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understand the reported AHI
#1
understand the reported AHI
Hello,

A newbie here, I was diagnosed with 8 AHI and my doctor recommended an Automatic CPAP machine. I've been using autoset for her with a p10 mask for few weeks now, about 4-6 hours per night. I still don't get good night sleep so I've been trying to analyze my sleep data... I want to understand in the attached image why does the AHI show at level 1 for about an hour even tough the CA event only lasted for few seconds? my AHI is 0.1 to 0.3 max for the last 2 weeks while using the machine.


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#2
RE: understand the reported AHI
That's because the AHI is 1 at this particular time.

Very simple example:

You start your therapy at 00:00 - at 05:00, one Apnea occurs, you end the therapy at 10:00.

At 05:00 with the apnea, your AHI will be 1/5, on 10:00 it will be 1/10.
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#3
RE: understand the reported AHI
Hope this helps clarify a little better:
http://www.apneaboard.com/wiki/index.php...ndex_(AHI)
OpalRose
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#4
RE: understand the reported AHI
Thank you, yes this is very helpful. So the AHI in the chart is based on the calculation of AHI. Why does the chart go down to 0 after an hour? instead of 1/2? I attached the full image. If you notice it just drops to 0 after the hour. A follow up question on the first image, the increased peaks and lows in the flow chart just before the CA event, is this due to the leak? There seem to be some correlation there.


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#5
RE: understand the reported AHI
That's because you have three different sessions and the AHI is calculated on a session basis.

   

I marked the individual sessions for you, hopefully that makes it clear to you Smile
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#6
RE: understand the reported AHI
Truthfully, the AHI graph is best ignored.  It mostly adds confusion and sheds little light. The developers have sometimes suggested eliminating that graph, but some people like it.

The way it works is this: when you have an apnea event, the AHI graph goes up by 1. It stays up for 1 hour, then that 1 is subtracted. If you had no other apneas, then you are back to zero. If you had an apnea in the middle, then the graph would go up by another 1, for a total of 2, and that new 1 would be held for an hour. 1 hour after the first apnea, 1 would be subtracted from the AHI total and the chart would be back to 1. One hour after the second apnea, the chart would drop to zero (assuming no other apneas).

What can you tell from this graph? If the graph peaks up like a mountain and then falls off, that means you had a cluster of apneas in a short time. (You can see exactly the same clustering on the Events or Flow graphs.) If the graph is relatively constant, your apneas are probably evenly distributed throughout the night.

It also shows how an events/hour index has varied throughout the night. The higher the peak, the more problems you were having at that time.
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#7
RE: understand the reported AHI
thanks everyone, learned a lot today!
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