Which of these is considered a DC channel?

In the context of sleep studies and polysomnography, a DC channel refers to a channel that measures direct current signals, which are continuous over time and do not change with an alternating current (AC) component. The correct answer indicates SpO2 as a DC channel because it measures the oxygen saturation of the blood continuously over time.

SpO2 refers to the peripheral capillary oxygen saturation, which is typically measured using a pulse oximeter. This device provides a real-time, continuous reading of oxygen levels in the blood and operates by emitting light through a pulsating capillary bed—it reflects the amount of oxygenated hemoglobin versus deoxygenated hemoglobin. Since this signal is a direct measure related to blood oxygen levels and is represented continuously, it is classified as a DC signal.

The other options represent different types of channels used in polysomnography. For example, C3-M2 refers to an EEG channel, which captures brain wave activity and is typically considered an AC signal due to the fluctuating nature of brain waves. Chin EMG measures muscle activity, usually exhibiting characteristics of AC signals as well. E1 may refer to a single electrode or a channel that is part of the sleep study, but without further context, it's usually associated with