Questions about pressure relieve, ramp and more

[emmayes]

The last couple of days I’ve read a lot about cpaps and more, but still do not understand some things:

1) pressure relieve. For some brands, a pressure relieve setting 2, is the same as “lowering pressure exhaling by 2 cm H20”. Not all, though, which is very confusing for me. Like the Z breathe algortim is different ( even though I’ve looked at the graph in the manual, I do not understand what it does).
But, let’s say yo have a dreamstation or resmed:
The cpap has pressure settings possible 4 - 20 cm.
You set the fixed pressure to 5 cm H20 and the pressure relieve on 3 cm H2O. Will the exhale pressure be 5 - 3 = 2 cm H20? Or will it never be below 4 cm? I do not understand why not, since my vpap does have that setting. I know it’s different, but why can a cpap never get below 4?

2) ramp mode
Basically the same question; if you set fixed therapeutic pressure at 5, ramp time 45 minutes, what is the lowest starting pressure possible? Is it possible to set a ramp pressure start at 3 (for example) even though fixed settings are only available 4-20?

Thank you all!

[Julie]

Machines have 'default' low and high settings - programmed so they cannot go below or above those regardless of anything else, so all settings and figuring need to be within those parameters. I hope your examples were just that - as actual settings they leave a lot to be desired!

[Pugsy]

why can a cpap never get below 4?

Because the machine manufacturers set the machine up so it can't go below whatever they don't want it to go below.
And actually I think Devilviss cpap/apap machines have a minimum of 3.
So not all cpap/apap have a minimum of 4.
Why did the machine manufacturers come up with 3 or 4?? I don't know but it might have something to do with the fact that if the pressure is much lower it's really not all that comfortable or the fact that there needs to be a minimal amount of air moving to clear out the carbon dioxide in the mask.

2) ramp mode
Basically the same question; if you set fixed therapeutic pressure at 5, ramp time 45 minutes, what is the lowest starting pressure possible? Is it possible to set a ramp pressure start at 3 (for example) even though fixed settings are only available 4-20?

The lowest starting pressure for anything is going to be the minimum pressure selection you see on the menu...with or without exhale relief and if you start with 4 (or 3) then exhale relief doesn't even kick in until the pressure is high enough for exhale relief to cause a reduction.

Example....if the pressure to be used is 5 and someone wants to use EPR of 3 and they want to start with 4 cm ramp (or 3 if the machine will do it) the exhale relief won't even start working until the pressure has increased so that there is some room for movement and even then you only get what room is available. If you are using a pressure of 5 and have EPR set to 3..you won't get 3 after you are at full pressure...you get 1 cm because it can't go below 4 cm. You can only get 3 if the pressure is at 7 or more.


Respironics is of course a little different and the Flex exhale relief isn't a per cm standard drop like ResMed.
With Flex the actual amount of drop in pressure is determined more by the person's own breathing (forcefully vs shallow) than it is by the Flex setting and even with the setting of 3 the biggest drop available is 2 cm and you only get that if your breathing is forceful enough.

Now when you get into the bilevel machines the exhale relief is called pressure support but the end result is the same....a drop in pressure during exhale but the amount of drop has a lot more choices available...no longer limited to max drop of 3 cm.

Are you still trying to figure out if you can get by with a tiny portable machine that will run off batteries and have it do what your bilevel machine does in terms of PS?
You really need to talk to your doctor about how safe it would be for you to reduce your PS to 3 or less.
I couldn't find one tiny bipap that would run off batteries that would be easy to carry outside.
Now we could probably add a lightweight battery to your existing bipap so that you can take a stroll outside but you would probably want something to put the machine and battery in or on...like the walker with a seat I told you about.

[emmayes]

Thank you so very much!

It is indeed a question within the same quest it’s just hard you know.
I def will talk to my doctors about it, but I want to be informed before I go. Especially since I have a complex / unique issue, I want to know “what’s out there” so I know what I would like to try, and take that with me to the docs.

So again, thanks, this is very helpful.