Help me understand my pressure graph in SH

I'm currently running my PR S1 760 in straight CPAP mode at a fixed pressure of 10 cmH2O. (Experiment). One would think then that the pressure graph in SH would simply show one straight line at 10. Instead it shows only EPAP and the line is up and down all the way at pressures slightly over 9 but never quite up to 10, almost as if it were indicating that it was somehow on auto (which the machine isn't capable of in CPAP mode) and never quite reaching the max setting of 10.

Can anyone enlighten me as to why this is?

Are you using any Flex exhale relief?
Exhale relief will cause the pressure line to vary and with Flex relief how much it can vary will depend on how forcefully your breathe so it isn't necessarily a fixed amount of reduction during exhale.
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As to why it doesn't reach 10...I would maybe need to see the actual detailed report

Pugsy wrote: ↑

Sun Jul 22, 2018 6:30 am

Are you using any Flex exhale relief?
Exhale relief will cause the pressure line to vary and with Flex relief how much it can vary will depend on how forcefully your breathe so it isn't necessarily a fixed amount of reduction during exhale.
.
As to why it doesn't reach 10...I would maybe need to see the actual detailed report

Thanks Pugsy. Yes, I'm using C-Flex on 3. You're right and I think I have it figured out.

The upper limit of the graph is 10 cm, which is exactly where my machine is set. The slightly lower EPAP pressure line is where the pressure dropped as called for by the PRS1 in it's infinite wisdom based on my breathing force as you mention. It may be instructive that although my Flex is maxxed out at a setting of 3, at no time in the ups and downs of the EPAP line did the pressure drop by more than 1 cmH2O and usually less.

It seems to me that ResMed's approach where 1-2-3 actually means 1-2-3 is a much better solution and more predictable. I would think that a patient could almost use a ResMed APAP as if it were a true bilevel machine, unless I'm missing something.

There's some documentation in one of the manuals about Flex exhale relief...the most you can get is 2 cm even at the setting of 3 and even that is based on the force of your own breathing.

I don't know why they did it this way...I also like ResMed's EPR per cm per setting way of doing things...but Respironics never asked me my opinion.
I did discover when I was using Respironics equipment that my body preferred AFlex over CFlex for some reason and the setting of AFlex at 2 seemed to match my own respiration pattern perfectly. It matched so good that I felt like I was breathing normally without even using the machine.

I tell people to just try the 3 settings and pick the one that feels the best to them and use that one no matter what the actual number of the setting might be.

Sorry for the little arrows in the image below. I couldn't figure out how to get it without the arrows but I think you can see what I mean. I found this in a provider manual a while back.

Thanks again Pugsy.

Since the 760 only runs CPAP in fixed pressure mode, I don't have A-Flex available but as you suggest I will experiment with all 3 levels of C-Flex. I have to admit that as it stands my breathing seems to want to unnaturally synchronize to the machine until I fall asleep. Since I'm accustomed to Bipap even at moderate pressures (11/7), I just defaulted to the max pressure relief available so I'll see if one of the other levels might work better.