Doctors perform sleep studies or polysomnography (PSG) to diagnose sleep related illness or symptoms. Traditionally, patients have a diagnostic study performed for an entire night to diagnose obstructive sleep apnea (OSA). Once the doctor confirms OSA, he sets up a separate therapeutic study. During this second study the doctor adjusts (or titrates) continuous or bilevel positive airway pressure (CPAP or BiPAP) to levels that eliminate or significantly reduce the number of respiratory abnormalities (apneas and hypopneas).

Doctors perform therapeutic PSG with CPAP titration if patients have a diagnostic study demonstrating an apnea-hypopnea index (AHI). They may also perform it if the patient