clinical electrophysiological assessment

stimulator

hand held bipolar for motor, ring electrodes for sensory, want to have directly over nerve

amplifier

differential amplifies difference between 2 inputs to get rid of background noise, also requires grounding electrode elsewhere

filters

remove signal artifact and noise

averaging

repetitive testing is averaged to determine signal, background noise goes to 0

rectification and integration

take everything negative and flip it up, determine area under curve

analog to digital conversion

analog continuous, digital separate info
more sampling allows for confidence you have signal of interest

latency

time from when you stimulate to deflection, has to do with myelin

other measurements

amplitude, shape, duration

factors that influence NCV

myelination, number nodes of ranvier, compression, temperature, location (proximal faster), age (infants slow, aging causes demyelination)

CMAP

compound muscle action potential, due to multiple muscle types muscle fibers contract at different points leading to sinusoid

NCV m-wave

most important, all the time, shortest latency response (fastest)
stimulating nerve sends AP to muscle fiber causing contraction

motor NCV testing

requires two tests, take difference between two to get part that is pure NCV without problems from NMJ steps
take distance between two test points and difference in time to get NCV and compare to norms, always convert to mm and msec

distal latency

can increase if problems going on

decrease in NCV only

most likely patho directly affecting myelin

increase in distal latency and decreased amplitude

myelin and axonal issue

NCV f-wave

tests integrity of proximal segment, slower and smaller than m wave, AP goes back to spinal cord before coming back to muscle
assess timing, only alpha MN

sensory nerve conduction

only 1 test, response much smaller so requires averaging
orthodromic conduction (sensory nerve end toward CNS), stimulate sensory area with electrode on nerve to pick up

CSNAP

combined sensory nerve action potential
still measuring latency and amplitude

h-reflex

assess integrity of length of entire nerve, sensory and motor nerve with at least 1 connection, estim DTR, more complex and longer latency
can measure gray matter excitability following CNS lesions

NCV general principles

test both sensory and motor nerve conduction, test several segments, test both sides and multiple nerves (UE and LE), interpret results in context

neuropraxia NCV/EMG

NCV: normal distal to lesion, reduced across compressed area and decreased amp CSNAP/CMAP
EMG: all normal except possible decreased recruitment with severity

axonotmesis NCV/EMG

NCV: <4 days normal, incomplete disruption decrease amp CSNAP and CMAP and possible changes distal segment, complete disruption complete loss response/absence CSNAP/CMAP distal segment
EMG: <4 days normal, prolonged insertional activity, fibrillation/positive sharp waves at rest, large motor unit AP with min contraction, decreased firing rate max activation

neurotmesis NCV/EMG

NCV similar to axonotmesis
EMG similar to axonotmesis but if complete no voluntary activity with max activation

blink reflex

CN V and VII, direct is side stimulated and indirect is contra side

repetitive nerve stimulation

repetitive supramaximal stimuli, analyze CMAP amp - normal is 5-8% drop
with myasthenia gravis see much steeper drop in amp

EMG contraindications/precautions

abnormal blood clotting factors, extreme swelling, dermatitis, uncooperative pt, recent MI, blood-transmittable disease, immune-suppressed condition, central-going lines, pacemakers, hypersensitivity to stimulation

EMG general principles

sample across full cross section muscle, exam muscle above/below suspected site, exam muscles innervated by other nerves in same limb, compare sides and UE/LE, eval in context

EMG insertional activity

normal: high frequency burst of spikes, response short lasting
abnormal: reduction in activity, prolonged activity, insertional positive waves

EMG resting activity

should be relatively flat, if near NMJ may see mini end plate spikes or end plate spikes if neuron active
abnormal: fibrillation potentials, positive sharp waves, fasciculation potentials, complex repetitive discharge, myokymic

EMG minimum activity

single biphasic or triphasic motor units
abnormal: interference pattern, polyphasic, smaller or larger than normal motor units

EMG maximal activity

interference pattern
abnormal: single motor units, reduced interference pattern

myopathies NCV/EMG

NCV: normal amp for motor and sensory
EMG: normal insertional, normal or fibrillations at rest, small motor unit APs with min activation, small amp with max activation but full recruitment pattern

myelinopathy NCV/EMG

NCV: decreased amp and velocity for motor and sensory
EMG: normal

UMN NCV/EMG

NCV: normal since tests peripheral nerves
EMG: normal for all but max activation low firing rate

SEMG amplitude

reflects size and numbers of muscle fibers activated, difficult to compare strength of contractions between muscles, amp depends on electrode size/location/muscle activity
some electrical activity from resistance of skin

SEMG amplitude normalization

measure during MVIC, use percentage of this to normalize

SEMG timing

onset, duration, and offset of muscle activity

SEMG fatigue

force output tapers off with fatigue