What physiological signal indicates an absence of breathing in a PSG study?

In a polysomnography (PSG) study, the airflow channel is used to monitor the patient's breathing. An absence of breathing is characterized by an "aflat-line" tracing on this channel, which indicates that there is no airflow detected for a specific period. This flat-line tracing signifies that the patient is experiencing apnea, a condition where normal breathing ceases temporarily.

This measurement is critical for diagnosing sleep-related breathing disorders, such as obstructive sleep apnea. When airflow is not detected, it indicates that the individual is not breathing, which is a key indicator for healthcare providers to assess the severity and type of the breathing disorder present. The airflow channel provides direct and clear evidence of respiratory status during sleep, making it a vital signal in sleep studies.