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AHI Question
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me50 Offline

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Post: #1
AHI Question
I was wondering how that when I had my machine in use for 2 hours that my AHI was 1.4. Thanks for your help
(This post was last modified: 08-29-2013 11:22 AM by me50.)
08-29-2013 11:03 AM
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RonWessels Offline

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Post: #2
RE: AHI Question
Depending on where you are getting that AHI value from, it's probably a running average.

Look at it this way. Imagine a purely periodic process. In other words, eliminate randomness and imagine that an apnea event happens every T minutes. Now, if T=60 minutes, then for 2 hours you would have experienced 2 events and your AHI would be 60/60 = 1.0. However, now imagine that T=61 minutes. At your 2 hour mark, you haven't yet had your second event, so there was only one event in that period. However, your "true" AHI is 60/61 = 0.98 and not 0.5. Going the other way, consider T=43 minutes. After 2 hours, you would have experienced 3 events, but your "true" AHI is 60/43 = 1.4.

Does that make sense?
08-29-2013 11:23 AM
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me50 Offline

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Post: #3
RE: AHI Question
So it depends on the setting of my machine as to the T factor in your example?
08-29-2013 11:42 AM
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PaulaO2 Offline
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Post: #4
RE: AHI Question
Ron is an engineer, forgive him for his technical viewpoint.

If I understand your question, you used the machine for 2 hours and your AHI was 1.4, correct?

That means that you averaged 1.4 events an hour. Like any average, it is the number of events divided by time. So to get the overall event count, reverse the math. 1.4 x 2 = 2.8 events. My guess is you had 3 events since you probably did not sleep for exactly 2hrs.

Quote:So it depends on the setting of my machine as to the T factor in your example?

I am not sure what you mean by setting. Time is time, no matter the machine.

PaulaO2
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08-29-2013 12:51 PM
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me50 Offline

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Post: #5
RE: AHI Question
meaning that T may equal 48 minutes on my machine rather than 60 minutes, etc.
08-29-2013 01:37 PM
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RonWessels Offline

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Post: #6
RE: AHI Question
(08-29-2013 12:51 PM)PaulaO2 Wrote:  Ron is an engineer, forgive him for his technical viewpoint.

You say that as if it were a disadvantage!! Madam, I believe I shall have to challenge you to pistols at dawn! Wink


To answer me50's question, the value of T that I was using was the period of time between hypothetical apnea events assuming they happen at regular intervals. It has nothing whatsoever to do with your machine settings.

I was using that example to show that, particularly for short periods of time, a "proper" AHI value is not simply the total number of events divided by the total amount of time. And, wherever that AHI value of yours came from, it may be that they used some more complicated math to get a better estimate of the "true" AHI value.

In other words, even though you probably had 3 apnea events in the 2 hour period, if they were on average 43 minutes apart, a better estimate for your "true" AHI value would be 60/43 = 1.4 (the top 60 comes from 60 minutes per hour) rather than a more simple calculation of 3/2 = 1.5.
08-29-2013 02:09 PM
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me50 Offline

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Post: #7
RE: AHI Question
okay so when it tells me that my AHI is 1.5 and I used the machine for 6 hours, the 1.5 means I averaged 1.5 per hour. wow!! nobody told me that meant the average episodes per hour so I thought that was my total AHI per the full 6 hours.
08-29-2013 10:15 PM
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Tez62 Offline

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Post: #8
RE: AHI Question
me50, it is the average number but 1.5 is good, remember a normal person's AHI can be up to, on average 5 per hour, so 1.5 is as good if not better than a normal person. It doesn't matter if it is 1, 1.5, 2, what you are comparing to is the AHI at your first sleep study. In my case at my sleep study my AHI was 30 (Servere), now it's around 1.5 per hour on average, so in theory I am 20 times better off than I was at the sleep study. The other important thing apart from the numbers is how you are generally feeling and more specifically how you feel the day after you use your CPAP. If you feel good, have more energy etc the numbers aren't really as relevant.
08-29-2013 10:30 PM
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me50 Offline

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Post: #9
RE: AHI Question
(08-29-2013 10:30 PM)Tez62 Wrote:  me50, it is the average number but 1.5 is good, remember a normal person's AHI can be up to, on average 5 per hour, so 1.5 is as good if not better than a normal person. It doesn't matter if it is 1, 1.5, 2, what you are comparing to is the AHI at your first sleep study. In my case at my sleep study my AHI was 30 (Servere), now it's around 1.5 per hour on average, so in theory I am 20 times better off than I was at the sleep study. The other important thing apart from the numbers is how you are generally feeling and more specifically how you feel the day after you use your CPAP. If you feel good, have more energy etc the numbers aren't really as relevant.

I think 1.5 is great but the DME company didn't explain it to me so I thought that was what I had all night, not per hour. not complaining as I don't have to fear dying b/c I stop breathing or any other repercussions from having apnea. The thing is that I still wake up just as much as I always have so even if I sleep 6 hours, as an example, it is interrupted sleep. but, a lot of risks are lessened b/c I have the cpap now and I have gotten a script for an auto-set cpap so I can take medication to try and help me stay asleep more than 2 hours at a time.

thanks for your help everyone
08-30-2013 12:08 AM
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Tez62 Offline

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Post: #10
RE: AHI Question
me50, I still get interupted sleep after 2 years of CPAP, I have become very sensetive to light, noise, temperature etc, like you, I never knew if I would wake up before being diagnosed. Even though I have faith in my CPAP, it helps us breathe but not necessarily helps us sleep if there are other factors. At least now I feel like most nights I get enough sleep (last night around 7.9 hours) where before I would be luck to get 1-2 hrs non quality sleep per night.
08-30-2013 12:15 AM
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