Are these flow limits my problem?

[k888]

Greetings,

I am surprised by recent results and would like to hear your thoughts.  Two nights ago, I had a fairly good night of 3.05 AHI, with individual spikes of pressure up to 19.72.  That pressure did successfully handle those events, or at least it did not turn into a string of uninterrupted blowing.  I had increased EPAP to 8.4, leaving PS at 4.8 and IPAP at 20.  Chart attached:
   

However, the number of events had increased over several days and a few of these events were looking very positional; therefore – knowing I have collar issues, I decided my collar should be replaced (after using it 18 nights.)  While I am convinced I need a collar, it is still an open question in my mind whether most of my events are collar-related, or if it is a combination of collar and fluctuating pressure needs – that is to say, possibly some nights I just need considerably more pressure than others?  Anyway, last night I used a new collar and increased IPAP to 21, just in case.  The results really surprised me.  It felt like a good night, but the chart is so good that I actually studied it awhile, thinking that perhaps the machine had not really recorded.  But the data is there, and I can still see many choppy and flat individual breaths on the zoom view, so it is real.  This was undoubtedly my best result to date, maybe the best I will ever get. (What an improvement, considering that my worst night since getting the machine was 24.8 AHI with a total time in apnea of 01:02:45.)  Here is last night:
   

I expect this night is an outlier, but I will be interested to hear your thoughts.  If it is always correct that pressure cannot correct positional apnea, then I must have fluctuating pressure needs.  Or maybe pressure can correct moderate positional issues and only fails when there are too many events?  Or. . . . ?  

I plan to increase PS to 5 in pursuit of more rounded breaths.  Should I increase minimum EPAP to reduce the pressure differential?  Or maybe if it aint broke, don't try to fix it?
Many thanks to ApneaBoard for getting me here.  Without all the help I have received, I would still be on my original machine and much closer to those poor results I cited above!
Awaiting your thoughts with interest,  k888
(–:

[SingleH]

Hi K888,

What an amazing difference between those nights.


I would not change anything right now as you have hit a perfect 0.0. I made exactly the same mistake of reaching a setting which achieved 0.0 and had a few good days, but then decided to fiddle with PS more to get a better waveform. I have never managed to achieve another 0.0 since, and I dont know if that is due to the disturbances of fiddling with PS too much.
From what you have written the issues seems related to your collar, as changing from an old one to a new one resulted in a massive change. The change to 21 IPAP had no effect as your machine basically never moved off its baseline settings for the whole night.

I would leave things as they are and just observe for a week or two if you continue to maintain these figures
I would try a night or two without the collar to see what happens.
The only thing I would look at is your respiration rate as that seems a bit low and maybe due to your long Timax. I think respiration rate should be 12 or higher. What is your typical spont cycle %

[k888]

Thanks SingleH,
Good advice, but of course I already increased PS to 5.  AHI was 1.46 last night, but half of that was in the first 20 minutes while I was awake/working through a stuffed-up nose.  Pressure went up to 17 at times and flow limits were good, but more frequent.  The chart is not a beautiful poster child like the night before, but I can't complain.  I wish there were a measure of the totality of flow limits and not just severity, as it seems to me more time with flow limits = worse sleep.  About respiration rate, mine is usually 12 or above, sometimes below.  I don't know anything about spont cycle %.  Is this something you monitor?  I can tell you that with the CPAP, my inspiration was always greater than expiration, sometimes by quite a bit.  That has now flipped with the Bipap.  The Timax setting is 3.2 to allow for the occasional long inhale, as suggested by several ApneaBoard members.  k888

[SingleH]

Yes exhalation should ideally be double inspiration, so its goo the bipap has fixed that.

To find spont cycle going into your machine settings, and look for sleep report. Set it to essentials plus.

When you wake up in the morning, go to sleep report and when you scroll down you will see your I:E ratio and also Spont cycle with a % figures. For reference this represents the percentage of transitions that either you or the machine makes from inhalation to exhalation. 100% means you cycled all breaths yourself and less means the machine did some of the cycling.

[k888]

Thank you – very interesting.  I went in to change the setting and found the data already there.  My spont cycle was 97.5%.  I have just been reviewing the data on Oscar.  k888

[Dormeo]

Overall things look good. Flow limits are high, but as long as sleep quality is good they are something to be watched.

It seems your flow limitations track pressure and as pressure goes up so do flow limits.

You are limited by your machines ability to provide more support than EPR 3, so we need to figure out an alternative. Consider setting your pressure to a fixed 9 with EPR 2 or 3. With the fixed pressure you will not get the FL’s from the pressure swings, and a bit of EPR should make things more comfortable.

If you don’t like that you can try dropping EPR to 2 and set your pressure range to 8-12. That will help with the flow limitations and pressure swings, but hopefully not cause more apnoeic events.

The pressure increases in response to the FLs; the FLs don't go up in response to pressure increases.

[SingleH]

Your Spont cycle is fine, although I would expect it to be as your Timax is quite long.

[k888]

Thank you both.  
And Dormeo, thanks for underlining the flow limit/pressure relationship.
What I am wondering about is whether it would be desirable to have a smaller differential between min and max EPAP, or perhaps it doesn't matter?  Last night I had a good AHI of .53, with FL .03-.17, but more of them.  Min EPAP is set at 8.4, average EPAP last night was 15.3, and average EPAP was as high as 19.72 over the last week.  I'm not sure how much base pressure I can tolerate, but would it be desirable to try increasing that min EPAP over time?  Also, is it "normal" to have that much variation across nights, or am I an outlier?  Thanks so much, k888

[PeaceLoveAndPizza]

The pressure increases in response to the FLs; the FLs don't go up in response to pressure increases.

I did not say otherwise. I said they “seem” to track, meaning pressure did not fully resolve the FL’s.

[Dormeo]

Thank you both.  
And Dormeo, thanks for underlining the flow limit/pressure relationship.
What I am wondering about is whether it would be desirable to have a smaller differential between min and max EPAP, or perhaps it doesn't matter?  Last night I had a good AHI of .53, with FL .03-.17, but more of them.  Min EPAP is set at 8.4, average EPAP last night was 15.3, and average EPAP was as high as 19.72 over the last week.  I'm not sure how much base pressure I can tolerate, but would it be desirable to try increasing that min EPAP over time?  Also, is it "normal" to have that much variation across nights, or am I an outlier?  Thanks so much, k888

It is normal to see a lot of variation from one night to another.  I'd suggest you stick with those "0.0" settings for a week or two before considering further changes.  It can also be helpful to make a few notes in the morning about how you're feeling -- before you look at your Oscar data.  With a nice low AHI, your daytime sense of well-being is the single most important factor for you to consider.