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NCV
NCV
124
Anatomy
Graduate
02/28/2012

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Cards

Term
what is the M wave
Definition
motor wave
Term
in what direction does an orthodromic M wave travel
Definition
from central to peripheral
Term
what is done and measured in M wave testing
Definition
we create an orthodromic action potential and measure the motor nerve
Term
setup of recording electrodes for motor NCV
Definition
ground electrode on back of hand/elsewhere; cathod on motor point; anode distal to cathod
Term
why is the cathode chosen as the active electrode
Definition
Pflueger's Law: for a given amount of electricity, you will get more activity under a cathode than you will under an anode because of resistance of the nerves
Term
does position of cathode/anode matter for biphasic balanced or pulsed monophasic?
Definition
pulsed monphasic
Term
what waveform is used in NCV
Definition
pulsed monophasic
Term
what does placement of stimulating electrodes in M wave NCV depend on?
Definition
depends on location of Nerve/segment being studied
Term
how many action potentials does the stimulating cathode set off?
Definition
2
Term
in m waves, what happens to the action potential that travels distally from the cathode
Definition
goes down the nerve orthodromically and is picked up and read by the recording/bar electrode
Term
how many action potentials does the stimulating anode set off?
Definition
2
Term
in m waves, what happens to the action potential that travels proximally from the anode
Definition
goes to anterior horn of spinal cord, hits the cell body, and dies out
Term
what action potential do we record and measure in m waves
Definition
the one that travels distally from the cathode
Term
in m waves, what happens to the action potential that travels proximally from the cathode and the action potential that travels distally from the anode
Definition
they hit each other and die out
Term
purpose of ground electrode
Definition
negate other electrical signals
Term
at what point in M wave EMG do you know you have the right wave
Definition
supramaximal; can't go any higher
Term
why do you need a supramaximal response for M wave NCV
Definition
insures that all motor nerves of the mixed nerve are activated including all slow and fast twitch motor units
Term
define latency
Definition
time from initiating stimulus from the cathode to first recording of response
Term
what do we look for in m wave NCV graph?
Definition
amplitude, shape, distal latency
Term
how to measure velocity using M wave
Definition
distance between cathodes/distal lateny
Term
how can the frequency of the oscilloscope affect your measurement
Definition
the oscilliscope has a frequency of 50 hz, meaning it refreshes 50 times asecond. It's possible that your action potential could occur during the time that the screen is refreshing. You have to be sure that the line being drawn on the screen is syncrhonized to the stimulator
Term
how to measure velocity at proximal portion of nerve using M wave
Definition
distance between stimulator sites/latency 2 - latency 1
Term
when to be concerned with m waves
Definition
if the conduction velocities are slower than normal or if the shape changes
Term
what to do if NCV is slow
Definition
send findings to physician
Term
indications for motor NCV
Definition
peripheral neuropathies, such as disc protruding and pressing on nerve
Term
purpose of F wave test
Definition
motor test for when you can't go farther up the nerve proximally because of space
Term
what is the position of the cathode/anode on the recording electrode for an F wave
Definition
cathode on motor point, anode distal
Term
what is the position of the cathode/anode on the stimulating electrode for an F wave
Definition
cathode proximal, anode distal
Term
is the cathode positive or negative
Definition
negative
Term
which action potential are we interested in in F waves
Definition
cathode sends action potentials up the motor nerve antidromically
Term
what is the path of the action potential sent antidromically to the CNS by the stimulating cathode
Definition
travels into the anterior horn of spinal cord, hits the cell bodies. Signal is reflected back down the motor nerve orthodromically. The orthodromic response is measured
Term
what is a possibility for error in F waves
Definition
nerves don't always respond; don't always get enough of a signal reflecting back orthodromically
Term
in particular, what part of the nerve is tested using F waves
Definition
nerve roots, plexuses
Term
describe orthodromic/antidromicnesss of M wave
Definition
orthodromic stimulus to get an orthodromic response
Term
describe orthodromic/antidromicnesss of F wave
Definition
antidromic stimulus to get an orthodromic resposne
Term
what happens if you do an F wave with the stimulus too proximal
Definition
there is a greater likelihood that M and F waves will hit the recording electrode at the same time. The M wave will overshadow the F wave.
Term
what happens if you do an F wave with the stimulus distal
Definition
the M wave will show up on the recording device very early and the F wave will show up later so that you can tell which one it is.
Term
are F waves consisten?
Definition
not really
Term
when to use F waves
Definition
proximal neuropathies, Guillian Barre, Charcot Marie Tooth, thoracic outlet syndrome, radiculopathy
Term
what is Guillain Barre
Definition
attack on anterior horn cells. F wave tells us how much it affects peripheral nerves
Term
what is charcot-marie-tooth
Definition
central motor responses occur with this. Can be assessed with f wave
Term
what is repetitive stimulating used to assess
Definition
problems of synapse trnasmission, such as for myasthenia gravis, botulism, some cancer
Term
what is the electrode configuration for repetitive stimulation
Definition
same as NCV M wave
Term
how to do repetitive stimulation testing
Definition
repeated stimulation of motor nerve. Constant stimulator amplitude applied. Measure waves before and after exercise or before and after ischemia
Term
how to determine outcome of repetitive stimulus
Definition
compare to normal responses
Term
what can cause errors in repetitive stimulus testing
Definition
drugs, position, temperature
Term
what does SNAP stand for
Definition
sensory nerve action potential
Term
what is the direction of orthodromic SNAP
Definition
distal to proximal
Term
what nerves are stimulated by SNAP
Definition
pure sensory nerves
Term
what is the direction of antidromic SNAP
Definition
proximal to distal
Term
what is a disadvantage of antidromic SNAP
Definition
produces potential movement artifact which can make sensory look bigger than it actually is
Term
how to achieve antidromic SNAP compared to orthodromic SNAP
Definition
reverse the stimulating and recording electrodes: plug them in oppositely so that recording electrodes are now the stimulating electrodes and vice versa
Term
where are the recording electrodes in SNAP (on the muscle or on the nerve)
Definition
on the nerve
Term
what type of stimulating electrodes are used for median nerve
Definition
ring electrodes
Term
is the stimulating cathode distal or proximal
Definition
proximal
Term
is the recording cathode distal or proximal
Definition
distal
Term
what distance is measured in SNAP
Definition
cathode to cathode
Term
is it easier to get a response in orthodromic or antidromic SNAP in overweight people
Definition
antidromic
Term
is the cathode black or red
Definition
black
Term
does antidromic SNAP stimulate sensory or motor nerves
Definition
both
Term
when do you use antidromic SNAP
Definition
in overweight people or when orthodromic doesn't work
Term
sensory waves are smaller than motor waves. What do you do if you can't see the wave on the screen
Definition
adjust the gain to increase sensitivity
Term
what outcomes do we look at for SNAP waves
Definition
shape, amplitude, time of wave
Term
what do SNAP waves look like
Definition
M waves
Term
what is the most stable part of a SNAP wave that you should use for measurements
Definition
peak
Term
what is H reflex
Definition
use of orthodromic motor afferent stimulation to produce motor efferent reaction
Term
when is the H reflex typically used
Definition
in S1 nerve root compression
Term
where are the recording electrodes in H wave
Definition
on soleus
Term
where is the stimulator for H wave
Definition
tibial nerve at popliteal fossa
Term
what is the H reflex an indicatin for
Definition
body's sensitivity
Term
what affects the H reflex
Definition
stress, body reactions
Term
why is the S1 nerve root used for H reflex
Definition
soleus is a postural muscle with many muscle spindles. It is easy to get a response out of the soleus.
Term
what is the position of the stimulating cathode in H reflex
Definition
cathode is proximal
Term
what types of action potentials are sent along what types of nerves in H reflex
Definition
antidromic up motor nerves and orthodromic up sensory nerves
Term
why does the H wave take longer than an M wave in the H reflex
Definition
H wave has to go up through the spinal cord and back down again.
Term
how does the H wave amplitude change with increase in intensity and why
Definition
H wave gets smaller as we turn the intensityup because H and M waves collide and cancel each other out
Term
what are sources of error in NCV
Definition
electrode placement, intensity, measurement, age, temperature
Term
is precise placement of electrodes more essential for motor or sensory readings?
Definition
sensory
Term
what can happen if your electrode placement is not precisely on motor point, nerve path
Definition
will affect readings/results
Term
what kind of error is associated with intensity
Definition
need supra-maximal stimulation to make sure you're getting all the axons in a nerve to fire. Not turning up intensity to supramaximal will give you different numbers of motor units and different readings
Term
what should you take account into measurement of distance to avoid error
Definition
measure the same way each time for each individual; body position should be recorded for comparison to other tests/norms
Term
how can you avoid measurement errors on the graph
Definition
print the graph to decrease parallax errors from reading off the oscilloscope
Term
at what age is NCV decreased
Definition
infants-3 years
Term
at what age is NCV at the low end of normal
Definition
over 65 years
Term
what do you need to have to be able to account for age related changes to NCV
Definition
table for age related changes
Term
what is the greatest source of error in NCV
Definition
measurement
Term
what is the 2nd greatest source of error in NCV
Definition
temperature
Term
at what skin temp does NCV begin to slow
Definition
below 25C
Term
what should be the minimum surface temp for NCV
Definition
30C
Term
what should be the temp min for repetitive stimulation
Definition
35C
Term
what should you establish to reduce error
Definition
protocols
Term
what are technique electrodes
Definition
indwelling electrodes; go into the muscle
Term
what equipment differences are there between NCV and technique
Definition
in technique, you don't need a stimulator. The patient contracts the muscle, and you record what comes out.
Term
when do you take measurements with technique
Definition
response at insertion; response at rest; response with voluntary contraction
Term
what do you look for in the technique recording
Definition
amplitude, duration, shape,sound, frequency
Term
how do you reduce error in technique recording that comes from area recorded by needle being so small
Definition
ssample many areas of the muscle
Term
what is a neuropraxia
Definition
compression of the nerve
Term
what are Saturday night palsies
Definition
fall asleep laying on one side, that side feels numb when you wake up
Term
what happens with neuropraxias
Definition
interference of neuroplasmic flow causes damage to outer portion of nerve, slowing down actoin potentials.
Term
what are some examples of neuropraxias
Definition
Saturday night palsy, carpal tunnel syndrome
Term
how is NCV affected by neuropraxias
Definition
shows increased latency across blocked area
Term
how is conduction/amplitude affected above and below a neuropraxia
Definition
normal
Term
how is EMG affected by neuropraxia
Definition
depends on duration and level of denervation
Term
what is axonotmesis
Definition
intact neural tube in which axonal damage has occurred
Term
what is the result of fewer axons traveling in the compound motor nerve
Definition
won't get as many motor units to contract
Term
can NCV be normal with axonotmesis
Definition
yes
Term
what causes axonotmesis
Definition
acute trauma, chronic neuropraxia
Term
what part of axonotmesis will cause a decrease in NCV amplitude
Definition
larger number of axons damaged
Term
as axonotmesis degeneration progresses, what wave changes occur in EMG
Definition
fibrillation and positive sharp waves
Term
what is neurotmesis
Definition
disruption fo neural tube. Full degeneration. Complete disruption. Cut off periphery and CNS. Muscle can't respond because action potentials can't bridge the area of damage.
Term
is there activity with voluntary effort in neurotmesis
Definition
no
Term
does an EMG show any activity in muscle with neurotmesis
Definition
spontaneous activity in resting muscle
Term
what is myelopathy
Definition
a neuropathy: sensory changes, distal weakness, hyporeflexia
Term
contraindications for NCV/EMG
Definition
bleeding disorders, anticoagulants, recurrent systemic infections
Term
should you use universal precautions with NCV
Definition
yes
Term
what is the display of a normally contracting muscle
Definition
amplitude, recruitment, and frequency will increase with increased contraction. Baseline obliteration occurs with maximal contractoin
Term
when might abnormal EMG waves show up?
Definition
myelopathy (diabetes, Guillian Barre), myopathies (dystrophies, polymyositis), motor neuron disorders (polio, ALS), myotonia, myasthenia gravis
Term
what are the acceptable number of polyphasic potentials
Definition
10% (abnormal if more than 10%)
Term
what is normal activity with EMG testing
Definition
noise is heard when needle is inserted, then muscle is silent unless it is at motor end plate, in which case it must be reinserted
Term
what is abnormal activity with testing
Definition
fibrillation potentials/positive sharp waves; fasciculations/complex discharges
Term
what is normal activity with slight contraction
Definition
single action potentials, usually biphasic or triphasic
Term
what is abnormal activity with slight contraction
Definition
more than 10% polyphasic
Term
what is normal activity with max contraction
Definition
obliteration of baseline due to all motr units firing all fibers; increase in frequency, amplitude, and recruitment
Term
what is abnormal activity with max contraction
Definition
may be decreased activity with max effort and increased activity with decreased effort. May see only a few action potentials firing
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