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Flow limits, leaks, what is real?
#1
Flow limits, leaks, what is real?
I'm trying to get a handle on what the machine (resmed A10) is trying to tell me about flow limits and leaks.

Here is the big picture from last night:
[attachment=32029]
More leaks than I'd like, but not so much as to be a problem, I think. Ok, what I want to focus on is the major leak, prolonged flow limit, and "squashed" flow rate curve that starts at 2:29 and lasts until 2:48. On the fitbit graphs, the fitbit saw a ~1min awake at the end of the REM at 2:29 -- scored it 2:28:30-2:29:30. Then the light sleep logged as 2:29:30-2:38:30 and the deep sleep from 2:38:30-2:48:00. Here's a zoom of that:
[attachment=32034]


I'm still trying to understand exactly what I'm seeing here, and the relationship between the flow limits, the leaks, and what the machine can measure if those are mouth leaks and I'm wearing a nasal mask.

First off, do those look like mouth leaks and not mask leaks?

Ok, if I'm inhaling through my nose and exhaling through my mouth (digression -- isn't that what horn players call "circular breathing"?) then how much air is actually going in and out my windpipe? And is that something that the machine is able to sense? In other words, do I believe the flow limits? Or are the sensors seeing the reduction in pressure coming back out my nose into the mask and interpreting that as an airway restriction, when in fact it's that a bunch of the air is moving in and out of my open mouth and things are not restricted?

What I think is definitely happening is that if the Fitbit is right, this is really screwing with my sleep architecture. Here's how the fitbit scored it:
2:06:00-2:11:00 --- awake
2:11:00-2:28:30 --- REM
2:28:30-2:29:30 --- awake
2:29:30-2:38:30 --- light
2:38:30-2:48:00 --- deep

With the cpap scoring it as 2:29:42 -- leaks take off, flow limits take off, flow rate drops almost to zero, minute vent and tidal volume plummet, and that lasts until 2:48 when I have an arousal, leaks stop, flow limits stop, flow rates oscillate between -30 and 30 instead of -5 and 3, minute vent and tidal volume recover.

Whatever happened, it clearly woke me up!

Now the fitbit saw a short burst of deep sleep 15 minutes later from 3:05:00 to 3:09:30, surrounded by light sleep, but the cpap didn't see anything interesting at all there.
[attachment=32036]
Does that mean that the severe flow limitation that the machine thought that it saw earlier during the leak was actually just mouth breathing outside the machine's ability to detect it?
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#2
RE: Flow limits, leaks, what is real?
Here are two zooms of the flow limit and leak fest (the zoom in the previous post broken into 2)

This is the transition out of REM and into light sleep at 2:29:30
[attachment=32037]

And then this shows the transition from light to deep sleep at 2:38:30 until the arousal at 2:48:00
[attachment=32038]

Does the closer zoom help?
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#3
RE: Flow limits, leaks, what is real?
The flow limits and leaks are real. The shape of leaks is more like a mouth leak than mask leak which tends to be much choppier or with large spikes.  My opinion of these issues is that there may be some residual positional issues, and you are a normal person that doesn't have perfectly pretty sleep. Welcome to the club. You're AHI is well below what I aspire to, and there is nothing here that will be addressed by changing settings.  I can't recommend you chase these issues.  Relax, sleep well, and above all:



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#4
RE: Flow limits, leaks, what is real?
Ok I think I'm coming to the conclusion that measured flow limits during mouth leaks are an artifact of the cpap machine being unable to accurately measure the flows because of the mouth leaks. It's a simple mechanical thing -- the machine can't measure what's going on outside of it's system of hose/mask/nose/airway/lungs, so when any significant amount of air is escaping by a side channel that bypasses the mask, it thinks that there is less air moving than there is moving.

Here's last night when I managed to keep my mouth shut all night.
[attachment=32041]

no significant leaks = no significant flow limits


Of course I need more than 2 nights to conclude this with any more certainty.

And to collect more data with a full-face mask, where mouth leaks don't matter.
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#5
RE: Flow limits, leaks, what is real?
I agree with your conclusion, and have seen it many times in others.
Sleeprider
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____________________________________________
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INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#6
RE: Flow limits, leaks, what is real?
I have now changed my mind.

From Friday night, I have a big, clear, sustained flow limit WITHOUT any leaks at the same time. AND it woke me out of deep sleep (if I believe my fitbit, which I do.)

I put the green highlight line on the 3-minute arousal
[attachment=32107]

Here is a close-up (ok, closer-up :-) ) of the 3:45:30 where the fitbit saw me come out of REM sleep and go to light sleep until 3:08:00, where I then transitioned into deep sleep with continuous flow limits and the pressure pegged at 15 (EPR of 3). Then the flow limits woke me up at 3:16:30 -- a pathetic 8-1/2 minutes of deep sleep -- I stayed awake for 3 minutes, light sleep for 2-1/2 minutes, awake another minute, returned to light sleep. Two more short arousals -- 30 seconds @ 3:48 and 1.5 minutes @ 3:53 -- and then 38-1/2 minutes of uninterrupted REM at 4:04. That REM started with ~10 minutes of leak.
[attachment=32108]

So it is now clear that what I thought before is NOT always true -- when I have simultaneous significant leaks and large flow limits, I was thinking from what I was seeing before that the flow limits aren't real and what the machine thinks are flow limits are actually just an artifact where it can't measure the flow accurately because of the leaks. Now I have a counterexample -- that's a real flow limit for sure, and it's not some erroneous reading caused by a leak, because there is no leak.

So now I can conclude that it is very possible that the flow limits come first and they cause the leaks -- by making me open my mouth to get more air.

AND I can conclude that the flow limits -- with or without leaks -- are just killing my sleep architecture.
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#7
RE: Flow limits, leaks, what is real?
I know you have worked hard to make a soft collar work, and this has the signature of a positional "chin-tuck". The flow limits correct with your change in position. I was expecting to see longer inspiratory time with that, but it is not there that I can see. You would not regret using a Vauto, but it will be very difficult to justify since insurance is all about AHI, and yours is great.
Sleeprider
Apnea Board Moderator
www.ApneaBoard.com

____________________________________________
Download OSCAR Software
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Optimizing Therapy
Organize your OSCAR Charts
Attaching Files
Mask Primer
How To Deal With Equipment Supplier


INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#8
RE: Flow limits, leaks, what is real?
I'm actually afraid that this might be more "positional flow limits" in the sense of my "position" is simply my upper airway anatomy. And nothing will fix it...

I might be able to get a trial of a vauto. Then when the machine is set at PS of 3/4/etc, sleep on my back without a collar. Then try the pressure support much higher, and do it wearing my cervical collar, and then the doc can say to the insurance company -- "Look! Her AHI goes from 79 on the A10 to 0.2 with the vauto! She gets to keep it!"

(Of course that assumes that I actually feel better with the vauto than the A10. If not, I would be happy with a new A10 with ForHer plus RERA detection...)

(I might also end up requiring a titration, of course)

(And all else fails, buy a vauto on my own.)

But, anyway, this started out with the theory that the extended flow limits that I was seeing in my data were not real, but rather an artifact caused by the leak interfering with the machine's ability to correctly determine the real flow rates.

I now have a hard counterexample that disproves that theory. My flow limits are real, can happen without leaks, are obvious on just looking at the flow rate and flow limit curves stacked atop each other. This last picture is the 37-1/2 minute "zoom" from my previous post, broken down into five 8-minute-long segments.
[attachment=32113]

We've been pooh-poohing the sleep doctor focus on back vs side vs belly sleeping and their theories about "floppy airways", and we've been  saying that it's ALL about chin tucking. I think maybe there is some "floppy airway" stuff going on that doesn't get fixed simply by keeping the chin up.
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#9
RE: Flow limits, leaks, what is real?
Another data point -- last night I had an entire hour of middling-to-massive flow limits with zero leaks.
[attachment=32144]

According to the fitbit, 3:05-3:43 was light sleep (the middling flow limits), 3:43-4:03 deep sleep (the massive flow limits).
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