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+--- Thread: AHI Data question (/Thread-AHI-Data-question)
AHI Data question - u2canbuild - 11-19-2014
So the other night I woke up after 3 hours and saw my machine was indicating an ahi of 6.5, which was very high for me;
I went back to sleep and after another 3 hours, the total nights AHI reading was 2.4
So help me understand the math......
AHI is events per hour..........
so after 3 hours, my ahi was 6.5 .................. and if I had no additional events...... in the forthcoming 3 hours ........ I should think that my ahi would be 6.5 divided by 2 or 3.2 ....... but it was not............... how did I get to a toal ahi of 2.4 for the night?
thanks
RE: AHI Data question - Crimson Nape - 11-19-2014
From my very limited experience, are these numbers from ResMed or SleepyHead data? Due to their different algorithms employed, they can and will report differently. I believe it's calculated by length of events/usage time. That way an apnea of 30 seconds carries a higher weighted average than one that lasted 10 seconds.
RE: AHI Data question - PaulaO2 - 11-19-2014
I'm not sure exactly what the screen reports. I looked through the manual and couldn't find it. Since it is reporting it "live", it could be reporting the peak AHI vs the actual.
RE: AHI Data question - zonk - 11-19-2014
From http://www.resmed.com/content/dam/resmed/global/documents/products/machine/s9-series/data-management-guide/368773r4_s9-bilevel-series_data-mgt-guide_amer_eng.pdf
Apnea Indices
For all indices, the value shown for Statistics is the total number of events divided by Daily Usage.
AHI — Apnea–Hypopnea Index
The total number of events is calculated by adding the number of apnea and hypopnea events.
For graphs, the AHI count is incremented at the occurrence of every event and reset every hour
RE: AHI Data question - PaytonA - 11-19-2014
Zonk,
Do you have the Resmed web site memorized??
Best Regards,
PaytonA
RE: AHI Data question - AshSF - 11-19-2014
I have seen the exact same thing in SH when you have more than 1 sleep session in the night. Sometimes, the AHI is lower for each individual session and higher for combined session.
Maybe its a bug in SH.
RE: AHI Data question - zonk - 11-19-2014
(11-19-2014, 03:26 PM)PaytonA Wrote: Zonk,Habit is second nature
Do you have the Resmed web site memorized??
Best Regards,
PaytonA
![[Image: Tea-Pot.jpg]](http://www.apneaboard.com/Tea-Pot.jpg)
RE: AHI Data question - PaulaO2 - 11-20-2014
(11-19-2014, 02:47 PM)zonk Wrote: From http://www.resmed.com/content/dam/resmed/global/documents/products/machine/s9-series/data-management-guide/368773r4_s9-bilevel-series_data-mgt-guide_amer_eng.pdf
Apnea Indices
For all indices, the value shown for Statistics is the total number of events divided by Daily Usage.
AHI — Apnea–Hypopnea Index
The total number of events is calculated by adding the number of apnea and hypopnea events.
For graphs, the AHI count is incremented at the occurrence of every event and reset every hour
So that's why it tracks the "peak" AHI. And looking at the screen while the machine is in use is kinda useless.
You're such a good alien, zonk. I like you.
RE: AHI Data question - PaulaO2 - 11-20-2014
(11-19-2014, 05:28 PM)AshSF Wrote: I have seen the exact same thing in SH when you have more than 1 sleep session in the night. Sometimes, the AHI is lower for each individual session and higher for combined session.
Maybe its a bug in SH.
The OP was seeing this data on the screen of his machine, not within SH.
The problem with combining sessions is the math. The machines (and SH) don't use 60 minutes, they use 3600 seconds, calculate the events, then round it up. Quite often the two sessions AHI added together don't equal the total SH comes up with.
Then there's the way the machine itself comes up the the total vs the way SH comes up with the total. And it can be a mess. But really, unless the two is off by more than 1.0, I'm not gonna be upset.