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AHI Accuracy from Brand to Brand
#1
AHI Accuracy from Brand to Brand
My wife has been using a ResMed S9 Auto for about 3 years now. She was diagnosed with an AHI of 67 or so. Probably about 50% of her AHI numbers are under 1.0 and virtually never over 2.0. I was just diagnosed with an AHI of 37, and am currently on a trial F&P machine. It is a very recent model and seems to have all the bells and whistles. However after 4 nights my AHI has ranged from a low of 2.7 to a high of 6.0. The machine is not supported by SleepyHead yet so I can't get into the detail of where my issues are.

This is a bit embarrassing as my starting AHI is nearly half what hers was, and I can't seem to get numbers anywhere close to what she gets. The machine setup is essentially the same for pressures and both are in Auto mode. So I am wondering if the AHI number is actually accurate/reliable enough to compare between machines of different brands? Or, is it just a relative number within the brand and useful only for determining relative treatment effectiveness?

Here is a link to a review of the F&P machine I am using. Oops, I guess I can't post that. Just google f&P sleepstyle review and you should find it.
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#2
RE: AHI Accuracy from Brand to Brand
As you say the machine setups are essentially the same, could there be any harm in swapping machines for a couple of nights and comparing the readings?
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#3
RE: AHI Accuracy from Brand to Brand
I am convinced that the various companies measure AHI differently.

I have both a Phillips DreamStation and a ResMed AirSense 10 Auto. I have them set to the same settings. On the DreamStation, my AHI is usually between 1.0-2.0, and I feel fantastic. On the AirSense 10, my AHI is usually between 0.1-0.6, and I feel lousy.

So... they have got to be measuring differently (and doing other things differently, too).
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#4
RE: AHI Accuracy from Brand to Brand
The tech told me that AHI can vary as much as 2 units between brands depending on their algorithm. In addition, it's kindof like breaking your leg. Everybody's leg breaks just a little differently or a lot differently. It's still a broken leg. I would assume that sleep apnea is the same.
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#5
RE: AHI Accuracy from Brand to Brand
(03-24-2018, 11:33 AM)Phill Wrote: As you say the machine setups are essentially the same, could there be any harm in swapping machines for a couple of nights and comparing the readings?

Yes, that came to mind as I was walking to the gym today. I will do just that in a couple of days.
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#6
RE: AHI Accuracy from Brand to Brand
(03-24-2018, 12:27 PM)Hydrangea Wrote: I am convinced that the various companies measure AHI differently.

I have both a Phillips DreamStation and a ResMed AirSense 10 Auto.  I have them set to the same settings.  On the DreamStation, my AHI is usually between 1.0-2.0, and I feel fantastic.  On the AirSense 10, my AHI is usually between 0.1-0.6, and I feel lousy.  

So... they have got to be measuring differently (and doing other things differently, too).

Interesting. Have you compared the SleepyHead results? It would seem that the AHI is basically a digital thing -- sum of the events. I suppose what gets flagged as an event could be different from machine to machine though. Also I wonder if there is a standard for the hours used in the denominator. The choice would be sleeping time, or total time in operation. The second one would tend to give lower numbers.
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#7
RE: AHI Accuracy from Brand to Brand
In the past I compared numbers for hours vs Events. As far as the ResMed and Dreamstation go, they both use sleep hours to figure AHI. As far as figuring events the only difference is how they count hypopneas. ResMed at or above 50%. Dreamstation at or above 40%. Not much of a difference.
There was a study done between machines and the ResMed was the quickest to respond which resulted in less events. I don't have the link but it's on the internet somewhere.
The one problem when trying to compare machines based on an overnight test is that a persons breathing can change from night to night. So you don't know if it was the machine that made the difference or the person.
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#8
RE: AHI Accuracy from Brand to Brand
The billing code is the same for an autoset. INSIST on an Autoset.
You do not have to accept the F&P. Call your insurance company and ask for 3 DMEs in your area. Tell them it is an AutoSet or they lose you as a customer.

Read the Dealing with a DME wiki article in my signature,

You have the choice, you are the customer,

Fred
Fred Bonjour - Project Manager and Lead Tester for OSCAR - Open Source CPAP Analysis Reporter 
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#9
RE: AHI Accuracy from Brand to Brand
(03-24-2018, 08:38 PM)bonjour Wrote: The billing code is the same for an autoset.  INSIST on an Autoset.
You do not have to accept the F&P.  Call your insurance company and ask  for 3 DMEs in your area.  Tell them it is an AutoSet or they lose you as a customer.

Read the Dealing with a DME wiki article in my signature,

You have the choice, you are the customer,

Fred

Fred, the situation is quite a bit more simple than that for me. Since I turned 65 we have had more basic insurance that does not cover a CPAP at all. So, I can basically buy whatever I want because it is all on my dime. The way it works in Canada, at least in Alberta where we are is that the sleep study test is covered by universal government health care. The companies that do it locally, do the test first, and then if the test indicates a CPAP is suitable, then my doctor prescribes it. The same testing company typically provides a trial machine to see if you are suitable for actually using one. You kind of have to take what they offer for the test, as it also is at no cost or obligation. My wife went to the same testing company 3 years ago and was offered the S9 for testing. Now they are using the F&P. The minor problem is that at the end of the test if you want to buy the machine they have an outrageous price on it. My wife's S9 was going to cost $2400 3 years ago. Instead of taking it, we just bought her an S9 for about $1100 from an on line company. In my situation today, they still want $2400 for the F&P. I have already ordered an AirSense 10 AutoSet for $900 from Supplier #32 . It should be here before I have to return the test F&P.

I'm just trying to figure out a bit ahead of time what I can achieve with a ResMed instead of a F&P. I'm curious, so I think I will try my wife's S9 to see what it will do tomorrow night --- if she lets me... If the results magically get better, I will still be left wondering if the machine is better or they are just way more optimistic in calculating AHI. If they don't get better for me, and my wife gets good results with the F&P then it will be clear. The problem is with me, not the machine. We'll see. 

Right now the surprising part is how drastically different the results are. This is not a minor difference. She is getting a reduction of almost 100 from her diagnosis AHI. I am only getting a reduction of 10. Order of magnitude difference!
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#10
RE: AHI Accuracy from Brand to Brand
No doubt that my devilbiss machine measures AHI differently to the Resmeds. Main difference is with hypopneas. The machine can even be adjusted to change it's 'definition' of what constitutes a hypopnea. Initially I was concerned as my score was higher than with the Resmed machine I hired, but after a year of nightly AHI scores (comprising around 90% hypopneas) of between 0.75 & 4.75, averaging 2.00 I don't think there is much to worry about.

However from this experience I would now assume that there really is no 'standardised' means of determining AHI's across all the different machines, but would expect them all to be in much the same ballpark.
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