Obstructive sleep apnoea syndrome (OSAS) is a condition where your breathing stops for short spells when you are asleep. The word apnoea means without breath - that is, the breathing stops. In the case of OSAS, the breathing stops because of an obstruction to the flow of air down your airway. The obstruction to the airflow occurs in the throat at the top of the airway. You may also have episodes where your breathing becomes abnormally slow and shallow. This is called hypopnoea. Because there can also be these episodes of hypopnoea, doctors sometimes use the term 'obstructive sleep apnoea/hypopnoea syndrome'.

When we sleep, the throat muscles relax and become floppy (like other muscles). In most people, this does not affect breathing. If you have OSAS, your throat muscles become so relaxed and floppy during sleep that they cause a narrowing or even a complete blockage of your airway. When your airway is narrowed and the airflow is restricted, at first this causes snoring. If there is a complete blockage then your breathing actually stops (apnoea) for around 10 seconds. Your blood oxygen level then goes down and this is detected by your brain. Your brain then tells you to wake up and you make an extra effort to breathe. Then, you start to breathe again with a few deep breaths. You will normally go back off to sleep again quickly and will not even be aware that you have woken up. Sometimes, the airway can just partially collapse and can lead to hypopnoea. Breathing becomes abnormally slow and shallow. If this happens, the amount of oxygen that is taken into your body can be halved. Hypopnoea episodes also usually last for around 10 seconds. If someone watches you, he or she will notice that you stop breathing for a short time and then make a loud snore and a snort. You might even sound as if you are briefly choking, briefly wake up and then get straight back off to sleep.

It is quite common for many of us to have the odd episode of apnoea when we are asleep, often finishing with a snort. This is of no concern. In fact, some people when they sleep have periods of 10-20 seconds when they do not breathe. However, people with OSAS have many such episodes during the night. For the diagnosis of OSAS, you need to have at least five episodes of apnoea, hypopnoea, or both events per hour of sleep. However, there are different levels of severity of OSAS (mild, moderate or severe). People with severe OSAS can have hundreds of episodes of apnoea each night.

So, if you have OSAS, you wake up many times during the night. You will not remember most of these times but your sleep will have been greatly disturbed. As a consequence, you will usually feel sleepy during the day. Daytime sleepiness in someone who is a loud snorer at night is the classic hallmark of someone who has OSAS.

OSAS can occur at any age, including in children. It most commonly develops in middle-aged men who are overweight or obese, although it can affect people who are not overweight. It is thought that as many as 4 in 100 middle-aged men and 2 in 100 middle-aged women develop OSAS. Factors that increase the risk of developing OSAS or can make it worse include the following. They all increase the tendency of the narrowing in the throat at night to be worse than normal. Overweight and obesity, particularly if you have a thick neck, as the extra fat in the neck can squash your airway. Drinking alcohol in the evening. Alcohol relaxes muscles more than usual and makes the brain less responsive to an apnoea episode. This may lead to more severe apnoea episodes in people who may otherwise have mild OSAS. Enlarged tonsils. Taking sedative medicines such as sleeping tablets or tranquilisers. Sleeping on your back rather than on your side. Having a small or receding lower jaw (a jaw that is set back further than normal). Smoking. You may also have a family history of OSAS.

People with OSAS may not be aware that they have this problem, as they do not usually remember the waking times at night. It is often a sleeping partner or a parent of a child with OSAS who is concerned about the loud snoring and the recurring episodes of apnoea that they notice.

Daytime sleepiness. This is often different to just being tired. People with severe OSAS may fall asleep during the day, with serious consequences. For example, when driving, especially on long monotonous journeys such as on a motorway. A particular concern is the increased frequency of car crashes involving drivers with OSAS. Drivers with OSAS have a 7-12 increased risk of having a car crash compared to average. You should not drive and you should not operate machinery if you feel sleepy. Poor concentration and mental functioning during the day. This can lead to problems at work. Not feeling refreshed on waking. Morning headaches. Depression. Being irritable during the day. Some people with OSAS find that they get up to pass urine frequently during the night. Less common symptoms also include night sweats and reduced sex drive.

People with untreated OSAS also have an increased risk of developing high blood pressure. Having high blood pressure can increase your risk of having a heart attack or a stroke. People with untreated OSAS may also have an increased risk of developing problems with blood sugar regulation and type 2 diabetes.

If you have daytime tiredness, sometimes a questionnaire is used to measure where you are on the Epworth Sleepiness Scale. This helps to gauge the level of sleepiness that you feel during the daytime. A high score indicates that you may have a sleeping disorder such as OSAS. If you have symptoms that suggest OSAS, or a high score on the Epworth Sleepiness Scale, your GP may refer you to a specialist for tests. There are various types of test that can be done whilst you sleep. The ones done may be determined by local policies and availability of equipment

You may be asked to spend a night in hospital for the tests to be done. However, some of the tests may be done in your own home from equipment supplied by the specialist. The information gained from the tests can help a specialist to firmly diagnose or rule out OSAS.

This is the most effective treatment for moderate or severe OSAS. It may be used to treat mild OSAS if other treatments are not successful. This treatment involves wearing a mask when you sleep. A quiet electrical pump is connected to the mask to pump room air into your nose at a slight pressure. The slightly increased air pressure keeps the throat open when you are breathing at night and so prevents the blockage of airflow. The improvement with this treatment is often very good, if not dramatic. If CPAP works (as it does in most cases) then there is an immediate improvement in sleep. Also, there is an improvement in daytime well-being, as daytime sleepiness is abolished the next day. Snoring is also reduced or stopped. The device may be cumbersome to wear at night but the benefits are usually well worth it. Comments like "I haven't slept as well for years" have been reported from some people after starting treatment with CPAP. Lifelong treatment is needed. Sometimes you can have problems with throat irritation or dryness or bleeding inside your nose. However, newer CPAP machines tend to have a humidifier fitted which helps to reduce these problems.