Rebreathing exhaled air?

[stubones99]

Has anyone else thought about how much we re-breathe the air we have just exhaled on the ResMed S9 AutoSet machine?

I use a Quattro full face mask with the vents at the bridge of my nose and have gotten used to the way it fits and can keep a pretty good seal most of the night.

My point is that when the unit is set up for bi-pressure, it falls off when you exhale. You can actually seen the hose fog up with your breath.The only way to limit how much exhaled air you breathe is to breathe out and hold it, then breathe back in. That lets the pressure built back up and blow your exhausted air out the vents and then you breathe fresh air back in.

One experiment I want to try is to use a pulse oxymeter and take a reading before i put my mask on and see if it goes up or down.

Someone needs to build a sliding valve that when you exhale, opens an exhaust port to vent to exhaled air out, and slides back shut when you breathe back in.

Put your hand behind your machine (where it picks up fresh air) and breathe out... you'll feel the air being forced out the inlet.

This sliding valve could be inserted right at the mask where the hose and mask connect.

Any suggestions?

Thanks!
stu

[greatunclebill]

put your mask on and go to sleep. stop over-thinking things. hey, you asked for suggestions.

[Slartybartfast]

Yep, but it's minimal. There is a constant flow of air out the vent holes, and when you exhale, you do so slowly enough that the exhaled air is forced out the vent holes by the positive pressure of the air coming in from the hose, so there is only a little exhalant that mixes with the incoming air by the time you take your next breath. And your exhaled air isn't 100% CO2, there's still quite a lot of O2 left over. Enough to save someone's life when you're administering CPR for them.

Look into it if you want, but don't expect to discover a problem. Masks are designed to have low retained volume.

[billbolton]

My point is that when the unit is set up for bi-pressure, it falls off when you exhale.

It may fall off but it doesn't cease.

As long as there is any airflow out of the vents, scavenging of exhaled air (due to the Venturi effect) will be occuring

Cheers,

Bill