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634: Electrotherapy Modalities > Basics Behind Nerve Conduction Studies > Flashcards

Basics Behind Nerve Conduction Studies Flashcards

1
Q

What happens to the nerve underneath the cathode?

A

it depolarizes

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2
Q

What happens to the tissue in the area of the anode?

A

it hyperpolarizes

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3
Q

What is the goal of electrical stimulation?

A

To create a sudden and rapid alteration in the resting membrane potential of the nerve being evaluated

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4
Q

In a voluntary contraction a supramaximal stimulus is needed for what reasons?

A

Reproducible results

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5
Q

What does the response generated from a voluntary contraction represent?

A

the capabilities of that peripheral nerve

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6
Q

Current flows most easily through _____-diameter axons due to what?

A

large

due to low resistance

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7
Q

What type of nerves will reach threshold faster? Why?

A

Smaller cell bodies and smaller axons will reach threshold easier because they have a higher resistance

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8
Q

What type of muscle fibers are activated first during a voluntary contraction?

A

Small, slow-twitch, type I muscle fibers

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9
Q

In what direction does current flow with an externally applied current?

A

Down the paths of least resistance, so from larger-diameter axons to the smallest

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10
Q

In an externally applied current a supramaximal stimulus is needed for what reasons?

A

In order to fully activate the peripheral nerve

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11
Q

What does the response generated from an electrically applied stimulus represent?

A

The capabilities of all axons associated with a given nerve

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12
Q

How is an electrically stimulated supramaximal stimulation verified?

A

By increasing the stimulus intensity until the compound action potential does not get larger with higher levels of stimulus

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13
Q

This stimulus level will vary from patient to patient, depending upon what 4 things?

A
  • Skin thickness
  • Adipose tissue
  • Connective tissue
  • Musculature
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14
Q

What is a nerve conduction study?

A

a test commonly used to evaluate the function of the motor and sensory nerves of the human body

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15
Q

What are nerve conduction studies mainly used for?

A

Evaluation of paresthesias and/or weakness of the arms and legs

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16
Q

What are 3 indications for a nerve conduction study?

A
  • Symptoms indicative of nerve damage, such as numbness and/or weakness
  • Differentiation between local or diffuse disease process (mononeuropathy or polyneuropathy)
  • Get prognostic information on the type and extent of nerve injury
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17
Q

What are 4 common disorders diagnosed by NCS?

A
  • Peripheral neuropathy
  • Myopathy
  • Radiculopathy
  • Diseases of neuromuscular junction
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18
Q

What are 3 types of peripheral neuropathies?

A
  • Mononeuropathy
  • Mononeuritis multiplex
  • Polyneuropathy (ex: diabetic neuropathy,)
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19
Q

What is an example of mononeuropathy?

A

carpal tunnel syndrome

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20
Q

What are a couple examples of mononeuritis multiplex?

A
  • vasculitides
  • RA
  • SLE
  • sarcoidosis
  • leprosy
  • Lyme disease
  • amyloidosis
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21
Q

What are 4 common types of myopathies diagnosed via NCS?

A
  • Muscular dystrophies
  • Myotonia
  • Congenital myopathies
  • Metabolic myopathies
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22
Q

What is a common disease of the neuromuscular junction?

A

Myasthenia gravis

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23
Q

What are the 2 things NCS are used to determine?

A
  • Nerve conduction velocity (speed of conduction)

- Size (amplitude) of the collective action potential

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24
Q

NCS evaluate the function of what 3 things?

A
  • Peripheral nerves
  • The N/M junction
  • The collective muscle fibers innervated by the nerve being examined
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25
Q

Does a NCS involve a puncture of the skin?

A

No

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26
Q

What does an electromyography (EMG) evaluate?

A

The electrical activity of the muscles and the muscle APs monitored from a sample of muscle fibers

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27
Q

What is the major difference between NCSs and EMGs?

A

EMGs utilize a needle electrode that is inserted to allow judgment regarding the function of the individual muscle fibers
NCS electrodes do no penetrate the skin

28
Q

When does the needle electrode monitor the individual muscle fiber?

A

at rest and during several stages of voluntary contraction

29
Q

What 6 things are obtained via a EMG?

A
  • Excitability of PNS
  • Nerve conduction time (sensory and motor)
  • Nerve conduction velocity (sensory and motor)
  • Amplitude of action potential following nerve stimulation
  • Duration of AP
  • Fatigability of peripheral neuromuscular system in response to repetitive stimulation
30
Q

What are the 3 electrodes that are attached to the patiented during a NCS or EMGs?

A
  • Active
  • Reference
  • Ground
31
Q

What is the purpose of the ground electrode?

A

It filters out background noise

32
Q

What are 3 specific types of electrodes that can be used during a NCS?

A
  • Sensory ring electrodes
  • Stimulation electrodes
  • Bar electrodes
  • Disk electrodes
33
Q

What are 2 specific types of electrodes that can be used during an EMG?

A
  • Monopolar needle electrode

- Concentric or coaxial needle electrode

34
Q

What are the electrodes plugged into?

A

Amplifiers

35
Q

What do the amplifiers do?

A

Take a very small signal and magnify it

36
Q

The first amplifier is called the _____, and it is the unit that the electrode leads are plugged into.

A

preamplifier

37
Q

What is the function of the preamplifier?

A

It subtracts out the portions of the signal that are common to both the active and reference electrodes

38
Q

The signal from the preamplifier is than sent to the _____, which is used to convert a low voltage potential to a higher voltage signal.

A

main amplifier

39
Q

What are the 2 types of display modes?

A
  • Oscilloscope

- Speakers

40
Q

Oscilloscopes provide ____ feedback, whereas speakers provide _____ feedback.

A

visual

auditory

41
Q

When the active recording electrode is placed proximal to the point of stimulation it is call ______ placement

A

orthodromic

42
Q

Orthodromic placement of the electrodes are placed ____ the direction that sensory fibers normally conduct an AP

43
Q

When the active recording electrode is placed distal to the point of stimulation it is call ______ placement

A

antidromic

44
Q

Antidromic placement of the electrodes are placed ____ the direction that sensory fibers normally conduct an AP

45
Q

Describe the process of a nerve conduction study

A

1) Skin will be cleaned
2) Electrodes will be taped to the skin along the nerves that are being studied
3) Small stimulus is applied that activate nerves
4) The electrodes will measure the current that travels down the nerve pathway

46
Q

How are nerve conduction studies altered if the nerve being evaluated is damaged?

A

the current will be slower and weaker

47
Q

How long does a NCS take?

A

30-90 minutes

48
Q

What types of complications can be expected with NCS?

A

There are no reported complications from the procedure, however the patient can expect to fell discomfort from the electrical current, but it is typically not painful

49
Q

What are a few preliminary considerations regarding the electrodes to consider beforehand?

A
  • Electrode care and cleaning
  • Testing of electrodes
  • Thin film of electrode (conducting) gel
  • Clean and abrade electrode sites on subject’s skin
50
Q

Where should the cathode be placed?

A

Toward the active (recording) electrode

51
Q

Filters should be set between 10 Hz – 10,000 Hz for ____ potentials

52
Q

Filters should be set between 20 Hz – 20,000 Hz for ____ potentials

53
Q

Sweep speed should be between - ms for motor potentials

54
Q

Sweep speed should be between - ms for sensory potentials

55
Q

In order to elicit a motor response sensitivity is usually set between ____ - _____ microvolts

A

1,000 – 5000 microvolts

56
Q

In order to elicit a sensory response sensitivity is usually set between ____ - _____ microvolts

A

5 - 10 microvolts

57
Q

Describe the placement of the active, reference, and ground electrodes.

A
  • The active (recording) electrode should beplaced over the nerve or muscle segment being studied
  • The reference electrode should be off of and distal to the muscle being studied
  • The ground electrode should be placed on a bony prominence BETWEEN the stimulating and active electrodes
58
Q

What are 2 of the most important factors that will have an impact on the results obtained via NCS?

A
  • Limb Temperature

- Age

59
Q

There is a(n) ______ relationship between temperature of the region being studied and the speed of the AP

60
Q

A cold limb will conduct electrical impulses ____ than a limb of normal temperature

61
Q

What should skin surface temperature be for the UE (hand)?

A

between 30-32 degrees Celsius

32 degrees in preferred

62
Q

What should skin surface temperature be for the UE (feet)?

A

30 degrees Celsius

63
Q

To promote an optimal environment for this type of testing, the room should be maintained at a temperature of at least __ degrees Celsius

64
Q

Individuals that are under __ years of age and over __ years of age may have APs that conduct at a slower rate

65
Q

By age 50, action potentials slow about - m/s per decade. After age 70, the slowing becomes much more significant.

634: Electrotherapy Modalities (11 decks)

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