Re High altitude soldering

G’day; I notice that in this thread nobody seems to have
mentioned what I call ‘hospital oxygen.’ When awakened in a
hospital ward after an operation involving anaesthetics, one
finds that one is wearing a small mouth/nose mask or just a
simple tube taped to one’s face. This delivers either pure
oxygen or air with an oxygen boost to help the healing
processes. This oxygen does not come from a cylinder, but from a
small device which sits on the floor, is plugged into a power
outlet and emits a gentle chugging sound the cause of which might
be a small pump. They wouldn’t let me get out of bed to examine
the thing properly, and although I made many enquiries, nobody
could tell me how it worked or upon what principle. To those who
used it, it ‘just was’. It occurs to me that it might be some
sort of molecular sieve which either allows only oxygen to pass
or vice versa, filters out the atmospheric nitrogen to waste when
air is pumped through it, but retains the oxygen. I have the
funny sort of mind that when confronted with anything new to it,
immediately asks how it might work, but ‘Yes, but what else could
it be used for?’ Well, one use would be for a gas torch. The
amount of power it used seemed very low, and it was quite
unobtrusive. There was a similar device in an ambulance in which
I travelled… It seems to me that it could even be operated by
foot bellows. Can anyone tell us about this? Cheers, John