What is an "Apnoea"?

If you search for "Apnoea" on Google, you will probably be given results for "Apnea" - it's the same thing but with an American spelling.

Quite simply, an apnoea is a pause in breathing.

There are different types and causes of apnoea, and in the last 10 years one type: "Obstructive Sleep Apnoea " has taken centre-stage. According to a recent tweet by @RespironicsUK it has gone from being not really recognised to a "huge epidemic".

Obstructive Sleep Apnoea occurs when the muscles of the throat relax in sleep, effectively closing the airway off and preventing breathing. This is despite the breathing muscles of the chest and diaphragm still moving. It's akin to trying to breathe with your mouth closed whilst someone is pinching your nose.

This is a graph of an apnoea. The blue line is the airflow (breaths). The highlighted portion shows anpnoea.

The purple line is the heartrate. The red is the oxygen levels.

The oxygen doesn't drop instantly (after all, we can hold our breaths for a fair while before we gasp for air), but when it does drop it drops rapidly past a certain point due to the oxygen desaturation curve (the graph looks a little like a slide in that you can shuffle along the top descending slowly but when you reach the tipping point you shoot down fast).

So, the blood oxygen levels fall (while the CO2 levels rise - not graphed). This causes the brain to briefly wake the sleeper so that they breathe normally. Sometimes they wake up with a snort, or a choking feeling.

So, they wake up and problem solved?

Not really.

Waking up deals with the immediate issue of low oxygen and high CO2, but this can happen hundreds of times a night, often without the sleeper realising it. In the morning they wake feeling groggy and tired because they have been deprived of sleep.

During sleep monitoring the number of apnoeas and hypopneas is recorded and converted into an hourly rate known as the AHI - Apnoea Hypopnea Index. 

A low AHI (under 5) is considered acceptable unless the sleeper is experiencing problems. but with a high AHI the sufferer isn't just "a bit tired" they are sleep-deprived and have to deal with the effects of that:

• making mistakes 
• napping
• falling asleep at inappropriate times
• depression
• heart problems
• stroke
• headaches
• weight gain

Obstructive sleep apnoea can be made worse by alcohol (it relaxes the throat muscles more) and by being overweight (because the increased mass around the neck adds to the burden). By losing weight and reducing alcohol consumption it is (in some cases) possible to eliminate the problem.

There are treatments available ranging from lifestyle changes to surgery. A common solution is a CPAP machine that keeps your airways open during sleep by maintaining a constant pressure of air in your airways via a face mask. 

Treatments  will be the subject of a later post. For now I just wanted to make a start.