[jws]

Didn't we just have an article about a liquid, injectable oxygen for emergency medical use? How about skipping the lungs as O2 input, keep them just for CO2 removal, and take an IV containing the liquid oxygenator?

You might need to keep a small amount of lung pressure (say, less than that used to blow up party balloons) to slow the egress of oxygen through the lungs.

The next problem is likely that your lungs catch fire as the O2 concentration builds up in them. One thing at a time though.