Help!!! Clueless about Flow Limitations

[Bright Choice]

I am struggling with trying to understand FL and how to interpret the graphs in Rescan. My AHI is low (rare obstructive, rare hypopneas) mostly CA and that maxes out at maybe 2.5 but mostly lower than that with CPAP 7, EPR 2.

When I look at the graphs it seems to me that there are a lot of "unscored" irregularities. They might be normal, but I have no way of knowing.

I'd post them here but it seems that there are so many that I wouldn't know what to grab. Plus, I don't know how to post them anyway.

I have studies SWS's flow shapes below so "kind of" have that understanding.

Here's that reference of flow-limited wave shapes:

Class 1 is the "normal" flow shape. Class 2 through Class 7 are flow-limited wave shapes. Additionally, it's possible to have hybrid FL shapes. Class 3 and Class 4 sometimes combine, for instance. Class 3 and Class 6 occasionally combine.

Can any of you direct me to where I could look at some "normal" flow graphs and some "abnormal" flow graphs so I could begin to understand what I am looking for.


I think I am dealing with UARS but have some question about the "centrals".

Thanks in advance!!

[Bright Choice]

A correction: I am actually looking at the flow charts, not the flow limitation chart but they do correlate I am sure.

It is the breathing rhythm irregularities that I am looking at along with the distortion of each inspiration and exhalation.

[SleepingUgly]

I wish I had some normal flow data to show you, but I have prevalent FLs. At one point someone posted some normal flow charts...Hmmm, who was it? I can't remember... Was it -SWS? DreamDiver? I am not sure!

I will PM you some instructions that someone sent me about how to upload data.

[Jayjonbeach]

I actually don't worry about the Flow or how well things are shaped etc at all (and that is getting down to the finer details that I A - no nothing about at this point and B - not sure I can do anything about either) but I see you have mostly Centrals so it would seem we have fairly different breathing issues.

I do look at the Flow Limitation Graph and consider it to be THE most important piece of information in everything that the ResScan shows (though again I don't know the finer details of the Flow). The S9 also reacts to the Flow Limitation as well which (on APAP mode) is another reason I focus on it.

On the Detailed Graph setting, I usually just look at the 1 hour time setting and scroll along looking at all of these in one view in the top portion: Events, Flow Limitation, Snore and Pressure. When Flow Limitation is Flat and at the top of its Graph, usually EVERYTHING else is good (including Flow, assuming leaks are in check). When there is Flow Limitation, the S9 APAP assess's how bad it is and reacts accordingly, if it continues it reacts again (assuming you leave it room to move up pressure-wise). The S9 also "ignores" CA's that shows up. The S9 does react to some snores and obtructive events but the Flow Limitation at least on my graph is THE key piece of info, it shows how well you are breathing and when its not good the machine always does it's job and most of the time prevents events from even taking place. (again where CPAP failed me, once in awhile an event still sneaks in with APAP and sometimes an apnea will even preempt Flow issues in which case the machine can do nothing for you [if your settings are optimal]). On CPAP when I had Flow Limitation and no pressure increase to compensate, obstructive events always followed and would continue until the Flow Limitations improved (my breathing improved) on its own, which could take up to 5 minutes (probably longer for others who are more severe) and could easily see 3 to 7 obstructive apneas just in that one episode, this is all mostly erradicated on APAP for me however I dont have arousal issues and have very few CA issues unlike you (usually only when first lying down and before getting up which are almost considered normal from my knowledge).

With Flow, the only way I can even get it to look like the picture you posted is to look at the 30 second or 1 minute time interval setting in the chart. To me and I could be wrong here but Flow Limitation does seem to be a direct result of Flow. If Flow is good, there are no limitations, Flow is bad, you see it show up on the Limitation graph and the S9 in Autoset mode reacts accordingly, another reason I don't really look at Flow (and admittedly for me likely don't need to). If I look closely (and I just did look at some recent charts) at my charts there are TONS of breathing irregularities in Flow that do not get scored, the S9 is only going to score actual events (as it classifies them) that may have resulted from the off-beat breathing and not the breathing itself.

Sounds like your breathing is pretty good if you are not having very many events and when you do usually Centrals. With a pressure of 7 which I consider to be pretty low, not sure what are you are going to be able to do to help prevent them (not sure if you tried EPR 1 or 0). I would be curious to know as I do have a friend who has maybe 3 to 6 Centrals per night and often his are during his sleep and not when first lying down or just before getting up.

[jnk]

So do I understand correctly that you are running your APAP as a CPAP?

I think one important thing to remember is that all the data our home machines give us is meant to be used as trending data--not as diagnostic data. So even though some experienced ones here look at the data from the S9 and use it to make calculated insights into a patient's breathing to see indications of non-obstructive problems, that is mostly a brilliant way of using the data beyond what it is supposed to provide, which is trending to see if a patient's breathing is better or worse at a certain pressure over time.

The important question for a self-titrating patient on PAP (with leak under control at a reasonable level) to have is, "What is the best pressure, or set of pressures, for me, with my particular breathing and this particular machine?" For the average OSA patient, that is a much more productive question to ask than such questions as, "Do I have flow limitations?" or, "Am I having centrals?" You look at the trending data and see if more pressure helps or not, because the primary thing you and your machine control about your PAP treatment is what pressure(s) the machine uses to make things better.

That is why comparing your flow tracings to someone else's flow tracings is usually a less productive thing to do than comparing your flow tracings at one pressure to your flow tracings at another pressure. It is your breathing you are trying to improve with pressure, so it is mostly your breathing you want to look at.

It is natural for us to get distracted with asking ourselves what the problem is instead of focusing on how to make best use of the solution to the problem. But it is often a distraction, nonetheless.

Of course, if someone comes to this board for help and has flow tracings from a home machine that may give a clue as to what a doc should be looking for, that is great and I support that help being given as well as it often is here. But still, for most of us, if we have been diagnosed with an obstructed-breathing problem, our focus needs to be primarily on finding what pressure, or pressures, improves our breathing the most in the most comfortable way. Our breathing.

The diagnostic process is one thing. The treatment process is another. We all breathe differently. Getting rid of obstruction effectively and comfortably is step one and is the step that generally helps other issues start to fall into place.

In my opinion.

[DreamDiver]

I wish I had some normal flow data to show you, but I have prevalent FLs. At one point someone posted some normal flow charts...Hmmm, who was it? I can't remember... Was it -SWS? DreamDiver? I am not sure!

I will PM you some instructions that someone sent me about how to upload data.

I'm not sure there is such a thing as a 'normal' flow graph, nor even a normal flow limitation graph. However, there might be good examples of steady flow and an ideal flow limitation: perfectly flat against the bottom of the graph. That said, what's 'normal' or 'steady' for you may be a little different from what you see here. I'll try to be careful not to compare apples to oranges. This is what's normal for me. Things may be different for you!

Here's an example of a recent night for me:

There are two areas where the flow looks steady. They're highlighted in the red bars. I know they're steady because I don't see lots of fluctuation in the height of the graph. At this resolution it's almost like a straight bar, but it's really a bunch of breaths so tightly packed at this resolution that all you can see is their uniformity of height.

So let's zoom in to a five minute window in one of the steady areas:

You can see that even at this resolution, the height hardly varies and the distance between waves is also relatively uniform.
Consistently, there are no events and no flow limitation -- flat along the bottom.

Let's zoom in even closer:

You might think: "Hey, those look like chairs." However, they're facing the wrong way. It merely means I pause for a brief period after each exhale. That appears to be normal for me. Ocassionally, I have brief periods (five to ten minutes) where my breathing really does look like sine waves. I assume that's good, and guess they may indicate a particular sleep phase, but cannot be certain. They are very elusive for me, so I haven't shown them here.

Let's look at an area where it's not so steady:

Here we see chairs and M's. A flow limitation is correspondingly marked.

That's how mine look. Yours may look similar or slightly different.

Sleeping Ugly, If I'm not mistaken, I've noticed a number of times when you've posted flow limitation graphs that your legend and readings are inverse from mine. In other words, it looks like flat across the top is correct for your layout. I'm not sure I understand how that can be, but your sine wave is on top, and flattened wave on the bottom. If I'm wrong, it might have been someone else.

[Rebecca R]

Sleeping Ugly, If I'm not mistaken, I've noticed a number of times when you've posted flow limitation graphs that your legend and readings are inverse from mine. In other words, it looks like flat across the top is correct for your layout. I'm not sure I understand how that can be, but your sine wave is on top, and flattened wave on the bottom. If I'm wrong, it might have been someone else.

Mine used to do that too. One of the older versions of ResScan plotted FL graph across the top and after I updated to a newer version it moved to the bottom. I don't remember which versions though.

[SleepingUgly]

DreamDiver, where you say they may look like chairs, but "they are facing the wrong way"...how are those different than what -SWS posted above as Class 6 FLs?

Yes, my graphs are inverted where "good" is at the top of the graph. I think I like yours better, but I'm too afraid to try to mess with getting a different version!

[DreamDiver]

DreamDiver, where you say they may look like chairs, but "they are facing the wrong way"...how are those different than what -SWS posted above as Class 6 FLs?

Yes, my graphs are inverted where "good" is at the top of the graph. I think I like yours better, but I'm too afraid to try to mess with getting a different version!

Huh - serves me right for not paying attention. There was a previous thread that talked in detail about flow limitation in particular. NotMuffy says something about how if the Ventilation Ratio is fairly high, the S9's 'Fuzzy Flow Limitation' algorithm does not count it as a flow limitation. In other words, the change in my tidal volume is too strong for it to measure as a flow limitation. Correspondingly, my flow graph looks relatively hesitant only during the forward chairs and m's, and marks them as flow limitation. I'm barely treading water where it's very deep, so if someone would like to throw me a rope by explaining that better than I can, I'd be grateful. (Erm... NotMuffy?)

[-SWS]

DreamDiver, where you say they may look like chairs, but "they are facing the wrong way"...how are those different than what -SWS posted above as Class 6 FLs?

Yes, my graphs are inverted where "good" is at the top of the graph. I think I like yours better, but I'm too afraid to try to mess with getting a different version!

Huh - serves me right for not paying attention. There was a previous thread that talked in detail about flow limitation in particular. NotMuffy says something about how if the Ventilation Ratio is fairly high, the S9's 'Fuzzy Flow Limitation' algorithm does not count it as a flow limitation. In other words, the change in my tidal volume is too strong for it to measure as a flow limitation. Correspondingly, my flow graph looks relatively hesitant only during the forward chairs and m's, and marks them as flow limitation. I'm barely treading water where it's very deep, so if someone would like to throw me a rope by explaining that better than I can, I'd be grateful. (Erm... NotMuffy?)

I don't think it's ventilation ratio with respect to comparisons of flow magnitude. Rather the FFL patent is preoccupied with duty cycle of inspiration compared to the overall respiratory period. So that particular ratio comparison (duty cycle) is time based rather than flow-magnitude based. I attempted a summary of that FFL patent description here as well:
viewtopic.php?f=1&t=61466&p=578181&hilit=ffl#p578181

The FFL patent is all about addressing those "M"s that presented an algorithmic challenge to Resmed's previous focus on flattening. The "chairs" weren't the big spoiler in the previous FL implementation----compared to the algorithmically-challenging "M"s. But the "chairs" come along for the ride in the new FFL patent implementation BECAUSE they frequently combine or hybridize with the algorithmically-problematic "M"s. Thus the FFL's algorithmic preoccupation with discerning both "M"s and "chairs" IMO.

Also, I'm under the impression that all FL shape analysis and scoring should be limited to inhale cycle. So when you see part of the chair shape dip into exhalation time, then that is not a flow-limitation. Rather THAT chair shape is "inhale paired with small exhale" rather than FL. So here we have a chair shape alright----but THAT chair is not a flow limitation since exhalation (and not inspiratory flow limitation) is what created the "seat" portion of the chair:


Flow limitation is an inspiratory phenomenon by clinical definition. My understanding is that FL-shape analyses should thus be confined to inspiration. Please take my own amateur interpretations with a grain of salt.

[jnk]

So, -SWS, based on that, would I be correct in assuming that, generally speaking, it is the shape of the portion of the flow curve above the red line that would be used in classifying the shape of an inspiratory flow limitation? Or am I missing the point? (I do that sometimes. )

[-SWS]

So, -SWS, based on that, would I be correct in assuming that, generally speaking, it is the shape of the portion of the flow curve above the red line that would be used in classifying the shape of an inspiratory flow limitation? Or am I missing the point? (I do that sometimes. )

Thanks for putting that key point so succinctly, Jeff. Yes, you described that right... Negative flow (below the red line) is exhalation, and positive flow (above the red line) is inhalation.

Here are those reference FL waveforms once again:



Below we can see the word "inspiratory" in the title of the document those FL images came from:
http://chestjournal.chestpubs.org/content/119/1/37.full
So those FL waveshapes are all above the red line...

[AMUW]

I like this thread.

would I be correct in assuming that, generally speaking, it is the shape of the portion of the flow curve above the red line that would be used in classifying the shape of an inspiratory flow limitation?

In answer to the original question, and supplementing the last example provided by Dreamdiver, here is a paper addressing mainly the shapes of the flow or pressure cycles, deviating from normal to disordered:
Expiratory flow limitation during sleep in heavy snorers, D. Stanescu et al, Eur Respir J, 1996, 9, 2116–2121 http://www.ersj.org.uk/content/9/10/2116.full.pdf

While I expect that an experienced sleep doctor can recognize a lot in the time histories, even better derived measures have been proposed (if the doctor and tech can handle the higher signal processing math and physics); for example the ratio of pressure to flow, plotted vs. time estimates the upper airway resistance... or frequency spectra ... or random analysis techniques. Here is one reference.
Expiratory Flow Limitation in OSA and Other Respiratory... Baydur et al. Am. J. Respir. Crit. Care Med..2009; 179: A6067

When I look at my ResScan flow curves, I perk up less to the shape of periodic sleep cycles, instead to the changes: gradual degradation of the curve shapes and amplitudes from periodic sleep at sleep frequency ... toward an increase in upper airway restriction ... going to an apnea ... and chalked up by ResMed when the flat portion is longer than 10 seconds. But a cluster of shorter cycles indicates to me arousals and sleep fragmentation.
Given that I finally have my AHIs under control, it is my current problem to recognize in the data from ResMed (much more limited than what a 30+ channel PSG provides) the other symptoms to correlate to my subjective suboptimal sleep experience ... such as caused by nasal congestion.

[-SWS]

Thanks for adding such good information, AMUW.

Expiratory flow limitation during sleep in heavy snorers, D. Stanescu et al, Eur Respir J, 1996, 9, 2116–2121 http://www.ersj.org.uk/content/9/10/2116.full.pdf

I was going to mention that there is ALSO expiratory flow limitation---but didn't want to "muddy the waters" so to speak. So far in this thread everyone has been trying to understand what the S9 does relative to FL. I'm glad you introduced that study anyway...

However, for the sake of clarification, I should point out that the S9 does not event-detect or pressure-increase in response to "expiratory flow limitation". Rather, the S9, like all APAPs, event-detects and pressure-increases in response to "inspiratory flow limitations":

Controlled positive pressure to the airway of a patient is adjusted by detecting flow limitation from the shape of an inspiratory flow waveform.

http://www.sumobrain.com/patents/wipo/A ... 38040.html

RERAs are one reason APAP algorithms attempt to address flow limitations. Those RERAs are Respiratory Effort Related Arousals that have to do with "respiratory effort". "Respiratory effort" arousals are an "inspiratory workload" problem. Exhalation, for typical obstructive SDB patients and the normal population, is a matter of passive muscle recoil or relaxation. It's not a respiratory-effort intensive breathing phase compared to inhalation. By contrast inspiration is the respiratory phase where we exert muscular effort to draw in air. When our airways are stifled during inhalation with high resistance, then our respiratory effort increases. When that increased respiratory effort during the inhalation phase causes an arousal, it's measured during the PSG as a RERA.

APAP manufacturers and PSG sleep-study scoring ALWAYS deal with inspiratory flow limitations rather than expiratory flow limitations. Reference the following excerpt from the above 1996 expiratory-flow-limitation study for an idea of how prevalence compares between the two:

To our knowledge, this is the first time that expiratory flow limitation during sleep has been reported

http://www.ersj.org.uk/content/9/10/2116.full.pdf

And while expiratory FL has recurred in literature since 1996, it isn't typically scored and treated as more common inspiratory FL is... Someone please correct me if I am wrong. Thanks in advance if you do!

[AMUW]

SWS, looks like you caught my trap on discussing inhalation vs. exhalation flow shapes.
Which I set unintentionally, and somewhat by insufficient immersion into the breathing process ... and of disordered breathing during sleep. Note that DreamDiver was also highlighting the lower portions of the breathing curve ... that's exhalation I believe.
I am told that in OSA the exhalation phase is more important than the inhalation phase. Not only is CO2 exhaled, but the remaining O2 in the blood stream is extracted. And there is a tight coupling between the gas exchange process and the vaso-constriction in the nose and the pressure variations in the upper respiratory system.
I admit that I haven't looked yet at what ResMed does with the shape of a single cycle, whether the inhalatory or exhalatory half of it. But note that ResMed measures the flow in the box ... not in one's throat or nose.