Absolutely!!!
The altitude affects the barometric pressure which in turn affects the available oxygen (not percentage but the actual number of molecules per liter of air). It also affects the volume of any gas (as pressure decreases volume increases, all other factors remaining the same). Spend a little time learning the gas laws (Boyles,charles,grahams,daltons , etc.,.) and it will all make sense. These things have less if any effect when transporting in a pressurized aircraft. However remember whether ground or air if you are transporting lets say from phoenix (1000ft altitude) Denver (5000 ft. altitude) it doesn't matter if it's pressurized or not you are going to altitude (just a slower arriving there).
Mike
