Understanding min pressures

When my wife first started treatment, they started her out at a low pressure setting hoping to prevent too many central events. They raised her pressure slowly over a six month period. Before her last adjustment, her pressure was set to a minimum of 12 and max of 20 and she was bumping up against the upper limit several times every night. Once they raised her min to 15, the max never exceeds 17. She was having a lot of nights where her flow limit would be right around 1, and her machine was reacting to these flow limits. Once the minimum was raised to 14, the flow limits were suddenly reduced to around 0.2 or 0.3 and the machine was no longer reacting like it was previously. So in her case, raising the minimum also lowered the maximum the machine was reaching. Once the wide pressure swings were eliminated, she began to sleep much better than when she first started treatment.

Okie bipap wrote:When my wife first started treatment, they started her out at a low pressure setting hoping to prevent too many central events. They raised her pressure slowly over a six month period. Before her last adjustment, her pressure was set to a minimum of 12 and max of 20 and she was bumping up against the upper limit several times every night. Once they raised her min to 15, the max never exceeds 17. She was having a lot of nights where her flow limit would be right around 1, and her machine was reacting to these flow limits. Once the minimum was raised to 14, the flow limits were suddenly reduced to around 0.2 or 0.3 and the machine was no longer reacting like it was previously. So in her case, raising the minimum also lowered the maximum the machine was reaching. Once the wide pressure swings were eliminated, she began to sleep much better than when she first started treatment.

How is she able to tolerate a min of 15? With ramp?

TedVPAP wrote: Sorry, didn't mean to offend you. It is difficult to separate the academic question from questions related to treatment since your thread discusses your treatment and clusters.
Regarding the academic question, without knowing the exact algorithm being used a correct answer can't be had. I suspect that the prescribed minimum is not just used solely to set the minimum, but it is also used as a target which would impact the machine's response. So my answer is still yes, the minimum pressure setting influences the pressure even when it is set below your generally observed lowest pressure.

No offense taken. Looking back I decided that my question seems senseless. But you say yes and others say no, that the min pressure has influence only when it's above the generally observed lowest pressure. Your answer seems to support what I've seen, that raising my min seemed to improve things even though it's still below my observed lowest pressure. I'll continue to experiment.

AMK wrote:

TedVPAP wrote: Sorry, didn't mean to offend you. It is difficult to separate the academic question from questions related to treatment since your thread discusses your treatment and clusters.
Regarding the academic question, without knowing the exact algorithm being used a correct answer can't be had. I suspect that the prescribed minimum is not just used solely to set the minimum, but it is also used as a target which would impact the machine's response. So my answer is still yes, the minimum pressure setting influences the pressure even when it is set below your generally observed lowest pressure.

No offense taken. Looking back I decided that my question seems senseless. But you say yes and others say no, that the min pressure has influence only when it's above the generally observed lowest pressure. Your answer seems to support what I've seen, that raising my min seemed to improve things even though it's still below my observed lowest pressure. I'll continue to experiment.

The academic thoughts are relevant and of interest, but not always the most important.
For example, the impact of minimum pressure is absolutely significant when it is above your normally lowest pressure. The impact becomes much less (and possible no impact) when set below.

The most important thing is to understand what you gain (e.g., lower AHI) versus what you may loose (e.g., leaking, bloating) by increasing the lower pressure. There are only a few absolutes so the response will be specific to the person and treatment (e.g., masks).
Keep in mind that the body will adjust so just because something doesn't work for you now doesn't mean that it won't work for you in the future.
My minimum pressure is 16 and it no longer bothers me at all.

TedVPAP wrote: The academic thoughts are relevant and of interest, but not always the most important.
For example, the impact of minimum pressure is absolutely significant when it is above your normally lowest pressure. The impact becomes much less (and possible no impact) when set below.

The most important thing is to understand what you gain (e.g., lower AHI) versus what you may loose (e.g., leaking, bloating) by increasing the lower pressure. There are only a few absolutes so the response will be specific to the person and treatment (e.g., masks).
Keep in mind that the body will adjust so just because something doesn't work for you now doesn't mean that it won't work for you in the future.
My minimum pressure is 16 and it no longer bothers me at all.

OK I see what you're saying here. It seems sometimes like these values can be ephemeral; a little weight gain, a different bed, and whatever the prescribed lowest pressure was goes out the window. An attentive and involved doctor or sleep nurse might be able to make recommendations but I am on my own. I think I'm on the right path though. I appreciate all the input!

TedVPAP wrote:properly setting the minimum pressure is strongly related to the maximum pressure you will need

This is not at all right.

There's no correlation between adequate minimum pressure and possible max pressure needs.

jnk... wrote:

TedVPAP wrote: . . minimum pressure is strongly related to the maximum pressure you will need . . .

I disagree. Minimum pressure may be set at or near the pressure that will be needed for much of the night, but for most users, that generally has nothing whatsoever to do with the highest pressures that may be reached occasionally. That's what the autotitrating algorithm is for.

There are often reasons to have the minimum set well below the maximum needed. Sure, you can run an auto in CPAP mode, if you choose to do so. But if you run it in auto mode, your highest-needed pressure does not dictate your min.

You are, of course, right.

TedVPAP wrote:I said a properly set minimum pressure is strongly related to your highest pressure need. .

Nope.

Pugsy's properly set minimum pressure is something like 7, her max may hit 18.

Perhaps what you're trying to say, and what you are saying, aren't the same things.

palerider wrote:

TedVPAP wrote:I said a properly set minimum pressure is strongly related to your highest pressure need. .

Nope.

Pugsy's properly set minimum pressure is something like 7, her max may hit 18.

Perhaps what you're trying to say, and what you are saying, aren't the same things.

I think we are tripping over some words but I think there is agreement on the concepts.

The auto algorithm works "perfectly" for some people so they can leave the range wide open (or a slight increase to the minimum for comfort reasons only).

Others need to alter the range to improve their therapy.
Some reasons for altering:
The upper should be lowered if you would rather live with a few more events in order to avoid going up to pressures that cause issues (leaking, bloating, arousals). I think this should only be done when absolutely necessary.

The lower limit should be set so that the algorithm can do a better job of minimizing events. This means setting the lower limit closer to where your needs will eventually become so that the algorithm can be more successful in preventing events. How close to set the minimum to the eventual need will be dependent on the person and the machine as they are using different algorithms.

I do not prescribe to setting the minimum to the observed maximum pressure, or the 95%, or the 90%, or the 50%, or the 10%, or ... . Instead I look at the daily charts to see if the pressure response is too late. If it is too late to prevent a large number of events, then I recommend increasing the minimum.

When it comes to using auto-pap, the two largest issues I see with the medical community is their failure to understand that 4 in uncomfortably low for some people, and that the algorithm may need help by properly setting the minimum pressure.

For example, If I need ~20cm-H2O when I am on my back and in REM, but I only need ~10 otherwise, setting the minimum to 6 may not be adequate to address sleeping on my back during REM.

AMK wrote:

Okie bipap wrote:When my wife first started treatment, they started her out at a low pressure setting hoping to prevent too many central events. They raised her pressure slowly over a six month period. Before her last adjustment, her pressure was set to a minimum of 12 and max of 20 and she was bumping up against the upper limit several times every night. Once they raised her min to 15, the max never exceeds 17. She was having a lot of nights where her flow limit would be right around 1, and her machine was reacting to these flow limits. Once the minimum was raised to 14, the flow limits were suddenly reduced to around 0.2 or 0.3 and the machine was no longer reacting like it was previously. So in her case, raising the minimum also lowered the maximum the machine was reaching. Once the wide pressure swings were eliminated, she began to sleep much better than when she first started treatment.

How is she able to tolerate a min of 15? With ramp?

Yes, she is using ramp. When I first started, my minimum pressure was 15 cm, and I turned ramp off after two or three weeks. I found I would lay there awake until the machine came up to full pressure. One I turned the ramp off, I began to go to sleep quicker.

TedVPAP wrote:

palerider wrote:

TedVPAP wrote:I said a properly set minimum pressure is strongly related to your highest pressure need. .

Nope.

Pugsy's properly set minimum pressure is something like 7, her max may hit 18.

Perhaps what you're trying to say, and what you are saying, aren't the same things.

I think we are tripping over some words but I think there is agreement on the concepts.

The auto algorithm works "perfectly" for some people so they can leave the range wide open (or a slight increase to the minimum for comfort reasons only).

Others need to alter the range to improve their therapy.
Some reasons for altering:
The upper should be lowered if you would rather live with a few more events in order to avoid going up to pressures that cause issues (leaking, bloating, arousals). I think this should only be done when absolutely necessary.

The lower limit should be set so that the algorithm can do a better job of minimizing events. This means setting the lower limit closer to where your needs will eventually become so that the algorithm can be more successful in preventing events. How close to set the minimum to the eventual need will be dependent on the person and the machine as they are using different algorithms.

I do not prescribe to setting the minimum to the observed maximum pressure, or the 95%, or the 90%, or the 50%, or the 10%, or ... . Instead I look at the daily charts to see if the pressure response is too late. If it is too late to prevent a large number of events, then I recommend increasing the minimum.

When it comes to using auto-pap, the two largest issues I see with the medical community is their failure to understand that 4 in uncomfortably low for some people, and that the algorithm may need help by properly setting the minimum pressure.

For example, If I need ~20cm-H2O when I am on my back and in REM, but I only need ~10 otherwise, setting the minimum to 6 may not be adequate to address sleeping on my back during REM.

In summary, my guidelines for setting an auto machine are "set the minimum so that it prevents regular events, and let the auto take care of the exceptions (rem/back sleeping, etc)", ignore max unless there are other issues, like aerophagia."

palerider wrote:

TedVPAP wrote:

palerider wrote:

TedVPAP wrote:I said a properly set minimum pressure is strongly related to your highest pressure need. .

Nope.

Pugsy's properly set minimum pressure is something like 7, her max may hit 18.

Perhaps what you're trying to say, and what you are saying, aren't the same things.

I think we are tripping over some words but I think there is agreement on the concepts.

The auto algorithm works "perfectly" for some people so they can leave the range wide open (or a slight increase to the minimum for comfort reasons only).

Others need to alter the range to improve their therapy.
Some reasons for altering:
The upper should be lowered if you would rather live with a few more events in order to avoid going up to pressures that cause issues (leaking, bloating, arousals). I think this should only be done when absolutely necessary.

The lower limit should be set so that the algorithm can do a better job of minimizing events. This means setting the lower limit closer to where your needs will eventually become so that the algorithm can be more successful in preventing events. How close to set the minimum to the eventual need will be dependent on the person and the machine as they are using different algorithms.

I do not prescribe to setting the minimum to the observed maximum pressure, or the 95%, or the 90%, or the 50%, or the 10%, or ... . Instead I look at the daily charts to see if the pressure response is too late. If it is too late to prevent a large number of events, then I recommend increasing the minimum.

When it comes to using auto-pap, the two largest issues I see with the medical community is their failure to understand that 4 in uncomfortably low for some people, and that the algorithm may need help by properly setting the minimum pressure.

For example, If I need ~20cm-H2O when I am on my back and in REM, but I only need ~10 otherwise, setting the minimum to 6 may not be adequate to address sleeping on my back during REM.

In summary, my guidelines for setting an auto machine are "set the minimum so that it prevents regular events, and let the auto take care of the exceptions (rem/back sleeping, etc)", ignore max unless there are other issues, like aerophagia."

I like your summary as it is suscinct, and generally good advice.
If the exceptions are considerable, then more pressure may be needed. The OP has a lower pressure setting that is serving her well for most of the nights. Based on discussions in this thread and other threads, it appears to be failing to address significant clusters. The only way to avoid those clusters is through a higher minimum pressure. Whether it is worth the possible downside can only be answered by trying.

These discussions are interesting but it is much better if we were talking about a specific person with daily charts where we could discuss the thought process behind a recommendation.

OP has an old thread where the clusters where shown and discussed.
So there are report images available...only they were when using the for Her apap mode.
I don't know that there were any shown after the switch to the regular apap mode.
I got the impression back then that the clusters were resolved for the most part with the switch to the regular apap mode at pretty much the same min/max that was being used in the for Her mode.

Since OP question here seemed to be more of a general question about minimums and OP didn't post reports for review I assumed not really wanting specific input on specific minimum pressure but was wanting only to educate herself about the process more than anything else.
To be honest I prefer to do the education process more than "use this setting" advice...
I like it much better when someone gets educated on how things work...for them...and then they can make and educated and informed decision on what works best....for them.

The "for them" is very important because of the huge YMMV stick that all this stuff comes with.
And then there's another big YMMV sticker that comes with our own personal wants and needs. I am willing to let one night with a not so great cluster slide...someone else might not and that's okay too.

TedVPAP wrote:The only way to avoid those clusters is through a higher minimum pressure.

Not to be overly picky--oh, heck, who am I kidding? I AM being overly picky -- I can't quite sign off on that statement. Just too universal for my blood.

Some clusters, although reported as obstructive by home machines, are actually set off by a form of central dysregulation, a variation of the old overshoot/undershoot problems of the body's attempting to sense CO2 clearance in different stages of sleep. Those events may be reported by home machines as fully obstructive, not mixed, because the airway closes too soon, at the instant of the pause, but they may still have central aspects at their root. In those cases, a high minimum may actually make those clusters more likely to occur, not less likely. True for all? Of course not. True for most clusters that occur during APAP use? Probably not. But possible and occasional? Yes. Those sorts of difficult-to-label events were a large part of my residual events after starting PAP therapy. They eventually resolved themselves after my body relearned to gauge it's clearance of waste gasses. But it took months for me, and it may never change at all for some people whose brains and sensors get "rewired" from years of untreated OSA. And that is why personal experimentation with what settings lower weekly-averaged AHI are often the key. Not everybody and every body is the same. A higher min may help some clusters, sure, but a lower min may help some clusters for some people too. And home-machines cannot report the deeper nature of all events that can start a cascade of more events that--although lacking the classically spaced waxing-and-waning patterns that would otherwise make their central nature recognizable--have central dysregulation as a significant contributing factor. Sometimes we forget that years of untreated OSA itself can cause central-apnea problems. Long-term untreated moderate-to-severe OSA makes for central events before and after treatment for some of us, and that can take time to resolve with successful PAP treatment, if it does resolve. But during the resolution, those mixed apneas can be reported by home machines as purely obstructive for those of us with an airway that is ready to shut completely at the slightest pause.

But hey, I ain't no expert. I did, however, draw some conclusions based on personal research into what I was going through early on myself with my breathing at the time, with a lot of help from some very wise forum experts back in the day. Not saying I was or am correct, but I felt it necessary to speak up here based on my personal beliefs and experiences.

jnk... wrote:Some clusters, although reported as obstructive by home machines, are actually set off by a form of central dysregulation,

Your comment got me to thinking about looking at that night 12/18 with my rather ugly clusters up close under the microscope and the clustering is flagged OA but it's just plain weird looking flow rate and not a typical OA flow rate that I usually get.
Almost sort of CSRish looking in a way.
The first OA flagged might look typical but the subsequent OA flags have some pretty weird flow rate showing up around the OA flags.
With some maybe arousal breaths mixed in.

I looked at the clusters and I am scratching my head as to whether they are real...apart from maybe the first or maybe second flagged OA....I am not certain if the are obstructive, central, mixed or SWJ arousal stuff.
Since this is my first such cluster using this mode with these pressures in over 3 months of using this mode...and I can't be sure what it is then I am for sure not going to be changing the pressures based on something that I am unsure of.