Tidal volume and Flow limitations

AmSleepnBetta · Post by **AmSleepnBetta** » Thu Nov 18, 2021 7:29 pm

palerider wrote: ↑
Thu Nov 18, 2021 5:54 pm

AmSleepnBetta wrote: ↑
Thu Nov 18, 2021 5:10 am
Glossing over, all apneas and hypopnea alike, if not some or all flow limits, are scored--if at all--according to criteria for drops in airflow, whether scaled as tidal volumes (TV) or, equivalently, as flow rate (FR) reductions of certain durations.
The issue is that while FL may frequently occur concurrently with TV reductions, that is not what a FL *means*.

I agree. Your "may" is correct, too, as I will elaborate. Resmed FL flags do not mean TV reduction in themselves. A Resmed FL mostly signals for most patients some level of real flow limitation that affects the FR and TV rate-volume alter egos very little.

But there are many patients, I'm one, who sees often sees Resmeds flagging mere wave shapes listed in its onbooard table of "menacing" waveshapes. Resmed FLs often confusingly indicate the Resmed is, or has been, "thinking about" incrementing pressure upward. My second graphic shows, roughly, the increasing, higher early FL signaling and the later pressure rise that eventually developed to knock down the flow limitations before airway would close.

(To that last point, before going on. As a Resmed using kind of student of all flow limitations I should have comprehended and commented about a (bias? )confirming FL "mountain" in the graphic mentioned, though it troubled me a bit there. My additional claim or hypothesis now is that that un-noted large FL mountain is a FL flagging instance where there was no real flow limitation, only bad-actor shapes. But as it often happens in such cases, something triggered the FL drop to or near zero. This is seen in a lot of comparisons of FL flagging vs TV drops. )

My preferred way of illustrating it to people is to tell them to take a straw, and breathe through that for a while, you can take a FULL breath, ie, TV, it just takes more work, and those will be FL breaths, because the flow rate is depressed, not the flow volume

Yes, our breathing through a partly constricted airway requires more inspiratory work, increases inspiration time and it shows up in the duty cycle. Surprisingly, we compensate for flow limitations and most of us maintain needed TV, but often with too many arousals that ruin our sleep. Sadly, many suffer from congenital or early-developed airway constrictions that inhibit flow.

dataq1 · Post by **dataq1** » Thu Nov 18, 2021 11:02 pm

AmSleepnBetta wrote: ↑
Thu Nov 18, 2021 7:29 pm
But there are many patients, I'm one, who sees often sees Resmeds flagging mere wave shapes listed in its onbooard table of "menacing" waveshapes. Resmed FLs often confusingly indicate the Resmed is, or has been, "thinking about" incrementing pressure upward.

And I am one of those "many patients" that sense that Resmed's algorithm for FL's does not necessarily represent a condition that requires an increase in pressure. Other observations (changes in duty cycle or decreased tidal volume) that occur concurrently with FL detection would dictate a remedial action.

AmSleepnBetta wrote: ↑
Thu Nov 18, 2021 7:29 pm
My claim or hypothesis now is that that un-noted large FL mountain is a FL flagging instance where there was no real flow limitation, only bad-actor shapes.

Agree completely ! Perhaps another way of saying it is that some FL flags are real flow limitations..... and some FL flags are not real flow limitations.

I wish that I could find it now, but I read just recently, (I think it was an excerpt from a Resmed patent) that described the concomitant observations required as to when Resmed devices would increase pressure in a Flow limitation background. I am certain that a change in duty cycle was one of those conditions.

AmSleepnBetta wrote: ↑
Thu Nov 18, 2021 7:29 pm
breathing through a partly constricted airway requires more inspiratory work...

And unfortunately, most (all?) home use PAP therapy devices don't directly observe respiratory effort or arousals.

dataq1 · Post by **dataq1** » Thu Nov 18, 2021 11:22 pm

FWIW: the Resmed Patent for "Automated control for detection of flow limitation" can be found at https://patents.google.com/patent/US20110203588A1/en (US Patent date 2016)

AmSleepnBetta · Post by **AmSleepnBetta** » Fri Nov 19, 2021 12:39 am

AmSleepnBetta wrote: ↑
Thu Nov 18, 2021 7:29 pm

palerider wrote: ↑
Thu Nov 18, 2021 5:54 pm

AmSleepnBetta wrote: ↑
Thu Nov 18, 2021 5:10 am
Glossing over, all apneas and hypopnea alike, if not some or all flow limits, are scored--if at all--according to criteria for drops in airflow, whether scaled as tidal volumes (TV) or, equivalently, as flow rate (FR) reductions of certain durations.
The issue is that while FL may frequently occur concurrently with TV reductions, that is not what a FL *means*.

I agree. Your "may" is correct, too, as I will elaborate. Resmed FL flags do not mean TV reduction in themselves. A Resmed FL mostly signals for most patients some level of real flow limitation that affects the FR and TV rate-volume alter egos very little.

But there are many patients, I'm one, who sees often sees Resmeds flagging mere wave shapes listed in its on-board table of "menacing" wave shapes. Resmed FLs often confusingly indicate the Resmed is, or has been, "thinking about" incrementing pressure upward. My second graphic shows, roughly, the increasing, higher early FL signaling and the later pressure rise that eventually developed to knock down the flow limitations before airway would close.

(To that last point, before going on. As a Resmed using kind of student of all flow limitations I should have comprehended and commented about a (bias? )confirming FL "mountain" in the graphic mentioned, though it troubled me a bit there. My additional claim or hypothesis now is that that un-noted large FL mountain is a FL flagging instance where there was no real flow limitation, only bad-actor shapes. But as it often happens in such cases, something triggered the FL drop to or near zero. This is seen in a lot of comparisons of FL flagging vs TV drops. )

My preferred way of illustrating it to people is to tell them to take a straw, and breathe through that for a while, you can take a FULL breath, ie, TV, it just takes more work, and those will be FL breaths, because the flow rate is depressed, not the flow volume

Yes, our breathing through a partly constricted airway requires more inspiratory work, increases inspiration time and it shows up in the duty cycle. Surprisingly, we compensate for flow limitations and most of us maintain needed TV, but often with too many arousals that ruin our sleep. Sadly, many suffer from congenital or early-developed airway constrictions that inhibit flow.

Oops!, a correction for the quote above after revisiting a zoom-in on the graphic cited in that second sentence within parentheses. I see I wrote above from faulty memory and sight. That FL "mountain" (without a green enclosure in my earlier post above) actually did collapse after a real flow limitation had to have triggered a breathing change with recovery breaths. The reason I did not call attention to that FL mountain then--though it troubled me a bit--was the fact there was no visible drop in TV, the OP matter, at that image's scale. Zoomed in, there is a small drop in TV and an increase in duty cycle, though the latter appears surprisingly later than in the left-framed instance. I can't put my finger on why extra effort was later. See my graphic below.

This is not a call for therapy advice but such is welcome. For interpretative benefit, here is the sleep night context of the graphic period and beyond. This is filled in here from memory and whatever I have learned from Autoset that night and later, from my readings (including those as well as advice from this forum and Apneaboard), oximeter, accelerometer, VAuto and Dreem 2 wanna-be EEG, all in overlapping successions later. I know something of my sleep habits and peculiarities. FFM, but no cervical collar then, didn't know of them then for chin tuckers. Sleep that night was left lateral until a later supine crash of OA arose a few mnutes and then I rolled rollover to right lateral, as in graphics. Right lateral, once my favorite, brings out pronounced cardio ballistic waves at end of expiration. It's difficult to discern when (Autoset then) the M-tipped inspiratory peak is from cardio or low level almost continuous flow limitation. There was much of both, superimposed at times before my VAuto came.

Note that the right hand green frame below captures what I omitted above. It and my lingering, still unanswered questions about it prompted the zoom-in. But what the heck, I'm just tentatively "sure" of anything except God, taxes and ultimately physical death. All else seems less sure or true everyday. Gotta keep on keeping on trying.

Any ideas or corrections for any of these posts of mine particularly regarding the second FL mountain below?

: 3rd cpaptalk-image-TVvsFL.gif (388.21 KiB) Viewed 10967 times

dataq1 · Post by **dataq1** » Fri Nov 19, 2021 10:20 am

AmSleepnBetta wrote: ↑
Fri Nov 19, 2021 12:39 am
Oops!, a correction for the quote above after revisiting a zoom-in on the graphic cited in that second sentence within parentheses.[/u][/i][/b]

Just so I'm sure of what you are correcting, is it this sentence? "As a Resmed using kind of student of all flow limitations I should have comprehended and commented about a
(bias? ) confirming FL "mountain" in the graphic mentioned, though it troubled me a bit there" .

Julie · Post by **Julie** » Fri Nov 19, 2021 1:59 pm

Please post a proper Oscar shot - with info down the left side and only wanted graphs on the right.

palerider · Post by **palerider** » Fri Nov 19, 2021 2:07 pm

Julie wrote: ↑
Fri Nov 19, 2021 1:59 pm
Please post a proper Oscar shot - with info down the left side and only wanted graphs on the right.

Nobody is asking for help in this thread.

AmSleepnBetta · Post by **AmSleepnBetta** » Fri Nov 19, 2021 3:59 pm

@dataq1:
Just lost to a web glitch a more extensive reply. Short answer here: No, the sentence is the second one inside the parentheses. That out of place hypothesis has only a bit of support already posted in my first graphic at about 02:05-02:10 and 03:58-04:09. But I've seen a lot of it and other ideosyncratic strangeness. I think phantom FL likely arise from a watch box the algo must refer back to (as it "thinks"), especially amid iffy waveforms as it stands ready to up pressure, which it often does without any associated TV drop. It's conceivable that hysteresis or even a sensitive dependence on initial conditions is manifest. (I think the latter would be a stretch).<br/>

@palerider: <br/>
Thanks.

dataq1 · Post by **dataq1** » Fri Nov 19, 2021 4:02 pm

Julie wrote: ↑
Fri Nov 19, 2021 1:59 pm

Below is my example OSCAR screenshot.
It looks like the severity of flow limitations accelerated at approximately 05:09.
However, the tidal volume is fairly consistant as it the respiration rate, inspiration time, expiration time, There does not seem to be any indication of duress or extra effort needed to ventilate.
Regardless of what appears to be a steady state of all other parameters, the increasing severity of "flow limitations" apparently commanded the device to increase output pressure by almost 20% (from 10.52 to 12.68).

: Bob 11-13-21.jpg (730.29 KiB) Viewed 10902 times

dataq1 · Post by **dataq1** » Fri Nov 19, 2021 5:13 pm

Julie wrote: ↑
Fri Nov 19, 2021 1:59 pm

Zeroing in on the flowrate waveform and the corresponding flow limitations graph (since all the other waveforms appear to be stable), it seems like the grading of severity of flow limitations is dependent on the shape inspiration.

: Peg 11-13-21.jpg (38.85 KiB) Viewed 10890 times

Now, consider a comparison: Is the breathing waveform depicted in the red area three times more severe that the breathing waveform in the green area? The Resmed severity index would suggest it is.

: Peg 11-13-21 markup.jpg (38 KiB) Viewed 10890 times

What I hope we've been discussing here is leading to a resolution to these questions:
1) Are these shapes really indicative diminished flow?
2) Are these shapes indicative of restricted flow due to physiologic (mechanical) obstruction or partial occulsion?
3) Are these shapes indicative of restricted flow due to central nervous disorder?
4) How normal are these shapes in non-compromised patients (i.e. "normal")?
5) Do these shapes these shapes require intervention?
6) How dangerous are these shapes?

AmSleepnBetta · Post by **AmSleepnBetta** » Sat Nov 20, 2021 5:10 am

Thoughts on several items on various topics, mainly questions you have raised, dataq1:

1. First a clarification of one sentence in my previous post:
It read, "That out of place hypothesis has only a bit of support already posted in my first graphic at about 02:05-02:10 and 03:58-04:09." It should have read: "My only support for that hypothesis that has been posted in this forum and thread is in my first graphic at about 02:05-02:10 and 03:58-04:09." The hypothesis is that some FL flags do not and need not reflect any drop in Tidal Volume at all, though they mostly do that. At least two of three other FL generating breathing irregularities do not entail Tidal Volume drops.

2. After pondering and annotating the OP's recent graphic, as it is shown below. I belatedly ask anyone who knows, what are time lags and with what moving average windows do Resmed devices present data for Tidal Volume, Minute Volume, FL flags Inspiration and Expiration times, Mask Leak, and Leak? Is it simply and strictly a sample rate of 0.5 Hz (2 seconds) for all that data as I have assumed (and appears to be indicated in a signals list for PLD file data)? The device manifold pressure and flow rate data are sampled and presented at 25 Hz (.04 seconds).

3. The graphic below is my attempt to show answers and some relationships in partial answer to item no. 2 above and more.

4. @dataq1- post 03:02 pm 11/19: It is interesting (and to be remembered) that your FR dips show there had to be at least small drops in breath by breath TV, yet there was only a small increase in duty cycle as can be seen in divergence of the I and E time curves (I get longer, E shorter--not a lot) from about 050745 to 050852, well before pressure increased.

5. @dataq1-post 04:13 pm 11/19: I'm not quite sure what your "Julie wrote" quote referred to.

6.Re your two like graphics: You indicate all other wave forms are stable and I assume that means that all earlier flow-relevant curves (for, say, the past 30-60 earlier seconds {not shown]) and all those same curves concurrent with depicted curves were very close to and remain visibly invariant.

That being the case, then welcome to what I might call the world of Resmed (RM) phantom flow limits ("phFL"?), those FL's that arise from shape shifts without TV drops, probably without any increase in duty cycle. That is the reason I use "fL" to mean anything, short of apnea, to mean real flow limitation/constriction that reduces, by my definition, breath by breath tidal volume. That is the reason I don't know what a person means by the words "flow limit". Mostly they are referring to the Resmed FL flags. In my just-previous post here I referred you to two short periods of same in the graphic of my first post in this thread. But elsewhere I have seen and posted it multiple times. It's was to answer that conundrum that motivated my work to see breath by breath TV and TV drop from fL.

No one should get me wrong. Unrounded wave shapes tell us there is flow limitation in most if not all real flow limitation cases. Everyone can zoom them and check theirs out. As I understand, Dr. Barry Krakow is attentive to flow limitations and he tries to titrate OA, IFL and UARS sufferers best he can to attain/approach rounded inspiratory waves. BUT he deals with real flow limitation, not our device's warning of bad actor wave shapes that have not reduced our TV.

7. Your hoped for resolution for us here (by your numbering).

(7-1) I believe there would be some TV variations, yes, but (from the hip) I believe what you show is benign absent a duty cycle increase to corroborate the FL.

(7-2) My belief is those two terms refer to the same problem. But the question is, "what do normal sleepers" present among these kinds of wave forms, how much and at what range of seriousness? Normal sleepers and others have been tested to find controls and test subjects. The research finding was that it is normal for sleepers to have up to 30% of their sleep time flow limited to some extent. Dunno other answers. (Sao Paulo study, googleable).

(7-3) I doubt, but don't know if there are CNS connections to wave deformities.

(7-4) I know of scattered references that shed much light. There have long been shape and severity investigations. There are at least three papers, one a catalogue showing shapes. You might start with Tero Aitokallio, Ph.D, in Finland, PhD, (a medical statistician?) for the early 7 basic shapes. I think those images are in the AB Wiki somewhere. Then there is a study that dealt with 47 shapes as work was done to use a polynomial curve fit for analysis of shape effects; that study showed or relied three levels of severity. Then there is a huge shape catalogue behind a pay wall .

(7-5, 6) I dunno on either item but very much doubt what you show is reason for any concern. Such shapes and far worse haven't put me under. Such concerns as I have raised with my teaching pulmonologist sleep MD--recommended to me as best in our area by a known sleep tech--were minimized by this MD to my satisfaction. First thing he did as I started with him, after firing another "you are at 5 and treated" MD, was send me for a full pulmonary evaluation at a hospital where I did all kinds of huffing, puffing, blowing hard and some other exercises. No sleep study yet, given my AHI of down to 0.2 for about 2 years after about 58 at start. Simple OA with a sub-treatable few FL on my SD card, thanks to my out-of-pocket VAuto. FL remained bad after my Autoset made OA's rare.

A closing disclaimer: I only know the limited bit I have learned from my experience and help of others. I have no medical qualifications at all. Consult your MD before making any change you might consider after reading what I or any other forum member has posted.

: dataq1-45-severity-FL-20pct-pressure-rise.GIF (191.37 KiB) Viewed 10866 times

dataq1 · Post by **dataq1** » Sat Nov 20, 2021 1:25 pm

AmSleepnBetta wrote: ↑
Sat Nov 20, 2021 5:10 am

PM sent to you.

AmSleepnBetta · Post by **AmSleepnBetta** » Mon Dec 27, 2021 8:56 pm

1. Housekeeping notes:

I was about to post this in member lars-the-bear's thread "What exactly is a 'flow limit?'". But in keeping with several comments there about keeping things in one place I've come back here to dataq1's thread where I have posted on this topic and its relation to tidal volume. Due to the change in thread, there will likely be duplications below where I made a couple adjustments.

lars-the-bear will read this response to his post if he is truly interested in flow limitation.

A novice and student in all these matters, I only recently learned how significantly our Resmed FL severity-value flag height can reflect increases in and elevated levels of our breathing duty cycle ratio (the measure of our sleep-breathing work). As related below, I believe a FL may reflect a little severity from inspiratory wave deformities, but also now believe the severity and duration metric are mostly driven by tidal volume drops and by above normal duty cycle ratios. I write that here and now after seeing I used the word "phantom" above. That was in an instance where I did not address (or may not have addressed) duty cycle effects when being dismissive of a large FL that did not then appear to have been caused by a tidal volume drop.

2. What I almost posted in lars-the-bear's thread:

First, before adding comments to pugsy and others' good comments in lars-the-bear thread, the following note is in passing and not intended to dismiss the NIH research dataq1 linked to there. It was sponsored by Respironics, done with Respironics devices and completed in or before 2012. Two of the researchers had done work partly funded by grants from Resmed and from Respironics. As dataq1 mentioned, flow limitation was not its focus and apnea were. Resmed APAP device performance is reportedly quite different and likely has changed in the interim (Resmed has connections to related patent applications dated in 2011 and 2018).

In fewer words than below, I summarize here my understanding of "flow limit" in claiming that a Resmed "FL" flag and the separate significations of "flow limitation" are two different but related things that are commonly confused. A FL is a Resmed symbol for a mix of real and potential airflow reducing and breathing effort related components. In general and in human breathing (i.e., in human ventilation) a flow limiter is a condition or device that causes a reduction in (air) flow and flow limitation is the effect of that flow limiter.

I've done a lot of work, some illustrated (now here below), analyzing raw Resmed flow rate and FL data in trying to understand only the Resmed "FL" informational flag. The FL is about flow (ventilation) reduction, detection of imminent threats of it and the level of breathing effort (work of breathing). Again, the more limited ordinary meaning of "flow limitation" of any flowing matter or substance is that a flow of that same matter is, was, or will be reduced from one rate to a lower rate for some period of time.

The four elements underlying a FL can be detection of airflow volume or flow rate reduction, detection of deformed chair- or M-tipped, flattened or other irregular inspiratory wave tips, detection of a flattened inspiratory wave and detection of one or the other or both of two breath timing matters. The interactive timing factors are respiratory rate (breaths per minute) and the ratio of inspiratory time to total breath time (the physical work time of a breath, the "duty cycle"). The exact relationships among and relative impacts of the four broad flow factors are patented secrets.

Among other things, analysis of raw Resmed flow rate data leaves me with an impression that detection of a wave shape irregularity mostly alerts the machine to be ready to raise pressure if a series of it develops or grows. However, as others can check their flow rate, I frequently see 4-second severity of 0.01 to .02 FL begin in the expiratory part of the breath cycle for one M-tip wave or of one sigh wave that has appeared amid very normal waves. How much shape alone may contribute to FL intensity and duration is unknown to me. I suspect ventilation drop and breathing work are main components of FL.

As I understand them the FLs addresses the two most important sleep ventilation and sleep soundness factors, tidal volume reductions and the work of breathing, while mere "flow limitation" signifies only one ventilation factor, tidal volume reductions. If excessive breathing effort is required to maintain adequate tidal volume (ventilation) then sleep becomes fragmented and it seems likely there would be additional detrimental health effects. We must get the ventilation we need (tidal volume, TV) without stressful effort to have restful sleep.

One of the lingering questions about FL in my mind is what determines a drop in a FL to or toward severity zero. How do favorable ventilation, duty cycle or shape changes from less desirable levels get reflected in FL? Work in dataq1's thread (below) touch on that in showing FL varying with TV drops.

Links to two research papers about breathing, one for human and one for equine breathing, follow. The equine account is very similar and simpler to read before tackling the more detailed human account. Both papers explain the many parallel factors in breathing airflow limitation. Both, among much else, emphasize the flow limitation effect of chin and muzzle tucking. The equine account describes the benefits of devices placed to open nasal breathing (valve?) passages. Don't some people use such external nasal devices?

Links:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3770742/
https://www.ivis.org/library/equine-res ... ory-system

lars_the_bear · Post by **lars_the_bear** » Tue Dec 28, 2021 7:23 am

AmSleepnBetta wrote: ↑
Mon Dec 27, 2021 8:56 pm
lars-the-bear will read this response to his post if he is truly interested in flow limitation.

Thank you -- I did.

AmSleepnBetta · Post by **AmSleepnBetta** » Sat Jan 08, 2022 6:31 am

The image shows a large Resmed Autoset FL flag of severity 0.79 and its relation to (a) actual tidal volume drop, my novel breath by breath drop basis (TVd), (b) usual Resmed moving average TV, (c) breathing work done as shown in the duty cycle ratio dC=Ti/(Ti+Te) and (d) all the other most relevant curves OSCAR presents showing Resmed sleep data from air flow.

The main takeaway--beyond whatever interrelationships the image may help one understand better--is highlighted as item "b" and explained some as matching item "B" in the text box below "b". Box "b" values are readouts from Insp. and Exp. Time curves where the green cursor intersects the two curves (Insp. curve above Exp. Curve) where the curves diverge and are most apart in the view. The same can be done by anyone having certain Resmed devices that report or make data available to OSCAR for showing inspiratory and expiratory times. The method can be used to assess sleep work done to fight flow limitation (whether flagged by FL or shown as any form of apnea or neither).

The single relevant research I've seen determined that normal sleepers, as tested, had a duty cycle ratio ("dC", I call them) of about 0.42 and sleepers with severe upper airway obstruction (UAO) had a ratio of about 0.53. As mentioned elsewhere, a Resmed patent application noted, however, that the ratio is about 0.3 for sleeping state and 0.4 for wake state.

Explanation of the TVd (in L) and dC ratio graphs:

Actual values were multiplied by 100 to enable use of the Somnopose import feature of OSCAR. (For example, a tidal volume of 0.5 would otherwise barely register in graph structure built for a range of 0 to 180, similarly for a duty cycle below 1.0).

TVd: bars or spikes upward show loss of tidal volume to flow limitation of any kind while spikes downward show the extra tidal volume over the baseline tidal volume of 0.5 for larger breaths. In a sense that is logically backward, but done that way to make FL flags be more easily compared to TVd, both increasing upward.

dC: The gray bar across the graph was intended to make it easier to estimate bar height; bottom edge agreeing with the first (lowest, 1/4 window height tic) tic mark at left, top edge agreeing with next to top (highest 3/4 height tic) tic mark at left. Anything between 1/4 and 3/4 could be visually estimated more easily from those edges.

I suggest taking notice of the relative timings, durations and magnitudes of all the curves' signals because those are typical of what I see in such analyses.

Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Re: Tidal volume and Flow limitations

Machine	Mask

Additional Comments: Reluctant side sleeper: DIY P10 headgear, Silipos sealed mouth, cervical collar, CMS50I SpO2, accelerometer (for position and motion), supinity block