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Dumb question #1 - MARrshh - 10-06-2021
Where does the stream of air from my CPAP machine go? It blows into my full-face mask, then into my nose (or mouth), makes a circle somehow ( ? ) and blows back out the exhalation port. If I understand correctly, some of that air that exits through the exhalation port has been all the way down into my lungs -- but some of it hasn't. So, from that stream of air provided by the machine, I "sip" some of it to breathe, to go into my lungs.
Is this even remotely correct?
(TIA. Hooting, pointing and guffaws fully accepted.)
RE: Dumb question #1 - SarcasticDave94 - 10-06-2021
That is correct. The PAP is blowing more than you inhale, in part to overcome leaks. You inhale a portion, another portion is leaked, and finally the part you've inhaled gets vented as well.
RE: Dumb question #1 - Sleepster - 10-06-2021
The stream of air that you inhale gets exhaled through the exhalation ports. You don't re-breathe a significant amount of it.
RE: Dumb question #1 - Gideon - 10-06-2021
that "excess" air exhaustion is in part to ensure that you are not breathing too much CO2.
RE: Dumb question #1 - MARrshh - 10-06-2021
So . . . does the machine increase the pressure because it senses that I'm getting overloaded with CO2 ?
My setting is 5 - 15, and everything is great when I go to sleep, but sometimes I wake up a couple hours later to a hurricane-strength 15.
Have had some mask air leaks, but not too bad until the 'Big Blow' kicks in, which wakes me up.
Could anybody really sleep with that kind of pressure? Wouldn't you almost have to duct-tape your mask to your face to prevent leakage??
RE: Dumb question #1 - SarcasticDave94 - 10-06-2021
No, PAPs don't increase pressures for CO2.
As for your issue, maybe it's increased flow limits driving pressures up. Best way to find out is get OSCAR the free report tool and post a standard Daily Detail chart.
RE: Dumb question #1 - mesenteria - 10-06-2021
You machine senses when you are not taking in enough air. It doesn't sample what you exhale so that it can determine how much CO2 you are producing.
Your machine has a set pressure that it can't exceed, a maximum set by you or your advisor. When you are exhaling, it should back off on the fan and let you exhale through the same port, or vent, that its bypass air exits when you are between breaths. When you breathe again, whatever exhaust is still in the mask is going to be severely diluted by the bypassing air it always sends to your mask and that is either trying to enter your lungs or exit from the same port as your exhalation. Technically, there will still be some spent lung air inside the mask, and even some still inside your airway, including of course the lungs themselves. But you can pretty much discount the air still inside your nasal mask. The larger full coverage masks are going to be different.
RE: Dumb question #1 - archangle - 10-07-2021
Fresh air comes from the CPAP machine into the hose and into your mask.
Some of the air escapes out the exhaust port and some goes into your airway and lungs when you inhale.
When you exhale, your used air goes out into the mask, some of it goes back up the hose part of the way, and some of it goes out through the exhaust port.
The air coming out of the exhaust port blows essentially the same rate all the time, whether you're breathing or not.
While you're between one exhale and an inhale, the CPAP machine is pushing the used air in the hose back into the mask and out of the exhaust port.
As you're inhaling, there may be some used air still in the hose, and you will get that air during the first part of your inhale cycle. However, part way through the inhale cycle, you'll be getting fresh air because the rest of the stale air has leaked out of the exhaust port. The fresh and used air will mix in your lungs and give you only slightly used air.
The leak rate of the mask, the pressure, and the dead air space inside the mask are all tuned such that you don't end up rebreathing enough used air to matter. However, with low mask pressure, it will sometimes feel like you're being smothered. You can also run into trouble if your exhaust port gets partially clogged. In theory, you might suffocate if the exhaust port got completely clogged.
RE: Dumb question #1 - MARrshh - 10-09-2021
Sincere thanks to everybody for the responses.
I occasionally make it thru the night without my new machine increasing the pressure to the max, but it does so most nights.
I know it's hitting near the max setting of 15 because I had the respiratory therapist at my DME's office set it to that level while I had my mask on, as an experiment.
The increased air pressure wakes me up every time, and I usually turn off my machine and take the mask off. But a few nights ago I had a weird experience after I turned it off -- I had to breathe really hard for a half-minute or so -- gulping for air, really. Was pretty scary. I have mild asthma, but this was different. I wonder it it was something like oxygen deprivation or ( ? ) .
Anyway, I've discontinued using my CPAP until I can see my doctor, who is notoriously hard get an appt with anytime soon. He's a specialist but not really a full time "sleep doc" -- and I just yesterday found out that we have a new 'genuine' sleep doc in practice in our city. Going to call for an appt on Monday. Probably going to need a new sleep study -- it's been a few years now. (sigh!)
RE: Dumb question #1 - SarcasticDave94 - 10-09-2021
We would be able to help more if we saw OSCAR data. It's free to download. It does sound like you're not getting enough air because your PAP is set too low or you need to enable EPR, but without seeing a chart, it's a guess only.
Why would increasing pressure and enabling EPR help? It will enable the PAP to treat flow limits then pressures don't go higher where it's uncomfortable.