EDT Device Setup & Operation 2 — Questions and Answers
Question 1: When performing a median nerve motor study, which filter settings are most appropriate for recording the CMAP?
- High-pass 2 Hz, low-pass 10 kHz (Correct answer)
- High-pass 20 Hz, low-pass 500 Hz
- High-pass 100 Hz, low-pass 3 kHz
- High-pass 500 Hz, low-pass 10 kHz
Correct answer: High-pass 2 Hz, low-pass 10 kHz
Motor NCS uses a bandpass of 2–10,000 Hz to capture the full frequency range of compound muscle action potentials.
Question 2: A technician notices 60 Hz artifact on the EMG display. Which step should be taken FIRST?
- Enable the notch filter immediately
- Check and improve electrode impedance and ground connections (Correct answer)
- Increase the sensitivity setting
- Reduce the sweep speed
Correct answer: Check and improve electrode impedance and ground connections
Poor electrode contact and inadequate grounding are the most common causes of 60 Hz artifact, and correcting these is preferred before using the notch filter.
Question 3: For an F-wave study, how should sweep speed typically be adjusted compared to a standard distal motor latency recording?
- Decreased to 1 ms/div
- Increased to 100 ms/div or more (Correct answer)
- Kept identical at 5 ms/div
- Set to 10 ms/div regardless of nerve tested
Correct answer: Increased to 100 ms/div or more
F-waves travel to the spinal cord and back, requiring a longer time window (100 ms or more) to capture the late response.
Question 4: Which electrode configuration is used for the active (E1) recording electrode in a standard nerve conduction study?
- Placed over the motor point or muscle belly (Correct answer)
- Placed at a fixed distance of 10 cm from the cathode
- Placed proximal to the reference electrode
- Placed over bone to reduce muscle artifact
Correct answer: Placed over the motor point or muscle belly
E1 is placed over the motor point (belly) of the target muscle to maximize CMAP amplitude.
Question 5: During repetitive nerve stimulation, at what frequency is slow repetitive stimulation typically performed to assess neuromuscular junction disorders?
- 1–3 Hz (Correct answer)
- 10–20 Hz
- 30–50 Hz
- 50–100 Hz
Correct answer: 1–3 Hz
Slow repetitive stimulation at 2–3 Hz reveals decremental responses characteristic of postsynaptic NMJ disorders such as myasthenia gravis.
Question 6: What is the purpose of the reference (E2) electrode in a sensory nerve conduction study?
- To provide the electrical ground for the patient
- To serve as an inactive site for differential amplification, canceling common-mode noise (Correct answer)
- To stimulate the nerve antidromically
- To measure skin temperature at the recording site
Correct answer: To serve as an inactive site for differential amplification, canceling common-mode noise
The reference electrode feeds into the inverting input of the differential amplifier, which subtracts shared noise and amplifies only the signal of interest.
Question 7: A sensitivity setting of 20 µV/div would be most appropriate for recording which type of signal?
- Compound muscle action potential (CMAP)
- Sensory nerve action potential (SNAP) (Correct answer)
- H-reflex response
- F-wave response
Correct answer: Sensory nerve action potential (SNAP)
SNAPs are low-amplitude signals (typically 5–50 µV) that require higher sensitivity (smaller µV/div) compared to the millivolt-range CMAP.
EDT Device Setup & Operation 2
When performing a median nerve motor study, which filter settings are most appropriate for recording the CMAP?