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Basic Eval II > Nerve Conduction Velocity > Flashcards

Nerve Conduction Velocity Flashcards

1
Q

What 4 pieces of information can nerve conduction velocity provide about peripheral nerve disease?

A
  • Demyelinated nerves
  • Axonal degeneration
  • Location of injury
  • Type of injury
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2
Q

What are the 3 types of nerve injury?

A
  • Neurapraxia
  • Axonotomesis
  • Neurotemsis
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3
Q

What are the 4 methods of measurement of nerve conduction velocity?

A
  • Latency
  • Amplitude
  • Duration
  • Configuration
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4
Q

What is the difference conduction velocity in a demyelinated motor nerve and a degenerated motor nerve?

A

A demyelinated nerve has in tact amplitude, but is slowed across the lesion

A degenerated nerve has little or no muscle response.

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5
Q

What is the difference between conduction velocity in a demyelinated sensory nerve and degenerated sensory nerve?

A
  • Slowed velocity in demyelinated nerve

- Reduced amplitude in axonal degeneration

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6
Q

What type of lesion would result in degeneration of sensory fibers?

A
  • Postganglionic (plexopathy/ neuropathy)
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7
Q

Why must a supermaximal stimulation be used for nerve conduction velocity?

A

Larger fibers are activated before smaller fibers, and if a low magnitude stimulation is used, not all fibers will be generated.

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8
Q

What are the 2 types of action potentials generated in sensory nerve conduction velocity tests?

A
  • Orthodromic: Travels to muscle

- Antidromic: Travels back to spinal cord

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9
Q

How should the patient be prepared prior to performing the test?

A
  • Tell them what to expect
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10
Q

What 2 things should be inspected on the patient before beginning a NCV test?

A
  • Check sensation

- Check skin integrity

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11
Q

How should the patient be positioned, and prepared for the NVC test?

A
  • Clean and mildly abrade skin with alcohol so that less juice needs to be used
  • Position patient so that the nerve can be accessed from all positions
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12
Q

Where should the cathode and anode of the recording site be placed? Which is the stimulating electrode, and which is the reference?

A
  • Cathode placed over the muscle belly
  • Stimulating
  • Anode placed over tendon of insertion distal to the cathode
  • Reference
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13
Q

Where is the ground reference placed?

A
  • Over a bony prominence
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14
Q

What are the parameters for stimulation of a motor nerve with NCV tests? Pulse? Frequency? Gain? Sweep?

A

Pulse: 0.1 ms
Frequency 1Hz; 3 Hz - 10 kHz
Gain: 2mV/ division
Sweep speed: 5 - 10 ms/div

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15
Q

How is conduction velocity calculated?

A

Distance between stimulating cathodes in mm/ (Latency 2 - Latency 1 in ms)

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16
Q

What type of disease are delayed latencies indicative of?

A

Demyelinated disease

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17
Q

Where are the stimulation electrodes placed?

A

Cathode distal

Anode Proximal

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18
Q

Describe the placement of the stimulation and pick-up electrodes for orthodromic sensory NCV tests.

A

Stimulation: (on fingers)

  • Cathode proximal
  • Anode distal

Pick-up: (proximally along course of nerve)

  • Cathode distal
  • Anode proximal
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19
Q

How are the electrodes shaped in sensory orthodromic stimulation?

A
  • rings to be placed around fingers of nerve distribution
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20
Q

Describe the placement of the stimulation and pick-up electrodes for antidromic sensory NCV tests.

A

Stimulating: (along course of nerve)

  • Cathode distal
  • Anode proximal

Pick-up (around fingers)

  • Cathode proximal
  • Anode distal
  • Ground over bony prominence
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21
Q

What nerves are usually tested?

A
  • Median
  • Ulnar
  • Radial
  • Peroneal
  • Sural
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22
Q

Which type of action potential is preferred for sensory testing? Why?

A
  • Nerves in skin are easier to read

- Antidromic preferred

23
Q

What are the settings for sensory NVC tests for: EMG? Stimulation?

A

Pulse: 0.1 ms
Frequency 1Hz; 3 Hz - 10 kHz
Gain: higher than in motor (which is 2mV/ division)
Sweep speed: 5 - 10 ms/div

** Intensity only high enough to produce sensory stimulus **

24
Q

How are sensory conduction velocities calculated?

A
  • Only latencies are used

- Record from stimulus artifact to peak of 1st phase of AP

25
Q

What is the calculation for sensory conduction velocity?

A

distance between stimulation and recording sites/ latency

26
Q

What can be used to measure nerves more proximally?

A

H-reflex, and F-waves.

27
Q

What is an H-reflex?

A
  • A quick delayed reactionary response after a small stimulation.
28
Q

What does a diminished H-reflex indicate?

A

The nerve problem is proximal

29
Q

On which muscle is the H-reflex typically conducted?

A
  • The flexor carpi radialis
30
Q

What is the F-wave?

A
  • Huge action potential travels back to motor neuron and depolarizes its self, and then returns as a late response
31
Q

Why must the F-wave be done 20 times? Which latency is used for the measurement?

A
  • The neuron may be in refraction

- Shortest latency is used

32
Q

What 3 factors may increase or decrease nerve conduction velocity?

A
  • Temperature
  • Nerve length (UE vs LE)
  • Age
33
Q

What temperature should the skin be kept at or above?

A

34 degrees celcius

34
Q

How much must the conduction velocity be increased by for each degree centigrade the skin falls below 34?

A

5 %

35
Q

Alternately, what temperature should the room be kept at during measurements?

A

21 - 23 degrees C

36
Q

Why are nerves slower in the LE than in the UE?

A

Longer nerves.

37
Q

Is NCV faster in proximal or distal segments?

A

Proximal

38
Q

When does NCV velocity reach adult values in children?

A

3 - 5 yo

39
Q

When do NCV tend to begin decreasing?

A

30 - 40 yo

40
Q

What percentage of adult NCV do infants possess?

A

About 50 %

41
Q

At what sites do nerve amplitude and configurations change as a person ages?

A

At sites of compression

42
Q

What specifically declines that as people age in NCV tests?

A

Latency.

43
Q

What is spread stimulation current?

A
  • Nerves or muscles not being tested may be recruited at higher intensities
44
Q

What area is specifically susceptible to spread stimulation current?

A
  • Axilla
45
Q

What anastomosis is present in the forearm that can cause false EMG readings? What nerves are involved? How many people does this occur in?

A
  • Martin-Gruber anastomosis of the median and ulnar nerve
46
Q

What is present in the leg in 20 - 28 % of people that may complicate NCV?

A

Accessory deep peroneal nerve branch of superficial peroneal nerve

47
Q

What effect does the accessory peroneal have on NCV in the leg?

A
  • AP of muscles will be small with stimulation to the deep peroneal nerve at the ankle than with stimulation of the common peroneal nerve at the knee
48
Q

What is temporal dispersion?

A
  • Different size nerves

- More proximal stimulation means there is a longer duration AP and a smaller amplitude

49
Q

What physiological process can always be a problem in NCV readings?

A

Physiological block

50
Q

What is a motor conduction block? What happens when sensory nerves are blocked?

A
  • If nerve is stimulated proximal to block is reduced in amplitude and disperes
  • Sensory nerves are almost unrecordable
51
Q

What is repetitive nerve stimulation?

A
  • Application of supramaximal stimulation at 2 Hz - 10 Hz.
  • Testing to see if there is enough acetylcholine in the synapse
  • If not, the amplitude drops
52
Q

What is needle EMG used for?

A
  • Measures small motor units with a manual contraction
53
Q

How many times is the same muscle assessed at different points?

A

3 - 4.

Basic Eval II (7 decks)

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