pressure response on Airsense 11

dataq1 · Post by **dataq1** » Tue Oct 19, 2021 9:18 pm

I've been laboring under the impression that my apap responds to events by increasing pressure incrementally. Today was the first day that I was able to examine the hourly detail via Oscar on my Airsense 11.
What surprised me was that despite no events being observed (no LL, no OA, no UA, no H) the pressure appears to be changing:

Settings APAP 5-15, Ramp 35 minutes

It looks like after the ramp period, pressure was increased - but in response to what ?
The first "event" (an H) occurred at 23:13

What am I not understanding?

Pugsy · Post by **Pugsy** » Tue Oct 19, 2021 9:26 pm

Most likely responding to snores and flow limitations.
Since you didn't include the other graphs...a guess but an educated guess.

Need to see the big picture....it usually offers more answers.

viewtopic/t158560/How-to-post-images-for-review.html

dataq1 · Post by **dataq1** » Tue Oct 19, 2021 10:01 pm

There were no snores reported, so I did not include that graph. It does appear that the flow limits began to show some activity around the time that the pressure was increased:
So, I know from the cpap glossary that Flow limitations are an indication of collapse of the upper airway. How is that measured (or inferred) and given the levels shown here (generally 0.25 or so, how significant is that? (I guess what I'm asking is what are the units of flow limitation, for example is a 1.00 Flow limit actually a 100% collapsed upper airway?)

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Pugsy · Post by **Pugsy** » Tue Oct 19, 2021 10:18 pm

ResMed has never really explained in much detail the whole flow limitation thing.
So I can't answer your questions. Sorry.
About all I have is this video.
https://www.youtube.com/watch?v=-gie2dhqP2c

In general snores and Flow Limitations are considered early signs of an impending airway collapse and the ResMed algorithm is designed to try to prevent the collapses so it is fairly aggressive in response to flow limitations but ResMed never really gave us the particulars in the algorithm....probably hidden in the patent somewhere but I am not going to go digging through the patents.

Also....flow limitations can also occur because of nasal congestion and more pressure won't fix those no matter how high the ResMed wants to go.

Are you having much nasal congestion at all???

palerider · Post by **palerider** » Tue Oct 19, 2021 11:25 pm

dataq1 wrote: ↑
Tue Oct 19, 2021 10:01 pm
How is that measured (or inferred) and given the levels shown here (generally 0.25 or so, how significant is that? (I guess what I'm asking is what are the units of flow limitation, for example is a 1.00 Flow limit actually a 100% collapsed upper airway?)

If you look at Resmed's software, the FL chart goes from 'rounded' at the bottom to 'flattened' at the top.

The numbers are just because that's what the graphing engine in Oscar shows.

RogerSC · Post by **RogerSC** » Wed Oct 20, 2021 2:17 am

Going to venture a reply to the OP. To put it simply, the events shown in your sleep data on the machine are the ones that the CPAP has not prevented. Events that the CPAP prevents aren't shown, since they were prevented *smile*. So the pressure can vary without an event being shown, and is likely to have been varied by the CPAP to prevent an event.

dataq1 · Post by **dataq1** » Wed Oct 20, 2021 9:40 am

Interesting reading:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4688581/
(I have not read the whole of this article)
It appears that Inspirational Flow Limitation (which I suggest is what Resmed is referring to) is largely (mainly) defined by the shape of the inspiration flow curve.
How one goes about quantifying that on a scale of unknown units is puzzling.

What is even more interesting is the epidemology of flow limitation. My interpretation of the article is that some flow limitation is observed naturally and not necessarily a physiologic anomaly.

[quoteThese results suggest that only IFL values greater than 30% should be used to support the diagnosis of Sleep Disordered Breathing. Conversely, the IFL pattern cannot be used exclusively to determine abnormality, as roughly 5% of the normal population has IFL greater than 30% of the night.][/quote]

Interesting that Resmed should attack IFL aggressively.

palerider · Post by **palerider** » Wed Oct 20, 2021 12:14 pm

RogerSC wrote: ↑
Wed Oct 20, 2021 2:17 am
Going to venture a reply to the OP. To put it simply, the events shown in your sleep data on the machine are the ones that the CPAP has not prevented. Events that the CPAP prevents aren't shown, since they were prevented *smile*. So the pressure can vary without an event being shown, and is likely to have been varied by the CPAP to prevent an event.

While that's effectively true, it doesn't provide any information.

APAPs raise pressure in response to four things:

Snores
Flow Limitations
Hypopneas
Obstructive Apnea

and nothing else.

palerider · Post by **palerider** » Wed Oct 20, 2021 12:16 pm

dataq1 wrote: ↑
Wed Oct 20, 2021 9:40 am
Interesting that Resmed should attack IFL aggressively.

Why? Try breathing through a straw for a few minutes, see how you feel.

That's flow limited breathing.

Miss Emerita · Post by **Miss Emerita** » Wed Oct 20, 2021 1:21 pm

Just so you know: not all flow-limited inspiration is flagged in Oscar, I think because the ResMed data don't provide a basis. You can zoom in on your flow rate in Oscar (try 1 minute intervals) to see what your flow traces look like.

Some people aren't bothered by FLs at all; others are bothered a fair amount. For people who are bothered by them, the best way to treat FLs is to introduce pressure support. (EPR is pressure support. EPR is measured via subtraction from IPAP; on some other kinds of machines, PS is measured via addition to EPAP.) Basically the boost in pressure when you inhale can support smoother, less effortful inhalation.

But as Pugsy cautions, FLs that are caused by problems in the nose can't be fixed this way -- only problems due to sagging tissues in the pharynx.

dataq1 · Post by **dataq1** » Wed Oct 20, 2021 2:22 pm

Just so you know: not all flow-limited inspiration is flagged in Oscar,

No, I did not know that. I assumed that Resmed's firmware flags events, and OSCAR simply reports what Resmed writes to the datacard.

dataq1 · Post by **dataq1** » Wed Oct 20, 2021 2:33 pm

palerider wrote: ↑
Wed Oct 20, 2021 12:16 pm
Why? Try breathing through a straw for a few minutes, see how you feel.

That's flow limited breathing.

Not questioning your analogy, but wouldn't shallow breathing also be flow limited?

palerider · Post by **palerider** » Wed Oct 20, 2021 4:05 pm

dataq1 wrote: ↑
Wed Oct 20, 2021 2:33 pm

palerider wrote: ↑
Wed Oct 20, 2021 12:16 pm
Why? Try breathing through a straw for a few minutes, see how you feel.

That's flow limited breathing.
Not questioning your analogy, but wouldn't shallow breathing also be flow limited?

No, there's no correlation at all.

it's right there in the name. FLOW limitation, and in this context, "flow" means "flow rate" not "quantity".

You can still take a full breath (tidal volume) while being flow limited, it just takes more work, and time to get the same volume of air as you can with an open airway.

Did you try the exercise?

"shallow breathing" doesn't really have any defined meaning, as Miss Em says, your TV is normal, hypopneas are a reduction in TV over what the normal breathing TV for that person is. (and are not the same as flow limitations)

palerider · Post by **palerider** » Wed Oct 20, 2021 4:06 pm

dataq1 wrote: ↑
Wed Oct 20, 2021 2:22 pm

Just so you know: not all flow-limited inspiration is flagged in Oscar,
No, I did not know that. I assumed that Resmed's firmware flags events, and OSCAR simply reports what Resmed writes to the datacard.

Resmed flags events, Oscar reports them. Flow limitations aren't events, which is why there's a running average chart of the severity of flow limitation on breaths.

dataq1 · Post by **dataq1** » Wed Oct 20, 2021 7:35 pm

palerider wrote: ↑
Wed Oct 20, 2021 4:05 pm

it's right there in the name. FLOW limitation, and in this context, "flow" means "flow rate" not "quantity".

I am honestly trying to understand this. As a starting point can you answer a question I raised earlier, specifically, what are the units (Yaxis) of the the graph of Flow Limitation as reported by Resmed? (OSCAR's explanation of the Y axis of the Flow Limitations graph is "severity graded 0-1.0" )

Does Resmed provide this grading (and OSCAR reports) or are suggesting that OSCAR calculates running grades based on other parameters?

Since it appears that flow limitations is an important factor, is there an similar factor with Respironics (dreamstation) machines?

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