Obstructive sleep apnoea (OSA) is a condition where the walls of the throat relax and narrow during sleep, interrupting normal breathing.
There are two types of breathing interruption characteristic of OSA:
- apnoea – where the muscles and soft tissues in the throat relax and collapse sufficiently to cause a total blockage of the airway; it is called an apnoea when the airflow is blocked for 10 seconds or more
- hypopnoea – a partial blockage of the airway that results in an airflow reduction of greater than 50% for 10 seconds or more
As many people with OSA experience episodes of both apnoea and hypopnoea, doctors sometimes refer to the condition as obstructive sleep apnoea-hypopnoea syndrome, or OSAHS.
The term “obstructive” distinguishes OSA from rarer forms of sleep apnoea, such as central sleep apnoea, which is caused by the brain not sending signals to the breathing muscles during sleep.
What happens in OSA?
People with OSA may experience repeated episodes of apnoea and hypopnoea throughout the night.
During an episode, the lack of oxygen triggers your brain to pull you out of deep sleep – either to a lighter sleep or to wakefulness – so your airway reopens and you can breathe normally.
After falling back into deep sleep, further episodes of apnoea and hypopnoea can occur. These events may occur around once every one or two minutes throughout the night in severe cases.
Most people with OSA snore loudly. Their breathing may be noisy and laboured, and it is often interrupted by gasping and snorting with each episode of apnoea.
These repeated sleep interruptions can make you feel very tired during the day. You’ll usually have no memory of your interrupted breathing, so you may be unaware you have a problem unless a partner, friend or family member notices the symptoms while you sleep.