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Question Regarding Minimum Pressure and APAP
#1
Question Regarding Minimum Pressure and APAP
How exactly does an APAP determine the correct pressure for your needs? I have always thought that the pressure would go to the best amount depending on what you require. This does not seem to be the case with me. Normally I have my ResMed Airsense10 set at 11-14 (cmH2O) and the 95% usually averages out ~ 11.5 - 12. The last couple of nights I reduced to 10-14 and the 95% averaged out to 10.88 and 10.94 respectively. I'm wondering why the machine doesn't level out at the same value regardless of the minimum set point?

Anyway the reason why I have been playing around with the pressure is that I'm trying to improve my mask leak rate. My theory was that my higher pressure of 11 may have been too high and maybe pushing my P10 nasal pillows out too much causing leaks. It doesn't look like it worked. I'm also thinking that I may have snored or gasped for air that woke me up last night even though my Oscar data didn't show any snoring.

I have attached a screen shot from a 11-14 session and a 10-14 session. Am I over reacting about my leak rate? Is it ok as long as I stay under the 24 L/min limit? I have been trying different masks lately with no significant improvement.  The most recent new masks were the P30i and the N30i. I seem to have very weird dreams and night wakeups with these masks.

Thanks in advance!

Sleepwreck


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#2
RE: Question Regarding Minimum Pressure and APAP
Following!
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#3
RE: Question Regarding Minimum Pressure and APAP
The algorithm does NOT determine the optimum pressure.
What the algorithm does is react to obstructive events including Obstructive Apnea (OA), Hypopnea (H), Flow Limits (FL), and Vibratory Snore (VS) depending on the brand, to increase pressure, and in the absence of events decrease pressure.  

In general, we see this in Phillips Respironics machines more than ResMed because they react slower and as such, they need to have a higher starting value to best minimize obstructive events.  ResMed's are designed to react faster and as such can manage lower set pressures.

Your belief is common among doctors, that is why many prescribe settings of 4-20 and assume the machines will automatically find the optimum pressure (again they will not)
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#4
RE: Question Regarding Minimum Pressure and APAP
You are getting excellent results at both settings. Most of your events are central apneas, which are not generally treated by pressure settings on a machine like yours. If you'd like to experiment, I think you could try an even lower minimum.

As long as your leaks are under 24, the machine can compensate fully. It would be nice to get to the point that you don't have any large leaks, though the percentage of the night you have LLs isn't horrible. A side benefit might be sounder sleep; leaks can sometimes be a bit disruptive.

The P10 is a wonderfully minimalist mask, but the straps do tend to stretch out over time. Washing will restore much of the elasticity for a while, but then you do need to replace the mask.

Do you have any reason to believe the leaks are from your mouth? A dry mouth would be a clue, or maybe you wake up realizing your mouth is open.
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#5
RE: Question Regarding Minimum Pressure and APAP
I have a question! I have a ResMed 10 Autoset with my APAP settings at 11-15 My numbers are good but I sometimes wake up staving for air! I know it's a CO2 issue! I have my EPR set to 3. My question is would raising the min number from 11 to 12 change anything? I never go above 14 with my treatment! Thank you!
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#6
RE: Question Regarding Minimum Pressure and APAP
Hello, Joe. You are asking good questions, but I'd like to suggest that you start a new thread to focus on your situation. When you do that, please also post a recent and typical Oscar chart. Thanks!
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#7
RE: Question Regarding Minimum Pressure and APAP
A small change. EPR will have the largest effect. Increasing EPR or increasing pressure would both tend to lower CO2 levels.
Another factor may be blocking the mask vent. Water can do it especially with a mesh vent.

With the starving for air try increasing pressure a couple cm to see if that works. I feel starved at low pressures.
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#8
RE: Question Regarding Minimum Pressure and APAP
These machines are reactive, not proactive. If your base settings are poor your breathing will be poor until the machine increases pressure (the only change the machine makes) to a satisfactory level. Then when the machine tries to lower past that point again your breathing will start to degrade and machine will increase pressure again. In cases of bad settings you will see pressure rise significantly early in the night and then bounce off a certain pressure throughout the night.

Your OSCAR data doesn't show any signs of poor settings being the issue. As you noted leaks are probably the biggest concern and if I had to guess they are mouth leaks so you might have to try mouth tape, chin strap or full face mask. Small leaks the machine can overcome but they can still cause arousal issues (waking up because air rushing out mouth).
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