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How accurate is our machine data
#1
Question 
How accurate is our machine data
Something I have been plundering for a while, is how accurate is the data we get from our machines. I've always had trouble believing that just a flow and a pressure sensor can give us so much different data. On top of this it's suppose to tell us things like the pressure at the mask which is some 2 meters away at the end of a hose.

Last week when I saw my sleep Dr he was looking at his laptop and made comment that he takes a lot of it with a grain of salt. That lead me to asking him about the data the machine provided and he seems to have a similar opinion as I do.  

 I may be way off base with this. Anyway I'm keen to hear what others think.
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#2
RE: How accurate is our machine data
My question would be what crystal ball does your Doctor use to treat you? I think I'd trust the machine more than your doctor.
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#3
RE: How accurate is our machine data
There have been various peer reviewed studies done indicating our machines are fairly accurate. When I find the links I will edit this post.

Edit: well after half an hour of fruitless searching for the thread I can't locate it. I recall two threads - one this year and one in 2015 dealing with the issue. Perhaps someone else can locate these threads.
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#4
RE: How accurate is our machine data
(08-18-2017, 07:27 PM)Walla Walla Wrote: My question would be what crystal ball does your Doctor use to treat you? I think I'd trust the machine more than your doctor.

He prefers the data from a in full sleep study.
As when my old machine was only providing 6 to 8 cmh2o and said that my ahi was less then 1.
He said he didn't have anyone my size that was under 10. Sleep study showed that I needed 14 to control apneas so I set the machine to cpap 14.
New as10 doesn't have that problem.
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#5
RE: How accurate is our machine data
How old was the machine? Granted a sleep study would be more accurate. But who gets checked that often by a sleep study? No one could afford it.
       Another problem is when the titration at the Sleep Center is flat out wrong. I'd rather go with an Auto machine than a fix pressure setting based on a bad titration. The equipment may be better at the Sleep Center but if you get a bad tech it doesn't do you much good.
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#6
RE: How accurate is our machine data
(08-18-2017, 07:29 PM)sonicboom Wrote: There have been various peer reviewed studies done indicating our machines are fairly accurate.  When I find the links I will edit this post.

Edit: well after half an hour of fruitless searching for the thread I can't locate it.  I recall two threads - one this year and one in 2015 dealing with the issue.  Perhaps someone else can locate these threads.

I found this thread by robysue dealing with the issue, Just found a 2015 Bench Test for APAPs. Perhaps it's the one you were thinking about.
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#7
Surprised 
RE: How accurate is our machine data
I bought a manometer and actually used it today on my machine for the first time.  The pressures were dead on.  I hooked it up at the point where the mask hose goes.. so 6-12 inches from my head.  So I spent $60 because I felt the same as you did "how accurate are these machines".. test completed and manometer put away probably for a year or two or until the next machine.

The algorithms by resmed, for example, are used for titration.. i think they are pretty much spot on.  Now can it determine all events 100% perfectly, no.. but generally it is extremely accurate IMO
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#8
RE: How accurate is our machine data
Yes, definitely want to know as well.  

Glad to see I am not the only one.

Maybe we can get the info!

Regards and Happy Holidays!
Plmnb
Huhsign  WARNING: It may take a while to sink in...I tend to get befuddled at times.
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#9
RE: How accurate is our machine data
The machine really knows only the flow rate and pressure at the source, ie inside the machine.

To determine the pressure at the mask, the pressure drop in the hose and elbow/mask must be considered, and of course the leakage. At 0 net flow, they have no effect, but at peak flow they can introduce significant error.

That is why it is important to set the hose type and mask type correctly. This allows the machine to adjust the pressure at the machine so that you get the proper pressure in the mask.

For example, let’s say the combined pressure drop of the hose and mask is 3cmH2O at 100L/m flow. If you are exhaling just enough to offset the vent flow, the net flow is 0, pressure drop is 0, and the machine pressure is the same as the mask pressure. At 100L/m though, the mask pressure will be 3 below the machine pressure. That means the machine has to compensate by delivering 3 cmH2O above the pressure setting so that the mask pressure is correct.

Luckily, the machines know how to do this - IF configured correctly. They constantly adjust the pressure at the machine to compensate for flow, so that the mask pressure will be correct.

One caveat: the Respironics clinician manual says to set the mask type restriction to X0 (no mask compensation) for non-Respironics masks. That is absurd (unless you sleep with the hose in your mouth) and clearly came from the lawyers instead of the engineers. So, for this discussion, I will assume that the mask type is never set below X1.
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