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flow limitations expressed as an index?
#31
RE: flow limitations expressed as an index?
looking back at pholynyk's post at #7, it's clear the flow limitation graph has an x as well as a y dimension, y being severity and x being duration. what's not clear (to me) is whether the severity index of 0-1 incorporates duration. it looks to me like it doesn't. if duration is factored in, my proposal is moot. if not, an important bit of information is overlooked. in that case, 2SleepBetta's suggestion at the top of post #25 would capture both dimensions. simply sum the x axis times at each y axis increment (in whatever incremental units the machine reports), divide by usage hours. this next step is beyond my mathematical capabilities but if the result is a huge number, divide it by some number to reduce it.
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#32
RE: flow limitations expressed as an index?
(04-13-2021, 08:33 PM)sheepless Wrote: I'd like this deeper dive into flow limitations to continue but hope my much less complicated proposal doesn't get lost.

"in some cases bigger FL number means more flow-limited than smaller FL number, where in other cases a smaller FL number means more flow-limited than a bigger FL number."

probably just me being obtuse but I'm not sure I follow. are your references to the flow rate graph, the flow limitations graph under the Daily tab, the flow limitations graph under the Overview tab or the flow limitations stats under the Daily tab? like, when you refer to the FL curve, it sounds like you might mean the flow rate curve?

"Without a cervical collar, I have dramatically more flow limits than when I wear one"

IF I understand your post (emphasis on the IF), I still think it makes sense as a definitional issue. I'd say the collar is keeping the airway open enough to reduce the restrictions from 90 or 100% (whatever the definition of oa is) to 40 or 50% (whatever the definition of flow limitation is). partial opening of the airway producing fewer apnea, more flow limitations.

To give an example of what I mean... Here's a 3-minute 45-second sample of me without a cervical collar on.
[attachment=31474]

Look at the first four breaths on the left vs the last 7 breaths on the right. All those are scored as FL of zero. Look at 2:20:44 and 2:21 -- more ludicrously non-zero zeros! Those last 7 breaths on the right there are truly not flow-limited (or not much, anyway). But the preceding breaths are a mess! And how the machine scores that mess is pretty haphazard, I think. Here's the actual data, with the FLG's marked in blue and green:
[attachment=31473]

When you look at the data, there is a time stamp associated with an amount of flow limitation. When the machine drops an FLG at a particular second, it's very unclear as to what interval that flow limitation is supposed to be associated with. In the OSCAR graph, the value begins with the time stamp and is drawn as persisting until the next FLG that gets logged to the card. Looking at my data, that's obviously not true in any general sense. It looks to me like the machine is calculating flow limitations based upon some data in the neighborhood of the timestamp, but I'm pretty sure that the time interval that the machine uses to produce the value is usually not all the way until the next FLG drop. It looks to me like sometimes the machine is paying attention to the FLs and doing a calculation and logging it. But whether the machine is paying attention to the level of FLs all the way to the next FLG data that gets logged -- uh-uh, I don't think so!
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#33
RE: flow limitations expressed as an index?
@cathyf I don't really understand where you are going with that.
If you are interested in the "why": there are crucial graphs missing.
Flow rate, the high res (mask) pressure, your Flowlimits and finally the leaks would be the minimum.

What is quite clear so far: quite heavy artefacts from heart (I would estimate a heart rate around 90). From the looks of the flow rate I would suspect EPR is working overtime and obviously triggered early or mis-timed ... which than of course results in those flowrates. ... we'll see about that in the high-res pressure curve^^
Where is your data coming from? Right from the SD-Card / EDF-file or from SleepyHead's own data-storage? (most likely the latter as ResMed reports that data at 0.5 Hz continuously and only SH with the time-delta-format is compressing that a bit)
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#34
RE: flow limitations expressed as an index?
(04-14-2021, 01:48 PM)TBMx Wrote: @cathyf I don't really understand where you are going with that.
If you are interested in the "why": there are crucial graphs missing.
Flow rate, the high res (mask) pressure, your Flowlimits and finally the leaks would be the minimum.

What is quite clear so far: quite heavy artefacts from heart (I would estimate a heart rate around 90). From the looks of the flow rate I would suspect EPR is working overtime and obviously triggered early or mis-timed ... which than of course results in those flowrates. ... we'll see about that in the high-res pressure curve^^
Where is your data coming from? Right from the SD-Card / EDF-file or from SleepyHead's own data-storage? (most likely the latter as ResMed reports that data at 0.5 Hz continuously and only SH with the time-delta-format is compressing that a bit)

The place I'm coming from is the suggestion "let's multiply the reported flow limit numbers by their durations and add it all up to get the area under the curve" -- because it looks to me like we don't know the durations. Sure, the duration is bounded by the timestamp of the next data point, but I'm maintaining that it looks significantly shorter than that.

As my physicist husband talks about data, the way that the data jumps around "is not physical". Reading the patent applications that makes total sense -- the algorithm is doing a lot of "if this look at that" and using numbers to mean big/little rather than more exact measurements, and not calculating at all when it doesn't make sense. And we look at the data and eyeball "this looks pretty good, that looks ugly" and I don't think you can get there by doing something as basic as multiply-and-add. Because there's way too much going on you are doing too much apples-to-oranges.

(And, yeah, I'm dumping the data out of OSCAR with the export data command.)

(And I would put more data up but I'm out of room for allocated attachments and need to spend some time cleaning up files.)

(And, annoyingly enough, my fitbit seems to be missing my sleeping heart rate data for just that night, although it's there in the whole day's data, and the statistics are calculated. I seem to have stumbled upon a fitbit bug!)
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#35
RE: flow limitations expressed as an index?
"The place I'm coming from is the suggestion "let's multiply the reported flow limit numbers by their durations and add it all up to get the area under the curve" -- because it looks to me like we don't know the durations. Sure, the duration is bounded by the timestamp of the next data point, but I'm maintaining that it looks significantly shorter than that.""

clearly most of us don't understand how fl are reported (maybe the oscar folks do?). I hope all you smart folks figure out how it can be better understood and improved.

while you work on that, why not take advantage of what we have. it gives us more information than currently reported (I haven't been told differently yet anyway; nor has anyone said it's a bad idea and why) to help determine the significance of fl in individuals and to compare in relative terms the results of settings changes. ideal or not, completely accurate or not, it moves us forward.

I've had my say (ad nauseum maybe). I don't sense much enthusiasm but it'll be up to the membership, moderators, advisory group and especially the oscar team to decide whether to do anything with it.

I hope you-all continue the discussion and I hope you figure it out!
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#36
RE: flow limitations expressed as an index?
(04-14-2021, 07:00 PM)cathyf Wrote:  I don't think you can get there by doing something as basic as multiply-and-add. Because there's way too much going on you are doing too much apples-to-oranges.
Well, mainly because the "Flow Limitation" reported by the machine is just a "Flow Grade" and as such measured on an ordinal scale.  Data of that kind must not be added, subtracted or divided by themselves or by other numbers.  Like school grades: It's pretty senseless to add an A to a C or multiply a D by 3 ...
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#37
RE: flow limitations expressed as an index?
@cathyf: "How" 'FLs' are reported is quite simple: ResMed logs every 2 seconds a number for that. This number refers to the last 2 seconds, which in the end means: the last breath (to be precise: the last completed inhalation as only the inhalation is taken into account) ... this means there can be 2 datapoints (= 4 seconds in total) for 1 single breath or 1 for 2 - depending on the respiratory rate at that moment.
The question is: what do these "FL" mean (exactly) and is there some value or deeper meaning to them?
ResMed says in their "Clinical Manual" for ResScan regarding this: 'Flowlimitations: from flat to round'

Well, Flowlimitations are 'a bit' more than just flattenings:
Sleeprider worded it quite nicely:
(04-09-2021, 04:17 PM)Sleeprider Wrote: but I have seen considerable differences between individual results at the same 95% flow limit. I generally like to see less than 0.1 in that statistic, and it is still disruptive for some people and impossible to get for others.

I wouldn't be that polite and frankly say: the real correlation is only slightly above a random number generator. This might or does change for those with non-hypoxic breathing disorders - BUT: the devices are not meant for diagnostic purposes - those are devices for treatment.
If you have a problem with flowlimitations and only take the flattenings this might have nevertheless 'some' meaning but that would be comparable to just taking OAs (or CAs or ... - just pick one) and call THAT "AHI".
AHI is a well established surrogate for sleep apnea syndrome (meaning a HYPOXIC SRBD) but that consists of apneas AND hypopneas (both obstructive and non-obstructive and even 'mixed') - if one takes only 1 single kind of those events and then says that this number is the same or even correlates to the AHI that is simply false or the result would be overall meaningless - for some that would show some kind of correlation but overall it would be hit or miss and that is NOT a correlation.

If you take an incomplete value and compress that even further you always end up with nothing (or: a random number would not be much worse).
If you nevertheless do that and put a shiny label on it, people will start to put even more meaning in it - but in this very case it never had that to begin with!

However: as OSCAR seems to be able to export that data, one could do that (e.g. in Excel) for oneself. As it seems to be in the time-delta-format that is no magic:
supposing the FL-values are all ordered by time (and already filtered to be just the FLs), time beeing column A and in C the value for that timestamp. In the original data from the machine the FL-value that is in row 'x' would repeat itself (every 2 seconds) until the timestamp that is in row x+1.
Sou you could sum them up over: Cx * (A(x+1)-A(x)) [that would be in seconds - divide it by 2 if you want the sum of the original datafrequency]
The Index would than be that sum divided by the total duration (well - more in hours to get a reading different from 0^^).

Expectation: meaningless and completely obscure value. (and I mean even more obscure than before)

If we stick to the school-grades (where at least for me just talking about the average or index is quite common): if someone applies to be a rockt-scientiest how much value is in the index of the scool-grades in sports, arts and history??
Well ... as "Turnvater Jahn" said: 'inside a healthy body is a healthy mind', for arts you have to be creative and it is always good to know where you are coming from ... all true - but the main focus for a rocket-scientist would be the STEM fields.


What might yield some information would be the index AND the average distance of prolongued episodes with those flattenings. (but this information is far easier and directly seen if one simply looks at that graph).
Keep in mind: the sao paulo cohort established up to 30% of the night with flowlimitations is healthy and normal. That would mean the 70-percentile needs to be different from 0.00 - If that actually would be the case this could also be seen at the first view: the pressure would be equal to CPAP and the FL-graph would be (nearly completely) black (or colored or whatever).
Flattenings are not all there is to flowlimitations - 95% is way to high ... something around 80 to 90 together with the amount of time where the resp. rate doubles should give a starting point for the actual amount of the residual flowlimitations. (personally I would consider the latter as worse ... but I know that I am sensitive to intra-breath pressure changes - so it is quite safe to assume that those would strike me more than just flattenings ... but I have 'just' OSAS and thus flowlimitations do not play such an important role for me anyway^^)

But to introduce an overall new index with real value it would be necessary to establish the importance or at least a clear (and preferably strong) correlation with the underlying data in the first place! And this - at least from my point - not given for ResMeds "FLs" - so far it is hit or miss: many have no trouble with that or at least the change in that value does NOT correlate to the subjective feeling (or as presented by sheepless: make it even worse), some have trouble with flowlimitations but the reading from the machine says there are none.
In most (if not all) cases other values or just the overall "look" from the respiratory flow are much better and have a much stronger correlation. (and that still does not mean that there is any causality in it)
FLs I would at most attribute a relation but definitely no correlation.
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#38
RE: flow limitations expressed as an index?
@TBMx: "If you take an incomplete value and compress that even further you always end up with nothing (or: a random number would not be much worse). If you nevertheless do that and put a shiny label on it, people will start to put even more meaning in it - but in this very case it never had that to begin with!"

Obviously, if GI, then GO, as in GIGO. However, as one who also read the Sao Paulo study months ago, here are a few comments about the quotation above and its context: 

(1) Limited in knowledge, I believe ResMed's FL is a valuable indicator of short-period flow limited breaths, if only for those with a high level of inspiratory flow limited breathing--the FL thing is more than marketing pandering. 

(2) We see and rely on high levels of FL "coaching us" to use EPR and pressure support, (PS), to fight it. Neither TBMx's quote of SR nor SR's apt observation supports dismissal or downplay of FL. The 95% number is patient relative, is relative to a particular sleeper's individual level of FL, his particular set of overall losses of air volume as a result of brief drops (neonate hypopneas?) in airflow delivery after and relative to a short period of higher delivery of air volume to the lungs. For patients A and B, 95% for A means nothing with respect to B's 95%.  Resmed, right or wrong, is credited by many knowledgeable PAPers as being more responsive to FL than other makers. Some (or all?) other makers do not even provide explicit FL markers. 

(3) sheepless's OP called for more revealing presentation of the overall effect of the FL we see. The simple summation of areas of the given indicators, as I suggested (and am not invested in), would simply consolidate the areas of the scattered FL. If the FL are garbage, of course the sum is.

Thanks to cathyf and her probing we are digging into and learning more about the matter of inspiratory flow limited breathing. I appreciate the OP question and all the solid contributions, TBMx's and cathyf's  particularly, which have helped me to learn more, to plow new ground as I hope to be converging on a helpful understanding of my arousals and micro arousals. I'd fiddled with the EDF and the large data file a year or two back, but in revisiting those last night, I am (and was) "all thumbs" with them.

In an effort to understand the airflow volume changes the FL indicates, my intent was to use EDF (its Excel CSV) to numerically integrate flow data and determine the areas (air volumes) of a span of inspiratory airflows--a span which had a variety of FL presences. I would begin that effort with singlets. That done, then take on multiples, some of those FL with near and far neighbors, including those situations where clustered FLs' indicators stack upwards. With a sub-goal integration done, then compare and contrast, try to reconcile areas and cumulative times found to the FL indications smart ResMeds provide. (In passing, my mostly locally-lonesome "M-tipped" inspiratory peaks with their own lonesome FL are most often flagged with a 10-second FL marker of 0.02 to .04. An "M-tip" peak looks like a good candidate to analyze first as there is a definite one to one correspondence when, as often, the preceding and following few  inspiratory wave are relatively uniform (i.e., are generally fairly rounded). Hopefully, the 25 Hz signal is sufficient for the short span of time. . . . But, whew, so many things for us to balance in our "look at" and "must do" prioritizations of time.)

Thanks to TBMx I now know or have some idea of what time frames Resmed use for registering a FL. But, as cathyf observed in a post, regularities we observe are often affected by overriding if-then controls, so anomalies and compromises (and probably omissions) confound our discovery process.

Harking back to a far-back post (maybe by sheepless?), I see my and our intent in trying to unravel the exact meaning of ResMed FL reporting is to get a better understanding of how to improve our sleep. Most of the relevant FL information is publicly available in ResMed patent applications. We are not trying to reverse engineer their algorithm for economic gain, but are trying to understand what FL means in our quest for our most restful sleep. To whom, for what, and how is the FL mark helpful or indicative? ResMed could have been more helpful to our understanding (or I haven't looked in its right places re FL). I would not be surprised to find that there are Resmed advances in handling of FL in its new 11 series of machines.
I have no particular qualifications or expertise with respect to the apnea/cpap/sleep related content of my posts beyond my own user experiences and what I've learned from others on this site. Each of us bears the burden of evaluating the validity and applicability of what we read here before acting on it.  

Of my 3 once-needed, helpful, and adjunctive devices I have listed, only the accelerometer remains operative (but now idle). My second CMS50I died, too, of old age and the so-so Dreem 2 needs head-positioning band repair--if, indeed, Dreem even supports use of it now.



 
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#39
RE: flow limitations expressed as an index?
(04-15-2021, 07:26 AM)TBMx Wrote: @cathyf: "How" 'FLs' are reported is quite simple: ResMed logs every 2 seconds a number for that. This number refers to the last 2 seconds, which in the end means: the last breath (to be precise: the last completed inhalation as only the inhalation is taken into account) ... this means there can be 2 datapoints (= 4 seconds in total) for 1 single breath or 1 for 2 - depending on the respiratory rate at that moment.

First off, TBMx, I think we are at pretty much the same place as far as the numeric usefulness of the flow limit numbers and durations, it's just that I think we got there from different directions. What I am seeing from my data is that while ResMed may log a flow limit value every 2 seconds it is not calculating that number every two seconds. I do have long stretches where each breath looks pretty similar to the breaths before it and the breaths after it. But I also have lots and lots of time every night where every block of 1-5 breaths looks totally different from the little groups of breaths before and after -- a wild, jaggy, ride. When I see long stretches where my breathing looks pretty consistent -- whether good, bad, or really ugly -- it looks like the flow limit graph is "tracking" the flow limitation in the neighborhood. But where the pattern of breathing is jumping up and down all over the place, the flow limit graph looks like it's unconnected from the waveforms in the same time slices. I think that a lot of those data points are "leftover" from calculations done shortly before over breaths before that, and it also looks like the calculations are not always looking at breaths over the same length of timeslice, too. Given what the patent applications say, that's really not surprising. As multicast says, it's more a "grade" than a "score".




(04-15-2021, 07:26 AM)TBMx Wrote: However: as OSCAR seems to be able to export that data, one could do that (e.g. in Excel) for oneself. As it seems to be in the time-delta-format that is no magic:
supposing the FL-values are all ordered by time (and already filtered to be just the FLs), time beeing column A and in C the value for that timestamp. In the original data from the machine the FL-value that is in row 'x' would repeat itself (every 2 seconds) until the timestamp that is in row x+1.
Sou you could sum them up over: Cx * (A(x+1)-A(x)) [that would be in seconds - divide it by 2 if you want the sum of the original datafrequency]
The Index would than be that sum divided by the total duration (well - more in hours to get a reading different from 0^^).

Expectation: meaningless and completely obscure value. (and I mean even more obscure than before)

I actually did that calculation. (but you knew that, LOL)

This was the night I was working with:
http://www.apneaboard.com/forums/attachm...?aid=31089

As you can see, the summary statistic median flow limit is worthless. (An aside -- in the statistics screen there is a column for flow limit which is the average median over the period -- it's worthless -- maybe replace it with either the average 95% or average max?) The 95% is 0.28 and the "max" is 0.79.

The calculation I did...
Took all of the FLG data points out of the file.
If a data point is in the same session as the data point that follows, I calculated a duration by subtracting this time stamp from the following time stamp. (if it's the last data point of a session, duration is zero.)

Total seconds: 30148
Total in-session seconds: 29580
Total seconds where FLG value > 0.00: 11544

Then, in the same spirit as we measure power in KilowattHours, I created the concept FlowLimitSeconds. I multiplied each FLG value by its duration, and then summed them all.

FlowLimitSeconds: 1432.76

1432.76 / 11544 = 0.12
1432.76 / 29580 = 0.05

So, are either of those numbers less useless than 0.00 / 0.28 / 0.79 ?

yeah, "meaningless and completely obscure value" -- I think that about sums it up!


(04-15-2021, 07:26 AM)TBMx Wrote: Keep in mind: the sao paulo cohort established up to 30% of the night with flowlimitations is healthy and normal. That would mean the 70-percentile needs to be different from 0.00 - If that actually would be the case this could also be seen at the first view: the pressure would be equal to CPAP and the FL-graph would be (nearly completely) black (or colored or whatever).

When was the Sao Paulo study done? Back at the beginning of my adventure I did an ApneaLink home study -- May 2014. None of my 3 in-lab studies have mentioned anything like flow limits, but the ApneaLink did.
breaths: 6324
Flow lim. Br. w/o Sn (FL): 3824
Flow lim. Br. w/ Sn (FS): 164
% Flow lim. Br. w/o Sn (FL): 60%
%Flow lim. Br. w/ Sn (FS): 3%
But the kicker is that under the "Normal" column it says that "normal" %FL is "< about 60%", and "normal" %FS is "< about 40%". So if ALL your breaths are flow-limited, with 60% w/o snore and 40% w/ snore, that's still "normal"!!! (AND -- the ApneaLink measures from power-on to power-off, so includes all of the awake time, and that's 60%/40% of the awake time, too!)

Also, as to your "nearly completely solid" -- no, that's not what they do. The solid color comes from the FL number whipsawing back and forth between zero and large numbers, which in my case is indication of arousals. because when I'm awake my FLs are zero. The more interesting cases are where the FL goes off zero for long enough to be seen as a "hump" on the zoomed-out whole-night view -- which indicates long periods of even, flow-limited breathing that I'm not fighting back against.

I'm back at seeing that the machine is fighting back against this thing that it is reporting, but I don't think that it's doing a very good job of reporting what it is calculating. And I'm not convinced that it's doing a very good job of adjusting pressure the way it should be. Because I know from long experience that if I constrain the pressures such that the machine can't react to the FLs, then that means the machine measures more FLs, but does NOT in general mean that I get apneas or hypopneas. The rationale for reacting to the flow limitations is the theory that 1) raising the pressure will eliminate or reduce the FLs, and 2) if the FLs are allowed to continue without a pressure change then apneas and hypopneas will follow, while if the FLs are reduced, the apneas/hypopneas will be prevented.

In my case, I think 1) is true, but 2) is not -- FLs are their own thing, and NOT early indicators of impending apneas/hypopneas.

Which I think is what you are saying, too, TBMx
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#40
RE: flow limitations expressed as an index?
Sorry for not checking back earlier.
I have a really hard time discussing this topic in my own mother language - does not get any easier in english. So please keep that in mind before starting to think that I want to sound rude or unpolite. That's why I made it that long and tried to explain as much as possible for me.

first: @cathyf: I think, we mean the same thing / are on the same page^^

Maybe I should clarify a little bit more where my thoughts and beliefs come from: (regarding the "FL"-Value from ResMed - just THAT very value ... nothing really more)

I mean I am not a medical professional of some kind or whatsoever - and to be honest I am not the biggest fan of ResMed either. They build and have extraordinary devices which even might be leading in terms of patient comfort.
What I actually don't like - not even a little bit - is the fact, that ResMed shows very little data(!). The do have the highest resolution on their flowrate and the pressure - I give them that - but that's about it (datawise). What is especially annoying is that they do not provide any form of raw data for the flow - I don't know if there is a (easy) way to capture the raw data from the device - many have outlets for the PSG, some have easy interfaces, others use proprietary and very expensive adapters for that.
There is just their filtered and processed "breathing flow" ... which leaves it up to the guessing range how good that is or how much they missed they actual leakage.
Sounds unimportant ... but infact it is crucial to know or see what got filtered (and how) - especially if your are after flowlimitations ... for me it looks like they actually do filter the heart out - but often enough one can see cardioballistic artefacts - but on the other hand those are not always present (not even a little bit). (and from my experience with a 25 Hz resolution the heart rate should always be detectable (under normal respiratory parameters that would be))

The next thing is - as already pointed out - the "FL" from ResMed are not per se equal to flowlimitations in general. ResMed itself talks about "flattenings - from round to flat" [taken from the clinical guide to ResScan - although the german one translated]
And that is what they do pretty good: detecting flattenings.
There actually is "a little bit" more to flowlimitations than just flattenings - at least if one actually has a real problem with flowlimitations in the first place!

Here in Germany the standard-care is not ResMed. ResMed is widespread too of course - but we see plenty from Löwenstein / Weinmann and from time to time Philips and even some other devices. ... but the medical system in germany is a total different one too .. the usual way to get a device would be: see a doctor and raise some concerns regarding SRBD (sleep-related breathing disorder) get a PG (polygraphy - meaning at home test, usually 4 channels including the effort belts / respiratory inductance plethysmography but usually no EEG thus sleepstages) - than it goes to a full lab sleep study (which often do there own PG again before) - after that comes the titration night. On the other hand we rarely see the diagnosis of UARS - somehow awareness for that is still lacking here in germany. (from my point of view we are about a decade away from the USA regarding OSAS and SRBD in general - awareness is rising fast - but the waiting time for the full diagnosis cycle here in germany goes currently up to 6 to 12 months!)

Löwenstein / Weinmann is targeting the same problem (OSAS that would be) quite differently - they rely much less on "flowlimitations" or "flattenings" and focus much more(!) on events as hypopneas and RERAs. (I really don't want to promote Löwenstein - fine devices .. I like them datawise very much ... but they have obvious pitfals and well, comfort-wise they are by far not the best - humidity and / or the lacking climatecontrol especially has been a very long ongoing pain in the ass - the last firmware update for the 20a wants to fix some issues - but still.) What interests me more are the differences in the algorithms for the pressure - comparing those 2 devices is really revealing for me!

The AutoSet-Algorithm is relying (nearly totally) on those flattenings (or ResMed Flowlimitations) - other manufacturers do NOT - at least not to that degree.
But the other devices work very well as well! .. some do better with the one device - others with another. (in most cases I have seen the choice or the change between devices was based on personal bias, marketing, expectations or some features of the other device which I attribute to the "comfortzone" - meaning: not really "therapy-relevant" in the narrow sense ... comfort is of course very important - personal like or dislike as well - adherence is the key - no argument there! ... I have seen very little which could not tolerate one device or where one device did not the job ... but on the other hand an in-lab-study is the (nearly only) way here to get a machine - so usually they are pretty good titrated .. the most problems arise if someone gets titrated on one device and chooses another later and just applies the exact same settings - in many cases a direct route to failure)

With that in mind it raises the question of the importance of the flattenings. Those are very good markers for adjusting the pressure - no argument there. But how can that be, that other devices which do not rely on flowlimitations to that degree can treat very effectively as well, if flowlimitations would play a very important role for EVERYONE!
I don't argue with the fact that there are the non hypoxic SRBD where the flowlimitations are the major issue! ... but than once again: flowlimitations are a bit more than just flattenings.

I myself are bit more complex regarding flowlimitations - mouth breather and with hay fever and other allergies ... I can actually produce flowmitations nearly at free will - and that beeing especially the "flattening" kind. I just need to breath through my nose with just a little bit hay fever and an AutoSet is going crazy on me^^
As my nasal passage is not bigger as it is - more pressure is not really the key. Even with much higher pressure those flattening will remain in that case. (which is easy to prove with other devices and higher pressure)
... now comes the fun fact: on an AutoSet those very good detected "FLs" diminish if I use EPR! (they do not completely vanish if they were severe enough in the first place - but they actually do diminish)

Well ... as I said: no raw data with ResMed ... you never know and can just guess!
OK - I do not need to guess in that case ... I checked that often enough with a PG - the Phase-TA (the difference between the abdomen and the thorax effort) did not really change with EPR (3 that was) on or off. Of course it went down a little bit - but nothing of any importance (it was in fact more the RIP-sum which went down a bit - and in the result the phase-shift went down accordingly)
Don't get me wrong this does not(!) mean that EPR is not working with flowlimitations - of course pressure support is working there ... in my case it just never was a flowlimitation in the deeper meaning of SRBD to begin with. The important thing for me there is: filtered data ... It simply does not always add up! .. that still does not make it bad or useless or whatever - it just disqualifies as a single(!) diagnostic value - especially if just the value decreases without anything it actually does in the end.

OK - I'm obviously special or simple enough regarding OSAS. I get on Weinmann / ResMed / Philips equally very low AHIs (under 1 and that beeing consistent) ... that is very good and there is not much difference between the therapeutic effect of the devices. I can however objectifiable say that the Weinmann is the device on which I am most productive / resilient. (That is the only thing I can 'objectifiable' measure - how "good" I feel is always biased and to be honest there is not much difference)
But I can NOT do that with the exact same settings - on the Weinmann I have APAP 8-14 (average pressure beeing just slightly over 8) .. on the ResMed that would be 8-10 (I actually do get problems with aerophagia at some point and pressures over 10 are only needed after more than just some beers or a night out ... I can manually adjust for that^^) - average pressure there going towards the 10 - depending on the allergy situation and the amount of nose breathing. Basically not much difference to CPAP pressure wise - besides the fact, that the pressure is unnecessary high.
... I don't want to go too much into detail but the same - although even more smaller in difference - holds through for the same CPAP-pressure on both devices. Intra-breath pressure changes seem to play some role for me ... although the ResMed feels more natural that does "less good" for me ... I can somehow tolerate EPR without problems - I can however not tolerate the exhale pressure relief from Weinmann ... Philips can be fine tuned enough that I am able to "endure" that ... but all in all: exhale pressure relief is not my thing.

I don't want to start a discussion about EPR and how it is implemented - the usual way for us is: turn it off if it is not absolutely necessary (meaning the first starting time or aerophagia) .. usually we recommend using EPR (if at all) together with the auto-ramp and only during the ramp.
Works well enough for the broad majority of OSA-Patients we see - and (and this is important for me) compared to the same results (meaning in measurable events) the resulting average pressure through the whole night is in most cases lower than compared to EPR (as the pressure there is raised during inhalation - although with high enough EPR the EPAP can be set slightly lower compared to without EPR).

Now EPR is really comfortable (even I have to admit that) - the ResMed devices in general produce a very natural and comfortable breathing "experience". They somehow manage to deliver the right pressure at the right time (in the breathing phase that means ... and with pressure I mean the actual pressure in the mask and maybe the airway and not the value measured at the outlet of the device).
But that gets in the way at some point: during the M-shaped flowlimitations. That is once again a problem with the data. ResMed obviously determines the breathing phase out of the raw-data - meaning: exhale starts for the machine if the total flow decreases (enough) - as the pressure in the mask rises during and through exhalation the flow needs to get lowered a bit resulting in a (theoretical) tiny pressure drop or the other way around: avoiding the pressure increase at the beginning of the exhalation.
This otherwise awesome preemptive mechanism obviously gets in the way during the more severe flowlimitations - further increasing them. Those are not scored as "Flattenings" (of course) but the respiratory rate doubles (or sometimes even tripples - although that should be capped at 50). Depending on the severity of those flowlimitations this can be mitigated (at first datawise) by turning EPR on and / or increasing that. (of course real Bi-Level would be the obvious choice as the breath timing can be set there - thus avoiding the problem in the 1st place) .. if EPR really resolves those flowlimitations still remains a mystery to me - simple vanishing in the data means nothing - in most cases the resulting flow picture still shown plenty of "recovery-like breaths" which is in most cases a good indicator for obstructive phases (at least those which are not movement artefacts)-
.. depending on the timing of the first spike in that flowlimitation raising the pressure alone helps more or less ... personally I consider the pressure-rise-speed and timing of that as a bit more important (but the other way around: too much too fast in that case seems to be contraproductive)
It is expected that at some point there will be simple flattenings too in those phases - the AutoSet picks those up and than finally raises the pressure - assuming that those didn't got rounded out (again: just datawise) with too much EPR.
(the 95% resp. rate is the first(!) thing I look at with data from an AutoSet ... after that I might take a brief look at the FL-Values - although in most cases the overall shape of the flowrate is much more revealing - meaning: looking for the amount of remaining and unresponded recovery breath phases)

@2SleepBetta I am unsure if I understood your part about the flowlimitations and tidal volume correctly?
I might be wrong but flowlimitations have nothing to do with tidal volume in the first place. Flowlimitations are the result of increased breathing effort - where the resulting air flow does not increase accordingly. If that would result in a drop in tidal volume that would be hypoxic or result in a desaturation (at least sooner or later).
Usually the breath-duty-cycle just increases accordingly. (to my belief one of the key parameters used by nearly all devices for the "FLs")
So flowlimitations are measured by the shape of the flow (just the inhalation in case of SRBD) - not the tidal volume.
Once again: talking about "plain OSAS" - flowlimitations themselves are NOT the issue - they are just the precursors of (maybe) upcoming obstructions (real obstructions like in hypoxic with real desaturations) ... and for now I have not seen any study or work that ever mentioned that one can have both OSAS and UARS at the same time - somehow UARS develops into the other and the current ICD-classification mixes them together - hard to grasp for me that they should be the same as with OSAS one wakes up (arouses) too late (after complete obstrutction) but with UARS one arouses too early (already at increased breathing effort). ... but on the other hand it was already proven that snoring damages the nerves in the tissue there - maybe we really should start treating just snoring in the first place?
So they are and stay good markers for the pressure regulation or avoidance of upcoming obstructions - but nothing more.

Once again with the comparison with Löwenstein: they do score central hypopneas (zH). They are a major .. well .. acutally pain in the ass to explain to newly diagnosed. Löwenstein started to ommit the zH in the total AHI-Score - which was a relief as people where complaining about their AHI-Scores compared to ResMed. (As ResMed does not score those they can not show up there - they are of course present as well)
This can be discussed an dissected from all angles ... in many cases they are just nothing - returning to normal breahting after (slightly) prolongued recovery breaths / phases gets (of course) scored as a zH as well.
Making the distinction between obstructive and non-obstructive hypopneas is however not trivial. Less flow - less to analyse .. if the flow is diminished enough detecting flowlimitations is like searching a needle in the haystack.

For ResMed a hypopnea is only scored if there is the reduction in the flow AND there is at least one obstructed breath. Makes total sense if you think about it - nothing you can do about zHs with an APAP.

With Löwenstein I have NEVER(!) seen someone (subjectively) satisfied with a high enough zH-Index (that would be someone who never checked their AHI from the device before and thus is not biased based on obscure values). They actually do point always towards some kind of problem. (although not always breathing related)
We ended up with a very simple rule, that works astonishingly well: treat zHs as oHs and act accordingly! (upping the pressure - especially the lower range that is) .. if they increase especially in the higher pressure zones they obviously are "real centrals" - but in the majority of cases they just vanish. This can only be the case if they were obstructive to begin with. (please note: we up the pressure - not turning on any exhale pressure relief, not switiching to Bi-Level (acutally I have a history of taking people off Bi-Level^^) - just pressure increase. ... and well: exhale pressure reliefs always turned off at first - of course^^)
Works very well - the flow (or more the rMV) smoothes .. the Prismas now have the funny "deepsleep-indicator" value (more marketing of course) - but that value determines the amount of phases with stable breathing - more there is always better^^ We actually do make a lot of fun about that value - but in the end as a single marker or value it is not bad or actually valuable. (the major problem is (as always) just that people take that literally! -.-)

Scoring those hypopneas on ResMed has to be done by hand (just look briefly for the spikes from the recovery breaths - check very briefly for the assumed ammount of movement artefacts and you are mostly done .. well .. there is negative effort dependence (NED) as a factor there - there is only so much one can do with just 1 data-channel from a therapy-device (and not diagnostic-device)) - the major problem there is the pressure tuning. If there are no flowlimitations around there is no pressure increase - of course CPAP is always a choice. In many cases switching the AutoSet-Response to soft helps enough - in some cases and if possible even "for her mode". (in germany only the white "for Her" modell has the for her therapy mode)


This thread started with the call for an somehow increased "FL"-Value ... at the beginning I just chimed in and asked what exactly it is that he was really interested in. (which remained inconclusive to me - besides FL-Values)
In my opinion there are much better values in the device data than just making the "FL"-Value look even bigger - but maybe someone did "increase" that value in the mean time and really got to reproduceable and useable results??
.. maybe just count the flowlimited breaths? (or the amount of data-entries (meaning the 0.5 Hz resolution) bigger than a certain cut-off value or different from 0 for starters) - that value is easy to obtain and should be big enough or at least different from 0. Maybe there acutally is value or even deeper meaning in that datapoint?

I looked (although briefly) at the other 2 threads from 2SleepBetta (R / Excel VBA) - honestly I do not understand what those are about - I mean I understand what you are saying there - I don't get what it is that you want to see or know ... they do not look that much different than the request from the OP. (Not again the re-representation of some obscure value - just in simple words what is you are AFTER - I am pretty sure there are much simpler ways to get there)
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