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CPAP function question - basic stuff...
#1
CPAP function question - basic stuff...
I just realized I don't understand the basics I guess, considering this question...
But I hope someone can enlighten me!

Central apnea is when the brain fails to "tell" us to breathe. We don't even "try" to breathe.
In the Oscar chart, as far as I understand, there is really no difference in the Flow Rate Chart between OA and CA. Both events will show as a flat line till breathing starts again. 
Is this correct?

Here comes the question:
How does the CPAP reduce the events?
In the case of OA, I assume it "blows away" the blockage. Just pure force, air pressure, moving the stuff that blocks breathing, and then once the blockage is "blown away", we can breath again. Also, the machine won't really help with blood oxygen levels as long as there is a blockage. No air can get through till the blockage is solved.
But if this is the case, then a CPAP wouldn't really reduce events, it would just shorten their duration. Apparently, a CPAP does reduce OA events - but how? Does the continuous air pressure simply prevent the tissues from collapsing by physical intervention, simply keeping tissues in place by the force created by the air pressure? And if so, how would a CPAP without APAP function be able to solve a CA? If the pressure level was not enough to keep the tissue from collapsing, how can the same pressure then be enough to clear the blockage, i.e. move the tissue back in place again?

But then the part I definitely don't understand, CA.
How does the machine reduce the number of CA events? There is no blockage to move with higher air pressure. There is no tissue to keep in place and preventing from collapsing.
I can understand though that the effect of CA is reduced greatly by a CPAP, since even though we are not breathing, the machine will help us fill our lunges with air, and hence we get the oxygen we need even though we are not actually breathing.
But in that case, why is even CA an issue with a CPAP? If we have a 20 second CA event while using a CPAP - why is that even a problem? Don't we get the oxygen anyway?
How does a CPAP "fix" a CA and make us start breathing again? There is no blockage to clear with the air pressure, no tissue to move.
And, as asked already, how does a CPAP help to reduce CA events? I have read that high pressure can even increase CA, so why would lower pressure reduce CA compared to not using a CPAP at all?

Also - if my guesses above are correct, does that mean that OA have a much more negative effect on us than CA while using a CPAP? Since during periods of CA we get our oxygen anyway? I assume the air moved down our lunges by the CPAP is even at moderate levels much more than what we could do by ourselves?

And the Hypopneas, what about them? That's partial blockage, is it? If so, why is that a problem when we use a CPAP? If the blockage is only partial, the pressure from the CPAP will be enough to give us the oxygen we need until our breathing starts again, or?

Final question: The Flow Rate Chart, what does it actually show? Only our own breathing, or the combined effect of our own breathing and the CPAP air? I assume our own breathing only since it flatlines at times. Does the Tidal Volume chart in that case show the combined effect, i.e. the total amount of air coming down our lunges, irrespectively of the source (ourselves or the CPAP)?

Please help me out here, I just realized I don't know half as much as thought I did...
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#2
RE: CPAP function question - basic stuff...
OK, there are some very interesting questions in there, and quite a few misapprehensions.

Let's start with a basic CPAP - continuous positive airway pressure. With this machine you have a single fixed pressure which stays the same all night. The pressure is determined by a titration study (or trial-and-error) and should be sufficient to prevent collapse of the tissues around the airway. If you do get an apnea or hypopnea, the machine doesn't do anything different - it just keeps the same constant pressure.

Next is the APAP - Auto-titrating positive airway pressure. This is more sophisticated, and reacts to obstructive events including hypopnea, snore or flow limitation. Whenever any of these occur the machine will increase the pressure to prevent an apnea from occurring. If an obstructive apnea does occur, the machine cannot produce enough pressure to "blow through" the obstruction - it waits until you start breathing of your own accord, then raises the pressure to prevent any further occurrence.

Obstructive apneas are caused by the tissues surrounding the airway collapsing and obstructing the flow. A central apnea (as you said in your question) occurs when the "breathe now" signal from the brain to the lungs doesn't happen. The reasons can be complex, so I won't go into them here. But a CPAP or APAP machine can't do anything about a central, so they do nothing. With Resmed machines, after 4 seconds of no flow, the machine sends a series of pressure pulses - if the airway is obstructed the return echo will be different from when the airway is open. By measuring the return echo, the machine determines if it's obstructive or central apnea. If it's obstructive, pressure will increase as described above. But if it's central, the machine won't increase pressure, as that could lead to more centrals.

To properly treat central apnea you need an adaptive servo-ventilator (ASV).

Now the flow chart. You asked if it shows only your own breathing or the combined effect of the machine plus your breathing. In fact you can't separate the two. So if you have an apnea and stop breathing, the flow chart will flat-line. The machine is still supplying pressure, but there's no flow. It's important to understand the difference between pressure and flow! The same thing occurs whether it's an obstructive or central apnea - there is pressure but no flow. So during any apnea, you're not getting oxygen into your lungs. Both types are bad, but obstructive apneas tend to be more traumatic - it's like the difference between holding your breath (central) or being choked (obstructive).

There's a very common misapprehension that CPAP/APAP machines pump air into your lungs - they don't, they just provide pressure to splint the airway open. To pump air into your lungs you need a ventilator, which is another step up in sophistication.
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#3
RE: CPAP function question - basic stuff...
I'm not an expert here, but I do have complex apnea. And I did purchase my ResMed ASV machine to address both types of apnea.

The ASV monitors your breath-over-breath progress many time per second (not sure how frequent the sampling is). And it dynamically adjusts the therapy pressure nearly instantaneously (well, as compared to CPAP). When a CA event occurs it tries to correct the situation as it is happening or otherwise ASAP. A CPAP algorithm calculates a change in therapy pressure after a certain number of breaths are analyzed, so timing is much slower to react as it determines your need to "splint" your airway open for an OA. I suppose that's also why my ASV cost exactly one arm and one leg as opposed to just one pinkie for a CPAP.

I'll let the experts dive in with more detail as I am not qualified. But, the ASV is quite an amazing therapeutic device for Centrals.
RayBee

~ Self-Treatment - via ApneaBoard experts.
~ Self-Pay - no help from Kaiser other than getting my script, then a pat on the butt and out the door.
~ Self-Educated - via ApneaBoard experts, its many users, and posted reference material.
~ Complex Apnea - All Night AHI=34.2/h, Supine AHI=45.5/h
~ Using a 2021 16" MacBook Pro M1 Max, 32 GB, 1 TB, macOS Monterey V12.6.
~ Pay no attention to the dog behind the cup, he ain't a docta, and does not give medical advise.
~ Woof, woof.

I-love-Apnea-Board
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#4
RE: CPAP function question - basic stuff...
Thanks for the reply.
Just not sure I still get it actually.

If I understand your reply correctly, a machine won't really do much...

It does nothing for CA, neither prevention, nor fixing them (i.e. making you start breathe again) and neither does it give you oxygen while they occur. So in other words - a machine does nothing for CA. Correct? I am surprised to read this though, as I thought a lot of people do get their CA down with a machine as well, but I guess this is incorrect then?

For OA, this is what I read:
Nothing really on how it prevents OA to happen in the first place. Apparently a machine (CPAP or APAP) will reduce events - this is sort of the main purpose I guess, to reduce AHI. And most of that AHI reduction comes from OA reduction. So how does it reduce the number of events?
There are two ways I guess. One is preventing them from happening in the first place, the other one is to detect when it starts, but then fixing it before it actually gets to the definition of an event (10 seconds).
Can someone explain how the machine does these two things:
How does it prevent OA from even occuring? Is it by applying pressure (the base pressure = min pressure) which by force prevents tissue from collapsing? 
And how does it fix OA when they occur? The reply says it does not "blow through" and open up the airway, so then I read that as once an OA has occured, the machine does nothing really to fix it. Just wait for us to fix the problem by ourselves (e.g. adrenaline rush, wake up, start breathe again).
What an APAP does is just increasing pressure to prevent the next OA from happening. But then after some time without an OA, pressure will return to baseline, and then the preventive effect is gone, right?

Bottom line, I just don't really see what the machine actually helps us with... Apparently it can reduce AHI from crazy numbers down to single digits. But how?
As I understand your answer, it doesn't do much. Nothing for CA, and basically just increasing pressure (APAP) for a few minutes after an OA (during which prevention effect will increase) and then returning to baseline again.
As I understand, increasing base pressure often reduces OA. But how? Why does a higher min pressure in most cases reduce OA? 
And does the machine reduce the duration of OA events? If so, how?

How does an APAP/CPAP prevent the OA in the first place?
And does it really do nothing to break them up and make us start breathing again during the event, during the time we can't breathe?

Sorry for all the questions, but I am desperate to understand how this works.

Maybe just a summary of questions is easier to answer one by one 

CA
How does a machine prevent CA? 
How does a machine fix/break up a CA, i.e. make us start breathe again?
How does a machine reduce negative impact of CA during its occurence? 
How does increased min pressure impact CA? 

OA
How does a machine prevent OA events to occur in the first place? 
How does a machine fix/break an OA event once it happens? 
How does a machine reduce the negative impact of an ongoing OA event? 
How does increased min pressure reduce number of OA events?



And to TonyVivaldi - sorry for not really being able to comprehend what you explain... I just feel that as I understand your answers, our machines don't really do much... Nothing whatsoever for CA, and not much for OA either (at least not breaking them and making us start breathe again)
I just feel that I really want to understand, this will be the first step for me to try to improve my situation.

Thanks in advance
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#5
RE: CPAP function question - basic stuff...
Even though we prefer to use OSCAR here, The Beginners Guide to SH should help clear up some of the information you seek.  The basics still apply.

I just copied a couple links for you, but you can scroll back to the beginning of the guide and look though it.

http://www.apneaboard.com/wiki/index.php..._to_events

http://www.apneaboard.com/wiki/index.php...ral_apneas

http://www.apneaboard.com/wiki/index.php...Rate_graph

Also read:
http://www.apneaboard.com/wiki/index.php..._The_Guide
OpalRose
Apnea Board Administrator
http://www.ApneaBoard.com

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INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE.  ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA.  INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#6
RE: CPAP function question - basic stuff...
Mandrake, yes, read up all the links Opal Rose has provided. To answer your questions specifically:

Quote:CA
How does a machine prevent CA?
Ordinary CPAP/APAP machines don't do much at all to prevent CAs. An ASV machine is specifically designed for central apnea and responds to changes in your breathing by adjusting pressures very rapidly, on a breath-by-breath basis.

Quote:How does a machine fix/break up a CA, i.e. make us start breathe again?
How does a machine reduce negative impact of CA during its occurence?
Again, a CPAP/APAP deliberately does nothing if a CA is encountered. An ASV will respond instantly by increasing the pressure support.

Quote:How does increased min pressure impact CA?
For a small percentage of people, increased pressure can cause CAs. We'd need to look at your data in detail to see if this is a problem for you.

Quote:OA
How does a machine prevent OA events to occur in the first place?
The pressure acts as a splint to maintain the airway in an open condition.

Quote:How does a machine fix/break an OA event once it happens?
How does a machine reduce the negative impact of an ongoing OA event?
During the apnea, a CPAP/APAP machine does nothing until breathing starts again. Once breathing has restarted, pressure is increased for a period to ward off future apneas.

Quote:How does increased min pressure reduce number of OA events?
Increased minimum pressure is probably the most important single factor. Increased pressure provides additional splinting to maintain the airway open.
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#7
RE: CPAP function question - basic stuff...
Mandrake,

Yup... What OpalRose and TonyVivaldi52 said.

Also, for a little light reading specifically on ASV and Central/Complex Sleep Apnea, check these out...

ResMed Healthcare Professional Products Support ASV

ResMed Support AirCurve 10 ASV

Pros and Cons of ASV for Sleep Apnea

WebMD - What Is ASV?

In a nut shell, and coming from a Complex Sleep Apnea guy - ASV works. And it works great. I truly believe that education on your particular apnea challenges and knowledge on the types of PAP device for your specific need is key to successful treatment. And of course another key factor with education is the desire to be the one in charge of your own therapy. The good people here on AB make your personal journey with PAP therapy quick, painless, and successful. I owe them many times over for my success.
RayBee

~ Self-Treatment - via ApneaBoard experts.
~ Self-Pay - no help from Kaiser other than getting my script, then a pat on the butt and out the door.
~ Self-Educated - via ApneaBoard experts, its many users, and posted reference material.
~ Complex Apnea - All Night AHI=34.2/h, Supine AHI=45.5/h
~ Using a 2021 16" MacBook Pro M1 Max, 32 GB, 1 TB, macOS Monterey V12.6.
~ Pay no attention to the dog behind the cup, he ain't a docta, and does not give medical advise.
~ Woof, woof.

I-love-Apnea-Board
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#8
RE: CPAP function question - basic stuff...
I'm going to try to simplify it

OA

This is rhetorical in that I don't think you can actually do all of this. Get one of those balloons they make balloon animals out of.  It represents your wind pipe.  Blow it up.  Now breathe in from it.  You can but there is too much pressure, actually quite a bit more than a CPAP can deliver, but as to your ability to breathe hat continues until you breathe out so much air that the balloon/your airway  collapses and you cannot breathe/an OA occurs.  Now (pretend) attach this balloon to your CPAP and program/titrate your pressure to the point where this balloon will not collapse while you are breathing thru the night. This pressure should ideally prevent any collapse and you should be able to comfortably breathe through the night.  The job of a CPAP is to simply keep a constant pressure during both inhale and exhale at all times.

The above is the basis of all PAP machines, including all APAPs, BiLevels, and the magical mystical IVAPS and ASV which maintain constant breathing volume, not pressure.

CA

CPAPs, APAPs, and BiLevels without Backup rate cannot treat central apneas and as such do nothing when we occur.  With these we find ways to avoid central apneas.  Central Apneas can be caused by a multitude of different things, including the simple use of using a CPAP. To do anything with a Central you must understand it's cause. We sometimes cannot identify a cause and those are called idiopathic central apnea which are treated by trying different therapies to find one that works.   NOt going into the the lessor forms but to say the ideal solution is to treat the cause first then to supplement with an appropriate xPAP machine.

First, very simply, what causes us to breathe?  Most people think the need for oxygen, but they would be wrong.  Simply put it is the need to get rid of CO2, carbon dioxide and its byproducts.  The most common form of central apnea that we see in the CPAP world is driven by losing the need to remove CO2 as indicated by our blood CO2 levels dropping below our apneic threshold which results in a central apnea occuring.  So how do we avoid this?  By reducing the amount of CO2 that we flush from the body by some or all of the following, reducing pressure differential between inhale and exhale, and/or reducing pressure.  Note that these actions are the opposite of what is used to treat obstructive events so you are looking for a balance.
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#9
RE: CPAP function question - basic stuff...
Thanks a lot for all the info.
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#10
RE: CPAP function question - basic stuff...
I have been on CPAP for two years and after reading a lot of posts in this forum and watched many videos, I wonder if ASV shold be the best treatment for sleep apnea if someone can affort It.

If I understand correctly, APAP reacts to the apnea events while ASV knows when the events is happening and apply the correct presure to eliminate them.

I am waiting for a soft cervical collar and O2 ring to corrlete the oxigen data and the apnea events.

Also, I belive Resmed devices seems to be better at managing apneas that the phillips ones.  I have a phillips device and I am really thinking in getting a Resmed ASV.
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