Pelizzari 75m "record" dive - air in suit or extreme farting?

[azapa]

This is actually not completely true. The partial pressures of the gases remain to great extent uninfluenced by the exhale. There is no reason for them to change when you exhale.

The partial alveolar pressure of oxygen is determined by two main factors: 1) the absolute pressure of gas in lungs, and 2) the ratio of the part of oxygen to the total volume.

1) The pressure in lungs is only dependent on the ambient water pressure, and is equal to the ambient pressure on inhale as well as on exhale, hence no change here. There may be a very slight overpressure due to extreme packing just on surface, or perhaps still a feet or two under it, but definitely no anywhere deeper. The overpressure may be accentuated by the progressed bloodshift on ascent, but in the same time reduced due to the loss of gas volume due to oxygen consumption (the CO2 production is slightly lower). But still, any excess overpressure concerns only the very last feet or two, hence the impact of exhaling on PaO2 during the ascent is inexisting.

2) By exhaling you do not change the ratio of O2 in lungs (at least not in short term). You cannot exhale oxygen without exhaling also the other gases in lungs, hence the percentage of oxygen after the exhale remains practically identical to the level before it.

So, as you see, there is no way the PaO2 could change, and strengthen so the "vacuum effect" due to exhale, as is often incorrectly claimed in freediving courses, or even in some books.

That told, when remaining longer time with considerably lower volume of gas in lungs, the gradient of oxygen intake from this remaining volume has proportionally stronger effect, so when the exhale is done a long time before surfacing, it could indeeed contribute to quicker drop of PaO2. There is though no such risk when done on the last few meters.

From this point of view the exhale at 20m as Eric tells, is surprising to me too, since it is still rather deep; but I guess he relies on strengthening the Diving Response, and perhaps uses it also for buoyancy control to slow down the last phase of the ascent (reducing so the risk of DCS). He will certainly tell us more.

A good reply as usual Trux, but in the end I think you agree with me and the text books?

"That told, when remaining longer time with considerably lower volume of gas in lungs, the gradient of oxygen intake from this remaining volume has proportionally stronger effect, so when the exhale is done a long time before surfacing, it could indeeed contribute to quicker drop of PaO2. There is though no such risk when done on the last few meters."

I would sum up, in my lay level, that at the critical last 10M every drop of 02 helps (and the higher blood pressure too as was well mentioned above), and any pressure drop (exhale) is not good if you are on the edge.

As I stated, this can be experimented with in competition scenarios with good safety. But, to think of badly watched spearo's trying the same ideas (that they may read here) would IMHO be very bad idea. I would therefore generally endorse the recommendation: don't exhale before the surface.

 

[trux]

I'd tell it depends on circumstances. If you dive FRC or just normally filled, it is certainly safe enough not exhaling before surfacing. But if you packed before the immersion, it may be in fact much safer exhaling a few last meters below the surface. Although you consume some oxygen during the breath-hold (and produce slightly less CO2) and hence the volume of the air in lungs is sligtly smaller than at the start, due to strong vasoconstriction and bloodshift, the inner lung volume is actually smaller too, and hence the resulting pressure may be equal or bigger than at the start. When coming back to the surface, the lungs expand, so besides a speculated lungs injury, they will crash the heart just like at heavy packing, reducing so its output and the blood flow to the brain. From this point of view, it may be then better exhaling a bit to avoid that the pressure builds up to the initial level (or above it).

However, personally I would only recommend it only very close to the surface anyway, not 10 or 20 meters deep. I guess Eric will chime in, and explain better why he does it. Although I speculated about some of the reasons previously, I am not sure at all they were the real reasons why he suggested it.

 

[efattah]

Although I have some theories as to why exhaling at 20m works well, I can't be certain why it works.

After 5 years of FRC diving, I found that when ascending on an FRC dive, I could be totally 'gone' at 20m and still make it to the surface clean. Then I switched back to packing. I tried doing hangs at 20m and I waited until I was similarly 'gone' (hypoxic), and then ascended with an exhale at 3m. I would have a BO/samba. So, the obvious solution was to wait at 20m until I felt as hypoxic as I would on an FRC dive, then exhale all the way down to FRC volume, which is basically a full exhale at 20m. Then I would ascend, but this time I would make it. I tried this experiment many times, the result was always the same; exhaling at 20m would convert the dive into an FRC dive, and for some reason when ascending at FRC volume I have a way bigger resistance to the blackout. Perhaps it is because there is no pressure on the heart due to expanding lungs -- perhaps some other reason. The main thing that mattered was that it seemed to work. Sebastien Murat also found a much bigger resistance to the blackout on FRC dives. A theory we both had independently was the 'theory of sudden hypoxia.' If you ascend with packing, the hypoxia comes suddenly in the last part of the ascent -- not enough time for defense mechanisms to kick in. When ascending at FRC volume, the hypoxia comes more gradually and earlier, allowing defense mechanisms to kick in.

I then started trying it on deep dives. Trying it on 85m dives, if I ascended but just exhaled at 3m, I would get a wave of mild hypoxia when recovering at the surface. Exhaling at 20m and I would get no such problem.

The big problem is to remember to do it when narked. I would get my friends to signal to me at 20m to exhale. Otherwise it was hard to remember. The other thing was to make sure the safety was always in front of me exactly at 20m, so I would try to remind myself to exhale as soon as I would see the safety diver. Unfortunately in competition this doesn't work, as sometimes the safety would meet me at 32m, other times at 9m.

Another thing is that when ascending at FRC volume you can crunch your abs and force the blood into your head as a method to avoid the BO. This is impossible in the last 15m with packing since there is too much air in your lungs.

 

[trullalla]

lotta and i did a series of 20 m dives on full lungs yesterday, and tried to exhale as much air as we could at 20m. i couldn't squeeze out more than 3 sad bubbles, while lotta had just a little more.
so exhaling on the ascent cannot explain the massive amount of air that we see during umberto ascent.

linda

 

[rddk]

One question to eric, exaling almost all air near 20 metres it wouldn't cause a drastical drop of lungs partial pressure that will cause a bo/samba? One of the things i've learned at apnea academy courses is that u must keep all the air u have taken from the surface for all the dive and at the end of dive at the surface do a passive exale and than a big inale for prevent bo/samba, they explained me that this practice is good for do not have a drastical drop parzial lungs pressure and conseguentially having a safe dive withouth bo/samba problems, if am not wrong they did many test with william trubridge. Thay you for ya answer and sorry for my bad english.

 

[efattah]

One question to eric, exaling almost all air near 20 metres it wouldn't cause a drastical drop of lungs partial pressure that will cause a bo/samba? One of the things i've learned at apnea academy courses is that u must keep all the air u have taken from the surface for all the dive and at the end of dive at the surface do a passive exale and than a big inale for prevent bo/samba, they explained me that this practice is good for do not have a drastical drop parzial lungs pressure and conseguentially having a safe dive withouth bo/samba problems, if am not wrong they did many test with william trubridge. Thay you for ya answer and sorry for my bad english.

Experiments on myself obviously gave different results than those done by the apnea academy. For me exhaling at 20m prevents the BO.

 

[rddk]

One question when u reach the surface do you still have some air inside your lungs or are you completely empty or near to it?

 

[jeremyanywhere]

After 5 years of FRC diving, I found that when ascending on an FRC dive, I could be totally 'gone' at 20m

5 years of FRC diving is one hell of a session. I am totally gone after 50 minutes

 

[efattah]

One question when u reach the surface do you still have some air inside your lungs or are you completely empty or near to it?

If I exhale down to near RV (say 2L) at 20m, this will expand three times its volume to 6L by the time I surface. So I still can exhale again just before the surface (I start a packing dive with 10.5L + 1.8L RV).

 

[rddk]

Tyvm eric for your info, i thinked about the boyle's law but didn't considered the facct that the residual volume "will increase" touching the surface, maybe u do not have bo/samba exaling at 20 cuz there's little difference between parzial lungs pressure. ty again

 

[trux]

As I explained earlier in this thread, the exhaling alone cannot directly and considerably change any partial pressure: the absolute pressure remains largely unaffected by the exhale (it will be still equal to the ambient pressure given by the depth as it was before the exhale), and the ratios of individual gases inside lungs won't be directly and immediately influenced by the exhale either.

On surface, there is a very slight difference of intrathoracic pressure on exhale and inhale due to the change of pressure of the rib cage, but that's largely eliminated underwater (the rib cage being compressed far below it maximal volume), and the pressure difference is by orders smaller than the influence of the water column.

And since partial pressure is the absolute pressure divided by the part of the gas in the mixture, when both the absolute pressure, and the parts in the mixture remain the same (as explained), the partial pressure simply does not change.

The only thing that changes is the volume of air remaining in lungs, and that can lead to faster gradients of consumption. But that needs some time to make any effect, and in the same time there are also other factors playing a role in the consumption.

I do not know why Apnea Academy teaches that the partial pressure changes with exhale, but I think they should either back it with some facts, or change the reasoning. For example if there is a drop of blood pressure due to the exhale, it might be a reason. But first I am not sure whether the exhale in depth will result in immediate change of BP, and second it is not easy to measure BP under water, so I do not know whether they really have such data.

 

[rddk]

Sorry i explained myself bad, is not the partial pressure that drop, infact it cannot change, what change is the "fuel" that u have in ur lungs, if u exale completely in the surface is like empty the fuel tank of your car near the fuel station so u blackout o have a samba, for this reason they teach ya to exale a little and inale a lot on the surface for do not loose the few oxigen u still have and for charging fresh one. Maybe exaling at 20 metres does not make so much difference to ur body and the residual oxigen remain almost the same.

 

[rddk]

Btw this week am going to taste de difference between exaling at 20 m and do the normal procedure they teached me.

 

[trux]

Reducing the available "fuel" as you tell, does not really justify the ban on exhale in the last few meters. In the last part of a breath-hold, the oxygen intake from lungs is seriously limited due to the shifted Bohr saturation curve, and due to the already low PaO2. Hence, on my mind, the exhale will barely make any difference, in scope of a few seconds. Now, when done in 20m depth, that's entirely something else, because the time is long enough. But it looks like the body reacts similarly as at FRC diving, by stronger Diving Response. However, that would need a much closer study - when it works for Eric, who has a long experience with FRC diving, it does not mean it will work for everyone. I would strongly discourage anyone testing it without having really excellent and redundant safety measures in place.

In contrary, I am persuaded that exhaling shortly before surfacing (1-2m), may prevent lung injury (especially at strongly packing divers), and perhaps it has also other advantages (being able to inhale right after surfacing, less sudden drop of pressure on surface). That's just my personal opinion, though, and the situation may be much more complicated than it appears. I think that a serious study would be needed to take in account all circumstances and effects.

 

[fcallagy]

Interesting discussion guys. Trux I am not speaking for AA but they do teach a small exhale at the surface and don't usually advocate packing but they also do advocate what works you as you know your body and its reactions.
The basis is the amount of BO and sambas on the surface of people not breathing properly on resurfacing which i think we can all agree is common. There are plenty of vids of people BO at the surface due to not starting to breathe properly. Eg: after 5 seconds at the surface they still have not taken a proper breath but are giving an OK signal or doing sp.
If it works for the diver to exhale slightly before the surface great but at 20m like mullins said I would also sink but Eric is a different case.

 

[rddk]

Trux don't worry about making testing i dive only with an experienced buddy that am sure is 100% able to help me in case of bo/samba, that's how i started to do some frc dive. Btw tyvm for all the info, you're giving me a lot of stuff to work on.

 

[efattah]

Just to clarify, I mentioned that after I exhale at 20m, this allows me to perform the 'ab crunch' maneuver to increase the BP in my head dramatically.

If you exhale at 20m but don't do the ab crunch move, it may not help at all, or it might make things worse.

Also it only works for me if I am ascending quickly. Exhaling at 20m and then ascending slowly doesn't work at all for me.

So you see, it only works in the very specific context of the circumstance and technique which I surround it. It is not correct to state that 'exhaling at 20m' helps in general. In many (and most) cases it probably makes things worse. But I believe in the correct circumstances it can help.

 

[rddk]

Tyvm again eric for sharing all the info u're giving us. Am saving some money for try to do a frc course, i think it will help me a lot for enjoy more and more freediving.

 

[fflupo]

where can you do a FRC course?

 

[ThomasB]

where can you do a FRC course?

So it seems:

Freediving and the dive response