Which statement best describes why electrode impedance levels are kept low in polysomnography?

Which statement best describes why electrode impedance levels are kept low in polysomnography?

• A. Reduces signal amplitude
• B. Increases artifact likelihood
• C. Reduces noise and artifacts
• D. Increases calibration time

Answer: (C)

Keeping electrode impedance low is essential because it directly affects signal quality in polysomnography. The brain signals you’re trying to record are extremely small, so any resistance at the skin–electrode interface can turn those tiny voltages into noisy, distorted data. When impedance is low and conditions are good, the signal travels into the amplifier with less interference from surrounding electrical activity and movement. Low, well-matched impedance also helps the recording’s common-mode noise rejection work effectively. In a differential measurement like EEG, if the impedances across channels are similar and low, the amplifier cancels out the same noise appearing on both inputs. High or uneven impedance makes the noise more likely to appear in the signal and can produce artifacts, such as spikes or baseline wander, especially with movement or sweating. That’s why this choice emphasizes reducing noise and artifacts. The other options don’t reflect the goal: high impedance doesn’t reduce signal amplitude; it tends to worsen noise issues. Impedance levels aren’t kept to shorten calibration time as a primary aim; calibration concerns are separate from the ongoing impedance management during recording.

Keeping electrode impedance low is essential because it directly affects signal quality in polysomnography. The brain signals you’re trying to record are extremely small, so any resistance at the skin–electrode interface can turn those tiny voltages into noisy, distorted data. When impedance is low and conditions are good, the signal travels into the amplifier with less interference from surrounding electrical activity and movement.

Low, well-matched impedance also helps the recording’s common-mode noise rejection work effectively. In a differential measurement like EEG, if the impedances across channels are similar and low, the amplifier cancels out the same noise appearing on both inputs. High or uneven impedance makes the noise more likely to appear in the signal and can produce artifacts, such as spikes or baseline wander, especially with movement or sweating.

That’s why this choice emphasizes reducing noise and artifacts. The other options don’t reflect the goal: high impedance doesn’t reduce signal amplitude; it tends to worsen noise issues. Impedance levels aren’t kept to shorten calibration time as a primary aim; calibration concerns are separate from the ongoing impedance management during recording.