Free BRPT Application of Electrodes and Sensors using the 10-20 System Questions and Answers — Questions and Answers
Question 1: According to the International 10-20 System, how is the location of the C3 electrode determined?
- 10% of the head circumference superior to the left preauricular point.
- 20% of the distance from the nasion to the inion, measured from the nasion.
- 20% of the distance from the left preauricular point to the right preauricular point.
- 20% of the nasion-inion distance to the left of the Cz point. (Correct answer)
Correct answer: 20% of the nasion-inion distance to the left of the Cz point.
The C3 electrode is located by first measuring the distance from the nasion to the inion. C3 is then found by moving 20% of this total distance to the left from the Cz (central zero) point, which is at 50% of the nasion-inion distance.
Question 2: What is the standard placement for the right electrooculogram (ROC) electrode according to AASM guidelines?
- Directly on the outer canthus of the right eye.
- 1 cm below and 1 cm out from the outer canthus of the right eye. (Correct answer)
- 2 cm above the inner canthus of the right eye.
- On the supraorbital ridge of the right eye.
Correct answer: 1 cm below and 1 cm out from the outer canthus of the right eye.
The right EOG (ROC) electrode is placed 1 cm below and 1 cm out from the outer canthus of the right eye. This placement, along with the left EOG electrode, allows for the detection of horizontal and vertical eye movements.
Question 3: What is the AASM recommended maximum impedance level for EEG and EOG electrodes?
- 1 kΩ
- 10 kΩ
- 5 kΩ (Correct answer)
- 50 kΩ
Correct answer: 5 kΩ
The American Academy of Sleep Medicine (AASM) recommends that impedances for EEG and EOG electrodes be at or below 5 kOhms (5,000 Ohms). High impedances can lead to signal artifact and poor data quality.
Question 4: In a standard polysomnography montage, the derivation 'C4-M1' refers to the electrical potential difference between which two points?
- The C4 electrode and the ground electrode.
- The C4 electrode and the right mastoid (M2) process.
- The C4 electrode and the left mastoid (M1) process. (Correct answer)
- The C3 electrode and the left mastoid (M1) process.
Correct answer: The C4 electrode and the left mastoid (M1) process.
A derivation represents the difference in electrical potential between two electrodes. 'C4-M1' means the C4 (right central) electrode is the exploring electrode (Grid 1) and the M1 (left mastoid) electrode is the reference electrode (Grid 2).
Question 5: When placing the three chin EMG electrodes, what is the primary physiological activity being measured?
- Jaw clenching and bruxism.
- Muscle atonia associated with REM sleep. (Correct answer)
- Swallowing and respiratory effort.
- Snoring vibrations.
Correct answer: Muscle atonia associated with REM sleep.
Chin EMG measures muscle tone (atonia) of the submental muscles. This is a key characteristic used to identify REM sleep, as muscle tone is significantly reduced or absent during this stage.
Question 6: If a patient has a lot of hair and measuring the nasion-inion distance is difficult, what is a common procedural step to ensure accuracy?
- Estimate the distance based on the patient's head size.
- Use a flexible tailor's tape measure and press down firmly.
- Use a piece of string to follow the scalp contour, then measure the string. (Correct answer)
- Place the electrodes based on visual landmarks only.
Correct answer: Use a piece of string to follow the scalp contour, then measure the string.
Using a non-stretchy material like string or thread allows the technologist to follow the contour of the scalp accurately through the hair. The string can then be laid flat against a tape measure for a precise measurement, which is more reliable than using a flexible tape measure directly on the head.
Free BRPT Application of Electrodes and Sensors using the 10-20 System Questions and Answers
According to the International 10-20 System, how is the location of the C3 electrode determined?