Does Max Pressure in APAP Machine Matter

I've seen some here question why clinicians bother to reduce the maximum pressure when "titrating" new patients on APAP therapy. I can see why in theory it doesn't make a lot of sense as in, if you don't need it, the machine shouldn't get up there. But that does assume that the machine's sensors and algorithms are accurate and fit for purpose.

But I'd like to share my personal experience after two months using a Deveibiss/Intellipap APAP machine. I've had ongoing access to a sleep technician since I rent my machine and that comes as part of the deal, but have learnt a lot here too. He started me out on a range of 5-14 and had narrowed that gradually to 6-10 a couple of weeks back. However, I was still waking frequently (maybe every 75 mins) and usually when the pressure was at or near the max. As I began to get a better understanding go how the APAP algorithms work on my machine, I could seen a clear pattern emerging on my Oscar charts. The machine reacts to snoring, flow limitations, hypopneas and apneas, with progressive vigour until it maxes out. I can see clearly from the Oscar flow rate graphs that when the machine detects snoring, it's usually correct. But it tends to flag some very dubious looking flow limitations (not necessarily false but definitely minor) and reacts to them by increasing the pressure. Some of the ensuing hypopneas looked suspiciously like semi-arousals triggered by the increased pressure. But they drove the machine onwards towards the maximum setting, eventually waking me.

So last night, I tried an experiment. I reduced my maximum pressure to just 7.5 (min unchanged at 6). The result confirmed my suspicions. The machine has been over-reacting to minor or false flags, thus triggering false hypopneas and eventual arousal/awakening. For a start I slept much better (less arousals and longer), but my AHI still remained low at 1.8. I had just one OA during the night and that occurred at the minimum pressure setting. Crucially, there were no hypopneas or apneas during the periods when the machine maxed out at 7.5 (10-12% of the total sleeping time). The technician has now agreed with me to reset the machine to 6-8 and leave it that way for a few weeks to see if my sleeping improves and there is no increase in the AHI.

Any thoughts?

MMcG wrote: ↑

Mon Nov 08, 2021 12:58 pm

Any thoughts?

Glad you had a good night. I would want more that one night of experience before coming to a conclusion.

You are essentially locking in what is almost a fixed pressure. Why not just set the mode to CPAP and lock in 8 as fixed?

This is interesting. After I had been on PAP three weeks, provider recommended a pressure window of 5-9.8 with EPR=3. Like the OP, I did some experimenting. In order to make EPR effective and minimize CAs, I moved to 7-7 with EPR=3 to control flow limitations. This has turned our to be a setting that has worked for me, with comfortable sleep and AHI <1. I have used it for about 60 days. I thought about straight CPAP at 7 but decided against it because I wanted EPR to control flow limits.

clownbell wrote: ↑

Mon Nov 08, 2021 2:42 pm

I thought about straight CPAP at 7 but decided against it because I wanted EPR to control flow limits.

EPR has nothing to do with auto adjusting pressures.

LSAT wrote: ↑

Mon Nov 08, 2021 2:22 pm

You are essentially locking in what is almost a fixed pressure. Why not just set the mode to CPAP and lock in 8 as fixed?

It was just an experiment. It looks like a constant pressure of 6 would eliminate most of my apneas on a good night. But that's assuming that I go to bed at the same time every night, don't eat dinner late, or worse have more than one beer (we're all human!). So the maximum has gone back up to 8. I'll only raise that max if my AHI's go up. It seems logical to me that a balance has to be achieved between eliminating AHI's almost completely and getting a decent night's sleep. The latter is the ultimate goal after all. I suppose what asking is whether having a high maximum pressure can lead to APAP machines going into a sort of tailspin based on response to false flag events. It seems to have been happening to me anyway (Devilbiss/intellipap Auto).

ChicagoGranny wrote: ↑

Mon Nov 08, 2021 1:57 pm

MMcG wrote: ↑

Mon Nov 08, 2021 12:58 pm

Any thoughts?

Glad you had a good night. I would want more that one night of experience before coming to a conclusion.

It's now set at 6-8 (min-max) in agreement with the technician. I'll keep people here posted on how it's going after another week or two.

clownbell wrote: ↑

Mon Nov 08, 2021 2:42 pm

This is interesting. After I had been on PAP three weeks, provider recommended a pressure window of 5-9.8 with EPR=3. Like the OP, I did some experimenting. In order to make EPR effective and minimize CAs, I moved to 7-7 with EPR=3 to control flow limitations. This has turned our to be a setting that has worked for me, with comfortable sleep and AHI <1. I have used it for about 60 days. I thought about straight CPAP at 7 but decided against it because I wanted EPR to control flow limits.

I'm not sure I fully understand. My question was about APAP (as opposed to CPAP). EPR is another feature - I actually have it but don't use it. The only thing I've learnt here is that it does tend to reduce the effective minimum pressure, so the advice is to increase the minimum pressure by a corresponding number to compensate, i.e. if min pressure was 5 without EPR, then with EPR set to 3, min pressure should be increased to 8.

MMcG wrote: ↑

Mon Nov 08, 2021 12:58 pm

The machine has been over-reacting to minor or false flags, thus triggering false hypopneas and eventual arousal/awakening.

Hypopnea is defined as a decrease of airflow for at least 10 seconds in respirations and a 50-percent reduction in ventilation

Hypopneas can cause disturbed sleep.

But I don't see how you got the idea that more pressure stenting can induce flow restriction.

More pressure reduces flow restrictions.

Edit: corrected percentage number - Both ResMed and Devilbiss define 50% for hypopnea

GrumpyHere wrote: ↑

Tue Nov 09, 2021 9:58 am

MMcG wrote: ↑

Mon Nov 08, 2021 12:58 pm

The machine has been over-reacting to minor or false flags, thus triggering false hypopneas and eventual arousal/awakening.

Hypopnea is defined as a decrease of airflow for at least 10 seconds in respirations and a 30-percent reduction in ventilation

Hypopneas can cause disturbed sleep.

But I don't see how you got the idea that more pressure stenting can induce flow restriction.

More pressure reduces flow restrictions.

It appears to be triggering false hypopneas which are really partial arousals/awakenings as a result of increased pressure. Anyway, I increased the max to 8 last night (just 0.5 of an increase) and there were hardly any hypopneas at all. With the higher pressure setting (originally 14 and gradually reduced to 10), there appeared to be lots of hypopneas as the pressure increased. It seems to me that these were false. They were mostly in the few minutes before the increased pressure woke me up. And the fact that they seem to have gone since I reduced the pressure seems to confirm this. Another week or so will definitely confirm one way or another. The reason I started this thread is that I was wondering whether it is just my Devilbiss/Intellipap machine or if others have had similar experiences with different machines.

MMcG wrote: ↑

Tue Nov 09, 2021 9:38 am

I've learnt here is that it does tend to reduce the effective minimum pressure, so the advice is to increase the minimum pressure by a corresponding number to compensate, i.e. if min pressure was 5 without EPR, then with EPR set to 3, min pressure should be increased to 8.

Correct up to a point and people need to understand the point and the fact that automatic increase in minimum pressure to offset EPR drop isn't something that everyone just HAS to do every time.
Like everything else it comes with the caveat "it depends".
What it depends on is if the drop during exhale using EPR drops the pressure down to a level that the pressure doesn't/can't continue to hold the airway open and prevent airway tissue collapse.

This can happen when a person is using a minimum that is very close to the line where things are either kept open or they collapse....but not everyone is running at that bare minimum pressure where if the pressure drops that the airway will collapse.
Believe it or not but there are people whose airway tissues are kept open with very modest pressures of 4 or 5 cm.
Now often those lower pressures aren't particularly comfortable in terms of air movement and they can feel rather stifling or suffocating but that is a perception issue in terms of comfort and really doesn't have any relationship as to effectiveness of the pressure itself preventing airway collapse. We won't/can't suffocate at the lower pressures despite it FEELING like we are UNLESS that lower pressure is actually allowing the airway tissues to collapse.

So your optimal minimum pressure setting really depends on where the line in the sand is for the pressure not being able to hold the airway open or not when in exhale using EPR. You don't want to drop below that line in the sand during exhale.
That line could be 4 cm...5 cm....8 cm....whatever cm. Most people are going to be using (when in apap mode) settings that won't be allowing a drop below that line in the sand unless using low minimums and restrictive maximum settings.
Auto mode will usually drive the pressure up to a level where the EPR setting isn't really going to be much of a danger of dropping below that line in the sand.

Example....say I have a line in the sand of 6 cm...but I am using 8 cm minimum setting without EPR and I decide I want to add EPR into the mix. As long as I don't ever drop below 6 cm during exhale then I should be good.
So if I wanted to add EPR set to 3 into the mix then I would only have to increase the minimum to 9 cm....not automatically to 11 cm minimum as the "general rule" implies.
Now if that 8 cm starting point was already my "line in the sand" and any drop could allow airway tissues to collapse the obviously I would need to compensate with the higher minimum....and 11 cm would be optimal choice.

So it all depends on several things whether we have to compensate for using EPR or not.
It depends on where the line in the sand is...it depends on what machine is being using because different machines have different auto adjusting algorithms...it depends on the apap algorithm takes the machine to a point where the drop during exhale doesn't bring the pressure below the line in the sand (and this is where snores and flow limitations can be a huge factor)....it depends on whether someone is using fixed mode or auto adjusting mode.

You are going to find that everything regarding cpap treatment comes with a big YMMV sticker and there really aren't any set in stones rules.....lots of "it depends".

I know it makes for muddying up understanding of all this stuff difficult at best.
But like what I always say....it is what it is but there are very few absolute rules when in comes to anything cpap.

BTW you can't really compare what the other machine showed you compared to the ResMed machine.
Totally different algorithms as well as criteria definitions for events along with whatever response.
Apples to oranges comparison...useless.

And yes...increasing the max to 8 (up from 7.5 I guess)...will reduce the hyponeas because the machine probably needed to go higher but couldn't previously to prevent the minor collapses that get flagged as hyponeas.
And yes...sometimes there are hyponea flags and we wonder what the hell the machine was thinking but remember we can't always see a lot of minute details.
Hyponea....flow reduction from 40 to 79% that lasts 10 seconds. It wouldn't be impossible for there to be a 41% reduction in air flow and us not even see it on the detailed flow rate.
Or it could be a false positive flag from arousal/awake breathing change.

Letting the machine go higher with the higher max could very well have prevented hyponeas from ever happening.

And the last monkey wrench....we don't sleep the same each night and it could be that your lower hyponea count is a result of just not sleeping the same. Could also simply be a coincidence that the increase in max happened on a night where there wouldn't have been many hyponeas anyway even without a pressure change.

MMcG wrote: ↑

Tue Nov 09, 2021 10:45 am

It appears to be triggering false hypopneas which are really partial arousals/awakenings as a result of increased pressure.

Sorry to be picky, but correct terminology is important.

Your machine is increasing pressure due to some events. It may be falsely flagging these events as hypopneas.
So your sleep may be disturbed by the increased pressure.

BUT it is different and incorrect to say that the higher pressure is causing hypopneas.

GrumpyHere wrote: ↑

Tue Nov 09, 2021 6:12 pm

MMcG wrote: ↑

Tue Nov 09, 2021 10:45 am

It appears to be triggering false hypopneas which are really partial arousals/awakenings as a result of increased pressure.

Sorry to be picky, but correct terminology is important.

Your machine is increasing pressure due to some events. It may be falsely flagging these events as hypopneas.
So your sleep may be disturbed by the increased pressure.

BUT it is different and incorrect to say that the higher pressure is causing hypopneas.

I said "false hypopneas", i.e. falsely flagging partial arousals/awakenings. I never said the machine was causing hypopneas. Of course it can't do that.

Pugsy wrote: ↑

Tue Nov 09, 2021 11:06 am

BTW you can't really compare what the other machine showed you compared to the ResMed machine.
Totally different algorithms as well as criteria definitions for events along with whatever response.
Apples to oranges comparison...useless.

And yes...increasing the max to 8 (up from 7.5 I guess)...will reduce the hyponeas because the machine probably needed to go higher but couldn't previously to prevent the minor collapses that get flagged as hyponeas.
And yes...sometimes there are hyponea flags and we wonder what the hell the machine was thinking but remember we can't always see a lot of minute details.
Hyponea....flow reduction from 40 to 79% that lasts 10 seconds. It wouldn't be impossible for there to be a 41% reduction in air flow and us not even see it on the detailed flow rate.
Or it could be a false positive flag from arousal/awake breathing change.

Letting the machine go higher with the higher max could very well have prevented hyponeas from ever happening.

And the last monkey wrench....we don't sleep the same each night and it could be that your lower hyponea count is a result of just not sleeping the same. Could also simply be a coincidence that the increase in max happened on a night where there wouldn't have been many hyponeas anyway even without a pressure change.

Thanks for the lengthy and considered feedback, Pugsy. I've now had two nights at maximum of 8 as well as the first at 7.5. I've hit the max of 8 for a few minutes each night, but no events during these periods. The other good news is that last night I probably had my best and longest night's sleep in two months with no increase in AHI (still less than 2). I can relate to your final thoughts though. Unless one lives like a monk, our sleep patterns are likely to vary from night to night, so the maximum pressure needs to provide some "cushion". Then again if my AHI went up to say 5 for maybe one might out of ten, that's unlikely to be much of health problem as I see it.