Folks..
CO2 retention = "
air hunger + anxiety"
It also causes rapid-onset CO2 narcosis on/after descent.
If your respiration is elevated due to increased physical demand, you need to ease the workload of, and resistance to, respiration.
Assuming properly functioning regulators, there should be far more respiration workload from the pressure differential between mouth and lungs when vertical at the surface, compared to breathing from a regulator when submerged
horizontally.
The lungs are submerged >40cm below the surface and your diaphragm has to work harder to compensate for overcoming that hyperbaric pressure.
Don't believe me? Try going down 40cm and breathing from a hose pipe to the surface..
Your heart also has to work harder to pump blood down to the lower extremities.
Don't under-estimate that added demand...
The physiological demands are much harder than having to work to inhale against the crack-pressure of a regulator if fully submerged and
horizontal.
While at the surface in a vertical position, swimmers lungs are at a greater pressure than surface air, and they must breathe against negative pressure caused by their immersion. While this is occurring, their heart is additionally stressed due to a shift of blood from the extremities, to their chest cavity, also caused by immersion.
DAN -
Advances in Immersion Pulmonary Edema Studies 2017
(
That article is also WELL worth reading for an understanding of IPE.. an increasingly critical concern for divers..)
Also, at the surface, most (nearly all?) novice divers make a lot of involuntary movements (especially needless finning and sculling) that markedly increase exertion and, thus, respiratory demand.
If you're relaxed.. and still.. and not getting swamped, splashed or fighting current... at the surface... then it's acceptable to rest and relax.. to normalise breathing, before descent.
It also pays dividends to 'lay back' when relaxing on the surface. .. as this raises the submerged depth of the lungs and reduces breathing workload.
Nonetheless, any perceived 'ease' of breathing at the surface with the regulator removed is more of a
psychological than physiological benefit.
More often than not
the underlying issue is physiological... so addressing the
psychological niceties (
which demand an entirely opposing course of action) is demonstrably
counter-productive in achieving a desirable resolution.
If surface conditions aren't optimal... or if you find yourself exerted for any reason.. and not recovering a relaxed respiration... then it can pay dividends to get down a few feet and chill out there.
The emphasis is on being
neutrally buoyant, to cut out exertion; and being in
horizontal trim to reduce the effect of mouth-lungs pressure differential on respiratory demand.
I accept that this advice is, indeed,
counter-intuitive to what most people might expect.. but I've seen it 1000 times... and seen it benefit divers as many times.
Needless to say... it assumes the individual is
capable of getting down a few feet.. getting neutral and horizontal... and that competency is woefully lacking after many OW courses, and beyond.