I have one more question (which may be stupid/useless) about the "how does it work" ?

[Albatros]

I understood, thanks to your help, that:

-the Inhale pressure limits the rise of FL's, which decreases the risk of an OA happening

-when an OA arrives, the machine does not emit enough air to open the throat. The OA can only be stopped when my brain demands it.

-the role of the Exhale pressure is, after the end of the OA, to make sure that another OA does not arrive, especially in a cluster. It is the Exhale pressure that will play this fundamental role, of keeping my throat open.

This being said, I ask myself the following question (perhaps useless in the context of therapy): intuitively I understand the Inhale pressure, it's the air that is sent to the nostrils.
But what about Exhale pressure? How does it work ? Air is sent into the nostrils when I exhale, therefore, how will this air, going against my exhalation, help to keep my throat open?

What am I missing ?

Thank you

[Respirator99]

There's no such thing as a silly question! Actually, that's a great question, which gets to the very heart of how CPAP works.

CPAP = Continuous Positive Airway Pressure

When CPAP was first invented it operated at a constant fixed pressure, maintaining a positive airway pressure to prevent your airway from collapsing. This is still the most fundamental mode of operation, in a machine having fixed pressure and exhale pressure relief (EPR or Flex) turned off. It was realised that some people struggled to exhale against the pressure, so EPR was invented to lower the pressure a little as you exhale. This is the EPAP (expiratory PAP). The problem is that lowering the pressure in this way also lowers the airway pressure, which is why they advise to increase your base pressure when you turn EPR on.

On a bilevel machine, the difference in IPAP (inhale pressure) and EPAP can be adjusted to a fairly high number, but the principle is the same. On bilevel machines the difference between EPAP and IPAP is called pressure support. EPAP + PS = IPAP

[chunkyfrog]

Trouble inhaling results from floppy bits inside getting in the way of air flow.
Exhale pressure keeps those floppy bits out of the way for the next breath in.
Don't even think about letting a surgeon in there--bad results are permanent.

[ChicagoGranny]

But what about Exhale pressure? How does it work ? Air is sent into the nostrils when I exhale, therefore, how will this air, going against my exhalation, help to keep my throat open?

You may be having trouble understanding it because the answer is so simple. The exhale pressure maintains pressure in the airway. The pressure helps to keep the airway tissues from collapsing.

[Albatros]

But what about Exhale pressure? How does it work ? Air is sent into the nostrils when I exhale, therefore, how will this air, going against my exhalation, help to keep my throat open?

You may be having trouble understanding it because the answer is so simple. The exhale pressure maintains pressure in the airway. The pressure helps to keep the airway tissues from collapsing.

Yes I can unferstand that. The air coming from my lungs, this exhale pressure, maintains the airway open.
But the Epap pressure (= Ipap - EPR), is coming from the machine to my lungs, the other way , therefore, how can it help ?! ?

What do I miss , here ?

[palerider]

But the Epap pressure (= Ipap - EPR), is coming from the machine to my lungs, the other way , therefore, how can it help ?! ?

What do I miss , here ?

What you're missing is that nothing "comes from the machine into your lungs", your lungs draw air in and push it out. that's how lungs work.

The machine slightly pressurizes the air that your lungs then act upon.

think of a balloon, (which the machine can't inflate, it's not strong enough), but what it *can* do is keep the balloon from collapsing, if you had a tube balloon, (like you make balloon animals from), and cut one end off, and try to suck air through it, you'll get nothing (apnea) because the balloon collapses, if however, you put the CPAP on the other end of the balloon, it'll keep the balloon open, and you CAN pull air through it, (and breathe out through it).

That's how CPAP works, it keeps the balloon (your airway) open so that you can pull air in. if the resting pressure (EPAP) is too low, then the balloon (airway) collapses and you can't breathe.

[Pugsy]

The air coming from my lungs, this exhale pressure, maintains the airway open.

No...the air you are exhaling from the lungs has nothing to do with keeping the airway open.

It's the incoming air pressure from the machine that holds the airway open. It needs to be high enough (with or without EPR use) to prevent the airway from collapsing.

So the minimum pressure (call it EPAP or whatever and with or without EPR being involved) is doing the bulk of the work holding the airway open and preventing the collapse.

[ChicagoGranny]

Yes I can unferstand that. The air coming from my lungs, this exhale pressure, maintains the airway open.
But the Epap pressure (= Ipap - EPR), is coming from the machine to my lungs, the other way , therefore, how can it help ?! ?

What do I miss , here ?

Pressure is pressure regardless of which direction the flow is.

[chunkyfrog]

Google this: "STENT".
You are welcome.

[Albatros]

Thank you very much for your comments.

They help me to imagine the "how it works".
Which I am now satisfied with.

I take the case of a face mask, but it would be the same whatever the masK.
there are 3 elements that intervene in the process

-there is the mask,with a permanent pressure coming from the machine (Ipad = Epad if EPR =0))
-there are the lungs that direct the process
-there is an inflatable "hose" between the lungs and the mask (the airway).

When the lungs inhale air, the amount of air inhaled is reinforced by the pressure in the mask. This helps to open/"inflate" the hose (airway) between the mask and the lungs.




When the lungs exhale air, they will do it against the pressure in the mask, coming from the machine.
This resistance will inflate the hose/airway twice.

This reinforces the fact that it is during exhalation that the airway is held open the most.

[palerider]

When the lungs exhale air, they will do it against the pressure in the mask, coming from the machine.
This resistance will inflate the hose/airway twice.

This reinforces the fact that it is during exhalation that the airway is held open the most.

Only, you're wrong about that.

The *fact* is that the pressure remains constant (and it's EPAP and IPAP, not "epad" and "ipad"). because the machines measure the pressure dozens of times *per second* and adjust the speed of the blower to deliver the exact pressure desired.

put your ear on the machine and you will hear the fan speeding up when you inhale and slowing down when you exhale. It speeds up to deliver more air to maintain the pressure while you inhale, and it slows down to deliver less air when you exhale,

If the fan in the flow generator (What you probably think of as the CPAP) was a constant speed, then the pressure would drop whenever there was a larger leak or when you inhaled, and the pressure would increase when there was less leak or you exhaled. That's not how it works.

[ChicagoGranny]

This reinforces the fact that it is during exhalation that the airway is held open the most.

It's unclear what you mean by "held open the most". In a properly operating CPAP system, the human airway is stented open on both inhale and exhale. The pressure created by the lungs on exhale is not additive to the CPAP mask pressure. The machine will maintain the set EPAP pressure throughout the exhalation.

there is an inflatable "hose" between the lungs and the mask (the airway).

Off-topic, but when a couple engages in a deep kiss, they create a tube that connects their buttholes.

[palerider]

Off-topic, but when a couple engages in a deep kiss, they create a tube that connects their buttholes.

You're such a romantic!