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Confused by AHI
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Iceracer Offline

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Post: #1
Confused by AHI
Hi all , I'm kinda of confused ( according to my wife that's nothing new lol )
This morning I woke up around 4 am and checked my readings AHI was 3.1 not great but hey whatever ! Shut machine off went to the washroom ,went back to bed tubed back up awoke back up at 6am checked again and it said Ahi was down to 1.0 how could if possibly go down if I had 3.1 shouldn't it read 4.1 ? I'd post my sleepyhead data but I am on work computer and can't at the moment .
03-04-2014 07:52 AM
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c0reDump Offline

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Post: #2
RE: Confused by AHI
First session (bedtime to 4am) you had an average hourly hypopnea index of 3.1. Second season (4am to wake time) your AHI was 1.0.

I think coupled with the fact you had two sessions (turned the machine off/on) and that these numbers are average hourly rates is causing the confusion.

First hour 2.0
Second hour 0.0
AHI = 1.0
03-04-2014 07:59 AM
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Iceracer Offline

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Post: #3
RE: Confused by AHI
(03-04-2014 07:59 AM)c0reDump Wrote:  First session (bedtime to 4am) you had an average hourly hypopnea index of 3.1. Second season (4am to wake time) your AHI was 1.0.

I think coupled with the fact you had two sessions (turned the machine off/on) and that these numbers are average hourly rates is causing the confusion.

First hour 2.0
Second hour 0.0
AHI = 1.0

Thanks I think I get ya however it did have an accumalated time so it read like one session
03-04-2014 08:25 AM
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skram Offline

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Post: #4
RE: Confused by AHI
To fully understand I think we'd need one of two things:

1. SleepyHead data - this would give you the full picture and show the details of when the events occurred.
2. How long each session was. We could then 'do the math' to determine how the average could change that much.
03-04-2014 10:33 AM
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trish6hundred Offline

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Post: #5
RE: Confused by AHI
Hi Iceracer,
WELCOME! to the forum.!
Hang in there for more responses to your post and best of luck with your CPAP therapy.

trish6hundred
03-04-2014 10:34 AM
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PaulaO2 Offline
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Post: #6
RE: Confused by AHI
Easy answer.

The AHI is an average. The number of combined events divided by the hours slept.

So if you slept 1 hr and had 3 events, your AHI would be 3. But if you went back to sleep and slept another 2 hours, but had no events, your AHI would be 1.

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03-04-2014 03:16 PM
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Iceracer Offline

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Post: #7
RE: Confused by AHI
(03-04-2014 03:16 PM)PaulaO2 Wrote:  Easy answer.

The AHI is an average. The number of combined events divided by the hours slept.

So if you slept 1 hr and had 3 events, your AHI would be 3. But if you went back to sleep and slept another 2 hours, but had no events, your AHI would be 1.
Easy Peasy lol
03-04-2014 03:28 PM
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c0reDump Offline

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Post: #8
RE: Confused by AHI
(03-04-2014 08:25 AM)Iceracer Wrote:  Thanks I think I get ya however it did have an accumalated time so it read like one session

It may well have, I don't know the machines well enough to know how they respond when there are multiple sessions in a day. But, since the AHI is the average number of events over the session/day it is easy to start off high, and have the AHI go lower.

I had a recent night where I hit a "Peak AHI" of 15.0 in the first hour (lot of hyponea events in that first hour), but ended the night with an AHI of 2.37

Once you get SleepyHead up and running it'll make more sense.

Sleep-well

*edited to fix a typo
(This post was last modified: 03-04-2014 07:55 PM by c0reDump.)
03-04-2014 07:53 PM
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Iceracer Offline

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Machine: Resmed S9 vpap auto
Mask Type: Full face mask
Mask Make & Model: F&P Simplus FF Swift FX and F & P HC405 Flexifit
Humidifier: Hi5
CPAP Pressure: 13-18.5 max 20
CPAP Software: SleepyHead

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Sex: Male
Location: Ontario Canada

Post: #9
RE: Confused by AHI
(03-04-2014 07:53 PM)c0reDump Wrote:  
(03-04-2014 08:25 AM)Iceracer Wrote:  Thanks I think I get ya however it did have an accumalated time so it read like one session

It may well have, I don't know the machines well enough to know how they respond when there are multiple sessions in a day. But, since the AHI is the average number of events over the session/day it is easy to start off high, and have the AHI go lower.

I had a recent night where I hit a "Peak AHI" of 15.0 in the first hour (lot of hyponea events in that first hour), but ended the night with an AHI of 2.37

Once you get SleepyHead up and running it'll make more sense.

Sleep-well

*edited to fix a typo
I have sleepyhead now and it is making sense thanks for the responses. This forum is awesome I have learned more here then 6 months of Sleep appt and appt with my RT Thanks
(This post was last modified: 03-05-2014 03:24 PM by Iceracer.)
03-05-2014 03:23 PM
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robysue Online
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Post: #10
RE: Confused by AHI
(03-04-2014 07:52 AM)Iceracer Wrote:  Hi all , I'm kinda of confused ( according to my wife that's nothing new lol )
This morning I woke up around 4 am and checked my readings AHI was 3.1 not great but hey whatever ! Shut machine off went to the washroom ,went back to bed tubed back up awoke back up at 6am checked again and it said Ahi was down to 1.0 how could if possibly go down if I had 3.1 shouldn't it read 4.1 ? I'd post my sleepyhead data but I am on work computer and can't at the moment .
The AHI at 4:00AM was calculated on the total number of events that you had between bedtime and 4:00 am.

The AHI at 6:00AM was calculated on the total number of events that you had between bedtime and 6:00 am.

If you had NO events from 4:00 to 6:00 am, the AHI number would naturally go down. But the only mathematical solution I can find for a system of equations that models what's needed to get a 4:00 AM AHI = 3.1 and a 6:00 AM AHI = 1.0 would indicate that you went to bed just after 3:00AM (which seems implausible) and had 3 events before waking up at 4:00 AM, and then had no events after returning to bed.

But if that 6:00 AM AHI was 2.0, then I can mathematically show that bedtime would have been about 12:25 and you would have had about 11 events between going to bed at 12:25 and waking up at 4:00 and no events between 4:00 and 6:00.
03-07-2014 06:15 PM
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