Polysomnography, which is performed in a hospital or sleep centre, is characterised by requiring the patient to be analysed in the evening in order to record nocturnal sleep patterns.
Only occasionally is it performed during another time frame, i.e. in the case of shift workers who habitually sleep during the day.
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What polysomnography is used for
The study monitors sleep phases and cycles.
The doctor may recommend this test if he or she has the following suspicions
- sleep apnoea or another sleep-related breathing disorder;
- periodic limb movement disorder (when you involuntarily bend or extend your legs during sleep: restless leg syndrome)
- narcolepsy, i.e. daytime sleepiness and sudden attacks of sleep;
- unusual behaviour during sleep, such as walking and moving around a lot;
- unexplained chronic insomnia.
The risks of polysomnography
Polysomnography is a painless and non-invasive test. Complications are rare.
The most common side effect is skin irritation caused by the adhesive used to attach the sensors.
An afternoon ‘nap’ before the test is not recommended.
How to prepare for the test
Your doctor may ask you not to drink alcohol or eat or drink anything with caffeine during the afternoon and evening before the polysomnography.
Alcohol and caffeine, in fact, can alter sleep.
The room in which the test takes place is similar to a hotel room, it is dark and quiet and is not shared with anyone.
The room also has its own bathroom and a video camera, so you can see what is happening even when the lights are off.
There is also a sound system that allows you to talk to the patient.
When ready for bed, one of the operators places sensors on the scalp, temples, chest and legs, using a gentle adhesive.
The sensors are connected to a computer via wires long enough to allow the patient to move normally in bed.
During sleep, the operator monitors
- brain waves;
- eye movements;
- heart rate;
- breathing pattern;
- blood oxygen level;
- body position;
- movement of limbs;
- snoring and other noises;
Each of these situations is recorded on a chart.
During the night, if assistance is needed, the caregiver can be talked to: he or she may enter the room to disconnect the wires, for example, if the patient feels the need to get up. In addition, a positive airway pressure machine for sleep apnoea may be used, i.e. a device that provides a gentle current of air to improve breathing.
Not falling asleep easily, as is the case at home, usually does not affect the test results, as it is not necessary to sleep a whole night to obtain accurate results.
In the morning, the sensors are removed and the patient can leave the room quietly, resuming normal activities, while waiting for the doctor to consult the test data.
Analysing the results
The measurements recorded during polysomnography provide a wealth of information on sleep patterns:
- brain waves and eye movements during sleep can help doctors assess sleep stages and identify interruptions;
- changes in respiration and abnormal blood oxygen levels may suggest sleep apnoea;
- frequent leg movements that disturb sleep may indicate periodic limb movement disorders;
- unusual movements or behaviour during polysomnography, assessed first by the technician and then by the physician;
It can take up to two weeks to receive the results.