Types of sleep apnoea

The most common type of sleep apnoea is 'obstructive' sleep apnoea (OSA). Obstructive apnoea events occur when the upper airway becomes so very relaxed during sleep, that it actually collapses as a person takes in a breath. Of all the people who have sleep apnoea, about 90% have obstructive sleep apnoea.

Once the airway has collapsed, the person is not able to draw air into the lungs, and begins a mild suffocation experience. Much of the available oxygen in the blood is used up, and carbon dioxide starts to build up in the body.

Eventually the person's sleep is disrupted, and they wake up just enough to start breathing again. Then they go back to sleep, and soon they relax and go into another apnoea period.

The less common type of sleep apnoea is 'central' sleep apnoea (CSA). Central apnoea events occur when the body is not actually trying to breathe. The airway may be open or closed - this is irrelevant in central apnoea. The point is that the diaphragm is not contracting to pull air into the lungs. About 10% of people with sleep apnoea have central apnoea, either alone or in combination with obstructive sleep apnoea.

There are many possible causes for central sleep apnoea, including problems with the heart or circulation, or strokes or other damage to areas of the brain. If you have been diagnosed with central sleep apnoea, it will be important for you to discuss the possible underlying causes with your doctor.

Severity of sleep apnoea

The severity of sleep apnoea is usually described in terms of the Apnoea-Hypopnoea Index (AHI). This is the number of times each hour that a person has an apnoea (stops breathing for 10 seconds or longer), or has a hypopnoea (a period of shallow breathing for 10 seconds or longer).

AHI explained (Apnoea Hypopnoea Index)

People who don't have sleep apnoea can be expected to have natural pauses in their breathing which may last for 10 seconds or slightly longer. These tend to occur after a deep breath or sigh, and a few of these each hour are completely normal.

Thus a person with normal breathing may have an AHI in the range of 0 to 5 events per hour of sleep.

When sleep apnoea is present, these periods of apnoea (no breathing) tend to be longer (typically lasting 20 to 40 seconds each, and possibly lasting even over a minute for each event). In addition, more severe sleep apnoea usually means more frequent apnoea events.

Severity of sleep apnoea as described by the AHI
  Normal Mild Moderate Severe
AHI: 0 to 5 5 to 14 15 to 30 above 30

If you have been diagnosed with sleep apnoea, you should discuss the appropriate treatment options with your doctor.