Doc Intrepid:Peter,
But this sentence is a problem.
When you are ascending (and trying to do something else simultaneously, such as screw with your regulator while it's out of your mouth), "clamping your jaws shut" is a recipe for a lung over-expansion injury.
Remember that bit about "never hold your breath: exhale out a tiny stream of bubbles" each time your reg is out of your mouth? It's important...make that a habit.
If there was any air actually *in* my lungs, I would be exhaling. There wasn't a
cubic millimeter, I had just exhaled through his reg, hence the reference to being
at (bottom lung).
Peter