[trux]

Thanks for the details, Eric. Very interesting! I'd never thought that you can do considerably more on sled than with a still surface apnea. Already holding to the sled, and operating it requires some muscle work and inhibits perfect relaxation (at least for me), so I thought the time would be rather inferior.

On the other hand it is true that the higher O2 partial pressure in depth allows to pull more oxygen from lungs than on surface, but that again would fire back on you when you ascent. It would cause a severe ascent hypoxemia (SWB) if you really used the effect, and went below the surface level of PaO2, at depth. And that would be the case if you ascent just from the deco stop at 6 m too. It means that you must be right with the stronger diving response at depth, which compensates not only from the less than perfect muscle relaxation, but apparently preserves the oxygen strongly enough to give this advantage.