Sleep disordered breathing (SDB), particularly the potentially life-threatening medical disorder obstructive sleep apnea, as well as the differential diagnosis of insomnia, narcolepsy, periodic limb movements of sleep, insufficient sleep syndrome, REM sleep behavior, and other medical conditions should be determined by sleep physicians, mostly based on an sleep study. 

POLYSOMNOGRAM (PSG): Polysomnogram is the most sophisticated instrumentation to record the body's activities during sleep and have been used routinely for various sleep tests, and is currently the best method to diagnose sleep breathing disorders.  It measures and records AHI, RDI, the brain waves and activity, heart rate, pulse rate, body movement, movement of eyes, length of sleep, sleep stages,  number of arousals, number of apneic episodes, volume of nasal and oral airflow, loudness of snoring, unusual leg and arm movement, oxygen saturation in the blood, cardiovascular abnormalities during sleep etc.

Sleep centers and major hospitals have this instrumentation in an adjoining room where an intercom and video cameras allow communication between the patient and the technician.  Usually, recordings are done throughout the night and the record is interpreted by sleep physicians and recommended proper treatment modalities depending on the patient severity, conditions, and acceptance.

HOME SLEEP STUDY: Due to advances in computer science and sleep technology, a sleep study can now be performed by ambulatory device at home, where the patient feels more comfortable and can sleep without putting multiple testing electrodes around the face and body.  This is a short version of a polysomnogram and provides essential data: loudness of snoring, severity of sleep apnea, blood oxygen saturation, pulse rate, body movement and position while sleeping, wake up and sleep state, identify REM and Non-REM sleep stages etc. 

DEFINITIONS: 

• Apnea= cessation of breathing, during sleep for 10 seconds and more
• Hypopnea= >50% decrease in airflow for 10 seconds or greater with a decrease in oxygen saturation of >4%
• Apnea/Hypopnea Index (AHI)= apnea plus hypopnea per hour during sleep
• Respiratory Disturbance Index (RDI)= AHI + snoring + RERA (respiratory effort related arousal) 
• SaO2 scale= oxygen saturation in the blood.  >89% (nomal)  80-89% (moderate)  <80% (severe)
• REM= rapid eye movement- dreaming stage of sleep
• NREM = regular sleep stage of sleep