RPSGT Exam Sleep Study Technical Setup & Electrode Application — Questions and Answers
Question 1: During PSG electrode application, an impedance check shows 18 kΩ on the C4-M1 EEG derivation. What is the correct action before starting the study?
- Proceed — 18 kΩ is within acceptable limits for clinical PSG
- Re-prep the scalp site and reapply the electrode to achieve impedance below 5 kΩ (Correct answer)
- Increase the amplifier gain to compensate for high impedance
- Apply a bandpass filter to eliminate the high-impedance artifact
Correct answer: Re-prep the scalp site and reapply the electrode to achieve impedance below 5 kΩ
AASM guidelines specify that electrode impedance should be ≤ 5 kΩ (ideally ≤ 2 kΩ) for all EEG electrodes. High impedance (18 kΩ) dramatically increases susceptibility to 60 Hz electrical artifact and degrades signal quality. The site must be re-prepped (lightly abraded and cleaned) and the electrode reapplied before the study proceeds.
Question 2: According to AASM recommendations for adult PSG, which EEG derivations should be used as the primary channels for sleep staging?
- F3-M2, C3-M2, O1-M2 (left hemisphere derivations as primary)
- F4-M1, C4-M1, O2-M1 (right hemisphere derivations as primary) (Correct answer)
- Fz-Cz, Cz-Oz (linked midline derivations)
- T3-M2, T4-M1 (bilateral temporal derivations)
Correct answer: F4-M1, C4-M1, O2-M1 (right hemisphere derivations as primary)
AASM (2007 and updated rules) recommends F4-M1, C4-M1, and O2-M1 as the primary EEG derivations for sleep staging, with F3-M2, C3-M2, and O1-M2 as backup channels. The right hemisphere is primary because the reference electrode M1 (left mastoid) is farther from the heart, reducing ECG artifact contamination in frontal leads.
Question 3: During pre-study biocalibrations, the technologist asks the patient to look left and then right several times. Which recording channel is this instruction designed to verify?
- Chin submental EMG
- EEG — specifically the occipital electrodes
- EOG (electrooculography) channels (Correct answer)
- ECG (electrocardiography)
Correct answer: EOG (electrooculography) channels
Horizontal eye movements produce large, out-of-phase deflections in the EOG channels (E1-M2 and E2-M1). Asking the patient to look side-to-side confirms that both EOG electrodes are properly placed and recording, and that the polarity (phase reversal) is correct. This is critical for distinguishing eye movements during REM and wake.
Question 4: What is the primary clinical purpose of the submental (chin) EMG channel in a standard PSG montage?
- To detect periodic limb movements in sleep
- To measure thoracic respiratory effort
- To distinguish REM sleep (atonia) from NREM sleep (normal muscle tone) (Correct answer)
- To identify artifact from patient movement
Correct answer: To distinguish REM sleep (atonia) from NREM sleep (normal muscle tone)
The submental EMG is essential for sleep staging because REM sleep is defined in part by muscle atonia (very low chin EMG amplitude). AASM requires that REM be scored only when the chin EMG falls to its lowest level of the recording. Elevated chin EMG during suspected REM may indicate REM sleep behavior disorder.
Question 5: In the standard PSG setup, leg EMG electrodes are placed on the anterior tibialis muscles of both legs. What minimum inter-electrode distance is recommended to ensure proper recording?
- 1-2 cm apart on the same muscle belly
- 2-3 cm apart on the anterior tibialis, one-third of the way down the lower leg (Correct answer)
- 5-7 cm apart, one on each side of the knee
- Electrodes placed on different legs are always referenced to each other
Correct answer: 2-3 cm apart on the anterior tibialis, one-third of the way down the lower leg
AASM recommends placing leg EMG electrodes 2-3 cm apart longitudinally on the belly of the anterior tibialis muscle, approximately one-third of the way down from the knee. This placement optimally captures tibialis muscle bursts associated with periodic limb movements, while minimizing cross-talk from adjacent muscles.
Question 6: The standard PSG epoch length used for manual sleep staging according to AASM rules is:
- 20 seconds
- 30 seconds (Correct answer)
- 60 seconds
- 5 seconds
Correct answer: 30 seconds
AASM scoring rules specify a standard epoch length of 30 seconds for sleep staging. Each epoch receives exactly one sleep stage designation (W, N1, N2, N3, or R). Thirty seconds was chosen to align with the traditional paper PSG speed of 10 mm/sec (which yields a 30-cm/page recording at that speed).
RPSGT Exam Sleep Study Technical Setup & Electrode Application
During PSG electrode application, an impedance check shows 18 kΩ on the C4-M1 EEG derivation.
What is the correct action before starting the study?