Fixed v variable pressure

The headline is fixed pressure seems to be giving me better results than variable and I'm curious if others have similar experience.

Some background.

I've been a regular user since 2004, mostly using Remstar machines on variable pressure with excellent results, long term AHI below 1.

Several things changed for me a year ago. I had a heart attack, then was diagnosed with cancer in the tonsil and lymph nodes of my neck. Fortunately I've had treatment and made a full recovery from both. During the recovery period, my sleep pattern and AHI were all over the place, AHI often near 20 and sometimes 30. Probable contributory factors were the medications for my heart and structural changes in my throat.

I've lost a significant amount of weight during the year, about 90lbs.

In January I changed to a Resmed Airsense 10 machine.

Since recovery, my results using the auto mode on the Airsense have improved dramatically but as they were still a little variable I experimented with various settings.

I've found that a constant pressure (7cm) is giving me better results than variable (tried several ranges including 4-20cm). The difference in AHI over a period is noticeable, below 1 for fixed pressure and around 2 for variable. More evident however are the peaks. The 'bad' nights at fixed pressure are far less frequent and typically produce AHI around 3, whereas the 'bad' nights on variable pressure are a little more regular and produce a higher AHI in the range 5 to 8.

Obviously, I'm getting decent enough results either way and I guess there are lots of factors at play: machine change with a different algorithm, changes to the structure of my throat due to radiotherapy, and weight loss. Be interesting to hear the thoughts of the experienced, knowledgeable people on here though!

Thanks

Paul

A range of 4/20 is the way machines com from the manufacturer. Not much thought was put into the setting. If you are doing well at fixed 7, the variable range probably should have been 6/10. If you are doing better at a fixed pressure by all means keep doing it .

When you discuss AHI numbers you always have to include the event category breakdown when talking about optimal pressures because not all event categories can be expected to be prevented with pressure.
Like the "bad nights" with AHI of 5 to 8 compared to "good" nights with around 1 AHI.

The AHI of 5 to 8 nights....what is the breakdown into the 3 categories that compose the AHI.
3 categories available
Central apneas
Obstructive apneas
Hyponeas.

If you are seeing a lot of central apneas (clear airway events on OSCAR/SleepyHead)...then we wouldn't expect more pressure or any pressure really to deal with central apneas. We would instead wonder why so many central apneas on a particular night and not look at pressure...fixed or auto adjusting as being the cause. These machines WILL NOT increase the pressure for central apneas....because it won't/can't fix them.

Now back to the overall fixed vs auto thing...some people do say they see better numbers AND FEEL BETTER overall when they use a fixed pressure. I don't doubt them one bit. It's been that way since I first started cpap therapy 12 years ago.
BTW....I always include the subjective feelings and don't go on AHI numbers alone as documentation of a "good" night or successful therapy. Numbers alone don't guarantee much and don't mean much.

Go here and watch all the videos so you will come to understand arousal/awake flagged events vs asleep events.
Bear in mind that while it talks mainly about central apneas (CAs on the OSCAR/SleepyHead reports) that we can have false positive flags in any event categories. It is NOT limited to centrals but central false positives are quite common.
http://freecpapadvice.com/sleepyhead-free-software
Our awake breathing is very irregular when compared to asleep breathing but the machine has zero way to determine sleep status. It can only measure air flow so it can and will flag awake/arousal irregular breathing as some sort of apnea event.
If we aren't asleep they don't count other than make us wonder why we weren't asleep.

A while back I had a "bad" night in terms of AHI...9.4...whoa..that's a really bad number for me when I see around 1.0 or less for AHI most of the time.
It was composed of a nice normal mix of all 3 category of flagged events. Wasn't primarily one category over another.
So I took the time to zoom in on each flagged event to verify if I was asleep or maybe awake when they were flagged.
I did a manual count....arousal flagged event vs for sure asleep flagged event.
95% of the flagged events were arousal related and so obviously arousal/awake related that a blind mind could see it.
So the rest of the story was I did have a bad night in terms of sleep quality that night....bad back pain because I had over did things working in the yard that day and my back was telling me I was a stupid old woman for doing more than I should have and I paid for it with my back hurting really bad all night long. Lots of tossing and turning and known awake time because I hurt like hell. So yeah....horrible AHI numbers for sure but related to poor sleep in general and NOT from sleep apnea issues.

So that is one explanation for higher AHI number that doesn't have anything to do with pressures at all...fixed or auto.

Another explanation is that sometimes people don't use minimum pressure when auto adjusting mode is used. The minimum pressure is the most critical setting and if too low then it takes too long for the machine to increase to where it is needed to be to prevent the airway collapses that make up the AHI (assuming asleep) from ever happening in the first place. There is a lot involved when the auto adjusting algorithm is supposed to kick in with more pressure ...it's not just the flagged event itself. During the flagged event itself the machine does absolutely nothing in terms of pressure increases because it can't blow the airway open with more pressure. A lot of people make the mistake in thinking that with auto mode the machine will just increase the pressure to blow open the collapse airway....and wonder why that doesn't happen...well it's because it can't in the first place. It simply can't generate enough pressure fast enough to blow past that obstruction. The machine was never designed for that action anyway. It has always been designed to PREVENT the collapse in the first place. There is a lot of criteria that is needed for the machine to decide a pressure increase is needed....snores, flow limitations, collapse history, etc. It won't just increase the pressure for a lone OA without other factors being involved.

So back to your observations....we really don't know what was going on when you had less than optimal nights in terms of AHI results. Was the minimum pressure simply too low? Were you just having a bad night of sleep and having a lot of false positives? Were you just having maybe a night where you slept on your back more or had more REM sleep (which both can cause OSA to worsen and/or need more pressure to prevent real asleep events)??? Were you having more lone events without accompanying other needed criteria to get the machine to increase the pressure??? What kind of apnea events were you having?
Lots we don't know.

So there is probably an explanation for the difference in results that is a logical explanation and more likely related to something more than just fixed vs auto alone. Most likely a combination of things. Without doing a lot of detective work we just don't know what the real explanation might be and it may not be worth all the work to sort it out. That's entirely up to you. My first suspicions...either minimum was too low during the auto adjusting mode experiments or the bad night was a lot of false positive flagging was happen just from a random bad night of sleep in general from any number of possible reasons.

Using an optimal fixed setting works well for a lot of people but not everyone. I am one that fixed wouldn't work out so great for me. My pressure needs can be quite high in REM stage sleep...common for this to happen. Documented in the sleep lab that my OSA is about 5 times worse in REM than in non REM sleep (same thing can happen for supine sleeping)..and REM accounts to only 20% of the night. I need 6 to 8 cm more pressure during REM to prevent the airway from collapsing. In non REM sleep a pressure of 7 or 8 does a real good job holding my airway open and preventing collapses. In REM I might need 16 cm pressure....if I were to use a fixed pressure and had to deal with REM then I would have to use 16 cm all night long just to deal with the REM stuff. While it could be done I suppose ....who really wants to do that when 7 or 8 works great for the other 80% of the night. 16 cm isn't much fun at all.
I use a minimum of 7...if I were to use a minimum of 4 the machine couldn't get to 15 or 16 fast enough to prevent what goes on in REM...I would have a higher AHI because of REM events that couldn't be prevented.

So there are a lot of complicated interconnected reasons for what causes the machine to increase the pressure in auto mode...and why a person needs so and so baseline minimum pressure to deal with whatever is going on.
It's so much more complicated than just fixed vs auto for a lot of people.

But hey...it works great for you and that's really all that counts and as long as it works and you are happy with the results then it doesn't really matter what what someone else does.
Though there is always a reason behind why something works or doesn't work for anyone. Your reasons may be entirely different than the next person's reasons.

Fixed isn't always better just like auto isn't always better but there is usually a good reason when auto doesn't work so great and it is usually the minimum is too low. That's the most common reason. There could also be potential outlier reasons not so common.

Me personally...I don't really care what a person uses ..either fixed or auto...as long as it is working well for them, they are happy with the results and they are sleeping good and more importantly feeling good as well.
Whatever is "best" is what works for the individual for whatever reason.

Switched to fixed pressure on my own without telling my sleep doc. I had asked her if I could switch but she said no.

Have tried FP with and without EPR (EPR = 3 is best for me). Overall getting better results than APAP mode.

Sudden increase in pressure during APAP mode can cause arousals in some folks. Depends on arousal threshold (the lower it is means more easily aroused during sleep phase).

ElusiveSleep wrote: ↑

Mon Aug 16, 2021 11:10 am

Sudden increase in pressure during APAP mode can cause arousals in some folks.

Auto mode doesn't do a "sudden increase in pressure"....any increase made takes place over several minutes.
Your EPR of 3...now that is a rapid pressure change...breath by breath. 3 cm change...rapid and with every breath it changes.

It takes many, many minutes for the machine to increase pressures and more it has to increase the more time it takes.
It is NOT a rapid change at all.
More likely it is the events happening the machine is trying to respond to that is causing the arousal.

I too sleep better with fixed pressure (10.2 when I inhale and 5 when I exhale -- a difference my particular kind of machine can produce). I'm not sure why this is. Pugsy notes that pressure changes are not actually sudden, but I do think the changes were somehow disruptive to my sleep. Because my AHI is generally under 1, with very few obstructive events, I see no need to use variable pressure. If your sleep apnea is being well treated, you should do whatever gives you the best night of sleep.

ElusiveSleep wrote: ↑

Mon Aug 16, 2021 11:10 am

Sudden increase in pressure during APAP mode can cause arousals in some folks. Depends on arousal threshold (the lower it is means more easily aroused during sleep phase).

That's a hoary old myth born from not understanding how auto machines work.

They *never* make sudden changes in pressure, NEVER. Pressures change over a period of minutes, they change pressures *slowly*.

Now, and ASV does change pressures rapidly, from breath to breath as needed, and all the ASV users sleep through that.

What's far more likely is that the breathing problems are what wakes people up (since obstructive breathing problems do disturb sleep, then the person wakes up enough and blames the poor, innocent apap for actually doing it's job and trying to prevent more apneas/hypopneas/snoring/flow limitations.

Miss Emerita wrote: ↑

Mon Aug 16, 2021 11:43 am

I too sleep better with fixed pressure (10.2 when I inhale and 5 when I exhale -- a difference my particular kind of machine can produce). I'm not sure why this is. Pugsy notes that pressure changes are not actually sudden, but I do think the changes were somehow disruptive to my sleep. Because my AHI is generally under 1, with very few obstructive events, I see no need to use variable pressure. If your sleep apnea is being well treated, you should do whatever gives you the best night of sleep.

I just spent a bit of time looking at my pressure increase during probable REM which are when I most likely will see a more marked change. The fastest I could find a 2 cm change in IPAP took around 2 minutes to make a 2 cm change.
Heck, I get 4 cm change with PS of 4 with every breath. Any other more than 2 cm increase did take a few minutes longer and some lessor increases took longer as well. I zoomed in on the pressure line that looked like it increased the fastest. Most changes upward took upwards of 5 minutes or more and went up in stages anyway.

I know a lot of people say that they seem to sleep and feel better with fixed pressures and these very same people might be using some form of PS (or EPR) where there is obviously a much larger change with every breath which does make a person wonder why a 2 cm change over 2 minutes might disturb sleep and 3 or 4 or 5 difference using EPR/PS doesn't.

I don't doubt them but when I see reports and they have a nice flat pressure line and then a cluster of OAs or hyponeas and THEN the pressure goes up...does make me wonder if the OAs/hyponeas caused the arousal in addition to causing the machine wanting to increase the pressure....it does make me wonder as to what exactly caused the arousal...was it the OA/hyponeas that preceded the pressure change????? It's not impossible. Do they remember awakening around the time of the flagged events and see the change in pressure and assume it is the pressure and forget about the flagged events?? That is indeed a possibility.
Is it just the body being used to a more stable pressure and the brain rebelling against more pressure...also a possibility.
The brain is well known to like predictability and not do well with changes of any kind for a lot of people...the PS/EPR big change is a part of a predictable pattern and the slight increase slowly in response to events might take it out of its comfort zone...it can't predict that change so it doesn't anticipate it. All that wouldn't be impossible either.

I can't answer the questions with 100 % certainty but I don't think it is worth getting all worked up over either. One example I was just looking at there is a flagged OA involved and it's so obviously a post arousal flag it isn't funny...arousal breathing before the flag and thus before the increase in pressure. My machine responded to a false positive with the fastest increase in pressure (2 cm in 2 minutes) that I could spot and that was unusually speedy response. The bulk of the pressure changes I see are much less remarkable in terms of speed of change.

IMHO...just another YMMV situation and it's not worth the fights over it that I see people get into here.
Each person is the ultimate judge as to what works best for them and I am quite happy to not try to change their minds with all my "what ifs" unless they want help in figuring it out or whatever. If someone is happy with their therapy ...I am happy for them no matter how they go about getting it and I am sure not going to try to get someone to change if they are happy. Heck if they told me they slept upside down in one of those upside down machines and feel great using their cpap with it...I say more power to you and whatever floats your boat and all that stuff. I don't care how they make themselves happy as long as they are happy. To them it isn't broke so it sure isn't my job to try to fix it.

I got enough to do with people who are unhappy with their cpap results to deal with. I am not going to go looking for people who are happy and don't think anything is broken and try to get them to change something. I just don't have time nor is there a need to add to my workload. If they don't think something needs fixing...far be it to me to try to get them to change their minds. That is NOT in my job description.

I sleep through some rather massive pressure changes which I attribute to REM pressure needs. I always have.
Doesn't mean someone else might not have a problem with just some small slow increases...I am me and they are them and everybody is different. I won't try to impose the way I do things on anyone.
Now if they are unhappy with their results...different story and we can discuss options and all that but I am not going to be twisting your arm to get you to try doing what I do because it simply isn't needed. You are happy with your results...and I am very happy for you...because that means I don't have to fix what you think isn't broken. In my mind...it's not broken if you don't think it needs fixing. I am lazy...no sense in looking for more work when there is no need.

If something isn't broke...I see zero need to fix it.

littlebaddow wrote: ↑

Mon Aug 16, 2021 3:14 am

The headline is fixed pressure seems to be giving me better results than variable and I'm curious if others have similar experience.

Some background.

I've been a regular user since 2004, mostly using Remstar machines on variable pressure with excellent results, long term AHI below 1.

Several things changed for me a year ago. I had a heart attack, then was diagnosed with cancer in the tonsil and lymph nodes of my neck. Fortunately I've had treatment and made a full recovery from both. During the recovery period, my sleep pattern and AHI were all over the place, AHI often near 20 and sometimes 30. Probable contributory factors were the medications for my heart and structural changes in my throat.

I've lost a significant amount of weight during the year, about 90lbs.

In January I changed to a Resmed Airsense 10 machine.

Since recovery, my results using the auto mode on the Airsense have improved dramatically but as they were still a little variable I experimented with various settings.

I've found that a constant pressure (7cm) is giving me better results than variable (tried several ranges including 4-20cm). The difference in AHI over a period is noticeable, below 1 for fixed pressure and around 2 for variable. More evident however are the peaks. The 'bad' nights at fixed pressure are far less frequent and typically produce AHI around 3, whereas the 'bad' nights on variable pressure are a little more regular and produce a higher AHI in the range 5 to 8.

Obviously, I'm getting decent enough results either way and I guess there are lots of factors at play: machine change with a different algorithm, changes to the structure of my throat due to radiotherapy, and weight loss. Be interesting to hear the thoughts of the experienced, knowledgeable people on here though!

Thanks

Paul

I started out with a fixed pressure machine and then after about a year, I acquired the first of several APAP machines.
Tried ranges of pressures and found I didn't like the variable pressures and that fixed pressure gave me optimal therapy.
For one thing, I hardly have any hypopneas or apneas to begin with and then don't have the preceding triggering events (snores or flow limitations) when they're supposed to happen to raise pressures, so what singular hypopneas or apneas I DO have occur without triggering the machine to raise pressures. I also found that my AHI numbers were slightly higher when using a range of pressures.

I always recommend that users get APAP (multi-mode) machines.......and then TRY the various options to see what works best for them.

Good to see you again "littlebaddow". Hope all is well with you.


Den

.

I've only been using a machine for 10 days. Resmed 10 auto. I changed the minimum to 8 and left the max alone. It doesn't seem to get over 12 according to OSCAR. Anyway I don't feel my airway being much affected at 8 but more than that and I have less comfort getting asleep. So it seems like a narrow range for me. Which has worked just fine as I sleep soundly now with low AHI. Still feeling sleepy during day though.

Wow, thank you so much for the speedy and detailed responses.

I have read and attempted to digest all of the information and the key messages I take from it are:
1. Everyone is different
2. The causes are complicated and it's likely to be a combination of them
3. If it's working, why change it

Whilst I don't have the knowledge or, frankly, the inclination to do really detailed detective work, I did take a look at the breakdown of events.

The chart shows the particularly bad periods do include a sometimes (though not always) high proportion of centrals, which I fully appreciate will not be addressed by the machine, whatever settings I'm using. (Key = Centrals purple, OAs light blue, Hs dark blue)

In the period immediately after the heart attack, September to January, I was on all sorts of medications which could undoubtedly be a factor. The period March to May was the period when I suffered quite severely from the side effects of the daily radiotherapy/weekly chemotherapy sessions, as my immune system was shot to pieces.

I take comfort from the fact that things seem to have settled as my health has returned!

littlebaddow wrote: ↑

Mon Aug 16, 2021 2:18 pm

I take comfort from the fact that things seem to have settled as my health has returned!

I am very happy that things have gone from exciting to boring and your good health has returned. You certainly had an extended rough patch to go through for sure.

Boring is a good thing.

Certainly doesn't sound like anything is broken or even cracked and I am very happy for you and I say leave well enough alone at this point. If it ain't broke...no need to go fixing anything and no need to go doing a lot of detective work.
Should the situation seem to change again in the future and you feel up to doing some detective work...we can always go down that road later. I don't see any reason to do so now at all.

That big old YMMV sticker...it's stuck on all of us.

Littlebaddow, your take-aways look just right!

Wulfman... wrote: ↑

Mon Aug 16, 2021 1:43 pm

Good to see you again "littlebaddow". Hope all is well with you.


Den

I'm fine thank you. Don't visit very often these days, unless I want to check or ask something. Had other things on my mind recently, but heart issue under control and latest scans showed I'm currently cancer free
Paul

Pugsy wrote: ↑

Mon Aug 16, 2021 11:18 am

ElusiveSleep wrote: ↑

Mon Aug 16, 2021 11:10 am

Sudden increase in pressure during APAP mode can cause arousals in some folks.

Auto mode doesn't do a "sudden increase in pressure"....any increase made takes place over several minutes.
Your EPR of 3...now that is a rapid pressure change...breath by breath. 3 cm change...rapid and with every breath it changes.

It takes many, many minutes for the machine to increase pressures and more it has to increase the more time it takes.
It is NOT a rapid change at all.
More likely it is the events happening the machine is trying to respond to that is causing the arousal.

Thanks Pugsy !

I had always thought that setting my machine to "Auto" would be best since it would adjust to the pressure needed to stop the Apnea events.

But after several conversations with my sleep Doc, he convinced me that may not be the best course to follow.

He explained exactly what you said.... it takes time for the machine to adjust and therefore, may miss handling events as needed, due to the lagging response time.

Ultimately, he made me understand whyy he wanted my machine adjusted to a set pressure.

I would only switch to the auto setting if I wanted to self-titrate.