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AHI Calculation
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Gary K Offline

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Machine: Philips System 1
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Post: #1
AHI Calculation
I am a new user of a Philips System one bi-pap machine. I have been uploading the data from my machine to Philips Respironics SleepMapper and I am confused as to how the calculations are made to determine AHI. During the first 30 days of use my AHI was 15. They then put me on a loaner machine that supposedly changes pressure automatically to determine what pressure level I should be on. The AHI is all over the map over the 15 days I have been on this machine. (from 25 to 10). My question is;
If he AHI is the average number of events per hour, how does the machine calculate the number of hours of sleep? I don't believe the machine knows when I am sleeping or just laying there breathing through machine. For example, if I have the machine on for 8 hours but am sleeping for only 4 hours and the machine detects a total of 100 events, will it calculate that my average AHI is 12.5? Since I assume all of these events would happen while I am sleeping, that would mean I had 100 events in 4 hours not 8 and my AHI is in reality 25.

Where am I going wrong?
10-12-2014 08:19 AM
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SleepyDreamCatcher Offline

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Machine: ResMed S9 AutoSet
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Post: #2
RE: AHI Calculation
Gary,

Your machine doesn't know whether you are asleep or not. It calculates your AHI bases on the hours the machine was running. So yes, if you had 100 events over 8 hours while sleeping only 4 of them the machine will use 8 hours to determine your average.

You will get more information from the SleepyHead software if your machine is recording all effiency data. There are links at the top of the board that will let you download the software. It is free shareware and there are friends here who can help you understand what it shows you.

When I see apneas or hypos during times I know for sure I was awake I ignore them. If I'm not sure I assume they occurred.
(This post was last modified: 10-12-2014 09:04 AM by SleepyDreamCatcher.)
10-12-2014 08:59 AM
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justMongo Offline

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Machine: ResMed VPAP Auto (S9)
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Post: #3
RE: AHI Calculation
You are correct that the machine cannot tell if you are awake or asleep. It only knows the hours run.

INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
10-12-2014 09:01 AM
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trish6hundred Offline

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Machine: Resmed S9 AutoSet for Her
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Location: Missouri, USA

Post: #4
RE: AHI Calculation
Hi Gary K,
WELCOME! to the forum.!
Hang in there for more answers to your question and best of luck to you with your CPAP therapy.

trish6hundred
10-12-2014 09:08 AM
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labtec6 Offline

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Posts: 16
Joined: Oct 2014

Machine: ResMed AirSense 10 Elite
Mask Type: Nasal pillows
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Other Comments: CPAP Since Sept 9, 2014

Sex: Male
Location: Toronto, Ontario, Canada

Post: #5
RE: AHI Calculation
(10-12-2014 09:01 AM)justMongo Wrote:  You are correct that the machine cannot tell if you are awake or asleep. It only knows the hours run.

I guess if it could, they would be red and white and we'd be calling it Santa Claus. Lol

Sorry I had to.
10-12-2014 10:28 AM
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PaulaO2 Offline
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Post: #6
RE: AHI Calculation
The machine, at least the latest ones, can tell if there is a human attached to the other end vs it just running to have the hose dried out.

It knows you are there, breathing, but it doesn't know if you are asleep or awake. There's no way for it to know since breathing patterns are so different from person to person. It could, perhaps, learn your patterns but that's a way down the road.

PaulaO2
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www.ApneaBoard.com


Breathe deeply and count to zen.

INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
10-12-2014 10:57 AM
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retired_guy Offline

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Machine: ResMed S9 Autoset
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Post: #7
RE: AHI Calculation
On the other hand, if you are laying there awake for 4 hours, or anything close to that, you are not yet Mr. Happycamper. So that needs addressed. Also it sounds like your ahi is still a bit high regardless of how it's figured.

You indicate you are now on a loaner machine that is auto capable. Do you know what your minimum/maximum pressures are? Downloading and installing the Sleepyhead software will give you the opportunity to figure out all you ever wanted to know and even lots of stuff you never even knew you wanted to know.
10-12-2014 11:50 AM
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herbm Offline

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Machine: ResMed AutoSet S9
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Other Comments: Backup Mask: Innomed Hybrid FFM -- Oral+Nasal Pillows

Sex: Male
Location: Austin, TX

Post: #8
RE: AHI Calculation
Everything above....

Also note that for those of us with (fairly) well controlled sleep apnea, we may actually be picking up (the majority of) our events largely while awake or during wake to sleep or sleep to wake transitions which mostly shouldn't even count in the average.

Ideally, the machine would only count asleep events and averaged based on actual sleep time.

So fix you sleep issues and use the software to see where your real issues remain.

Sweet Dreams,

HerbM
Sleep study AHI: 49 RDI: 60 -- APAP 10-11 w/AHI: 1.5 avg for 7-days (up due likely to hip replacement recovery)

"We can all breathe together or we will all suffocate alone."
10-12-2014 01:19 PM
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PaulaO2 Offline
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Posts: 8,068
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Machine: S9 Autoset
Mask Type: Full face mask
Mask Make & Model: F&P Simplus
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CPAP Pressure: 14-20
CPAP Software: SleepyHead

Other Comments: Ehlers-Danlos Syndrome, Hypermobility Type; chronic sarcasm

Sex: Undisclosed
Location: western NC, USA

Post: #9
RE: AHI Calculation
For good sleep hygiene, we should not be laying in bed with the mask on for 3 - 4 hrs. If not asleep within a half hour or so, you should get up, do something to distract your mind or whatever it was that was keeping you awake, then try again later.

If you are one of those folks who just insists on laying in bed and watching television, don't put on the mask until you are actually ready for sleep. If you know you are going to watch two hours of television, and that's your limit before you fall asleep, then set a gentle alarm (gentle sound that will not blast you 'awake') to remind you in 2 hrs to turn the thing off and go to sleep.

I have a bad habit of doing the opposite. I wake up and don't take it off. Sometimes I fall back to sleep in the morning but most of the time I don't. I pet a dog, lay there thinking, listen to music, do some stretches. But I don't take the mask off. Mostly because when I take it off, the congestion hits. My sinuses love the humidifier! LOL

PaulaO2
Apnea Board Moderator
www.ApneaBoard.com


Breathe deeply and count to zen.

INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
10-12-2014 11:04 PM
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Galactus Offline

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Machine: Phillips Respironics System One PRS1 DS760P Auto BiPAP
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Post: #10
RE: AHI Calculation
(10-12-2014 11:04 PM)PaulaO2 Wrote:  I have a bad habit of doing the opposite. I wake up and don't take it off. Sometimes I fall back to sleep in the morning but most of the time I don't. I pet a dog, lay there thinking, listen to music, do some stretches. But I don't take the mask off. Mostly because when I take it off, the congestion hits. My sinuses love the humidifier! LOL

I know just how you feel, and if I take the mask off and lay in bed I inevitably do fall back to sleep and then feel crappy because I didn't have it on while I was sleeping. Just infuriating.

If everyone thinks alike, then someone isn't thinking.
Everyone knows something, together we could know everything.
10-12-2014 11:10 PM
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