Understanding sleep apnea

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Understanding Sleep Disordered Breathing

Must-see video for new Sleep Apnea patients

Layman's terms

Article 1

a forum article written by forum Advisory Member pholynyk with very minor edits by forum Advisory Member and Wiki Editor bonjour

Hi there, welcome to the forum. It sounds like your doctors have told you as much about sleep apnea as my doctors told me about chronic kidney disease, or sleep apnea.

So lets start at the beginning: the average person breathes about 15 to 20 times a minute while sleeping; that's 900 to 1200 times an hour. Your doctor has told you that you had 73 apneas (on average) each hour that you were asleep. This means that your breathing either paused or significantly diminished for at least ten seconds 73 times each hour. So you missed out on (roughly) 150 to 200 (or more) breathes each hour. Maybe 10 to 15 per cent doesn't sound like a lot, but it's enough to disturb your sleep, and give you a jolt of adrenaline that make your heart beat faster and your kidneys work harder - over time that causes damage to other organs as well. And even partial wake-ups make you sleepy the next day.

Now, what can cause you to pause your breathing? There are two causes, in general. An obstruction may cause the airway (nose, mouth, throat) to close up, preventing airflow; or the nerve signals that tell the chest and abdomen to expand may not get sent from the brain (stem?). The first is called an 'obstructive apnea', the second is called a 'central apnea' or 'clear airway apnea'. The first kind is more common, and more easily treated; the second can require a fancier and more expensive machine.

There are two aspects to treatment of sleep apnea, the machine and the mask, and you will find lots of excellent advice here in the forum.

One thing about the machine that doesn't get mentioned very often is that it can move what seems to be a lot of air, but only at very low pressure. To be exact, if you take a straw and hold it in a glass of water with about two or three inches under water, and then blow 'just hard enough' to create a gentle stream of bubbles, you will have about the pressure a lot of people use in their CPAP machines. If you have a very long straw, and can dunk it 8 inches into the water, the pressure required for that gentle stream of bubbles is the maximum most people's machines can create. That gentle pressure is enough to keep our airway expanded and open, allowing us to breathe. Now the reason for that 'high flow'? We don't want to re-breathe our exhaled, CO2-rich, air - it would kill us. So the machine provides lots of extra air, and the mask has lots of tiny holes to allow the extra air to dilute and pull out our exhaled air.

And that long-winded explanation is the basics of sleep apnea and its treatment with a CPAP machine. Feel free to ask more questions. others will chime in. I'm tired of typing.

Article 2

another forum article written by forum Apnea Board Monitor and Wiki Editor DeepBreathing with very minor edits by forum Advisory Member and Wiki Editor bonjour


I don't know much about DreamMapper, but I understand it's a bit of a cut-down version which gives the bare minimum information. OSCAR is the full deal and gives you more than you will ever need to know.

Just answering some general questions, though...

1. An obstructive apnea (O) occurs when your tongue, soft palate and/or other tissue collapses during sleep and totally block (obstruct) the upper airway.

2. A clear airway (central) apnea (CA) occurs when there is no obstruction but you fail to take a breath. Typically this occurs because the "breathe now" signal is either not generated by the brain or not received by the lungs / diaphragm. This can occur when the level of CO2 in the blood does not reach the threshold required to trigger the "breathe now" signal. New CPAP users often get a few (or more) centrals until their body adjusts to the pressure.

3. An hypopnea (H) is a partial obstruction - there is still some air getting through, but not enough.

The machine reports the number of apneas and hypopneas which actually occurred. A poorly set up machine will let a lot of events through and you'll have a high AHI. A well set-up machine will prevent most events, but a few will inevitably slip through. It's not realistic to expect a zero AHI, though these occasionally happen.

Using OSCAR with my Resmed it reports the total number, time and duration of each event - your Dreamstation will probably do the same. The indices are the average number per hour over the night. So if you slept for 8 hours and had 16 obstructive, 8 clear airway and 4 hypopnea, your indices would be:

  • Obstructive OAI: 16 / 8 = 2.0
  • Central CAI: 8 / 8 = 1.0
  • Hypopnea HI: 4 / 8 = 0.5

The apnea hypopnea index (AHI) is the sum of these other indices: AHI = OAI + CAI + HI = 2.0 + 1.0 + 0.5 = 3.5

There's no direct correlation between AHI and mask fit, except that if the leakage goes over a predetermined red line (24 on a Resmed) the machine can't diagnose and treat events. Obviously there are other downsides to leaks, such as blowing into your eyes or causing face farts which can disturb your sleep (or get an elbow from SWMBO).

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