Baseline for Desaturations and Flow rates

[robysue1]

Using that process (a non-static baseline) the peak amplitude for each of the breaths changed in percent by a small amount, for example what I had previously calculated as 38.53 should be 38.42.

After doing all the recalculations what I had originally said still stands, only two of the breaths following the big breath only two crossed the 30% threshold, one at 38% and one at 33%.

You are still ignoring the basic fact that neither you nor I know the exact algorithm that Resmed uses for computing a baseline flow rate. We know it's a numerical algorithm. We know that peak heights---as measured by the machine---are part of that algorithm. We also know that human beings eyeballing a graph drawn by a computer program on a scale where it's easy to make mistakes when eyeballing the data are not going to get the same "numbers". I've drawn a horizontal line that is a reasonable guess as to what baseline flow might look like and when I look at the vertical scaling on the graph, I can conclude that the flow reduction might be right around the 50% that Resmed uses as the criteria to flag a hypopnea:



You try to eyeball the tips of each and every peak and come up with different numbers. We're both introducing human error into our calculations. But the fact is your machine did flag this event, and so the event must have satisfied the definition of hypopnea used by the Resmed engineers.

But here's the important point: Resmed's engineers had to make a cutoff for the program to use in order to score a hypopnea. It's not like a flow reduction of 45% is somehow magically "better" than a flow reduction of 50% or 55%. And when the actual data is really, really close to the cutoff, it can be hard, if not impossible, to just tell by "looking" at the flow graph that one event has a flow reduction of 50% (and gets flagged) and another has a flow reduction of 45% (and doesn't get flagged).

And here's a second important point: The event you keep arguing with me about is most likely a false positive event in the first place. It's not a false positive because the algorithm was inaccurately applied; it's a false positive because the event is a post-arousal event. Whatever the moving baseline was that caused this event to be flagged, it remains the fact that after you aroused and took that big, big breath, your breathing effort naturally declined significantly as you were transitioning back to sleep. The fact that the machine detected a flow limitation distortion in the shape of the small inhalations, however, forced the machine's rigid programming to flag the event: For whatever reason, the machine's calculation is that your flow did decrease by 50% and there was a flow limitation. Hence, the program says the thing must be flagged as an H.

And here's a third important point: In terms of measuring the efficacy of therapy, a few false positives is significantly less important than a whole slew of false negatives.

In other words, try commenting on Rubicon's post from page 2:

Check out all these obvious hypopneas that... aren't:

Are those "real" hypopneas that didn't get flagged (i.e. false negatives) or are they not hypopneas at all and the machine did its job correctly?

Can you tell me and Rubicon whether you think those are real and should have been flagged? And if so, can you then explain why they were not actually flagged by the machine? If you don't think they're real, can you explain why you think they're not real?

[Wondering1]

We know that peak heights---as measured by the machine---are part of that algorithm.

Do we know that? (that peak heights) is used in the hypopnea detection algorithm)

[Rubicon]

We know that peak heights---as measured by the machine---are part of that algorithm.

Do we know that? (that peak heights) is used in the hypopnea detection algorithm)

Your queue of things you need to respond to has overflowed and has clogged the thread.

[Wondering1]

.

Actually there's one basic question that has yet to be answered, all the rest is superfluous,

Is the instantaneous peak amplitude of an inhalation used to evaluate hypopnea condition OR
is the volume of an inhalation used to evaluate hypopnea condition.

Obviously the baseline (whether it cover 2 minutes or 5 breaths) would have to be consistant.

How is this significant? Recognizing that false-positives hypopnea events can and do occur
AND when one's AHI is predominately H events (88%),
close exanimation of H events are appropriate.

[Rubicon]

Actually there's one basic question that has yet to be answered

OK then, good luck on your search!

[robysue1]

Actually there's one basic question that has yet to be answered, all the rest is superfluous,

Is the instantaneous peak amplitude of an inhalation used to evaluate hypopnea condition OR
is the volume of an inhalation used to evaluate hypopnea condition.

Wondering1,

Way back on page 5 I gave you this assignment, which is specifically designed to help you answer your one basic question as stated above. You didn't do the assignment back then, and I reiterated that you needed to complete this assignment on page 8. So I'll once again assign it here:

Here's a homework assignment for you:

Read or skim throughThe role of flow limitation as an important diagnostic tool and clinical finding in mild sleep-disordered breathing,
which is a scientific paper about the subtleties and problems of diagnosing sleep disordered breathing.

Now answer these questions for me:

1) How many times is tidal volume mentioned in the entire article? What's the context of when tidal volume is mentioned?

2) Click on the link for Figure 4. What are the names of the three graphs in the figure? And what are the units for each graph in the figure?

3) In light of your answers to Question 2, what units do you think the authors of the paper use to measure what they call "flow" throughout the paper? Do the authors of the paper use the word "flow" in a way that is consistent with thinking of "flow" as a volume function or as a rate function?


And here's a Google assignment for you: Find me a scientific paper on sleep disordered breathing that makes the argument that tidal volume should be used as a criteria for scoring hypopneas on a PSG. Give me the full citation or a web link to the article.

The entire world of professionals working in sleep medicine has decided that decreases in the flow rate (i.e. the thing that is measured in L/min) are critical to the definition of hypopnea. Nobody in sleep medicine looks at the volume of inhalations to decide when a hypopnea has occurred.

[Rubicon]

Well IMO at this point he's just looking for some way to crawl out of here with some shred of dignity.

[robysue1]

Obviously the baseline (whether it cover 2 minutes or 5 breaths) would have to be consistant.

How is this significant? Recognizing that false-positives hypopnea events can and do occur
AND when one's AHI is predominately H events (88%),
close exanimation of H events are appropriate.

False positives---i.e. things that get "flagged" that should not be flagged can only be definitively teased out by having the missing EEG data. And this is just as true of things flagged as CAs and OAs as it is for things that are flagged as Hs. Here are a pair of CAs flagged last night by my AirCurve 10. Care to speculate on whether either of these events are likely to be false positives? I've included the tidal volume graph as well as the flow graph:





Here are some of OAs from a couple of different nights. Care to speculate on whether any of these events are likely to be false positives?







Here are a couple of Hs from my data. Care to speculate on whether any of these events are likely to be false positives?







Changes in tidal volume do not magically allow you to figure out whether a person was (or was not) asleep when a particular "event" happened. Certain characteristics in the very high resolution flow graph, however, can be associated with a high probability of an arousal. In the hypopnea you keep talking about from you own data, the big breath immediately before the hypopnea is the tell-tale sign that this is most likely a post-arousal event, and as a post-arousal event it would not be scored on an in-lab PSG.

[Wondering1]

Way back on page 5 I gave you this assignment, which is specifically designed to help you answer your one basic question as stated above. You didn't do the assignment back then,

So honestly, I looked at it and the abstract, but since it was dealing with flow limitations, it didn't seem to pertain.

Looking through some old OSCAR charts, I was able to find a snip that I believe illustrates the difference between what you are saying and what I am saying:



My position is that all three of these inhalations are equal. All provide approximately 530 ml to the lungs in approximately 1.3 sec.

You seem to take the position that the two inhalations on the left are somehow superior to the rightmost inhalation because the first fraction of the 530 ml is provided at a faster rate.

Your method of classifying the third inhalation would suggest that the "FLOW" to the lungs was slower during the phase of the inhalation, therefore the inhalation was inadequate.

Overall, I am trying to say that the lungs (and the rest of the body) doesn't care what the velocity of the air through the nose is at any millisecond, provided the lungs continue to be fed with (in this case) 530ml in 1.3 seconds.

[palerider]

Overall, I am trying to say that the lungs (and the rest of the body) doesn't care what the velocity of the air through the nose is at any millisecond, provided the lungs continue to be fed with (in this case) 530ml in 1.3 seconds.

And you're wrong about that too. All three of those breath's are utter dogshit. The patient is working harder to get the air in, and as a result will have more disturbed sleep.

Yes, there may be a full volume of air in the last breath, but it's more work.

Go get a drinking straw and breathe through it for 10 minutes.

Report back.

And just don't bother to post anything else until you've actually DONE some of the things that have been requested of you, or are you just trolling, like it seems you are? wasting good people's time.

[robysue1]

Way back on page 5 I gave you this assignment, which is specifically designed to help you answer your one basic question as stated above. You didn't do the assignment back then,

So honestly, I looked at it and the abstract, but since it was dealing with flow limitations, it didn't seem to pertain.

Flow limitation is the name of the game: It's what drives obstructive sleep apnea: Your airway gets partially obstructed which makes it harder for air to flow into the lungs. And the shape of the inhalations in the flow graph get distorted in a way that indicates the increased effort the body is making to suck air in through the partially blocked airway. The usual analogy is that a flow limitation is created when the airway is obstructed enough to create a situation where inhaling now requires the same kind of effort as sucking air in through a small straw. Hypopneas are when the airway has collapsed to the point where inhaling now requires the same kind of effort as sucking air through a very tiny straw and the air flow through that very tiny straw is significantly less than the normal airflow into the lungs.

Looking through some old OSCAR charts, I was able to find a snip that I believe illustrates the difference between what you are saying and what I am saying:



My position is that all three of these inhalations are equal. All provide approximately 530 ml to the lungs in approximately 1.3 sec.

I will agree that all three of those inhalations are equal---they are all equally bad. All three show significant signs of serious distortion from the normal shape of an inhalation. Hence they all indicate that the airway is in someway compromised and your body is making tremendous effort to inhale that air. In other words, what makes those three inhalations equally bad is that they all show that your body is having trouble getting air into the lungs in a smooth, relaxed, normal fashion. And either the airway will eventually collapse enough for a hypopnea or apnea to be flagged or you will arouse enough to open the airway and eliminate the flow restriction and start breathing normally again. Either way, your sleep architecture will be adversely affected.

You seem to take the position that the two inhalations on the left are somehow superior to the rightmost inhalation because the first fraction of the 530 ml is provided at a faster rate.

You are misrepresenting what I've said.

Resmed engineers have programmed their machines to look for decreases in flow from baseline combined with flow limitations to determine when to flag something as a hypopnea. That's not "my position" or "my opinion". It's a fact that is backed up by what Resmed actually says about how their machines detect hypopneas:




Now you are welcome to reject the entire sleep medicine community's decision to use a decrease in airflow that accompanies an increased effort to inhale as a criteria for scoring a hypopnea on a PSG. And you are welcome to reject Resmed's engineer's decisions to use a decrease in airflow accompanied by a flow limitation to flag hypopneas. But if you reject the professionals in an effort to promote your pet theory that tidal volume should be used instead, you're not going to persuade anybody that you know what you are talking about.

Overall, I am trying to say that the lungs (and the rest of the body) doesn't care what the velocity of the air through the nose is at any millisecond, provided the lungs continue to be fed with (in this case) 530ml in 1.3 seconds.

The body does care about the effort it has to make in order to get air into the lungs. The flow limitations indicate that more effort must be made in order to inhale the same amount of air. And when the airway collapses enough, the body can no longer get as much air into the lungs even though it is trying very, very hard to get air into the lungs---that's when the flow of air into the lungs decreases significantly and a hypopnea winds up being scored. If the airway collapses completely, the body is still trying desperately to get air into the lungs (that's recorded by the belts on a PSG), but the effort to inhale is futile because the airway has completely collapsed so no air can flow into the lungs even the body is trying desperately to inhale.

Hypopneas get scored by the xPAP when the characteristics in the flow curve indicate the body is trying very, very hard to inhale air, but all of that effort is only resulting in a reduced flow of air into the lungs.

[robysue1]

Overall, I am trying to say that the lungs (and the rest of the body) doesn't care what the velocity of the air through the nose is at any millisecond, provided the lungs continue to be fed with (in this case) 530ml in

It's also worth pointing out:

Flow is not a measure of the velocity of the air through the nose.

Flow is a measure of how much air is being moved in a particular direction with respect to time. A flow of 15 L/min means that if the flow were constant for one whole minute, 15 Liters of air would be moved in that one minute. Velocity would dictate how far that 15 Liters of air would move during one whole minute.

To go back to math-speak:

Flow is the derivative (or rate of change) of the volume of air in the lungs and flow is measured in units like L/min.

Velocity is the derivative (or rate of change) of the position of the air that is being moved and velocity is measured in units like cm/min.

They're not the same thing. And our machines track the flow of the air into and out of our lungs with each and every breath we take during the night.

[robysue1]

Overall, I am trying to say that the lungs (and the rest of the body) doesn't care what the velocity of the air through the nose is at any millisecond, provided the lungs continue to be fed with (in this case) 530ml in

And it's worth reiterating one more time:

What the body cares about is the effort it takes to inhale. In other words, what the body cares about is the effort needed to establish a flow of air into the lungs.

In normal sleep breathing, very little effort is needed to establish a flow of air into the lungs with each inhalation, and the shape of the flow throughout the whole inhalation is nice and smooth and rounded.

When the upper airway is compromised and starting to collapse, the effort to inhale increases, and that increased effort is due to the flow limitations created by the compromised airway. And those flow limitations show up as distortions in the shape of the inhalations in the flow graph; hence they can be quantified and measured.

When the airway has partially collapsed, the body continues to make a desperate effort to inhale, but the flow of air into the lungs is limited by the partial obstruction and the flow decreases substantially from baseline. And that's the criteria for scoring a hypopnea, which is presumed to be obstructive.

When the airway completely collapses, the body continues to make a desperate effort to inhale, but the flow of air into the lungs has essentially dropped to 0 L/min because no air can flow through the completely obstructed airway. And that's the criteria for scoring an obstructive apnea.

In all cases, the brain will eventually realize that the flow of air into the lungs is not sufficient, and at that point an arousal of some sort occurs and the body wake up enough to clear the obstructed airway so that normal breathing can resume.

[Wondering1]

Yes, there may be a full volume of air in the last breath, but it's more work.

How much “more work” ?
How did you measure this work?

BTW, the flow limitation graph is flat at 0.02 (and of course that graph has no measurement units - highly suggestive that it is not a measured quantity

[Wondering1]

in an effort to promote your pet theory that tidal volume should be used instead, you're not going to persuade anybody that you know what you are talking about.

Yet another area of dispute. "your pet theory that tidal volume should be used instead".

I have consistently said that TV should be considered; I've NEVER suggested that TV should be used instead.

Rather, I have suggested that TV data should be CONSIDERED when "we" the OSCAR users look at graphs.