How accurate are AHI measurements done by CPAP Machines?

NewtoMe · Post by **NewtoMe** » Sat Apr 21, 2007 1:05 pm

Howdy,

I just started on a REMStar Pro M set at 7. The setting was titrated at a lab by someone who has lots of experience titrating patients.

I hacked the machine to show what the AHI reading was (the machine had been set up not to show this item; it shows the 7-day and 30-day averages -- I do not have the s/w yet, so do not know the nightly results).

My machine is displaying a 7.3 average AHI for me, and want to know how accurate that result really could be. If it is accurate, Im obviously concerned. If it isn't...

thanks for any suggestionscomments.

Slinky · Post by **Slinky** » Sat Apr 21, 2007 1:14 pm

I wouldn't be too concerned. <=5.0 is considered a "normal" AHI. With the software and reader and a little patience you should be able to "tweak" that AHI down below 5.0.

Just when you do make any changes, only do one at a time and wait a week before making another change. Patience can be a frustrating virtue!

Wulfman · Post by **Wulfman** » Sat Apr 21, 2007 1:19 pm

NewtoMe wrote:Howdy,

I just started on a REMStar Pro M set at 7. The setting was titrated at a lab by someone who has lots of experience titrating patients.

I hacked the machine to show what the AHI reading was (the machine had been set up not to show this item; it shows the 7-day and 30-day averages -- I do not have the s/w yet, so do not know the nightly results).

My machine is displaying a 7.3 average AHI for me, and want to know how accurate that result really could be. If it is accurate, Im obviously concerned. If it isn't...

thanks for any suggestionscomments.

The internal sensors and programs for these machines are based on air flow whereas a PSG uses sensors attached to the body. For what these machines record "WHILE WE'RE ASLEEP" I believe the are probably pretty close, otherwise the manufacturers wouldn't be selling this type of technology to the doctors and RT's.
Since we breathe differently when we're asleep than when we're awake, if there's alot of "awake" breathing, it won't be quite as accurate as when it records the "sleep" breathing.

You probably shouldn't get too concerned until you get the software. That'll make alot of things clearer.

Best wishes,

Den

Ergin · Post by **Ergin** » Sat Apr 21, 2007 1:47 pm

The AHI detection algorithm is pretty mature and unless you have a mask leak it should be accurate.

NewtoMe · Post by **NewtoMe** » Sat Apr 21, 2007 2:52 pm

Thanks folks for the info.

It could be a mast leak. I've got an 8 L leak; I'm using a swift mask, and find sometimes it leaks from the side that has the hose swivel.

What is a "normal" level of leakage?

thanks for the help, much appreciated.

David

DP · Post by DP » Sat Apr 21, 2007 3:03 pm

If the machine uses a pressure transducer to measure flow then it is very accurate. In fact a lot of sleep labs use pressure transducers to measure flow. Sutdies have been done comparing a pressure transducer vs thermistor. The transducer did a far better job and was able to pick up UARS where as the termistor really did not.

dsm · Post by **dsm** » Sat Apr 21, 2007 3:32 pm

The issue of how useful AHI (altogether) is one we have debated many times.

Some specialists feel that AHI (AI & HI) are comparatively meaningless but the problem those people then present is what we can use instead of AHI & thus far there isn't anything that really does a better job for the ordinary person.

So then we come to the separate issue of how accurately the AHI data from each type & brand, gets reported. The reality is they will give different results for the same person for the same night (if it were possible to run two on one person at the same time).

But, there is nothing really problematic because what any person wants is the info relative to their own patterns night by night & to the end the AHI data from one brand used consistently will give you a pretty good indication of your variance night-to-night.

DSM

NewtoMe · Post by **NewtoMe** » Sat Apr 21, 2007 6:40 pm

I suspect it's a pressure tranducer... it is very responsive to changes in my breathing while awake -- I've got cflex turned on. I'm fairly impressed w/ how well it maps to what I am doing.

Part of the problem might be that I put the thing on before I turn lights out -- while reading. doing this to get more quickly acclimated to it, which I'm finding it not easy for me.

thanks again
David

WearyOne · Post by **WearyOne** » Sat Apr 21, 2007 6:49 pm

NewtoMe wrote:Thanks folks for the info.

It could be a mast leak. I've got an 8 L leak; I'm using a swift mask, and find sometimes it leaks from the side that has the hose swivel.

What is a "normal" level of leakage?

thanks for the help, much appreciated.

David

The vent rate (intentional mask leak) should be in the manual that came with the mask, or you can check here

http://www.internetage.com/cpapinfo/leak-rates-1.html

Pam

NewtoMe · Post by **NewtoMe** » Sun Apr 22, 2007 11:52 am

thanks Pam,

Yep, 27 L / M for my mask (from the pamphlet that came w/ the mask) and also the page you provided). Weird, 'cuz the 7-day avr, for me is only 8 L/M. Who knows...

David

Guest · Post by **Guest** » Sun Apr 22, 2007 1:32 pm

dsm wrote:
Some specialists feel that AHI (AI & HI) are comparatively meaningless but the problem those people then present is what we can use instead of AHI & thus far there isn't anything that really does a better job for the ordinary person.

I quoted this because the one thing I have found useful is sort of subjective -- whether or not I feel better.

I had an AHI of 6 in my initial sleep study -- barely high enough to 'qualify' as having sleep apnea at all, and my AHI with the CPAP runs at an average of about 5.5, but I feel measurably better with the CPAP. If you looked at the numbers, it would make no sense.

Minerva

How accurate are AHI measurements done by CPAP Machines?

How accurate are AHI measurements done by CPAP Machines?

Re: How accurate are AHI measurements done by CPAP Machines?