Polysomnography

Check your sleep score!

What is an overnight sleep study?

Check your sleep score! Overnight sleep study is also known as Polysomnography. Sensors are placed at different locations on the body and are connected to a computer. A sleep technician is present for attaching the electrodes and for monitoring the patient during the study.

What are the parameters studied during a sleep study?

A sleep study measures the sleep cycles with sleep stages and many body functions by recording the following information:

• Eye movements during sleep by electro-oculography (EOG)
• Brain rhythms by electro-encephalography (EEG)
• Heart rhythms by electrocardiography (EKG)
• Movement of body muscles by electromyography (EMG), usually limb muscles.
• Oxygen levels in blood are recorded continuously by an oxygen monitor (pulse oximeter).
• Breathing monitors show the number of times breathing stops. They can also detect low air flow and snoring.

What are the indications for a sleep study?

The main reason for getting a PSG done would be to confirm a diagnosis of obstructive sleep apnea (OSA), a sleep disorder in which a person has repeated obstruction to breathing as he sleeps. In addition, PSG is used to diagnose other sleep disorders like narcolepsy, restless legs syndrome, REM behavior disorder, parasomnias, and sleep rhythm disorders.

How to prepare for the procedure?

The study is done at a sleep laboratory with facilities for the patient to stay overnight. The following steps are recommended before a sleep study:

• Avoid napping on the day of the study.
• Avoid coffee or tea after 10 a.m on the day of appointment.
• Stay away from stimulants, alcohol, or sedatives. Most sleep centers request to continue regular medications.
• Shower or wash hair on the day of appointment so that it becomes easier to place the electrodes.
• Avoid using any hair products, skin lotions or powder.
• Eat a normal evening meal before arrival at the sleep lab.
• Bring nightclothes or wear the hospital gown.
• Bring you own pillow or other items which will make you comfortable

Typically, the patient will be asked to come to the sleep laboratory an hour or two before the patient’s usual bedtime. 

How are the results interpreted?

The collected data in the study is reviewed in terms of "epochs" of 30 seconds each, looking for:

Sleep latency, shows the time interval between lights being switched off and the initiation of sleep in the patient. The EEG shows whether the patient was awake or was sleeping.

Sleep efficiency, which is the minutes of total sleep divided by the minutes spent on bed. In normal cases, it falls between 85%-90%.

Sleep stages, are based on the data coming from the five channels, EOG (2), EEG (usually 2 channels), and chin EMG. The stages of sleep are:

• Wake
• Stages 1-4 (NREM Sleep)
  1. Transition from wake to sleep
  2. Light sleep
  3. Transition into REM sleep
  4. Deep sleep
• REM Sleep

Apnea is the complete cessation of breathing for at least 10 seconds in sleep while hypopnea refers to partial cessation, again lasting for at least 10 seconds. Apnea/ hypopnea index (API) is calculated from these observations. For normal persons, it must be below 5.

"Arousals" are indicated by a sudden shift in the brain wave activity due to a variety of reasons such as leg movements, atmospheric conditions, breathing irregularities etc. A higher than normal number of "arousals" could be indicative of disturbed sleep or other symptoms like fatigue and/or sleeplessness.

Cardiac rhythm abnormalities, body position during sleep, leg movement patterns, and oxygen saturation are charted during the study.

When do we get the results?

It usually takes about two weeks to get the results of a sleep study. Once the study has been analyzed and "scored", the results are then sent to the sleep physician for interpretation. A sleep physician reaches a conclusion after considering the patient's medical and drug history, and the results are in turn sent across to the referring physician with specific recommendations based on the analysis for further treatments or tests.