electrophysio exam Flashcards
What is electrophysiology exam
Evaluate integrity of neuromuscular system
Measures electrical activity
Biofeedback
Monitoring and transforming physiologic data into understandable feedback
Enables individual to gain voluntary control over muscular or autonomic nervous system functions
Visual or auditory stimuli
Adjunct tool and not a treatment itself
Evoked potentials
Applies electricity to evoke an action potential
NCV
Peripheral, motor, and sensory neurons
Orthodromic and antidromic responses
Orthodromic
normal
Antidromic
reverse
SNAP
Provides info on sensory nerve axon
Cutaneous receptors to DRG
CMAP
Motor nerve fibers from origin in anterior horn cells to neuromuscular junction of muscle it innervates
NCV Answers the questions:
Is there involvement of peripheral nerves? Sensory? Motor? both? Where? How many? Magnitude? increasing/decreasing impairment? localized/systemic disorder?
NCV motor components
Stimulating electrode coming from machine
2 small electrodes applied on nerve
2 cm apart
Handheld electrodes
Cathode distal to anode
active/recording electrode: on muscle or nerve
Reference: distally placed
Ground: over bony areas for elimination of noise
motor vs. sensory ncv
Stimulate sensory nerves distally instead of proximally
what info do we get from ncv test
distance = Distance from stimulating to recording electrode (mm)
Latency
Conduction time between stimulus and start of muscle contraction or activation of nerve
(Msec)
Latency
Conduction time between stimulus and start of muscle contraction or activation of nerve (msec)
ncv =
distance/latency
factors affecting ncv
Body temp UE is 7-10 m/s faster Proximal segments are faster Age Less than 3-5 yr old is slower than normal adults >40 - gradual slowing 60-70- 10 m/sec less than middle aged
in compression lesions, ncv is
reduced
NMJ transmission
Also known as jolly test Test for myasthenia gravis Weakness of skeletal muscles Affects diaphragm Function of neuromuscular junction
centrally evoked potentials
Generated by nervous system in response to sensory stimuli
SSEP: what we feel, light touch, pressure
VEP
BAEP
Induce a stimuli and computer reflects if stimuli was received by brain
REACTION OF DEGENERATION
Faradic and galvanic test
Assessment of lower motor neuron lesions
A motorpoint is stimulated
Screening test for differentiating with normal peripheral innervation vs muscle with peripheral denervation
Not specific location
Not a standalone test
Not done at least 10 days after onset of problem
May be indicated in conditions of unexplained paralysis
faradic current
short pulse duration less than 1 msec
monophasic or asymmetrical PC
cathode is active
smooth tetanic
galvanic current
long pulse duration >100 msec
monophasic or interrupted dc
cathode is active
brisk muscle twitch
partial RD faradic vs galvanic
F; partial or diminished tetanic
G: partial or diminished sluggish twitches
partial RD
degeneration of part of nerve fibers
complete RD
degeneration of all nerve fibers
muscle tissue remains
absolute RD
degeneration of all nerve fibers; muscle is non-contractile
complete rd f vs. g
f: no contraction
g: very slow, sluggish twitches
STRENGTH-DURATION CURVE AND CHRONAXIE TEST
After 3 weeks of nerve injury Used to check for improvements Square monophasic PC / sawtooth/ triangular Cathode is stimulating 8-10 pulse durations
usual pulse durations in SD curve
100, 30, 10, 3, 1, 0.3, 0.1, 0.03, 0.01
must be strong enough to depolarize threshold
rheobase
least intensity needed to elicit contraction
normal: 3-35 v/2-18 ma
chronaxie
Minimum time needed to produce a muscle contraction with intensity set at twice the rheobase
Normal: 0.05-0.5 msec or <1 msec
compute for chronaxie
2 x rheobase
Factors affecting sd curve
Skin resistance Subcutaneous tissue Skin temperature Electrode size Electrode placement Age Fatigue
Advantages of sd curve
Quick and easy
Minimal training
Economical
Disadvantages of sd curve
Provides qualitative data in relation to degree of denervation
Cannot locate site of lesion
Few fibers can be assessed
emg biofeedback
We are getting the muscle activity Determines best management for pt Can increase or decrease muscle activity Detects electrical activities Not a treatment
Facilitatory feedback
inc muscle activity
post injury or post op
inhibitory feedback
dec muscle activity
hypertonic muscles
EMG + components
Electricity produced by voluntary movement
Electrical stimulator not needed
Electrodes:
Recording electrode: over muscle being tested
Avoid crosstalk: input from other muscles
Surface EMG
Needle EMG: invasive
Ground electrode: minimize noise
Signal amplification and filtration
Minimize distortion
Maximize signal to noise ratio
High pass filter
blocks low frequency, 5 Hz/10-20 Hz cut off
Low pass filter
blocks high frequency, 500 hz cut off
Signal rectification
Absolute value of all signals
Rectification + low pass filter = linear envelope
Process of traditional low pass filter = butterworth or chebyshev
Signal smooth
Moving average Certain amount of data are averaged using sliding window technique Root mean square Square root calculation Reflects mean power of signal Preferred method
EMG can determine
Muscle activation
Muscle fatigue
Muscle fatigue index
Identifies weak muscles
Determines effectivity of exercise
normal and abnormal EMG at rest
normal: (+) insertion activity, miniature endplate action potentials, no muscle action potentials
abnormal: (+) fibrillations/fasciculations, complex discharges, inc or dec insertional activity
normal and abnormal EMG w mild contraction
normal: biphasic or triphasic muscle AP, mup from small amplitude potentions become progressively large amplitude potentials
abnormal: polyphasic, amplitude dec or inc, altered recruitment pattern
normal and abnormal EMG with max contraction
normal: inc frequency, (N) step wise, inc interference patterns
abnormal: dec interference pattern, early full interference pattern
