evoked potentials Flashcards
what makes an evoked potential unique
uses a machine to produce ES
kinds of electrophysiologic eval under evoked potentials
NCV
NMJ transmission
centrally evoked potentials
reaction of degeneration test
SD curve
what is the purpose of electrophysiologic ecam
evaluates integrity of neuromuscular system by detecting nerve potentials
what does NCV test
tests peripheral motor & sensory neurons on both orthodromic & antidromic responses
define orthodromic
sensory - distal to proximal
motor - proximal to distal
define antidromic
sensory - proximal to distal
motor - distal to proximal
what are the 2 types of NCV tests
SNAP and CMAP
exp SNAP
Sensory Nerve Action Potential
tests sensory nerve axons - distal cutaneous receptors to DRG
exp CMAP
Compound Muscle Action Potential
tests motor nerve fibers - anterior horn cells to NMJ of the innervated muscle
what type of current does NCV use
rectangular monophasic PC
explain the electrode placement of NCV
apply active electrode to nerve - cathode is distal part and closest to recording electrode
recording electrode - over muscle or nerve
ground - usually on bony prominence
what is measured in NCV
distance - betw stim and recording electrode; mm
latency - time bet stim and muscle contraction or nerve acitvation; msec
d/l = NCV; m/sec
relate body temp to NCV
inc body temp = inc NCV and dec latency; hence uses gel for accurate results
relate UE/LE to NCV
UE is 7-10 m/s faster than LE
relate proximal/distal segments to NCV
more proximal = faster
relate age to NCV
<3-5 y/o = lower by 50% vs normal adults
> 40 = gradual slowing vs middle-aged
6th & 7th decade = 10 m/sec less than
middle-aged
what conditions reduces NCV
CTS
PNI
demyelinating disorders
specifically tests for myasthenia gravis
NMJ transmission
exp NMJ transmission
assesses the function of the neuromuscular junction
type of test under NMJ transmission
repetitive nerve stimulation test (RNS) or jolly test
what is myasthenia gravis
chronic autoimmune neuromuscular disease - nag wweaken skeletal muscles and affects breathing if diaphragm
exp centrally-evoked potentials
cental = CNS
machine induces stim tas computer measures if brain receives the stim from the receptor tested
kinds of test under centrally-evoked potentials
somatosensory evoked potentions (SSEP)
visual evoked potential (VEP)
brainstem auditory evoked potential (BAEP)
what does RD test assess
lower motor neuron lesions - peripheral nerve injury only
what kind of current does RD test use
faradic muna tas galvanic
explain faradic current in RD test
Short pulse duration (<1msec) and >20-50 Hz frequency
Monophasic or asymmetrical biphasic PC using cathode as active electrode
smooth tetanic or sustained contraction
explain galvanic current in RD test
Long pulse duration (100msec)
Monophasic or Interrupted DC using cathode as active electrode
brisk muscle twitches
outcome in faradic and galvanic if normal peripheral nerve
faradic - smooth tetanic or sustained contraction
galvanic - brisk muscle twitches
outcome in faradic and galvanic if partial RD
faradic - partial or diminished tetanic contraction
galvanic - partial or diminished, sluggish twitch
outcome in faradic and galvanic if complete RD
faradic - no contraction
galvanic - very slow, sluggish twitches
outcome in faradic and galvanic if absolute RD
faradic - no contraction
galvanic - no contraction
exp partial RD
degeneration of part of nerve fibers
exp complete RD
degeneration of all nerve fibers; muscle tissue retains contractile elements; so wala pa atrophy, fibrotic changes
exp absolute RD
degeneration of all nerve fibers; muscle tissue severely atrophic, fibrotic or non-contractile
when do we use RD
if we want to know if may PNI or if unexplained paralysis
should be done > 10 days post injury; kc need mag wallerian muna or mag manifest yung injury
what does SD curve and chronaxie test assess
location, severity, and progress of peripheral motor nerve degeneration
when do we use SD curve and chronaxie test assess
after 3 wks post-injury para may wallerian na
type of current used in SD curve and chronaxie test assess
square monophasic PC or sawtooth/triangular if walang square
what are the pulse durations usually used in SD curve and chronaxie test
100, 30, 10, 3, 1, 0.3, 0.1, 0.03, 0.01 msec - start from 100 msec then pababa
usual chronaxie of normal nerve
0.05 - 0.5 msec or <1 msec
usual chronaxie of fully denervated nerve
30-50 msec
usual rheobase for normal nerve
5-35volts / 2-18mA
exp the curve from normal to denervated
shifts upward and to the right
exp the curve from normal to partially denervated
may kink
factors that affect SD curve
Skin resistance
Subcutaneous tissues (eg fats)
Skin temperature
Electrode size
Electrode placement
Age
Fatigue
advantages of SD curve test
Quick and easy to perform
Requires minimal training
More economical (vs
other tests)
disadvantages of SD curve test
Only provides qualitative data in relation to degree of denervation
Cannot locate site of lesion
Only few fibers can be assessed in large muscles
