RPSGT Technology & Tools 4 — Questions and Answers
Question 1: The International 10-20 electrode placement system divides the head based on measurements that are what percentage of total skull dimensions?
- 5% and 10%
- 10% and 20% (Correct answer)
- 15% and 25%
- 20% and 30%
Correct answer: 10% and 20%
The 10-20 system uses 10% and 20% intervals of total nasion-to-inion and preauricular distances to place electrodes.
Question 2: Which electrode placement is used for the left eye's recording derivation (E1) in standard AASM PSG montages?
- 1 cm above and 1 cm lateral to the outer canthus of the left eye
- 1 cm below and 1 cm lateral to the outer canthus of the left eye (Correct answer)
- Directly on the outer canthus of the left eye
- 1 cm medial to the inner canthus of the left eye
Correct answer: 1 cm below and 1 cm lateral to the outer canthus of the left eye
AASM recommends E1 placement 1 cm below and 1 cm lateral to the left outer canthus to capture both horizontal and vertical eye movements.
Question 3: Respiratory inductance plethysmography (RIP) measures thoracoabdominal movement by detecting changes in:
- Electrical resistance of the thoracic cage
- Inductance of wire coils embedded in elastic bands (Correct answer)
- Pressure transmitted through the chest wall
- Infrared reflectance from the skin surface
Correct answer: Inductance of wire coils embedded in elastic bands
RIP bands contain sinusoidally wound wires whose inductance changes as cross-sectional area of the thorax or abdomen changes with breathing.
Question 4: A patient's PAP device data shows a residual AHI of 15 events/hr despite a fixed CPAP pressure of 12 cmH2O. The waveform pattern shows clustered events. This pattern is MOST consistent with:
- Persistent obstructive apneas requiring higher pressure
- Treatment-emergent central sleep apnea (Correct answer)
- CPAP pressure set too high causing aerophagia
- Mask leak artifact falsely inflating the AHI
Correct answer: Treatment-emergent central sleep apnea
Clustered central events emerging after initiation of CPAP therapy for OSA is the hallmark of treatment-emergent (complex) central sleep apnea.
Question 5: What is the primary purpose of using a reference electrode (e.g., M1 or M2) in EEG derivations during PSG?
- To provide the ground connection for safety purposes
- To serve as the electrically inactive reference point for differential amplification (Correct answer)
- To record eye movement artifacts for subtraction
- To monitor electrode impedance continuously
Correct answer: To serve as the electrically inactive reference point for differential amplification
Reference electrodes (mastoids) provide a relatively electrically quiet site for differential amplification, allowing the active electrode's signal to dominate the derivation.
Question 6: The leg EMG electrodes for PLMS detection are placed on which muscle, and at what inter-electrode distance?
- Tibialis anterior; 2–3 cm apart
- Gastrocnemius; 2–3 cm apart
- Tibialis anterior; 5–7 cm apart (Correct answer)
- Gastrocnemius; 5–7 cm apart
Correct answer: Tibialis anterior; 5–7 cm apart
AASM recommends placing leg EMG electrodes on the tibialis anterior muscle with inter-electrode distance of 2–3 cm apart.
Question 7: When performing a biocalibration at the start of PSG, asking the patient to hold their breath for 10 seconds primarily tests which channel?
- EEG montage integrity
- Respiratory airflow and effort channels (Correct answer)
- ECG signal quality
- SpO2 probe placement
Correct answer: Respiratory airflow and effort channels
Breath-holding calibration verifies that airflow (thermistor/nasal pressure) and respiratory effort (RIP/piezo) channels correctly show cessation of breathing.
RPSGT Technology & Tools 4
The International 10-20 electrode placement system divides the head based on measurements that are what percentage of total skull dimensions?