Ch 5 - EDX: Clinical Instrumentation Flashcards

1
Q

What does the cathode of the stimulating electrode do?

A

Generates a - impulse and attracts + charges from the axon

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2
Q

What does the anode of the stimulating electrode do?

A

Generates a + impulse and attracts - charges from the axon

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3
Q

What is anodal block?

A

Reversing stimulator’s cathode and anode hyperpolarizes the nerve and inhibits generation of AP

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4
Q

What is threshold stimulus?

A

Electrical stimulus sufficient to produce potential from a nerve

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5
Q

What is maximal stimulus?

A

Electric stimulus in which no further increased evoked potential will occur with added stimulus intensity

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6
Q

What errors can occur with submaximal stimulus?

A

Falsely lower amp Prolonged latency

Can give impression of axonopathy or conduction block

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7
Q

What is the supramaximal stimulus?

A

Electrical stimulus intensity at leaset 20% above maximal stimulus

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8
Q

What can too high of a stimulus intensity lead to?

A

Decreased conduction times
Shortened latency
Altered waveforms
Amp unchaged

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9
Q

How can stimulus artifact be minimized on NCS?

A

Placing ground electrode b/w recording electrode and simulator
Appropriate anode and cathode placement
Cleansing skin of dirt, perspiration and lotion

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10
Q

What does the High Frequency (Low Pass) Filter (HFF) do?

A

Removes signals with frequencies higher than its cutoff setting and signals below not affected.
Affects faster portions of the summated waveforms

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11
Q

What does the Low Frequency (High Pass) Filter (LFF) do?

A

Removes signals with frequencies lower than cut off and frequencies above not affected.
Affects slower portions of summated waveforms

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12
Q

What are the filter settings for NCS and EMG?

A

Motor NCS: 2Hz-10kHz

Sensory NCS/EMG: 20Hz-10kHz

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13
Q

What does increasing the LFF do to waveforms on NCS?

A

Reduces peak latency
Reduces amp
Changes potentials from bi- to triphasic
Does not change onset latency

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14
Q

What does reducing the HFF do to waveforms on NCS?

A

Prolongs peak latency
Reduces amp
Creates longer negative spike
Prolongs onset latency

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15
Q

What is the sweep speed?

A

Time allocated for each x-axis division and measured in miliseconds

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16
Q

What is the sensitivity?

A

Height allocated for each y-axis and measured in milivolts (mV) or microvolts (uV).

17
Q

What is a normal sweep speed setting?

A

Motor: 2 ms
Sensory: 5 ms
MG: 10 ms

18
Q

What is a normal sensitivity setting?

A

Motor: 5 uV
Sensory: 10 uV
EMG: 100 uV (insertional acitivity)
1 mV (recruitment pattern)

19
Q

What is the onset/distal latency?

A

Time required for electric stimulus to initiate an evoked potential.
Recorded from stimulus to initial deflection from baseline

20
Q

What is the Common Mode Rejection Ratio (CMRR)?

A

Selectively amplifying different signals and rejecting common ones

Should be 90 dB or >

The > CMRR, the > efficient amplifier

21
Q

What are CI to NCS?

A

External cardiac pacing wires

Central line catheters

22
Q

What are relative CI to EMG?

A

Platelets <50,000

INR >3