Following the CPAP thread with interest. Don't need one yet, but assuming that I will at some point.
Geoff's comment about CO2 driving respiration got my attention. Going to forward that to the doc I've been talking with.
Aircraft pressurization is based on the limits of the pressure vessel (fuselage) structure. They are designed for a maximum differential pressure between inside and outside (max diff). The engine(s) provide bleed air that flows continuously into the cabin. A calibrated outflow valve lets air out. It's either open or closed. A controller can call for a cabin altitude and the outflow valve holds it. If the cabin altitude desired is too low, the controller is overridden and the outflow valve keeps the cabin at max diff. If the outflow valve fails, there is a second one that takes over. It's pretty primitive - the whole thing is a calibrated leak and goes back to the commercial airliner, Boeing 307 just before we were in WWII.
