Stupid Question.

Hugh Jass · Post by **Hugh Jass** » Thu Dec 16, 2004 8:42 am

Just started using APAP last night. Still woke up 4 times during the night (although the sleep I had in between seemed deeper).

My stupid question is what prevents the machine from blowing back through the hose my exhaled air ? Since the tube is 6 feet, is my exhaled air really being vented before the next breath of (fresh?) air.

Seems to me I would be breathing a mixture of O2 and CO2 all night...

Thanks

0nemorething · Post by **0nemorething** » Thu Dec 16, 2004 8:51 am

I can't help you, but maybe Titrator can.

Also, any question asked in this forum is NOT STUPID!! We are all still learning about CPAP. SO thanks for the GREAT question!

onemorething

JudyAnn · Post by **JudyAnn** » Thu Dec 16, 2004 9:24 am

First of all, there are no "stupid" questions here. Everyone is here to help us and that is the beauty of this list. I never thought of this question and you have a good point.

Personally, I think that it is not so much what air but just the amount of air pressure that we need to open our throats and maybe the force of the machine air is more than what we exhale. Something like that..........? Maybe this doesn't make sense.

A sleep tech would know better as I am just new to this since July and have learned all I know on these lists, even more than I learned from the medical field or those DME's.

Judy

snamvar · Post by **snamvar** » Thu Dec 16, 2004 1:54 pm

I have read the manuals that came with my CPAP, mask etc. back to back. It does mention that you will inhale some of the exhaled air (most of it goes out of the mask vent). I think it is so small, it should noy affect anyone in a great deal. Remember that the machine is pumping fresh air continiously that replaces most of the exhaled air.

rested gal · Post by **rested gal** » Thu Dec 16, 2004 1:55 pm

I'm not techie at all, but I think the mask designers take the CO2 issue very seriously. Probably the FDA has the final word. And yes, I think almost all your exhaled carbon dioxide is indeed vented out the exhaust port of the masks. The higher the pressure, the faster it's washed out. I believe that's why the lowest pressure machines can deliver is 4cm H2O, or perhaps with variances that might dip just barely under 4. Takes at least "4" to clear the exhalation out of the mask. (And I've seen cautions that 4 might not really clear it well with some masks.)

If you are using a pressure of 5 or more (as most people do) the force of incoming air should be easily pushing your exhaled breath out the exhaust port of any mask well before you'd be rebreathing it. I don't think your exhalation gets a chance to go back down into the main air hose from the machine - it's being moved out continuously through the exhaust ports of the mask. At least, that's the plan, as I understand it.

chrisp · Post by **chrisp** » Thu Dec 16, 2004 3:46 pm

The air we breathe contains 21% oxygen. The air we exhale contains 16% oxygen. The mask has a high washout rate. I doubt that there is any rebreathing of air when on cpap.

Cheers,

Chris