Help to validate my understanding of the basics of CPAP

[Albatros]

I would like help in understanding the basics of CPAP

What I think I understand:
With a Resmed Airsense11 machine, the machine sends air into my airways according to a pressure that will evolve between Min and Max pressure in order to prevent or correct a closure (OA or H).

The Flow Limitations announce an OA/H. Even if the OA/H can happen with FL =0
In general when FL increases, the pressure increases to stop the aggravation of the limitation.

There is an inhalation pressure Ipap and an exhalation pressure Epap. By adjusting EPR I decrease the pressure during expiration Epap. This is for comfort.
If Epr = 1 Epap = Ipap -1

When I am not to sure:
The important thing is the Ipap pressure because it opens the airways.
Epap pressure has no role vs OA/H ?

When I start not to understand :
if we do +1 on EPR, we should do +1 on min pressure to keep Epap constant? Why ?

What I don't understand at all, what I read in the "Apnea Therapy optimization":

"It is the exhale pressure that needs to be elevated to prevent Obstructive Apnea (OA), and it is the pressure differential between inhale and exhale that helps relieve hypopnea."

"A good rule of thumb is to keep your minimum pressure setting about 2-cm below your 90% pressure or near the average if they are close. The goal is to raise support (Min Pressure / IPAP) to reduce/minimize/if we are lucky, eliminate Obstructive events. These include Hyponeas, Flow Limits, and Snores. The Max Pressure / EPAP is lowered to minimize other issues (Aerophagia , swallow too much air, too much pressure causes wakeups) if needed. Typically it is set at either MAX pressure (20 cmH2O) or just above the max pressure to prevent wild running high.

Thank you

[robysue1]

I would like help in understanding the basics of CPAP

What I think I understand:
With a Resmed Airsense11 machine, the machine sends air into my airways according to a pressure that will evolve between Min and Max pressure in order to prevent or correct a closure (OA or H).

Not quite correct. Your Airsense 11 machine is not going to "correct a closure" by increasing pressure if "correct a closure" means "force the airway open." APAPs do not generate enough pressure to force a collapsed airway to open up. Rather, when an OA happens, the machine waits for you (the person) to arouse enough to open that airway up and then the machine increases the pressure to prevent future collapses.

The Flow Limitations announce an OA/H. Even if the OA/H can happen with FL =0
In general when FL increases, the pressure increases to stop the aggravation of the limitation.

Flow limitations do not "announce" an OA/H. Flow limitations indicate the airway may be in increased danger of collapsing. And so the machine increases pressure in the presence of flow limitations to prevent future collapses. This has the effect of smoothing out the flow limitations and making the inhalation part of the flow rate graph look more normal.

There is an inhalation pressure Ipap and an exhalation pressure Epap. By adjusting EPR I decrease the pressure during expiration Epap. This is for comfort.
If Epr = 1 Epap = Ipap -1

Strictly speaking, an AirSense 11 does not have IPAP and EPAP. It has a Pressure and EPR. Now there is a rough analogy between the two systems:

IPAP on an AirCurve 10 VAuto = Pressure on an AirSense 11 APAP = the pressure delivered when you are inhaling.

EPAP on a AirCurve 10 VAuto = Pressure - EPR on an AirSense 11 APAP = the pressure delivered when you are exhaling.

Min EPAP + PS on a AirCurve 10 VAuto = Min Pressure on an AirSense 11 APAP = minimum pressure delivered when you are inhaling.

Max IPAP on a AirCurve 10 VAuto = Max Pressure on an AirSense 11 APAP = maximum pressure delivered when you are inhaling.

When I am not to sure:
The important thing is the Ipap pressure because it opens the airways.
Epap pressure has no role vs OA/H ?

Wrong, wrong, wrong.

IPAP does not "open the airways". And EPAP has an extremely important role in preventing OAs (and Hs).

In general: EPAP needs to be high enough to prevent the upper airway from collapsing when you are exhaling. And the problem with OSA is, in fact, airway collapse during exhalation: Once the airway has collapsed during exhalation, you can't inhale until the brain wakes up enough to realize what's going on and sends the appropriate signals through the nervous system to the muscles controlling the upper airway to get that airway to open back up.

IPAP is used to help smooth out flow limitations and on PR BiPAPs, IPAP will increase without increasing EPAP for flow limitations and Hs if I recall correctly.

When I start not to understand :
if we do +1 on EPR, we should do +1 on min pressure to keep Epap constant? Why ?

On an AirSense 11 for a particular EPR we have:

• minimum pressure on exhalation = Min Pressure on AirSense 11 APAP - EPR = Min EPAP on a Air Curve VAuto

When you increase EPR by +1, that drops Min Pressure - EPR by 1 unit. So if you need a minimum exhale pressure of 7cm and you want EPR = 2, then you need to set Min Pressure on AirSense 11 APAP = 9 since

• minimum pressure on exhalation = 7 = Min Pressure on AirSense 11 APAP - 2

which implies that Min Pressure needs to be 7 + 2 = 9.

If we want the minimum pressure on exhalation to be 7 and we want to increase EPR from 2 to 3, then we need to set Min Pressure = 10 since 7 = Min Pressure - 3, which implies 7+3 = 10 = Min Pressure.

What I don't understand at all, what I read in the "Apnea Therapy optimization":

"It is the exhale pressure that needs to be elevated to prevent Obstructive Apnea (OA), and it is the pressure differential between inhale and exhale that helps relieve hypopnea."

"A good rule of thumb is to keep your minimum pressure setting about 2-cm below your 90% pressure or near the average [Note: This should read median] if they are close. The goal is to raise support (Min Pressure / IPAP) [Note: This should read Min EPAP] to reduce/minimize/if we are lucky, eliminate Obstructive events. These include Hyponeas, Flow Limits, and Snores. The Max Pressure / EPAP Note: This should read Max IPAP] is lowered to minimize other issues (Aerophagia , swallow too much air, too much pressure causes wakeups) if needed. Typically it is set at either MAX pressure (20 cmH2O) or just above the max pressure to prevent wild running high.

The upshot of this is all about using an APAP to find a good pressure range that will control your OSA while also allowing you to sleep well with the machine.

So the idea is to find a Min Pressure that is close to what is needed to eliminate most of your events. If you don't have an artificially low Max Pressure, the 90% (or 95%) pressure level will almost always be high enough to control most of the obstructive events. If the median pressure is not too far away from the 90% pressure, then the median pressure is probably enough to control most of the obstructive events.

The next step is to set the Max Pressure high enough where the machine can increase the pressure as needed to respond to the events that do get through at lower pressures while also being low enough so that you don't have problems like aerophagia or leaks triggered by rapid, steep pressure increases, or wakes triggered by rapid pressure increases. Some people never face any of these problems, and they can simply leave Max Pressure = 20 and the machine doesn't increase the pressure past a reasonable amount; other people find leaving Max Pressure = 20 allows the machine to increase the pressure unnecessarily in response to certain kinds of flow limitations without that pressure increase actually improving the quality of the sleep itself.

Now there's a final thing to keep in mind: When you are looking at the data in Oscar, there are two Pressure curves for the AirSense 11. The top curve is the Pressure curve (akin to the IPAP pressure curve on an AirCurve 10 VAuto) and the bottom curve is Pressure - EPR (akin to EPAP pressure on an AirCurve 10 VAuto). So you have to take that into account if you start changing the EPR setting.

For example: If you start off with EPR = 2 and your 95% pressure level is reported as 9.5, that means your inhalation pressure was AT or BELOW 9.5 cm for 95% of the night. It also means that your exhalation pressure was AT or BELOW 9.5-2 = 7.5 cm for 95% of the night. And it's reasonable to set Min Pressure = 8.5, which is 1cm below that 95% pressure level. That means the minimum pressure on exhalation can go as low as 8.5-2 = 6.5 cm. And now let's assume that when you set Min Pressure = 8.5, your AHI is nice and low. In other words, when your minimum exhalation pressure is 6.5, the machine is doing a good job of controlling your apnea.

Now you want to experiment with EPR. If you want to increase EPR to 3 and still have a minimum exhalation pressure of 6.5cm, then you will need to increase Pressure to 9.5 since 9.5-3 = 6.5. You will most likely see an increase in median pressure and 95% pressure, but because the minimum pressure is still at a level that controls your EPR, there should not be any noticeable increase in AHI over days and weeks. (Any individual night can be an outlier.)

If you increase EPR to 3 and you leave Min Pressure at 8.5, then your minimum exhalation pressure is reduced to 8.5-3 = 5.5 cm. And 5.5 cm might not be enough pressure to adequately control your apnea. If 5.5 cm is too low to prevent airway from repeatedly collapsing, you'll see an increase in AHI and you'll see clustering of OAs and Hs occurring whenever that lower pressure graph (the one that is Pressure - EPR) drops too low.

Does this help you make more sense out of the information you find confusing?

[Albatros]

Thank you Robysue for this deep and clear clarification.

Things are more subtle than I thought!
I guess your clarification will be useful for many members of the forum.

I still have a last question
If I don't have any problems/inconveniences with expiration, why play with the EPR?
What are its effects on the OSCAR data?

[Julie]

DON'T 'play' with EPR if you don't need it (to help with expiration). You're needlessly complicating things.

[JOinPA]

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[ChicagoGranny]

Summary numbers are not very useful for the level of detailed understanding that you are seeking. Post the OSCAR Daily Details for a typical night or two. Instructions in my signature.

[JOinPA]

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[JOinPA]

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[Dog Slobber]

I hope the OP does not mind if I piggyback on this thread.

You have just turned the OP's topic into a topic about your therapy.

Why would you do that?

Create you own topic.

[ChicagoGranny]

Create your own topic.

Ditto. My oversight for not immediately telling him that.

[Pugsy]

Here is a typical night at 10-14, EPR =2, if that is helpful. I think I'm OK on either setting, just wanting reassurance that moving from 10-14 to 9-14 won't be a bad idea.

So what are your goals?

You already say you are sleeping great and feeling great.....so what are your goals with zeroing in on such a teeny tiny difference in minimum pressure?

Here's the deal...we don't sleep the same each night and it's not impossible that maybe one night you would do a tiny bit better (somewhere) with minimum of 9 and the next night you might do a tiny bit better with minimum of 10.
Do you know for sure which night you are going to need one over the other?

As for the hijacking.......Shrugging here....Technically yes a hijacking but the explanations are sort of on topic and it's not like this is the first thread hijacking and I am pretty sure it won't be the last.

[robysue1]

Thank you Robysue for this deep and clear clarification.

Things are more subtle than I thought!
I guess your clarification will be useful for many members of the forum.

You're welcome!

I still have a last question
If I don't have any problems/inconveniences with expiration, why play with the EPR?
What are its effects on the OSCAR data?

I'm a big believer in if it ain't broke, don't fix it. Of course, I have that attitude because it took me so long (6-12 months!) of PAP therapy before I'd found a working compromise that didn't trigger severe aerophagia, didn't trigger severe insomnia, and did allow me to sleep reasonably well (most nights) with the dang mask on my nose. And it was only after a very long and very difficult adjustment period of 6 months that I started to feel about as good as I did before PAP and it took another 6 months before I was genuinely feeling better on most mornings.

That said, there are some people who are natural "fiddlers" who want to experiment just to see what happens. And when your sleep is pretty good to start with and you know you don't have problems with non-OSA related sleep problems (like insomnia) that could get worse if an experiment "breaks something" about your PAP therapy, it's fine to indulge that desire to experiment.

EPR is primarily a comfort setting. For some of us, the pressure relief on exhalation is critically important in making it possible for us to use the machine every night, all night long. For others? It's not important at all. And for a few people, using EPR actually increases discomfort because they don't like the constantly shifting pressure with each and every inhalation and exhalation. If you don't have any problems with expiration, there's not compelling reason to play with EPR. But on the other hand, if you're curious about it, there's also not a compelling reason to not experiment if you really want to run the experiment.

The answer to the question, "What are its effects on the OSCAR data?" depends on the person.

The most obvious "effect" on the Oscar data when using a Resmed machine is that you will have two pressure curves. The top curve is the set Pressure setting and the bottom one is Pressure - EPR.

If Min Pressure - EPR is too low to keep your airway from repeatedly collapsing, then you will probably see an increase in events: The number of OAs and Hs (and RERAs if they're scored) will likely go up AND you might see clusters of them when the pressure is near the min pressure setting. You might also see an increase in snoring and flow limitations. All of this will likely be reflected by your not feeling as good when you wake up in the morning.

If Min Pressure - EPR is high enough to keep your airway from repeatedly collapsing, the you probably won't see much change in the Oscar data outside of the second pressure graph. You might see a small difference in the activity in the flow limitation graph, but it might be an improvement rather than a deterioration. (Some people's flow limitations seem to be minimized with more pressure support, which is the additional pressure added on inhalation; other people's flow limitations seem to be more tied to making sure the exhalation pressure is sufficient.)

[Albatros]

An other thank you, Robysue!