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Sleepyhead - Pressure vs Mask Pressure Graphs
02-26-2016, 12:35 PM
I've noticed, without caring too much but now am curious, that the mask pressure data and the machine pressure data do not tend to coincide. For instance, my max pressure is 7 but the max mask pressure last night was 8.98 but only for an instant. I could see no obvious reason for the mask pressure jump (and I see this most nights happening for short blips of time) such as flow limitation up or leak rate up etc... Can someone please explain what the factors are that make the mask pressure rise even when the machine pressure is staying relatively constant but well below the mask pressure? TIA
02-26-2016, 01:18 PM
While we're at it, how is the mask pressure even sensed? I assume the pressure sensor is actually in the machine, and the mask pressure is interpolated.
02-26-2016, 03:00 PM
Sleeprider - Yes indeed. An additional question I was pondering as well.
03-05-2016, 12:34 PM
Given the lack of responses I guess no one else has figured this out either.
03-05-2016, 12:47 PM
I think that while coding SleepyHead it was one of those "Seemed Like A Good Idea At The Time" type of things.
03-05-2016, 01:17 PM
As far as I can see, the mask pressure must be a result of the pressure at the machine reduced by the pressure drop caused by the hose and mask. The 8.98 may be the actual pressure the machine generates in order to give you 7 at the mask. Why it flashes up at the beginning, I do not know.
03-06-2016, 12:38 PM
Certainly a possibility but that doesn't explain the low end either. So some nights the low mask pressure is actually below what the machines can do. For instance, SH is reporting the mask pressure low for last night at 2.96. At the time that occurred the pressure was at 5.7. I use an EPR of 1. So mask pressure should be 4.7 one would think. On most nights SH reports a minimum max pressure of 0. Really? BTW last nights mask pressure high was 8.5. Pressure at that time was 6.99.
Does your mask pressure data report highs and lows that don't match your actual pressures?
03-07-2016, 03:04 AM
I don't know about the AutoSet but on the ASV machine (VPAP Adapt) the mask pressure is a high resolution data stream while the regular pressure is low resolution. You can see how the mask pressure jumps up and down in response to any disturbance in the airflow on a breath by breath basis. Because of the difference in resolution the regular pressure chart will give you the pressure averaged over a second or so, while the mask pressure goes into split seconds and is likely more accurate at any particular instant.
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