Free RST Artifact Recognition and Troubleshooting Questions and Answers — Questions and Answers
Question 1: During a polysomnogram on a patient with a history of obstructive sleep apnea, the technologist notes very low-amplitude, slow, undulating waves across multiple EEG and EOG channels. The patient appears to be perspiring heavily. What is the most likely artifact, and what is the best initial troubleshooting step?
- 60 Hz artifact; check the ground electrode and unplug nearby electronics.
- Movement artifact; wait for the patient to settle into a stable position.
- Sweat artifact; decrease the room temperature and use a fan if possible. (Correct answer)
- ECG artifact; re-reference the affected channels to a common average.
Correct answer: Sweat artifact; decrease the room temperature and use a fan if possible.
Heavy perspiration can cause slow, rolling artifacts on the recording due to changes in skin conductivity. The primary intervention is to cool the patient and the room to reduce sweating, which addresses the root cause of the artifact.
Question 2: A technologist observes a thick, uniform, fast frequency line in all AC-coupled channels (EEG, EOG, EMG). Which of the following is the most probable cause and first corrective action?
- Electrode 'pop'; re-prep and reapply the single affected electrode.
- Muscle tension artifact; ask the patient to relax their jaw.
- 60 Hz interference; check the integrity and placement of the common ground electrode. (Correct answer)
- Pen blocking; recalibrate the amplifier for the affected channels.
Correct answer: 60 Hz interference; check the integrity and placement of the common ground electrode.
A thick, consistent, high-frequency line across all or most AC channels is the classic presentation of 60 Hz electrical interference. When this artifact is generalized across many channels, the issue often lies with the common ground or reference electrodes, or a nearby piece of electrical equipment. The first step is to check the ground electrode connection.
Question 3: While monitoring a study, the signal from the nasal pressure transducer becomes flat, while the oronasal thermistor and respiratory effort belts continue to show clear respiratory cycles. What is the most appropriate immediate action for the technologist to take?
- Reposition the patient's head to open the airway.
- Initiate the emergency response protocol.
- Document the sensor failure and continue monitoring with the remaining signals.
- Check the cannula for displacement or blockages and re-seat it if necessary. (Correct answer)
Correct answer: Check the cannula for displacement or blockages and re-seat it if necessary.
When a single respiratory sensor fails but others show continued breathing, the issue is almost always localized to that specific sensor or its interface. A flat line on the nasal pressure channel, while other respiratory signals are normal, strongly suggests the cannula is either dislodged from the patient's nares or the tubing is kinked or blocked. The technologist should physically check and correct this first.
Question 4: A patient is observed bruxing (teeth grinding) during sleep. Which of the following artifacts would be most prominent in the polysomnogram during this activity?
- High-amplitude, high-frequency activity in the chin EMG and temporal EEG channels. (Correct answer)
- Slow, rolling waves in the EOG channels synchronized with respiratory effort.
- Repetitive, sharp spikes in the ECG channel that are not time-locked to the QRS complex.
- A sudden loss of signal in all respiratory effort channels.
Correct answer: High-amplitude, high-frequency activity in the chin EMG and temporal EEG channels.
Bruxism involves the contraction of the masseter and temporalis muscles. This generates significant electromyographic (EMG) artifact, which appears as high-frequency, high-amplitude signals. This artifact is most prominent in the chin EMG channels but also frequently contaminates nearby EEG electrodes, particularly those in the temporal regions (T3/T4).
Question 5: During a recording, a single, sharp, high-voltage vertical deflection appears in C3-M2 and F3-M2, but not in any other channels. This is most likely an example of:
- A K-complex, indicating Stage N2 sleep.
- An electrode pop artifact. (Correct answer)
- A generalized spike-and-wave discharge.
- Cardioballistic artifact.
Correct answer: An electrode pop artifact.
An 'electrode pop' is a sharp, spike-like deflection that is typically isolated to a single electrode due to a sudden change in impedance, often from a loose connection. Because it appears in channels that share a common electrode (in this case, likely M2 if C3 and F3 are referenced to it, or if the pop is from a common reference), but not in channels without that electrode, it points to a technical, non-physiological artifact related to that specific electrode.
Question 6: A technologist notes that the respiratory inductance plethysmography (RIP) belt signals appear flattened and squared-off at the peaks of inspiration and expiration. What is the most likely cause of this artifact?
- The patient is having central apneas.
- The belts are too loose and are moving with the bed sheets.
- The belts are too tight, causing the signal to clip at its maximum range. (Correct answer)
- The filter settings for the effort channels are incorrect.
Correct answer: The belts are too tight, causing the signal to clip at its maximum range.
When respiratory effort belts are applied too tightly, the transducer is unable to register the full expansion and contraction of the chest and abdomen. This causes the signal to reach its maximum and minimum output limits prematurely, resulting in a "squared-off" or "clipped" appearance on the recording. The technologist should slightly loosen the belts to allow for a full, rounded waveform.
Free RST Artifact Recognition and Troubleshooting Questions and Answers
During a polysomnogram on a patient with a history of obstructive sleep apnea, the technologist notes very low-amplitude, slow, undulating waves across multiple EEG and EOG channels.
The patient appears to be perspiring heavily.
What is the most likely artifact, and what is the best initial troubleshooting step?