Performing and Verifying Physiologic Calibrations Flashcards
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What is the primary purpose of performing physiologic calibrations (biocals) before starting a sleep study recording?
Answer: To verify the integrity and proper response of all recorded signals.
Biocals are essential to confirm that all electrodes and sensors are working correctly and responding appropriately to the patient's physiological changes. This process verifies signal integrity, confirms correct channel derivations, and ensures high-quality data will be collected.
During EOG calibrations, the technologist asks the patient to 'look left, then look right'. What is the expected signal response in the LOC-M2 and ROC-M1 channels?
Answer: The signals should be out-of-phase (move in opposite directions).
When the eyes move, the cornea (positive potential) moves toward one electrode and away from the other. This creates opposite deflections in the two EOG channels, resulting in an out-of-phase signal, which confirms proper electrode placement and function.
During physiologic calibrations, a flat line is observed in the C3-M2 channel, but the impedance check was low (under 5 kΩ). What is the most likely cause?
Answer: A salt bridge has formed between the C3 and M2 electrodes.
A 'salt bridge' occurs when conductive paste or gel from two nearby electrodes (like C3 and the reference M2) makes contact. This shunts the electrical potential between them, resulting in a flat line because there is no potential difference to measure, even though the individual electrode impedances are good.
What is the purpose of asking the patient to hold their breath for 5-10 seconds during calibrations?
Answer: To confirm the function of the respiratory airflow and effort channels.
Asking the patient to hold their breath creates a voluntary central apnea. This allows the technologist to verify that the respiratory effort belts (thoracic and abdominal) and the airflow sensor (thermistor/cannula) correctly detect and display the cessation of breathing and effort.
To verify the function of the chin EMG channels, what command should the technologist give the patient?
Answer: Clench your teeth together.
Asking the patient to clench their teeth or jaw activates the submental muscles. This should produce a high-frequency, high-amplitude burst of activity in the EMG channels, confirming that the electrodes are placed correctly and are detecting muscle tone.
During EOG calibrations, both the LOC and ROC channels deflect downward simultaneously when the patient looks up. What does this indicate?
Answer: A possible problem with the reference electrode (M1/M2).
When both EOG channels move in the same direction (in-phase), it typically indicates a common reference issue, most often a referenced M1 or M2 electrode picking up artifact. The eye movements themselves should be out-of-phase. This requires troubleshooting the reference electrode placement or connection.