Equipment
The test involves placing various sensors on the scalp, face and chest that can monitor sleep stage and heart rhythm. There are also sensors that monitor oxygen level, pulse rate, chest and waist movements, body position, leg movements, snoring and nasal airflow.
Home or in a sleep centre?
You will usually be required to spend a night in a sleep centre where you can be monitored by staff.
Who attaches the equipment?
A sleep specialist usually attaches the equipment.
How long does it take?
- Up to one hour to attach the equipment before bed
- At least four hours of sleep (preferably all night)
- 30 minutes to remove the equipment in the morning.
What is monitored?
Behaviour and body movements
A video camera monitors your movements to check whether you show any unusual behaviour or talk in your sleep, or whether you are very restless. It can also be used to show seizures during sleep, although these are quite rare.
Sleep stage
Several small sensors are placed on your scalp, cheek and forehead, two near your eyes, and two underneath your chin which can monitor whether you are awake or in light, deep or dream sleep. The aim is to see whether your sleep problems are occurring in one sleep stage, or all stages. This can help to diagnose many different sleep disorders.
Heart rhythm (ECG)
Several sensors are placed on your chest and abdomen. These sensors can check whether you have sleep apnoea by picking up characteristic changes in your heart rhythm during each pause in breathing. They can also check whether you have any problems with your heart rhythm.
Amount of oxygen in the blood / pulse rate
A plastic or rubber finger sensor is worn to check whether you have sleep apnoea. After each pause in breathing, the level of oxygen in your body dips and your pulse rate rises before returning to normal. If this happens repeatedly, sleep apnoea can be diagnosed.
Airflow at the nose / snoring
A nasal cannula is placed on your face. This consists of two tiny prongs that sit just inside your nostrils and branch into left and right tubes. The tubes loop over each ear and rejoin underneath the chin. The nasal cannula can check for snoring and pauses in your breathing.
Effort to breathe
An elastic belt is worn around your chest and another around your waist. This can distinguish between obstructive and central apnoeas.
During obstructive apnoeas your airways close off, blocking the passage of air to your lungs. In response to the obstruction you show increasingly forceful efforts to breathe, so the belts move vigorously until you partially or fully wake up and your airways finally reopen.
During central apnoeas the muscles of your lungs fail to move and inflate them. You show no effort to breathe, so the belts will barely move until you partially or fully wake up and your lung muscles are kick-started into working once again.
Body position
A sensor can be placed on the chest belt that shows whether you are lying on your back, left or right sides or front. This can identify positional sleep apnoea, for example, where you have the majority of apnoeas when lying on your back.
Leg movements
A sensor is placed near the shin bone on each leg. This can check whether your muscles are relaxed and you are asleep, or whether they are active and you are awake. The measurements can also help to diagnose periodic limb movement disorder, where your legs (and less commonly, arms) move repeatedly during sleep.
Results
The sensors are connected to a small, lightweight device, which is usually worn on a strap around the chest. The device sends the information from the sensors to a main computer, which gives a reading in the form of several graphs.
The graphs are viewed and interpreted so that a sleep specialist can form a diagnosis. You will be given an appointment with the specialist to receive your results.
This may seem like a great deal of equipment to wear, but if you are chronically tired it is likely you will be able to fall asleep on the night of the test.
