Higher #s AHI

General Discussion on any topic relating to CPAP and/or Sleep Apnea.
sidesleeper7
Posts: 126
Joined: Fri Jan 25, 2013 12:36 pm

Higher #s AHI

Post by sidesleeper7 » Mon Dec 05, 2022 2:11 pm

I have noticed if I sleep in past noon and wake up at 12:30 my numbers are always a little off or higher than usual .. when the machine reads the report as a half hour .. is this a calculation error or is the machines half hour estimates always accurate?

Thanks
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robysue1
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Re: Higher #s AHI

Post by robysue1 » Mon Dec 05, 2022 2:25 pm

sidesleeper7 wrote:
Mon Dec 05, 2022 2:11 pm
I have noticed if I sleep in past noon and wake up at 12:30 my numbers are always a little off or higher than usual .. when the machine reads the report as a half hour .. is this a calculation error or is the machines half hour estimates always accurate?

Thanks
It's not really a calculation error nor is it really an issue of accuracy.

It's just plain old statistics coming back to bite you because that last 1/2 hour of sleep is not being glommed together with the rest of the night's data. And then there's the fact that you may have some SWJ tossed into that last half hour if you're just lying in bed thinking that you just don't want to get up yet.

In other words, if you have 10 hours of usage that runs from 1:50:00 AM to 11:50:00 AM and you have a total of 15 events all night long and the last 2 of those events occur in the last half hour of usage, the machine will report an AHI = 1.5 = 15/10.

If you have 10 hours of usage that runs from 2:30 AM to 12:30 PM and you have a total of 15 events all night long and the last 2 of those events occur in the last half hour of usage, the machine would report an AHI = 1.5 if it could be programmed to make the start of the new day after 12:30.

But the data is artificially split over 2 "days": On the first day, there are 13 events in 9.5 hours of usage for an AHI = 1.37 (truncated to 1.3 on a Resmed's screen). On the second day, there are 2 events in 0.5 hours of usage for an AHI = 2/0.5 = 4.

In the statistical data gathered over a week or a month or a year, however, that night would be contributing 15 events to the total number of events and 10 hours of usage to the total usage.
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sidesleeper7
Posts: 126
Joined: Fri Jan 25, 2013 12:36 pm

Re: Higher #s AHI

Post by sidesleeper7 » Tue Dec 06, 2022 12:22 am

robysue1 wrote:
Mon Dec 05, 2022 2:25 pm
sidesleeper7 wrote:
Mon Dec 05, 2022 2:11 pm
I have noticed if I sleep in past noon and wake up at 12:30 my numbers are always a little off or higher than usual .. when the machine reads the report as a half hour .. is this a calculation error or is the machines half hour estimates always accurate?

Thanks
It's not really a calculation error nor is it really an issue of accuracy.

It's just plain old statistics coming back to bite you because that last 1/2 hour of sleep is not being glommed together with the rest of the night's data. And then there's the fact that you may have some SWJ tossed into that last half hour if you're just lying in bed thinking that you just don't want to get up yet.

In other words, if you have 10 hours of usage that runs from 1:50:00 AM to 11:50:00 AM and you have a total of 15 events all night long and the last 2 of those events occur in the last half hour of usage, the machine will report an AHI = 1.5 = 15/10.

If you have 10 hours of usage that runs from 2:30 AM to 12:30 PM and you have a total of 15 events all night long and the last 2 of those events occur in the last half hour of usage, the machine would report an AHI = 1.5 if it could be programmed to make the start of the new day after 12:30.

But the data is artificially split over 2 "days": On the first day, there are 13 events in 9.5 hours of usage for an AHI = 1.37 (truncated to 1.3 on a Resmed's screen). On the second day, there are 2 events in 0.5 hours of usage for an AHI = 2/0.5 = 4.

In the statistical data gathered over a week or a month or a year, however, that night would be contributing 15 events to the total number of events and 10 hours of usage to the total usage.

I have the time period set To day : I guess I’m wondering if it’s accurate, today it said 30 minutes and the reading was higher than normal .. does it average for a full hour if the machine is stopped at 12:30 and it’s resetting days at 12:00?
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ozij
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Joined: Fri Mar 18, 2005 11:52 pm

Re: Higher #s AHI

Post by ozij » Tue Dec 06, 2022 12:40 am

sidesleeper7 wrote:
Tue Dec 06, 2022 12:22 am
: I guess I’m wondering if it’s accurate, today it said 30 minutes and the reading was higher than normal .. does it average for a full hour if the machine is stopped at 12:30 and it’s resetting days at 12:00?
1 apnea in half an hour makes for an AHI of 2.
And so on.
It's "total number of events divided by time period in which they occured".

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