Right, here's the science Jaap... feel free to ignore all this as its off the top of my head
Oxygen is carried by the haemoglobin (globular protein, red pigment) in red blood cells. Per mm3 blood there are 5-6.5 million red blood cells. Each contains approx 270 million molecules of the oxygen-carrying molecule haemoglobin. Thats already plenty!
Anyway, each haemoglobin molecule can only carry four molecules (8 atoms) of oxygen. Haemoglobin in blood in the lung capillaries is around 98% saturated with oxygen.
Haemoglobin cannot carry more than 8 atoms of oxygen, no matter how many excess oxygen atoms are potentially available. And remember, we don't use all of the oxygen available to us in one breath even at sea level, 1 atm.
In other words, even though the deeper you go, the denser the gas delivered becomes, your haemoglobin cannot physically bind to and utilise all that excess oxygen, so it is simply breathed out into the loop, and sent round again.
This is why the pO2 appears to be dropping more slowly and doesn't need replenishing as often at elevated ambient- your body is actually metabolising a smaller proportion of the denser gas delivered.
Yes, blah blah blah some extra oxygen maybe carried in plasma at elevated partial pressure but this is an infintessimally small amount
I checked my 'specifics' with Dr I Gallagher (Head of Gas Physics at some toff university and she said that it sounded about right
So there - I woz right
and dont even get me started on the BOHR effect...maybe i should write some CCR text books
