What's that red curve in the Pressure graph? (Geek/nerd question)

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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by palerider » Thu Sep 22, 2022 8:23 pm

lynninnj wrote:
Thu Sep 22, 2022 8:11 pm
I wish there was a delete option on the posts. I realized I made the error right after posting.
There is, hit the X.

You can only do that while it's the last post in the thread.

You can also go back and edit your post at any time, by hitting the pencil icon.

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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by ozij » Thu Sep 22, 2022 8:48 pm

lynninnj wrote:
Thu Sep 22, 2022 8:11 pm

Thank you.

I wish there was a delete option on the posts. I realized I made the error right after posting.
There is. Look at the upper right corner of your own post after you've posted: there's a pencil for edit, and an X for delete.

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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by ozij » Thu Sep 22, 2022 9:01 pm

palerider wrote:
Thu Sep 22, 2022 8:23 pm
lynninnj wrote:
Thu Sep 22, 2022 8:11 pm
I wish there was a delete option on the posts. I realized I made the error right after posting.
You can also go back and edit your post at any time, by hitting the pencil icon.
... and when you do that, the post informs everyone that you've edited it, and you yourself can add text to explain what the edit was all about.

Here's an example of me editing a post when I realized, thanks to Janknitz, it was not clear, and Janknitz editing hers in response to my edit
viewtopic.php?f=1&t=185015&p=1420132&hi ... t#p1420132

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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by robysue1 » Fri Sep 23, 2022 9:47 am

Rubicon wrote:
Thu Sep 22, 2022 3:20 pm
I think it might be

Average IPAP Over a 2-Minute Window

https://www.documents.philips.com/asset ... 013046.pdf
Here's today's detailed data:
Image
Note that just like on the previous data the mysterious red curve is strictly between the purple IPAP curve and the green EPAP curve.

So I don't think that red curve can be the average IPAP over a 2 minute window because the red curve is always well below the minimum parts of the IPAP curve itself. And the average anything can't be below the minimum anything. Averages just don't work that way.

But I'm beginning to suspect that the red curve is the average overall mask pressure over a 2 minute window or some similar window. In other words, I think this curve is averaging my EPAP values (accumulated over my exhales) combined with my IPAP values (accumulated over my inhales) combined with the transition times between IPAP and EPAP for some fixed time interval.

Now I know that red curve has nothing to do with Bi-Flex since since I don't have BiFlex turned on. So the pressure is suppose to simply drop to EPAP as soon as I start exhaling and it's not supposed to start increasing the pressure to IPAP until the machine detects the beginning of an inhalation. I do have RiseTime set to 3, which means that the transition from EPAP to IPAP is as slow as the machine is willing to do it. (I'm not looking up the specs right now. Once upon a time I knew them by heart.)

For what it's worth, I compared my PR Dreamstaion Auto BiPAP data to my husband's PR System One Series 60 APAP machine. Here's his detailed data from last night:
Image
Note: Hubby has A-Flex set to 3. And his pressure data includes only two curves: A purple curve, which is his therapeutic pressure setting and a green curve, which shows the affect of A-Flex, albeit not with anywhere near the detail that a Resmed "Mask Pressure" curve would show the affect of EPR.

So whatever OSCAR is doing to create that red curve from my Auto BiPAP data, it's not doing the same thing with my husband's APAP data.

Some final observations that have nothing to do with my red curve, but are relevant for folks interested in EPR vs. A-Flex/C-Flex, which used to be a very hot topic around here:

PR's A-Flex setting is PR's "exhalation relief" for their APAP machines. It's (vaguely) similar to Resmed's EPR in that it reduces pressure on exhalation, but it's quite a bit different from EPR in how much it reduces the pressure and how & when it starts to increase the pressure back up.

One of the big differences between EPR and A-Flex/C-Flex is this: EPR reduces the pressure by exactly the same amount on every exhalation. But A-Flex/C-Flex reduce the pressure by a variable amount. That shows up in my husband's green curve: It's more raggedy than the red curve and the green curve is not always the same vertical distance below the red curve, albeit it doesn't vary all that much.

Another difference between EPR and A-Flex/C-Flex is that EPR reduces the pressure by a specified amount: EPR = 3 means the pressure goes down by 3 cm on each and every exhalation.
That's not what happens with A-Flex set to 3, at least not for my husband. Here's a zoomed in shot with a better y-range for showing the difference between the therapeutic setting (top curve) and what's going on with A-Flex:
Image
First note that for the most part, hubby is getting about a 2 cm reduction in pressure when he exhales, not a 3 cm reduction. Second, note that there are places where the reduction is visibly a bit less than average and a bit more than average because even in the zoomed in shot, the two curves are not equidistant.
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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by Rubicon » Fri Sep 23, 2022 10:01 am

robysue1 wrote:
Fri Sep 23, 2022 9:47 am

So I don't think that red curve can be the average IPAP over a 2 minute window because the red curve is always well below the minimum parts of the IPAP curve itself. And the average anything can't be below the minimum anything. Averages just don't work that way.
The minimum parts of the IPAP curve itself, are, by definition, EPAP. I believe your description only relates to IPAPpeak.
But I'm beginning to suspect that the red curve is the average overall mask pressure over a 2 minute window or some similar window. In other words, I think this curve is averaging my EPAP values (accumulated over my exhales) combined with my IPAP values (accumulated over my inhales) combined with the transition times between IPAP and EPAP for some fixed time interval.
Correct. IOWs, a breath waveform. If we could have been able to generate a Mask Pressure waveform I think this would have been more apparent.
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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by Pugsy » Fri Sep 23, 2022 10:03 am

I wonder if the mysterious red line has anything to do with rise time being on???? Just musing out loud here.

While I have some old System One BiPap Auto reports...not on this new laptop as I never bothered bringing them over.
If I have time later today I will see if I can fire up that old laptop and check out what my pressure graphs looked like with BiFlex on since I used BiFlex. I may or may not have some success since the old laptop got replaced because it didn't want to power on reliably... :lol: :lol:
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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by Rubicon » Fri Sep 23, 2022 10:04 am

From the manual:

Image
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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by Rubicon » Fri Sep 23, 2022 10:10 am

Pugsy wrote:
Fri Sep 23, 2022 10:03 am
I wonder if the mysterious red line has anything to do with rise time being on???? Just musing out loud here.
Wanna see something really weird take a look at debbiek's waveform with 3 of Flex.
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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by Rubicon » Fri Sep 23, 2022 10:12 am

Image
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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by Pugsy » Fri Sep 23, 2022 10:18 am

Rubicon wrote:
Fri Sep 23, 2022 10:10 am
Pugsy wrote:
Fri Sep 23, 2022 10:03 am
I wonder if the mysterious red line has anything to do with rise time being on???? Just musing out loud here.
Wanna see something really weird take a look at debbiek's waveform with 3 of Flex.
:shock: Totally weird and it would bother me for sure. I am wondering where/how in the hell they came up with those settings.

Is she sleeping and feeling great??? That's always one of my prime criteria to take into account.

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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by robysue1 » Fri Sep 23, 2022 10:36 am

Rubicon,

You've given me a lot to read and a lot to think about. Thanks! This looks like a real opportunity for me to learn a whole lot more about what's actually happening when my BiPAP is doing its work changing the pressures with my inhalations and exhalations. I'm looking forward to spending some time digging through what you've posted this evening.

Totally off-topic (or maybe not): In order to figure out the time drift on my husband's PR System One Series 60 machine to enter it into OSCAR so his sessions line up with reality, I did a short 6 minute session on his APAP machine this morning. His pressure range is 7-10cm and he has A-Flex = 3. I was once again reminded of just how awful the sensory stuff was when I was first starting out:
  • I felt like that 7cm was a hurricane. (My own bipap starts at 7/4 and it does not feel like a hurricane when I start it up.)
  • On every exhalation I could feel the beginning of the pressure increase along with that old "stuffed goose" feeling of being forced to inhale before my exhalation was done. (This does NOT happen on my BiPAP unless I have Bi-Flex turned on, which is why I keep Bi-Flex turned off.)
  • Even though I only had his mask on for 6 minutes, I could tell the beginnings of the aerophagia monster starting in my stomach. (I no longer fight the aerophagia monster on a nightly basis when using my BiPAP, and in fact, I can go weeks between "attacks by the aerophagia monster.")
  • That pressure increase was tickling the back of my throat on every breath. (This also does not happen on my BiPAP.)
Overall, I guess it was a nice reminder that switching from APAP to BiPAP back in January 2011 was in fact the right thing for me to do.
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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by robysue1 » Fri Sep 23, 2022 4:54 pm

Rubicon,

The mathematician in me is still very confused about how a moving average IPAP value over 2 minute windows can possibly be less than the minimum IPAP value for the whole night.

You included this figure
Rubicon wrote:
Fri Sep 23, 2022 10:04 am
From the manual:

Image
So just out of curiosity, what manual is that figure from?

And just to make sure I understand the information in that figure:
  • The red line at the top is the Max IPAP setting. (My Max IPAP = 9cm, so for my data that Max IPAP line would be drawn at 9cm, wouldn't it?)
  • The blue shaded area is the made up of a whole bunch of blue rectangles all of which have the same width (like a Riemann Sum in calculus) where the width of the rectangle is Delta-t, and Delta-t is the time interval for the box. And the actual value for the IPAP at each time value for a given rectangle is somewhere between the bottom of the box and the top of the box. So the top of a blue shaded box is the maximum IPAP that was used during that particular time interval? Is the bottom of the blue box the minimum IPAP that was used during that particular time interval? And is Delta-t equal to 2 minutes for each of the rectangular boxes?
  • The thick red squiggly curve in the middle of the blue boxes is the moving average IPAP calculated over a 2 minute window.
  • The thick blue line at the bottom of the boxes and below the boxes is the moving average EPAP calculated over a 2 minute window.
  • The data for the range of EPAP values in each time interval is not presented. (If it were, we would possibly have overlapping shaded rectangles, one for the IPAP range for each time interval and one for the EPAP range for each time interval.)
  • Although Minimum EPAP is listed on the right, there does not seem to be a corresponding line drawn for the min EPAP value. If there were, it would be a horizontal line that is at or below the "Average EPAP over a 2 minute window" curve?
  • Why is there no average EPAP curve shown to the left of t=5? And why is the red Average IPAP curve broken to the left of t=5? Is that because we're not seeing the bottom of the IPAP boxes and we don't see the EPAP boxes at all?
Now to put this in terms of my PR Auto BiPAP, the detailed data shown in OSCAR and what my machine is actually doing when I'm breathing with the mask on my nose and the machine turned on.

Here are the settings on my PR DreamStation Auto BiPAP:
  • Max IPAP = 9cm
  • Min EPAP = 4 cm
  • Min PS = 3 cm
  • Max PS = 5 cm
  • Bi-Flex = Off
  • Rise Time = 3
Given these settings, I would expect that when my EPAP is at 4cm, the IPAP would have to be somewhere between 7 and 9 cm. In other words, as long as my EPAP=4, my IPAP should satisfy 7 <= IPAP <= 9. And when I turn my machine on, it's LCD reports the pressure as 4cm when I'm exhaling and 7cm when I'm inhaling.

So that should mean that bottom edge of all the blue boxes for the IPAP range for each time interval should be at least 7. (If not, why not? What am I missing?)

And the top edges for all the blue boxes for the IPAP for each time interval should be no more than 9. (If not, why not? What am I missing?)

Is my Purple IPAP curve drawn (roughly) where the top of each of the blue boxes is drawn?

And are you saying that my IPAP is not actually equal to 7cm and my EPAP is not actually equal to 4cm even though the machine's LCD says the IPAP is "7cm" when I am inhaling and EPAP "4cm" when I'm exhaling at the very beginning of the night?

And now the mathematician in me has to skate out onto even thinner ice:

Are you saying that the blue boxes in my data would include as IPAP pressures the sub-IPAP setting pressures that the machine goes through during that RiseTime transition from EPAP to IPAP?

If I recall correctly, RiseTime = 3 means that my BiPAP takes 300ms to increase the pressure from EPAP to IPAP once the start of the inhalation is detected. So for every inhalation I take, there are 300ms where the pressure is between the current EPAP setting and the current IPAP setting. So there are 300ms where the "IPAP" pressure is technically below the set IPAP pressure. Again, at the beginning of the night, this would mean that for every inhalation, there are 300ms where my "IPAP" pressure is technically below 7cm. But that 300ms is over and done with before or while my machine is updating pressure shown on the LCD.

Now I'm in full blown mathematician mode here, but I want to get this written down before I lose it: My inspirations (according to OSCAR) have a median time of about 2 to 2.5 seconds and a 95% of about 3-3.5 seconds. Since 300ms = 300/1000=.3 seconds, as a very rough estimate, there's at least 1/10 of the time where my IPAP would be below the IPAP setting. That would bring the moving average IPAP over a 2 minute window down below the IPAP setting. But would it be enough to bring it closer to the EPAP setting than the IPAP setting?

Or is that moving IPAP average actually a moving pressure at mask average that also includes the pressure when you're exhaling? (In that case, why would it not be referred as "moving average pressure' instead of "moving average IPAP"?

So what does it seem like I understand? And what am I still missing?
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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by Rubicon » Sat Sep 24, 2022 3:45 am

robysue1 wrote:
Fri Sep 23, 2022 4:54 pm
So just out of curiosity, what manual is that figure from?
As noted in my post above, an Encore manual:
Rubicon wrote:
Thu Sep 22, 2022 3:20 pm
I think it might be

Average IPAP Over a 2-Minute Window

https://www.documents.philips.com/asset ... 013046.pdf
BTW, do you have a voice-to-text translator?
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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by Rubicon » Sat Sep 24, 2022 3:58 am

So

We (or at least I) have NFI how Respironics does that calculation;

The assumption is that Oscar is correctly plotting that value (they probably are);

I wish my memory was better so I could remember what I was going to say next;

The 2 minute average value appears to be written after the fact, preceding the actual monitored pressures, and by a time that looks to be slightly > 2 minutes; and

I think what they are actually reporting is Mean Airway Pressure.

If we (I) use the formula

Mean Pairway = (IPAP – EPAP)(Tinsp/Ttime) + EPAP

your values look to be right on target. Although IDK what Flex converts to in actual pressure I think it explains debbiek's (her husband's) waveform as well (where EPAP changes make an exponentially greater difference than IPAP changes).
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Re: What's that red curve in the Pressure graph? (Geek/nerd question)

Post by Rubicon » Sat Sep 24, 2022 4:42 am

robysue1 wrote:
Fri Sep 23, 2022 4:54 pm
If I recall correctly, RiseTime = 3 means that my BiPAP takes 300ms to increase the pressure from EPAP to IPAP once the start of the inhalation is detected. So for every inhalation I take, there are 300ms where the pressure is between the current EPAP setting and the current IPAP setting. So there are 300ms where the "IPAP" pressure is technically below the set IPAP pressure. Again, at the beginning of the night, this would mean that for every inhalation, there are 300ms where my "IPAP" pressure is technically below 7cm. But that 300ms is over and done with before or while my machine is updating pressure shown on the LCD.

Now I'm in full blown mathematician mode here, but I want to get this written down before I lose it: My inspirations (according to OSCAR) have a median time of about 2 to 2.5 seconds and a 95% of about 3-3.5 seconds. Since 300ms = 300/1000=.3 seconds, as a very rough estimate, there's at least 1/10 of the time where my IPAP would be below the IPAP setting. That would bring the moving average IPAP over a 2 minute window down below the IPAP setting. But would it be enough to bring it closer to the EPAP setting than the IPAP setting?
Depends if you're looking from the machine's POV:

Image

Or the patient's:

Image

but I don't think anybody uses purely square-wave technology, and you also have to factor in lung compliance and inspiratory effort.

Looking at that sample of Mask Pressure, I think it becomes more apparent that the patient actually spends very little time at IPAPpeak.
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