NCS instrumentation Flashcards by Emmanuel Easterling

3 Variables

1.Intensity of stimulus voltage fixed (0-400N); Amperes (0-100)mA amount of current 2. Duration aka pulse width of stimulus (50-1000ms) 3. Rate of stimulus 1-50 stim/sec(Hz)

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What do Pre Amp/Amplifiers do?

Convert low voltage signal to higher voltage copy

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What does the Differential Amp do?

2 amps- measure diff b/w active and reference

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Common Mode Signal

Seen in both amps (active and reference)

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What is the Common Mode rejection ratio (CMRR)?

ability of amp to amplify desired signal while rejecting common mode signal; measured in decibals-clinical amplifiers >90Db

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What does the HF/Low Pass filter do?

resistors filter out high frequency

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What does the LF/High Pass filter do?

resistors filter out low frequency

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What is recommended filter setting for motor studies?

LF- 2-10Hz; HF- 10KHz

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What is recommended filter setting for sensory studies?

LF- 2-10Hz; HF- 2KHz

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What is recommended filter setting for EMG?

LF- 20-30Hz; HF- 10KHz

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What is effect if INCREASE LF filter?

DECREASE AMP and DECREASE LATENCY Stabilize baseline

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What is effect if DECREASE LF filter?

INCREASE AMP and INCREASE LATENCY

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What is effect if INCREASE HF filter?

INCREASE AMP and DECREASE LATENCY

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What is effect if DECREASE HF filter?

DECREASE AMP and INCREASE LATENCY

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What is typical sweep speed?

10ms/div = duration (entire screen) 100ms Set sweep speed at 100ms/div= duration of 1 second if have 10boxes across

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What is CMAP?

summation of individual mm fiber action potentials

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What is SNAP?

summation of individual sensory fiber action potentials

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What do mixed studies test?

record largest sensory nerves (1a) afferent mm spindle, largest and most myelinated so usually affected 1st in demyelinating lesions

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What does amplitude represent?

of fibers that depolarize

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What does NCS duration represent?

measure of synchrony- extent that fibers depolarize at same time

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What does conduction velocity measure?

speed of the fastest conducting fibers

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How is motor conduction velocity measured?

calculated in proximal segment only! CV=distance/(prox lat-distal lat)

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How is sensory conduction velocity measured?

calculated in proximal and distal segments distance/time

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What temp should we maintain for NCS performed in UE and LEs?

UE-32 and LE >29

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What is the effect of having decreased temp?

increased amp, duration, prolonged latency decreased CV

How does age variable affect CV?

decrease 1-2ms per decade past 20 years old

How does UE CV compare to LE CV?

UE CV is faster than LE CV

How does proximal CV compare to distal CV?

Faster proximal; closer to trunk/nutrition, larger diameter

How does segment size LONG vs SHORT studied affect calculations?

Measure a short segment, risk for more error, since small error has SIG effect on calculation

Describe a MUP morphology.

3 phases, amp-300-500uV, duration-\<10-12ms

What does MUP EMG duration represent?

of mm fibers within motor unit. 'pitch' will increase as number of fibers and territory increases

What does a long duration MUP mean?

dull and thuddy, sign of chronic condition-motor unit remodeling

What does a Short duration MUAPs sound like?

'crisp'

What does polyphasia represent?

measure of synchrony and axonal sprouting

What does MUP amplitude affect?

Volume

What does a unstable MUAP mean?

NMJ disorder or increased jitter

MM fiber recruitment follows what rule normally?

Rule of 5s 1 MU at 5Hz; 2nd MU will come in at 10Hz

How can you increase force?

Increase rate of fire (activation) or recruit more MUs

What is recruitment ratio?

Rate of fastest firing MU/total number of MUs \>10= decreased recruitment (neuro); \<5=increased/early recruit (myopathic)

What is decreased recruitment?

caused by LOSS OF MUAPs; conduction block or axonal loss, can't bring enough soldiers to the fight

What is increased/early recruitment?

caused by LOSS OF MM FIBERS; get lots of MUs fire to produce small amount of force

Describe what chronic axonal loss MUs will look like.

large amp, long duration, polyphasic-reinnervated mms

What would demyelination look like on EMG?

MUAP morphology-normal-C.B-decreased recruit (GBS and CTS)

What would a myopathic MU look like?

decreased # of mm fibers- short duration low amp (BSAPP)

How many mm fibers can contribute to a MUP?

at max 12

How close to the needle tip do mm fibers have to be?

1-3mm

How many MUPs in each mm can be analyzed?

@ least 12; 4 quadrants-3 probes each quadrant

The mm fibers of 1 MU can be spread over oval x-sectional area of what size?

5mm

How many MUs can be recorded from needle tip?

12-15

A typical MU has how many phases?

3 phases

What would increase duration of MUP?

increased phases and turns; axonal sprouting/regeneration

Why would we have 0 MUPs?

No axons, complete CB, pain or lesion in CNS

What happens to mm fibers when needle is briskly moved in mm?

Depolarize the mm and get insertional activity

How long does normal insertional activity last?

\<200-300ms

What is increased insertional activity?

\>200ms; usually with myotonic disorders

What is decreased insertional activity?

mm damage/chronic denervation; if get resistance to needle insertion=poor prognosis since getting mm fibers turning into fibrotic tissue

To observe spon activity settings are...

10ms sweep speed, 50mV/div

What things can cause abnormal spon activity?

trauma, inflammation and denervation

Fibs and PSWs are signs of what?

acute 'active' denervation/mm membrane instability

Prejunctional

problem w/motor nerve terminal branch

Postjunctional

lesion in mm fiber

Any potential that fires \<4-5Hz

is not under voluntary control

What types of potential do you see that are MFAP/post

fibs, psws, myotonic, CRD

What types of potential do you see that are MUAP/pre

fasiculation, myokymic, neuromytonia,cramps

What causes a EPP/EPS?

needle touches axon terminal causing depolarization

What is a unstable membrane potential cause by?

decrease in intracellular K+

What are EMG characteristics of fibs?

+deflection, 3phases, amp: 30-800uV, duration\<5ms, regular fire rate (post-junct), click, raindrop

What are EMG characteristics of psws?

biphasic, duration 30-100ms

How soon post injury should EMG be performed?

3wks/21 days

What are EMG characteristics of EPS?

Irregular fire (pre), biphasic, -deflection, hiss/sputtering

Why is it incorrect to refer to fibs/psws as denervation potentials?

Can see them in myopathic conditions

What are EMG characteristics of Myotonic d/c?

+deflection, phases 2-3, duration 2-3ms, rate 50-100Hz, WAX AND WANE; dive bomber sound

What are EMG characteristics of CRDs?

Pacemaker ephatic D/C=chronic pathology, phases-polyphasic, duration 10-15ms, amp 50-1000uV, regular fire rate- MACHINE

What are EMG characteristics of myokymic d/c?

undulating/quivering skin, post radiation- same MUAP fires, burst, soldier marching

What are EMG characteristics of neuromyotonia d/c?

WANING, AMP decreasing, highest freq- stiffness ‘Issac’s Syndrome’