Where does the air go?

[Hydrangea]

It doesn't need to go anywhere. You are confusing a pressure with a flow. You can, for example, have full pressure and no flow at all. Pressure is how hard the air is pushing, flow rate is how fast the air is moving.

The engineering marvel of the CPAP machine is that it's able to maintain a constant pressure over a wide range of flow rates.

Wow, Sleepster!  You just blew my mind!!!!  Of course that makes perfect sense, but I had never considered that before.

[Hydrangea]

Pressure vs Flow.  These are separate, but related things.  CPAP is low pressure.  If you put your hand over the end of the tube you can completely stop the flow very easily, but when you let the tube flow freely, it will flow a large volume of air. 

Your CPAP is not blowing air down your windpipe. You must spontaneously breathe, or no flow happens in or out.  It may be slightly easier to inhale with CPAP pressure, but you can easily overcome that pressure.  Without your ribs expanding, and diaphram tightening, the CPAP cannot cause you to inhale. There are non-invasive ventilators that can accomplish that magic.   The discussion of pressure and flow is actually pretty high level stuff and it's not a dumb question, but I might not be bright enough to explain it.  I'm sure another member will step in.

Wow!!!!!  So true!!!

Sometimes, while I'm falling asleep (and probably experiencing an obstruction beginning), I can feel the pressure cranking open my breathing tube (whatever it's called)... but I don't feel air rushing into my lungs. So, that makes sense to me!

[Hydrangea]

to answer what you asked, you need to break down what is going on into 3 steps: you are not inhaling or exhaling, you are inhaling, you are exhaling.

Basic things that need to be accepted:
The pressure in your airway is the same as in the mask and the same as in the hose all the way back to the "fan"
Yes the flow rate is important to the treatment, but not so much with what you are asking

First set, from above, what is going on when you are NOT inhaling or exhaling:
The CPAP machine has a target pressure setting, you at this point are a fixed volume. so, you have a volume, you have an exit port (the vents)- all those little holes or not depending on your mask usage. so the "fan" builds up the pressure to maintain the mask/airway at the pressure specified. This pressure should splint you airway open.

2nd from above, you are inhaling. In this case you are increasing the size of the hose/mask/airway so the fan must speed up to fill the new volume and bring it up to target pressure

3rd you are exhaling. You are the one increasing the pressure, so the fan decreases speed as you are now controlling the pressure. Most of your air is going out the vents

These are the only things that are going on and what is happing and where the air is going

WOW!!!!!!  This makes sense!

[Hydrangea]

Okay, so this is interesting. Before, I thought that the "splint" was maintained by a constant flow of air moving down through your throat/windpipe, but what you're saying is that that is not happening?...that it's just pressure that is what's keeping the airway open.

I'm thinking about this, too.  So... essentially, the flow of air from the machine *creates* the pressure. But when there's enough pressure, the flow then functions to *maintain* the pressure?

[Sleepster]

Sometimes, while I'm falling asleep (and probably experiencing an obstruction beginning), I can feel the pressure cranking open my breathing tube (whatever it's called)... but I don't feel air rushing into my lungs. So, that makes sense to me!

It's quite possible you feel the tissue move out of the way, so that your airway is unobstructed when your muscles are relaxed.

[jomama]

Okay, so this is interesting. Before, I thought that the "splint" was maintained by a constant flow of air moving down through your throat/windpipe, but what you're saying is that that is not happening?...that it's just pressure that is what's keeping the airway open.

I'm thinking about this, too.  So... essentially, the flow of air from the machine *creates* the pressure. But when there's enough pressure, the flow then functions to *maintain* the pressure?

Seems so. Very interesting. This has been very educational!

[Melman]

Yes, the pressurized air goes all the way down into the lungs. This doesn't mean the air from the CPAP machine goes all the way down into the lungs!

Given that for the entire time we have the mask on air from the CPAP is all we breathe, it would seem we would be asphyxiated if the air from the CPAP didn't go all the way down to the lungs.

[DaveL]

And when it all works we dont have apnea events, our blood oxygen levels increase and we feel better.

I'm grateful.

and I'm looking forward to more improvements in sleep quality in future.

[Sleepster]

Yes, the pressurized air goes all the way down into the lungs. This doesn't mean the air from the CPAP machine goes all the way down into the lungs!

Given that for the entire time we have the mask on air from the CPAP is all we breathe, it would seem we would be asphyxiated if the air from the CPAP didn't go all the way down to the lungs.

You're right, of course. I was referring to the breath-by-breath depicted on the video. Pressure reaches the depths of the lungs (think sound waves) on each breath. I was thinking the cloudy trails on the video depict regions of high pressure.

[OMyMyOHellYes]

the pressurized air flows down the windpipe.

So...where does the air go once it flows down the windpipe?

Not all of it goes down the windpipe.  Sometimes it goes in the stomach.  And then you fart.  Or belch.