A polysomnogram (PSG) is a special test that measures the function of your body while you sleep. This test is used to detect the cause of sleep problems in people who have insomnia or excessive daytime sleepiness. This may be due to:

The test, done in one of Northwestern Medicine's Sleep Health Centers, is often carried out at night so that normal sleep patterns can be monitored.

What to expect during a PSG

  • Electrodes are placed on the scalp, the outer edge of the eyelids and the chin to record brain, heart and muscle activity and eye movement.
  • Flexible elastic belts are placed around your chest and abdomen to monitor your breathing.
  • A soft plastic tube (cannula) is placed in your nostrils to record airflow.
  • A clip is placed on your index finger to check the oxygen level in your blood and your heart rate.
  • Patients are also videotaped while they sleep to review any abnormal changes observed during the study.

If a breathing problem is seen during your sleep study, a technician may wake you and ask you to use either a Nasal Continuous Positive Airway Pressure (CPAP) or a Bilevel Positive Airway Pressure (BiPAP) mask.

CPAP keeps the airway open by providing ongoing flow of air delivered through a soft mask. The mask is worn over the nose or the nose and mouth. The air pressure that is delivered remains the same at all times.

BiPAP is similar to CPAP, but it offers the option of having different airflow pressures during inhalation and exhalation. While breathing in, the airflow pressure is higher in order to keep the airway open. During exhalation, the pressure is lower and reduces the work of exhalation.

Using the PSG results, along with the results of other testing that may have been done, treatment options may be selected based on your specific needs.

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