Ch 5 - EDX: Clinical Instrumentation

Question 1

What does the cathode of the stimulating electrode do?

Answer 1

Generates a - impulse and attracts + charges from the axon

Question 2

What does the anode of the stimulating electrode do?

Answer 2

Generates a + impulse and attracts - charges from the axon

Question 3

What is anodal block?

Answer 3

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

Question 4

What is threshold stimulus?

Answer 4

Electrical stimulus sufficient to produce potential from a nerve

Question 5

What is maximal stimulus?

Answer 5

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

Question 6

What errors can occur with submaximal stimulus?

Answer 6

Falsely lower amp
Prolonged latency
Can give impression of axonopathy or conduction block

Question 7

What is the supramaximal stimulus?

Answer 7

Electrical stimulus intensity at least 20% above maximal stimulus

Question 8

What can too high of a stimulus intensity lead to?

Answer 8

Decreased conduction times
Shortened latency
Altered waveforms
Amp unchaged

Question 9

How can stimulus artifact be minimized on NCS?

Answer 9

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

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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

Question 12

What are the filter settings for NCS and EMG?

Answer 12

Motor NCS: 2Hz-10kHz

Sensory NCS/EMG: 20Hz-10kHz

Question 13

What does increasing the LFF do to waveforms on NCS?

Answer 13

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

Question 14

What does reducing the HFF do to waveforms on NCS?

Answer 14

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

Question 15

What is the sweep speed?

Answer 15

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

Question 16

What is the sensitivity?

Answer 16

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

Question 17

What is a normal sweep speed setting?

Answer 17

Motor: 2 ms
Sensory: 5 ms
EMG: 10 ms

Question 18

What is a normal sensitivity setting?

Answer 18

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

Question 19

What is the onset/distal latency?

Answer 19

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

Question 20

What is the Common Mode Rejection Ratio (CMRR)?

Answer 20

Selectively amplifying different signals and rejecting common ones

Should be 90 dB or >

The > CMRR, the > efficient amplifier

Question 21

What are contraindications to NCS?

Answer 21

External cardiac pacing wires

Central line catheters

Question 22

What are relative contraindications to EMG?

Answer 22

Platelets <50,000

INR >3