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AHI Formula
#1
AHI Formula
Team - I am trying to calculate my AHI by using the number of events found on the event tab in Oscar, and the total sleep session hours.  I cannot come out with the same number as Oscar is showing.  Would you be so kind as to give me the exact formula that is used by Oscar to calculate AHI. I just want to understand the methodology since I am relying on that number as a key indicator of success. Thanks so much.
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#2
RE: AHI Formula
Suppose you have 13 events within a sleep time of 8 hours and 25 minutes that is 8 + 25/60 hours = 8.417 hours. Divide 13 by 8.471 to get 1.54 -- the value which OSCAR will show in this case.
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#3
RE: AHI Formula
Got it. Thank you so much for that information.
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#4
RE: AHI Formula
If the sleep time was 6 hours and the AHI score was 5 that means there was a total of 30 events.  But it does not indicate when those happened, right.  The first 2 hours I could have had 15 per hour and 0 the next 4 hours and arrived at the same score of AHI 5.  So the AHI really do not tell me if I constantly have a bad time getting to seep but when soundly asleep I am OK?

Last night the AHI after 56 minutes of very restless sleep was was 25.8  After a bathroom break and a glass of water, I slept for 5 hours and 16 minutes and machine reported an AHI of 6.1 this morning.  So that is telling me I had 25 events the first hour and only 11 events in the next 5 hours?  So one really bad hour makes it seem like a moderate sleep problem?  When I actually had one hour of 25 events and 5 hours of 2 events per hour.

I have a RX of 9 but that is impossible to use.  The dry mouth makes me get up to take a sip of water about every 90 minutes and I awake exhausted in the morning.  I use a flex of 3 and a heat of 3 currently but have tried multiple variations.  I am using pillows currently with the hose on top of my head, but have tried several over the nose mask that were horribly uncomfortable and constantly had leaks.  The current set up shows mask fit at 100% most of the time with a few 99%'s thrown it occasionally.  I get a great night of sleep at a pressure of 6 but really bad AHI's.  I have tried pressure of 6,7,8,9 and trying to keep a EXCL spread sheep since Oscar does not support this Dreamstation 2 Advanced yet.  
I am trying to convince myself the AHI is actually significant since one bad hour skews the Auto/Cpap machine results so bad and having a hard time convincing myself of the value of this.  I got this on June 3 rd and have used it all but one night so far.  My RX is dated Sept so you can see how long I put this off.  BUT, my question is, Is the AHI a reasonable barometer of how I am doing?
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#5
RE: AHI Formula
As you note, AHI is an average for the entire night.

I was going to say that to see what is happening during the night, you need OSCAR.  But OSCAR does not yet support the DreamStation 2. Sad
Useful links
Download OSCAR (current version is 1.2.0)
Best way to organize charts
How to attach charts to your post

Membership in the Advisory Members group does not imply medical expertise or qualification for advising Sleep Apnea patients concerning their treatment.
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#6
RE: AHI Formula
(07-13-2021, 03:26 PM)carcath Wrote:  So the AHI really do not tell me if I constantly have a bad time getting to seep but when soundly asleep I am OK?

Exactly, that's the trouble with means ... 

Concerning your mouth-desert: you're using a nasal mask, right?  In this case there's a strong indication that you're heavily breathing through you mouth.  What about your leaks?  They must be significant.

Mike
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#7
RE: AHI Formula
Add to that the concept of SWJ, and you have a further imperfect measurement, albeit the best available and certainly an important gauge. Last night, while I laid awake looking at my ResMed APAP machine, I saw the AHI, for the first 7 minutes of my turning out the lights, jump to 25. I asked myself, "why is it doing this, I am not even close to asleep."  Turns out this registered as CA's on Oscar, further adding to my CA problem. For the total evening, my AHI dropped to 4. Just adding to the confusion over this measurement, particularly when CA's are involved.
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#8
RE: AHI Formula
Mike, I have been using this since June 3 rd.  the Mask fit has been 100% every night except for 1 and that night showed mask fit at 99%.  I do not think mask fit is an issue.  This machine is among those that have been recalled but mask fit was not one of the issues for the recall.
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#9
RE: AHI Formula
The only software that I can use is the Dreammaker by Phillips.  I checked with my provider and they say the software phillips provides them only shows the same thing Dreammakes provides me.  My physician says he uses Oscar so no help there since Oscar will not read this machine yet.

That is the 'prologue' to my response.  I only have access to 'clear airway apnea's' and 'obstructive apneas'.  Perhaps your CA is the same thing as a 'clear airway'?

I also cannot find out what a SWJ is.

Its tough being a newbe in a high tech world.
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#10
RE: AHI Formula
There has been a lot of discussion about whether our machines can detect a Central Apnea, since that implies some measurement of central nervous system activity (or lack thereof). ResMed calls it one thing, Philips the other. In any event, the effect is the same, no breath and no obstruction (clear!) of the airway. It's a CA in either case...

As for SWJ, that's Sleep-Wake Junk - the random messiness of breathing as we transition from wakefulness to sleeping, and vice versa.
Apnea Board Monitors are members who help oversee the smooth functioning of the Board. They are also members of the Advisory Committee which helps shape Apnea Board's rules & policies. Membership in the Advisory Members group does not imply medical expertise or qualification for advising Sleep Apnea patients concerning their treatment.
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