Rationale for Setting an Upper Pressure Limit?

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Slartybartfast
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Rationale for Setting an Upper Pressure Limit?

Post by Slartybartfast » Sun Oct 31, 2010 3:05 pm

I've been experimenting with pressure settings on my S9 Autoset and think I have found the ones that work best for me. Just to do a sanity check, I often go back to my fixed 11 cm prescribed condition and sleep a few nights and compare the numbers and my feelings against those generated when in APAP mode.

It seems clear to me that I'm more comfortable with the 8 - 13 cm setting. The pressure graph below shows the pressure in auto mode never seems to spend much time as high as 11 cm. And when in CPAP mode at 11 cm, I don't sleep as well, I'm more aware of my lungs being expanded, if that makes sense, and my upper back hurts the next day. Those feelings are absent when in auto mode. So since my AHI averages 0.5 or less, I think that's the way I'm going to tell my sleep doc I'm going to leave it.

But I've been wondering. What is the reason for the common recommendation to set an upper limit on the pressure? My pressure has never risen above 12 cm when in auto mode. So what's wrong with not setting a maximum upper pressure limit? And why do some experienced folks here recommend setting a very narrow (e.g. 2" H2O) therapeutic range? Is a puzzlement to me.

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john5757
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Re: Rationale for Setting an Upper Pressure Limit?

Post by john5757 » Sun Oct 31, 2010 3:12 pm

It is more of a safety conform issue and to prevent the autoCpap to run away with pressure in certain situations.

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Re: Rationale for Setting an Upper Pressure Limit?

Post by jonquiljo » Sun Oct 31, 2010 6:17 pm

I have a Respironics system one APAP and find that it tends to raise pressure and "chase" snores - a bit more than necessary. Keeping a limit on the pressure keeps it under control sometimes. It works better for me anyway.

I am just now seeing that it does in detail with Encore Pro (vs. EncoreViewer). The wave form graphs are really interesting and tell you a whole lot more about what the machine really does and why. So far, I've been able to use these graphs to see my machine chase snores.

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DoriC
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Re: Rationale for Setting an Upper Pressure Limit?

Post by DoriC » Sun Oct 31, 2010 6:22 pm

Good job. Looks like you've got it dialed in perfectly. You don't show your leak graph but in some cases with the maximum pressure left wide open and you have some leaks and/or snores, pressure raises to compensate and on it can go all night. I would think once you've got leaks under control it wouldn't matter what the max pressure is because you would never need it. At least that's my understanding.

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Re: Rationale for Setting an Upper Pressure Limit?

Post by jnk » Sun Oct 31, 2010 8:45 pm

Slartybartfast wrote:. . . What is the reason for the common recommendation to set an upper limit on the pressure? . . .
In harmony with Dori's wise words, I would only set an upper limit if my machine tended to "run away," to increase pressure needlessly. If that never happens to you, the upper limit does not matter for you, just as you say. It is the minimum-pressure setting, the lower limit, that tends to have the greatest effect on treatment and comfort for most, as Rested Gal often points out.

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Re: Rationale for Setting an Upper Pressure Limit?

Post by jonquiljo » Sun Oct 31, 2010 11:17 pm

Right. But I have set the limit too low when trying a new mask and things got messy when I developed unanticipated leaks. I don't think I slept too well that night.

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Goofproof
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Re: Rationale for Setting an Upper Pressure Limit?

Post by Goofproof » Sun Oct 31, 2010 11:29 pm

It takes "X" pressure to hold your airway open in a certain position at a time. Our worst position for Apnea, it makes no sense to exceed your needed pressure to correct your worst apnea position, by over 2 CM. (this amount added for a really bad night) Using a top pressure that's too high, doesn't help your treatment, it just makes leaks worse and your treatment bad overall. If you mouthbreath, every CM above what you must have to keep your airway open is just a invite to more mouthbreathing and less real treatment. jim
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Slartybartfast
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Re: Rationale for Setting an Upper Pressure Limit?

Post by Slartybartfast » Sun Oct 31, 2010 11:41 pm

Thanks, all, for your wise words. That makes sense to leave the top limit off, or high enough so that it doesn't interfere, so long as there are no runaway issues. And I've not encountered anything like that (yet).

Re: leaks, they haven't been much of a problem. Occasionally I'll get a leak that will last 5 minutes or so, but the data shows that I evidently move and quench the leak within a few minutes. And the flow trace keeps its sawtooth profile, indicating that I didn't awaken when that happened.

AHI consistently under 1.0, usually 0.5 or lower. The trace I attached to my initial post was for last night at 0.2 AHI. And the only time it's over that is when I'm out of my groove. Chinese food or Italian food will do that to me. Might be too much salt. Or if I overdo the exercise.

It's pretty scary that I went all those years with untreated OSA, the suffocating dreams, the lethargy, the chronic bronchitis. I think I was heading for something bad. There are lots of folks still out there, though. I've been telling everyone who will listen about CPAP.

JNK, I just read Restedgal's comments. Looks like good advice. Thanks!

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Re: Rationale for Setting an Upper Pressure Limit?

Post by rogerbohl » Tue Mar 03, 2015 8:16 pm

New CPAP user (ResMed AirSense 10). Machine "runsaway" several times a night to 14 or so, interrupting my sleep. Dr. recommended 4cmH2O, and Apria has not returned my calls. I'm inclined to set high limit just above 4 (say, 6). Is there a medical reason to use a high limit > 6?

I've been unhappy with Apria so far; their failure to return a call to me, after my Dr.'s office specifically asked them to return my call is highly objectionable.

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Re: Rationale for Setting an Upper Pressure Limit?

Post by ChicagoGranny » Tue Mar 03, 2015 8:23 pm

rogerbohl wrote:New CPAP user (ResMed AirSense 10). Machine "runsaway" several times a night to 14 or so, interrupting my sleep. Dr. recommended 4cmH2O, and Apria has not returned my calls. I'm inclined to set high limit just above 4 (say, 6). Is there a medical reason to use a high limit > 6?

I've been unhappy with Apria so far; their failure to return a call to me, after my Dr.'s office specifically asked them to return my call is highly objectionable.
You need to download SleepyHead software so you can see exactly what is going on with the pressure and your events if you are having any.

If your machine is set at min 4 max 20 pressure then the pressure has not been optimized and you can optimize it with SleepyHead and help from the forum.

At the top of the index page, see viewtopic.php?f=1&t=88983&start=0

One suggestion about Apria: forget 'em. They will be nearly worthless to you at this point even if they do return your call.

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Julie
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Re: Rationale for Setting an Upper Pressure Limit?

Post by Julie » Tue Mar 03, 2015 8:38 pm

You're misunderstanding the pressure settings - the low one should start at least at 6, if not higher (no one can breathe at less than 6) and the high one could be set - to start, to see how things go - at e.g. 12 or 15. It's the low setting that matters and that will 'treat' your apneas... the high one is just kind of a control but not half as meaningful.

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Re: Rationale for Setting an Upper Pressure Limit?

Post by palerider » Tue Mar 03, 2015 8:47 pm

rogerbohl wrote:New CPAP user (ResMed AirSense 10). Machine "runsaway" several times a night to 14 or so...
Is there a medical reason to use a high limit > 6?
the machine raises pressure in response to things that happen, flow restrictions, snores, hypopneas, obstructive apneas, it doesn't just "run away".

and, the medical reason for setting the limit higher is that you need a higher pressure.

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Re: Rationale for Setting an Upper Pressure Limit?

Post by archangle » Wed Mar 04, 2015 3:38 am

Welcome. rogerbohl.

Please sign up for an ID and fill in your equipment on your profile. There's a link in my signature line at the bottom of this post on how to do that.

4 is probably too low a starting pressure. You may feel out of breath, but if it works for you, it's OK.

If the machine is pushing you up to 14, there's a good chance you really do need it.

You can set the max pressure at a lower number, but you really need to get SleepyHead and look at your data to be sure you haven't compromised your therapy.

There is info in the "useful links" in my signature line below that will tell you how to get SleepyHead and how to change your own pressure if you want to.

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Chevie
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Re: Rationale for Setting an Upper Pressure Limit?

Post by Chevie » Wed Mar 04, 2015 6:06 am

Julie wrote: (no one can breathe at less than 6)
Oh really?

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49er
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Re: Rationale for Setting an Upper Pressure Limit?

Post by 49er » Wed Mar 04, 2015 6:46 am

Chevie wrote:
Julie wrote: (no one can breathe at less than 6)
Oh really?
Chevie,

Aren't you a little old at 76 to be trolling this forum since you never have anything nice to say to folks? You only show up with your extreme negativity and hostility.

At least other similar type folks on this forum do help people which I will totally give them credit for. Unfortunately, you're not one of them.

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