Flow limitation: when are they considered significant?

Tan, I don't have enough data to draw any definite conclusions (I've had my S9 less than 1 yr and my S8 didn't report FL), but, subjectively, I seem to sleep better and feel more rested, regardless of AHI, when my 95% FL is around .07, which is about the lowest I see. Somewhat less subjectively, it appears that the percentage and amount of Deep Sleep as measured by Zeo is also greatest when my FL are at their lowest, again, regardless of AHI. A bad night with minimal deep sleep occurs with FL somewhere above the 0.25 95% mark.
I wear a FFM due to throat leaks and use the cpap mode to prevent disturbing pressure variations. I also find I do better without EPR. I have no trouble minimizing my AHI. My 1 yr average is 1.4, of which 0.4 is CA. I do have difficulty minimizing my FL. Increasing the pressure beyond that which is required to eliminate most OA does little to reduce FL without getting to a level which starts to increase leaks, bloating, and CA. For me, this level is about 10 cm. At or above 10 cm (either manually or auto) I begin to sleep quite poorly, even though my AHI might be less than 1.0.
The one thing I've found which seems to be effective in reducing FL is a soft neck brace. At the same time, the neck brace reduces the pressure requirement to eliminate OA, from about 9 cm without down to about 8 cm with. This lower pressure is obviously more comfortable and I tend to sleep better (I think), again with more deep reported by Zeo. But, because the brace is a little uncomfortable I have not yet begun to wear it every night. However, I think that is about to change. The evidence of better sleep with the brace is becoming just to strong to ignore.

tan wrote:it is the "bad" night that has many FL spikes. Makes me wonder

How are you determining "good" or "bad" nights? By the pressure variations? Sleep quality? (which could be affected by the pressure changes)
The number of your "flow limitations" in any of those nights is pretty insignificant, but still enough to cause the machine to chase them.
And, the fact that you don't have a consistent amount of flow limitations could be an indication that it's not real "problem". Could be caused by congestion, sleep position, or other possibilities on random nights.


Den

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Wulfman... wrote:

tan wrote:it is the "bad" night that has many FL spikes. Makes me wonder

How are you determining "good" or "bad" nights? By the pressure variations? Sleep quality? (which could be affected by the pressure changes)
The number of your "flow limitations" in any of those nights is pretty insignificant, but still enough to cause the machine to chase them.
And, the fact that you don't have a consistent amount of flow limitations could be an indication that it's not real "problem". Could be caused by congestion, sleep position, or other possibilities on random nights.


Den

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Tan: There are 2 options on what is causing your bad nights. Is it
A) the pressure spikes OR
B) the flow limitations.

Since they are both correlated in a Auto Bilevel mode, the only way to evaluate which one is the culprit is to put you machine in a straight bilevel mode, titrate it to the IPAP and EPAP that keeps your AHI below (pick any number below 3 lets say) and see how you feel. Your machine will still report FLs and you can then see if it is FLs that are making you feel bad OR is it the pressure variations.

Wulfman... wrote:Could be caused by congestion, sleep position, or other possibilities on random nights.

Or artifact (like movement after arousal).

And chasing sleep fragmentation with pressure may not be the best approach.

Morbius wrote:

Wulfman... wrote:Could be caused by congestion, sleep position, or other possibilities on random nights.

Or artifact (like movement after arousal).

And chasing sleep fragmentation with pressure may not be the best approach.

Thank you for those comments. That last one has been my belief for a long time (in various ways).


Den

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Wulfman... wrote:

tan wrote:it is the "bad" night that has many FL spikes. Makes me wonder

How are you determining "good" or "bad" nights?

Sometimes, I can have multiple awakenings.

By the pressure variations? Sleep quality? (which could be affected by the pressure changes)
The number of your "flow limitations" in any of those nights is pretty insignificant, but still enough to cause the machine to chase them.
And, the fact that you don't have a consistent amount of flow limitations could be an indication that it's not real "problem". Could be caused by congestion, sleep position, or other possibilities on random nights.

My pressure changes much more with every exhale/inhale (13IPAP and 9EPAP) and it is not disruptive. Yet, according to you, the minor variations that correlate with FL spikes are. Why is that?

Jay Aitchsee wrote:Tan, I don't have enough data to draw any definite conclusions (I've had my S9 less than 1 yr and my S8 didn't report FL), but, subjectively, I seem to sleep better and feel more rested, regardless of AHI, when my 95% FL is around .07, which is about the lowest I see. Somewhat less subjectively, it appears that the percentage and amount of Deep Sleep as measured by Zeo is also greatest when my FL are at their lowest, again, regardless of AHI. A bad night with minimal deep sleep occurs with FL somewhere above the 0.25 95% mark.
I wear a FFM due to throat leaks and use the cpap mode to prevent disturbing pressure variations. I also find I do better without EPR. I have no trouble minimizing my AHI. My 1 yr average is 1.4, of which 0.4 is CA. I do have difficulty minimizing my FL. Increasing the pressure beyond that which is required to eliminate most OA does little to reduce FL without getting to a level which starts to increase leaks, bloating, and CA. For me, this level is about 10 cm. At or above 10 cm (either manually or auto) I begin to sleep quite poorly, even though my AHI might be less than 1.0.
The one thing I've found which seems to be effective in reducing FL is a soft neck brace. At the same time, the neck brace reduces the pressure requirement to eliminate OA, from about 9 cm without down to about 8 cm with. This lower pressure is obviously more comfortable and I tend to sleep better (I think), again with more deep reported by Zeo. But, because the brace is a little uncomfortable I have not yet begun to wear it every night. However, I think that is about to change. The evidence of better sleep with the brace is becoming just to strong to ignore.

Thanks for your sharing your experience and suggestions, Jay. We have some similarities: low AHI is irrelevant -- and we have our differences: even EPR==3 wasn't good enough for me, I needed something higher. Is the neck brace to keep your jaw up?

tan wrote: My pressure changes much more with every exhale/inhale (13IPAP and 9EPAP) and it is not disruptive. Yet, according to you, the minor variations that correlate with FL spikes are. Why is that?

Tan: I would like to think that:
1) Our body is already accustomed to a difference in Inhale and Exhale pressures. As per laws of physics, a positive pressure gradient is needed for air to flow. So the pressure gradient will switch between inhalation and exhalation to reverse the air flow direction. You can also research the concept of Auto PEEP (equal to 5cm H20).
2) What our body is NOT accustomed to is a difference in inhale pressures between 2 inhalations OR exhale pressures between 2 exhalations.

Morbius wrote:

Wulfman... wrote:Could be caused by congestion, sleep position, or other possibilities on random nights.

Or artifact (like movement after arousal).

And chasing sleep fragmentation with pressure may not be the best approach.

Unless such fragmentation is caused by flow limitation?

Is there a reliable way at home to understand what causes what? I guess only statistical approach. Accumulate data with different pressures for several nights. Right?

Guest1 wrote:

tan wrote: My pressure changes much more with every exhale/inhale (13IPAP and 9EPAP) and it is not disruptive. Yet, according to you, the minor variations that correlate with FL spikes are. Why is that?

Tan: I would like to think that:
1) Our body is already accustomed to a difference in Inhale and Exhale pressures. As per laws of physics, a positive pressure gradient is needed for air to flow. So the pressure gradient will switch between inhalation and exhalation to reverse the air flow direction. You can also research the concept of Auto PEEP (equal to 5cm H20).
2) What our body is NOT accustomed to is a difference in inhale pressures between 2 inhalations OR exhale pressures between 2 exhalations.

I guess for the sake of the argument, I will have to test these assertions. I remember limiting pressure changes and even trying straight pressure, each mode for a few days, without much success, which could have been affected by other factors, of course. But now I have a baseline of consistently having a good sleep, I guess I could... I hope not to regret it

tan wrote:

Wulfman... wrote:

tan wrote:

Wulfman... wrote:Doing some Google searching will produce LOTS of stuff to read.

Here are some of the excerpts from documents I've saved over the years include the following:

Den
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Thanks, but how to apply this at home for regular people without sophisticated equipment? How much should pressure be increased? Should one keep increasing, if tolerated, until the machine stops doing the same?

In my opinion, one has to determine just how much of a problem the flow limitations are. They can definitely be a problem when using an Auto in a range of pressures. And, IF they're typically NOT preceding events (including snore) to apnea events, are they worth pursuing?

Of course, flow limitations MAY be worth pursuing for they MAY result in frequent arousals without becoming apneas. Why else some people with low AHI may feel tired until they increase pressure some more in order to sleep better?

I agree. I have reviewed my sleep study data sec by sec and most of my microarousals were caused by flow limitations.

Another point to consider is when brains are sleep deprived for a long time, the arousal threshold actually decrease (easier arousal from FLs). I think this is important, at least for UARS patient.

musculus wrote: I agree. I have reviewed my sleep study data sec by sec and most of my microarousals were caused by flow limitations.

We must have been looking at the same data

tan wrote:Thanks for your sharing your experience and suggestions, Jay. We have some similarities: low AHI is irrelevant -- and we have our differences: even EPR==3 wasn't good enough for me, I needed something higher. Is the neck brace to keep your jaw up?

Yes, originally I tried the neck brace as an alternative to a chin strap to prevent my jaw from dropping and changing the shape of my face which would cause leaks. It did work for this purpose, but there are less cumbersome alternatives such as a chin strap affixed to the mask described elsewhere in the forum. However, after using the neck brace a few times I began to notice the reduction in FL and increase in Deep Sleep that occurred when the brace was worn that did not occur with chin straps. So, it would appear that the brace does more than just keep the jaw from dropping. I surmise it also keeps the head from tilting down which in turn helps to keep the airway open thereby reducing flow limitations.

So, I started using the neck brace to prevent leaks and now I'm looking at it as a way to lower the pressure needed for effective therapy.

tan wrote:

Morbius wrote:

Wulfman... wrote:Could be caused by congestion, sleep position, or other possibilities on random nights.

Or artifact (like movement after arousal).

And chasing sleep fragmentation with pressure may not be the best approach.

Unless such fragmentation is caused by flow limitation?

Is there a reliable way at home to understand what causes what? I guess only statistical approach. Accumulate data with different pressures for several nights. Right?

Well, the flow limitations elicit a response of increased air pressure from the machine. It COULD be the pressure changes are disturbing (fragmenting) your sleep.


Den

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Wulfman... wrote:

tan wrote:

Morbius wrote:

Wulfman... wrote:Could be caused by congestion, sleep position, or other possibilities on random nights.

Or artifact (like movement after arousal).

And chasing sleep fragmentation with pressure may not be the best approach.

Unless such fragmentation is caused by flow limitation?

Is there a reliable way at home to understand what causes what? I guess only statistical approach. Accumulate data with different pressures for several nights. Right?

Well, the flow limitations elicit a response of increased air pressure from the machine. It COULD be the pressure changes are disturbing (fragmenting) your sleep.


Den

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Which means that if the pressure does not raise in response to FL (fixed), then there will be no arousal? This argument fails based on the experiences shared by UARSers.

Besides, according to this study "Auto-CPAP therapy for obstructive sleep apnea: induction of microarousals by automatic variations of CPAP pressure?", it caused micro-arousal only for small portion of subjects.