(11-22-2012, 10:31 PM)archangle Wrote: You don't have to worry about rebreathing CO2 as long as you're using standard CPAP equipment in proper working order.
First, realize that you exhale Carbon Dioxide, CO2, not Carbon Monoxide, CO. Carbon MONoxide is the stuff that kills you if you have a car exhaust leak. A fair number of people confuse the two. There is no Carbon Monoxide involved in CPAP. (Except whatever pollution is in the air you breathe even without CPAP.)
Long before CPAP was thought of, we figured out the hazards of rebreathing CO2 from using ventilators. The physics of the situation are very well understood, safe levels were established, and CPAP equipment was designed to have a large safety margin.
The minimum pressure most machines will produce is 4 cmH2O. The exhaust holes are designed such that they leak out enough air at that pressure that they will clear out the exhaled air enough to prevent the build up of CO2 and depletion of O2 to harmful levels. Unless the exhaust air holes are plugged, or the machine is producing less than 4 cmH2O, you won't get enough rebreathing to be harmful.
By the way, the hazard to rebreathing air is not so much from high CO2, as it is from low O2.
Also, the effect of rebreathing some of your exhaled air is much the same as having apnea. In either case, O2 has a hard time getting into your lungs and CO2 has a hard time getting out.
Enough for one post. Time to stop to let my keyboard breathe for a bit.
Thanks Arch, I did mean carbon dioxide. my bad.