Where does exhaled air go using a face mask?

When you exhale, only some of your breath goes out the vent hole in the mask. Much of it backs up into the supply tube. The percentage varies with the machine's pressure -- with higher pressure more gets out the vent hole. More is pushed out the vent hole while you inhale, but not all. The first part of your inhalation is the volume of your exhaled breath still left in the supply tube. The rest of your inhaled volume is fresh air.

Rebreathing some of your exhaled air increases the level of CO2 in your lungs, but not seriously. Central sleep apnea, as opposed to obstructive sleep apnea, is from the brain not sending signals to breathing muscles. Elevated levels of CO2 trigger an autonomic nervous system reaction that tells your muscles to breath. So the slightly elevated level of CO2 in your system from CPAP rebreathing may help with central sleep apnea, if that's your issue, and maybe with obstructive sleep apnea. CPAP-raised CO2 levels may be one reason CPAPs work.

Significant sleep apnea will raise your CO2 levels while your breathing is stopped, until the elevated CO2 makes you suck in a breath. CO2 builds higher than for a normal breather, and then is cleansed after a sharp intake.

So if you have sleep apnea your system's overall CO2 levels will probably be lower (but far steadier) with CPAP than without.

My web searches didn't find references to rebreathing percentages or changes in CO2 levels or O2 levels with CPAP, compared to a base-line of normal (non-apnea) breathing.

Classify this under what your doctors and the CPAP manufacturers don't tell you.

Maybe after 4 years of waiting for your answer he got better.

Goofproof wrote: ↑

Thu May 07, 2020 6:04 pm

Maybe after 4 years of waiting for your answer he got better.

Or died because he let his imagination prevent him from getting effective treatment.
It has happened.

T.D. wrote: ↑

Mon Aug 29, 2016 2:48 pm

By the way ramp was set at 45 minutes because respiratory thought perhaps that would give him enough time to get to sleep.

I told him tonight to come to bed an hour earlier since I noticed he WAS laying on sofa in loft.

I've been using CPAP for 3 years and was required to average 6 1/2 hours per night for 75% of the nights order to keep my job in the transportation industry. High motivation to use it. I turned off the ramp within just a couple of nights because as soon as I'd fall asleep, it would ramp up and wake me up. Now I fall asleep under its normal pressure so there is no change. This might solve two problems, as it won’t make him feel like he’s not getting air to start, and it won’t wake him up if he is able to go to sleep with it. It took 2 weeks to not feel panicky when putting it on, about 3 months to get to be okay with it, and about two years before I don’t know that I'm wearing it. Sometimes I have to put my hand to my face to sure it’s on. It can be done!

You are welcome to step into the WAYBACK MACHINE and tell him--that was several years ago!

Amphioxus wrote: ↑

Thu May 07, 2020 5:39 pm

When you exhale, only some of your breath goes out the vent hole in the mask. Much of it backs up into the supply tube.

It *ALL* goes out the mask vent.

Amphioxus wrote: ↑

Thu May 07, 2020 5:39 pm

The percentage varies with the machine's pressure -- with higher pressure more gets out the vent hole. More is pushed out the vent hole while you inhale, but not all. The first part of your inhalation is the volume of your exhaled breath still left in the supply tube. The rest of your inhaled volume is fresh air.

This is wrong.

Amphioxus wrote: ↑

Thu May 07, 2020 5:39 pm

Rebreathing some of your exhaled air increases the level of CO2 in your lungs, but not seriously.

Masks vent over 20 liters of air per minute *at four cm pressure* and up to around 50 liters per minute at 20.

That's plenty to flush out the exhaled air.

Amphioxus wrote: ↑

Thu May 07, 2020 5:39 pm

Central sleep apnea, as opposed to obstructive sleep apnea, is from the brain not sending signals to breathing muscles.

Congratulations, you finally said something that's correct. Let's see if you can keep it up.

Amphioxus wrote: ↑

Thu May 07, 2020 5:39 pm

Elevated levels of CO2 trigger an autonomic nervous system reaction that tells your muscles to breath. So the slightly elevated level of CO2 in your system from CPAP rebreathing may help with central sleep apnea, if that's your issue, and maybe with obstructive sleep apnea. CPAP-raised CO2 levels may be one reason CPAPs work.

And, there you go again

Amphioxus wrote: ↑

Thu May 07, 2020 5:39 pm

Significant sleep apnea will raise your CO2 levels while your breathing is stopped, until the elevated CO2 makes you suck in a breath. CO2 builds higher than for a normal breather, and then is cleansed after a sharp intake.

it takes more than "a sharp intake".
The entire reason that people start struggling to breathe when their airway is blocked is because of the buildup of CO2, and it takes several recovery breaths to bring things back to normal.

Amphioxus wrote: ↑

Thu May 07, 2020 5:39 pm

My web searches didn't find references to rebreathing percentages or changes in CO2 levels or O2 levels with CPAP, compared to a base-line of normal (non-apnea) breathing.

Because it's a non-issue.

Amphioxus wrote: ↑

Thu May 07, 2020 5:39 pm

Classify this under what your doctors and the CPAP manufacturers don't tell you.

Classify this under "stuff you've made up".

And now we know how "over-thinking" can involve NO THOUGHT AT ALL.