Exhale ascent

[OceanMan]

Hello,

Check this paper out. It's about seals exhaling during the ascent of a deep dive.

The idea is to exhale during ascent to keep a lung volume close to residual.

I think there could be several advantages:
- preventing the O2 from going back in the lung (from the blood) during the last 30-20m of ascent. Thus reducing the risk of BO/samba at the surface.
- keeping a strong bloodshift until breaking the surface. Hence, the legs don't burn much oxygen and the extra effort due to the fact that the diver is less boyant is not that worrying (in theory).
- when packing I have always thought that not exhaling during the last few meters of ascent is dangerous for BO/samba reasons (blood suddenly going back into legs/arms/tips) and also for packing injuries reasons (max lung volume+packs reached in a few seconds).
- you can do a strong inhale as soon as you break the surface and renew a lot of air from your lung immediately.

Severals drawbacks:
-increased risk of decompression accident maybe for very deep dives.
-it's pain in the ass to let precious air go away and to sink until the surface

What do you think?

Cheers

[pyro]

No way man, you let go of not just co2 but air as well, I wouldn't want to risk that in 5m let aone in 30-20m! But then again what do I know?

[naiad]

Originally Posted by OceanMan

I think there could be several advantages:
- preventing the O2 from going back in the lung (from the blood) during the last 30-20m of ascent. Thus reducing the risk of BO/samba at the surface.
- keeping a strong bloodshift until breaking the surface. Hence, the legs don't burn much oxygen and the extra effort due to the fact that the diver is less boyant is not that worrying (in theory).
- when packing I have always thought that not exhaling during the last few meters of ascent is dangerous for BO/samba reasons (blood suddenly going back into legs/arms/tips) and also for packing injuries reasons (max lung volume+packs reached in a few seconds).
- you can do a strong inhale as soon as you break the surface and renew a lot of air from your lung immediately.

I have heard that it is good to exhale a bit when ascending after packing, because of the risk of injury. I am not so sure about whether exhaling a lot is a good idea. I have been told that exhaling before surfacing is not good in pool training, because of the risk of blackout. I wouldn't do it because of the risk of blacking out before reaching the surface, and sinking with empty lungs, possibly inhaling water.

I'm not an expert though.

Lucia

[cdavis]

Very interesting question. Is pretty well established that a moderate exhale in the last few meters of CW, (5-10 ?) reduces the possibility of BO. Generally quoted reasons include gas exchange in reexpanding lungs and reduced chance of cranial blood preasure changes as expanding lungs put preasure on carotid blood vessels. The possibility that exhale helps maintain blood shift adds a reason I had not considered, maybe an important one. The question of how deep to start an exhale is also a good one. Some of the old descriptions of polynesian pearl divers diving 20-30 meters, mention slow exhales starting on the bottom. Starting an exhale very deep might bring in some of the characteristics of frc diving, with effects I can't quite imagine. Seems like the energy cost of fighting to get down then fighting more to get back up would be pretty prohibitive, but maybe not if blood shift was strong enough.

Anybody experimented with very deep exhales??

Connor

[efattah]

I read the paper. It is very interesting.

However, I strongly believe it doesn't apply to humans, for the following reason.

According to Sebastien Murat's research, the human lung collapses from the top down -- the throat/bronchi close, then (eventually) the alveoli would collapse.

In marine mammals, the opposite happens. The alveoli first collapse, then the bronchi collapse.

In the latter case, a passive exhale on the ascent would prevent gas exchange during the ascent.

In the human case, a passive exhale on the ascent would NOT prevent gas exchange during the ascent.

Further, even in the classic method of exhaling at the end of a dive, this would, even in theory, only prevent a reverse O2 transfer in the case of EXTREME hypoxia. If you are only slightly hypoxic, then exhaling at the end would be detrimental.

[Walrus]

I don't see how exhaling in the last 5m or so is detrimental in any way. You still have to exhale at some stage before you can inhale so if that's done underwater it means you are actually getting your inhale in quicker. I wouldn't see any benefit doing it apart from the last few seconds before hitting the surface. Also PFI teaches it as a "relaxed" exhale so you probably hit the surface with about a half lungful.

I don't think anyone buys into the reverse O2 exchange ie the Terry Maas book "suction" theory anymore. Like Connor already pointed out exhaling before reaching the surface may reduce rapid blood pressure changes. This can have a big effect on blackouts if you are already hypoxic. It's the same sort of reason you don't want to jump up and stand after a static.
Obviously if you use packing then you want to exhale before reaching the surface to avoid lung injuries.

Cheers,
Wal

[OceanMan]

Originally Posted by efattah

According to Sebastien Murat's research, the human lung collapses from the top down -- the throat/bronchi close, then (eventually) the alveoli would collapse.

In marine mammals, the opposite happens. The alveoli first collapse, then the bronchi collapse.

Interesting Eric.
Is there strong evidence about this or is it just a theory?