What does the time axis represent in a polysomnographic recording?

In a polysomnographic recording, the time axis is represented horizontally on the graph. This axis tracks the progression of time throughout the recording period, allowing for the correlation of various physiological parameters captured during the sleep study. By having the time plotted horizontally, technologists can observe how different sleep stages, events, and metrics change over the course of the night, providing valuable insights into sleep patterns and potential disturbances. This setup facilitates an understanding of when specific occurrences, such as apnea events or arousals, take place during the sleep cycle.