks (like gait), the EMG from many reps of a particular movement are averaged together before analysis
Reduces variability and gives a truer picture of typical EMG during the task
What does higher levels of EMG indicate?
greater electrical activity in the area of a muscle being sampled, but this may or may not equal greater force or torque
Mononeuropathy:
one nerve in one location
Multiple mononeuorpathy:
one nerve in different locations
Polyneuropathy:
many nerves
Traumatic myelinopathy (Class 1):
Some neurons go to sleep and then wake back up a few weeks later
After a few weeks pt is able to contract a little again
Which axons are the first to fail after the are compressed?
larger diameter and ast to come back
Compound motor unit action potential
collective depolarization of many motor units
What does a reduction in amplitude of CMUAP indicate?
some neurons are not conducting
Sharp waves:
variation of fibrillation, presence suggest axonopathy
Fibrillation potentials
involuntary contraction of a single muscle fiber that is denervated (6-month recovery)
Nascent units
new motor units are beginning to appear leading to recovery of function
Purpose of NVC:
assess time and quality of conduction of neural impulses in peripheral motor and sensory nerves
Commonly tested nerves for NVC:
median, ulnar, peroneal, posterior tibial
Factors influencing NVC:
fiber size temperature myelination chemical state of nerve age of patient
Motor NCV:
AP is generated under cathode (negative electrode)
Motor NCV for median nerve:
Abductor Pollicis Brevis
Motor NCV for ulnar nerve:
Abductor Digiti Minimi
Motor NCV for peroneal nerve:
Extensor Digitorum Brevis
Motor NCV for posterior tibial nerve:
Abductor Hallicus (or Abductor Digiti Minimi)
Distal latency:
Time it takes AP to travel to stimulus to recording electrode for the most distal piece of motor nerve
What can longer distal latency and slower velocity indicate?
some degree of demyelination and are conducting more slowly, or it might indicate that the largest and fastest conducting axons are not conducting at all
Decreased amplitude might indicate:
might indicate axonal degeneration or partial denervation with fewer innervated motor units contributing to the recorded potential
Increased duration might indicate:
partial demyelination (some fibers)
Antidromic study:
Yellow electrodes would be stimulating, rings would be rings to have AP travel backwards
Opposite the direction a signal normally goes (antidromic) for sensory nerve, from proximal to distal
F wave:
Indicated for disorders known to have a more proximal neuropathology
Antidromal action potential “bounces back” from cell body and is recorded at muscle
H wave
Electric tendon tap
primarily of value in assessing the continuity and function of the sensory and motor pathways of the first sacral nerve roots (S1)
Normal during needle insertion:
insertion activity (brief, small amplitude polyphasic discharges as needle pierces muscle fiber membranes) Stimulates muscle fibers not nerves
Abnormal during needle insertion:
May be decreased over normal
May be increased over normal
Fibrillation potentials
Spontaneous depolarizations of single muscle fibers (possibly resulting from increased sensitivity to circulating acetylcholine). Generally not visible through the skin.
Positive sharp waves
Spontaneous depolarizations of single muscle fibers or groups of muscle fibers. (Possibly resulting from increased sensitivity to circulating acetylcholine or from mechanical depolarization by needle itself).
Fasciculations
“Spontaneous potentials seen with irritation or degeneration of the anterior horn cell, nerve root compression, and muscle spasms or cramps. They are believed to represent the involuntary asynchronous contraction of a bundle of muscle fibers or a whole motor unit.” (Portney in O’Sullivan) Can often be seen through the skin (twitches). Not necessarily abnormal.
Repetitive discharge
Seen with lesion of the anterior horn cell and peripheral nerves, and with myopathies. Characterized by trains of rather high frequency potentials.
