How high air pressures can a human survive?

[Lojzek]

Does anyone know what is the maximum pressure in which a human body
can function? And how does air pressure affect the minimum breathing frequency?
I suppose increased pressure would allow a person to hold breath longer. For example:
a scuba diver or a person in a diving bell 50m bellow water surface would breathe air that
is about 6 times denser than above surface. If that air had normal oxygen share would it
allow the person to hold breat 6 times as long as above the surface?

 

[mgb_phys]

The deepest commercial diving is about 700m
I think somebody did an experimental dry chamber dive of 3500ft but I can't find the details

The difficulty is that oxygen becomes toxic at high pressures - so as you go deeper you need to lower the percentage of Oxygen.
At 700m you have < %1 O2, since you can't breath this at sea level you have to continually adjust the gas mix as you go deeper.