The Cleveland Clinic

Sleep Disorders: Making the Diagnosis

A sleep study or polysomnogram (PSG) is a multiple-component test that electronically transmits and records specific physical activities while you sleep. The recordings become data that are analyzed by a qualified sleep specialist to determine whether or not you have a sleep disorder.

There are four kinds of polysomnographic studies, including:

  • Diagnostic overnight PSG: General monitoring of sleep architecture (for example, the amount of Non-REM and REM sleep, number of arousals, etc.) and a variety of body functions during sleep, including breathing patterns, heart rhythms and limb movements.
  • Diagnostic daytime multiple sleep latency test (MSLT): Used to diagnose narcolepsy and to measure the degree of daytime sleepiness. To ensure accurate results, it is performed on the morning following a diagnostic overnight PSG.
  • Two-night evaluation PSG and CPAP titration: CPAP (continuous positive airway pressure) is a sleep apnea treatment that involves the delivery of air into the airways through a specially designed nasal mask. On the first night of the two-night protocol, general monitoring and diagnostic evaluation is conducted. If sleep apnea is discovered, the patient returns for a second night to determine the necessary CPAP pressure required to alleviate apnea.
  • Split-night PSG with CPAP titration: Split night PSG is conducted when moderate or severe sleep apnea has been discovered or strongly suspected during the first part of the nights study. The second half of the night is used to determine the necessary CPAP pressure required to alleviate apnea.