Questions regarding AHI's

[salinas212]

G'morning guys! Been awhile since I was here but lately I've been stumped by the question of how many AHI's are in a fractional number like .1 or .3? Let's say my machine shows I slept for 1 hour and had .1 AHI or slept 8.5 hours and had .3 AHI's. I'm struggling to understand how one can have 1/10 of an AHI or 3/10 of an AHI.

Thanks in advance for any/all help!

[Pugsy]

AHI numbers are per HOUR AVERAGES of how many events got flagged over the number of hours the machine was on.
Divide total number of events by hours the machine was on.
Obviously we can't have a fraction of an apnea event but we can have fractions when dividing hours of use by the total number of apnea events.

It would make it easy to understand if we didn't have the fractions.
Example....lets start with something simple like 8 events over 8 hours of machine use (note I didn't say "asleep" because the machine can't tell if you are asleep or not). It only measures air flow...doesn't really have any way to measure sleep status.

Anyway 8 events over 8 hours gives an AHI of 1.0. We may or may not have more than one event during an hour but it isn't impossible to have all those 8 events in just one cluster in one hour and simply no events at any other time.....AHI is still 1.0

Lets complicate things just a little....same 8 hours of machine use but total of 15 events over those 8 hours.
Divide the 15 event total by the 8 hours and you get a fractional AHI of 1.875. See how easy it is to get a fractional AHI number?

The fractions mean nothing and no need to worry about it or even think about it.
You can't change it so why worry? Wasted mental energy IMHO.

Does this clear up your mind on fractional AHI numbers?

[salinas212]

Thanks Pugsy!

As you wrote; "Obviously we can't have a fraction of an apnea event but we can have fractions when dividing hours of use by the total number of apnea events." Only question remaining for me is how many AHI event(s) is .1 in 1 hour? If it's 1 why doesn't the machine show 1.0 vs .1?

This is an actual number my machine gave me yesterday after a nap and started me down this road of fractional AH event questions.

Thanks in advance!

[Pugsy]

Only question remaining for me is how many AHI event(s) is .1 in 1 hour?

Again it depends on the number of hours the machine is on. That is a critical component of the AHI numbers.

There are hundreds (maybe thousands) of math combinations that will give you 0.1 AHI depending on the hours of use part of the equation.
The machine will either round up or down since it only goes to 2 decimal points to the right.

I don't seem to have an example handy of a 0.1 AHI but I have one with AHI 0.44 and I got that the same way I would have got 0.1.
Divide the hours of use by 9 hours and 7 minutes (I normally don't mess with minutes unless it's close to a quarter of an hour and then I might use it). The difference is minimal.
total of 4 events divided by 9 hours is 0.444 and if I use 9 hours and 7 minutes (7 minutes is about 1/8 of an hour which is roughly 0.125 hours).
4 events divided by 9.125 hours is 0.438 AHI Obviously a tiny difference and not event worth doing the work to get it.

[salinas212]

Again Pugsy, Thank You! And I realize what I'm doing here, with these numbers is akin to picking pepper out of fly poop as my numbers are small and insignificant but for the life of me I cannot understand how .1 AH events in 1 hour of machine use is possible. Hey I'm just 7 months out of a dual regimen of radiation, chemo and infusions so please forgive my brain fog.

[Pugsy]

I cannot understand how .1 AH events in 1 hour of machine use is possible.

It's not possible to have 1 hour of machine use and 1 flagged event to come up with AHI of 0.1.
Something else is being factored in somewhere. Without seeing what you are seeing it's impossible for me to tell what.

1 event in 1 hour of machine being on will give you 1.0 AHI for that single hour.
You've got some other variable in there that you aren't seeing or factoring in.

[Pugsy]

Put it to rest and quit pickin pepper out of fly poop. It will drive you crazy.

[salinas212]

I understand but it's what the machine was showing when I got up. Then it was still there later when I went to bed for the night. I didn't go scrolling to look for a deeper understanding/analysis but you can bet next time it shows I'll take a pic! Meanwhile, please pardon my OCD.

Thank ya ma'am!

[Pugsy]

I understand but it's what the machine was showing when I got up. Then it was still there later when I went to bed for the night.

Oh....this number is from the machine's LCD screen???? There's your other variable but you can't see it because the machine doesn't always get the entire night's numbers figured in.

In the mornings the machine will sometimes not get the "hours of use" correct because if the machine gets turned off for any reason for more than a handful of minutes it will reset the session hours of use to most recent but it doesn't reset the number of events so it takes that last hour recorded of use and still factors in past events bringing the average way down.

You are going to need to use more than just the machine's LCD screen to see how that happens....hence the OSCAR software use.

Or....don't ever turn the machine off during the night so it won't have a chance to report a short session like that hour.

[salinas212]

Yes'm it was the machine's LCD screen and only for an hour's nap in the mid-afternoon and not the entire night and no electrical interruptions occurred in that time or I would've had to go thru the house and reset things like oven, range hood etc clocks that start to flash on/off and not reset even it the electricity goes out for a millisecond.

[Pugsy]

Yes'm it was the machine's LCD screen and only for an hour's nap in the mid-afternoon and not the entire night and no electrical interruptions occurred in that time or I would've had to go thru the house and reset things like oven, range hood etc clocks that start to flash on/off and not reset even it the electricity goes out for a millisecond.

Ahh....more clarification...a one hour nap in the afternoon (remember the machine reset hours of use and data at noon) so you should be starting with a clean slate.
Where and how it pulled a 0.1 for AHI in a one hour nap.......I would need to see that report in detail to maybe explain it.

About all we ever tell people is the data from a nap really can get screwed up and we don't know why .... and it's notoriously inaccurate when it comes to naps.

[salinas212]

Now that's an answer I can live with tho struggle to understand how/why naps are such an issue for the machine. Either way, thanks so much for stickin' with me. I super-appreciate ya P!

[zonker]

Oh....this number is from the machine's LCD screen???? There's your other variable but you can't see it because the machine doesn't always get the entire night's numbers figured in.

huh. it's been a very long time since i've looked at oscar. I just glance at the screen in the morning. so my .1 ahi COULD be 0.0!!

(as my mother would say, live in hope and die in despair.)

[Pugsy]

Oh....this number is from the machine's LCD screen???? There's your other variable but you can't see it because the machine doesn't always get the entire night's numbers figured in.

huh. it's been a very long time since i've looked at oscar. I just glance at the screen in the morning. so my .1 ahi COULD be 0.0!!

(as my mother would say, live in hope and die in despair.)

Sorry to burst your bubble but I should have qualified my statement above a little better.

the machine doesn't always get the entire night's numbers figured in.

Maybe could have added "when naps or short sessions are involved".

Did you look to see if that flagged event giving you a 0.1 AHI was real asleep or not?
Pretty much 80% of any flagged events I see are SWJ false positives. On occasion 100% have been SWJ and I can pat myself on the back for getting an unofficial 0.0 AHI.

[zonker]

Did you look to see if that flagged event giving you a 0.1 AHI was real asleep or not?
Pretty much 80% of any flagged events I see are SWJ false positives. On occasion 100% have been SWJ and I can pat myself on the back for getting an unofficial 0.0 AHI.

now, you KNOW I never let facts get in the way of my fantasies!


one of these days, i'll put the card in the computer and see what's what in oscar.