letting the air out

[fishindave07]

Scenario: You dive under look for some fishies and so forth...is it ok to let out air when you are under water? is it harmful?

 

[yaffle]

Depends on where it comes out of....
But i am always told that blowing out air reduces of course you oxygen reserve, but you also lose co2, which is a great heart-rate slower, and thus very welcome while you dive....

Yaffle

 

[trux]

Depends on where it comes out of....
But i am always told that blowing out air reduces of course you oxygen reserve, but you also lose co2, which is a great heart-rate slower, and thus very welcome while you dive....

Sorry to disappoint you, but you won't lose any CO2. Better told you can blow out some air from your lungs, including some of the CO2, but it will not change the concentration (or the partial pressure) of CO2 in any way (unless you have a miraculous skill to blow out only CO2 ). And since for the gas exchange in lungs and blood, only the CO2 concentration plays a role, and not at all the absolute volume in your lungs, exhaling some air does not bring any physiological advantage.

As you wrote, you reduce the oxygen reserve, and in the same time the exhaling gives the body a false signal about ventilating air, which may suppress the urge to breath and can bring you into blackout. This effect may be amplified if you ascent and due to the decreasing pressure and expanding air in lungs oxygen is being removed from the the blood circulating through the lungs (ascent / depressurizing blackout also often called Shallow Water Blackout or SWB).

Besides it, by exhaling you also change your buoyancy and will need more effort to ascent. Also, exhaling is usually the sign of blackout, so buddies watching you may be alerted, but if you start doing it regularly and then once getting in real troubles they won't rush to help.

Better than exhaling during the apnea is learning to dive on empty lungs from the beginning. It has many advantages. I won't go into depth, since the topic was discussed here on DB very frequently, so I just advice you to use the search function above in the menu and look for threads about empty lungs diving, e-dives, or FRC dives, or threads about Sebastien Murat and his methods. You can also check this article: Fridykning

 

[SanderP]

Besides it, by exhaling you also change your buoyancy and will need more effort to ascent.

Doesn't using up the O2 from your lungs decrease your buoyancy as well?

Great post, trux!

 

[trux]

Doesn't using up the O2 from your lungs decrease your buoyancy as well?

Although the organism uses O2, it is not a black hole where matter disappears. Due to the metabolism process that consumes O2, it produces CO2, water vapor, and other waste products. The absolute change of volume is minor.

 

[azapa]

i feel the question is valid as sometimes, letting out small (tiny) amount of air out is relaxing (for me), normally at the very start of a dive. I would say its relaxation benefits (for me) outweigh any seconds I could gain from the extra 02.

 

[RuhRoh]

Was reading the manual of freediving the other day and I read a passage specifically discouraging this. It was focused on exhaling before you reach the surface because you drop the partial pressure of Oxygen. Especially after a long dive the level of oxygen is already low and blowing out air can lead to higher possibility of shallow water black out.

With so much to be discovered about SWB still its safer not to. Now letting air out at the begining should have no effect, and if you aren't pushing your limits its less risk. But once you go down about 10m the amount of air you have in your lungs won't be as tough to hold in as on the surface.

Hope it helps.

 

[trux]

Yes, that's what I described above. However there is also another theory (though unconfirmed) suspecting that some lung squeeze cases (barotrauma) may be caused during surfacing due to the overpressure, hence some exhaling may be needed in that cases. That is the case if you pack before diving, have a strong diving reflex with strong blood shift reducing the inner volume of lungs, and then surfacing faster than the blood shift can drop off. So ascending closer to the surface, the inner pressure in lungs will be higher than at the beginning (when it was already higher than the atmospheric pressure due to the buccal pumping). So in this case some exhaling would be necessary to avoid the barotrauma, but the risk of the ascent blackout (sometimes called SWB) remains, so you would need to reduce the dive length accordingly to reduce the risk. Paradoxically, the lung packing not only (possibly) increases the risk of a lung squeeze, but in fact also increases the risk of a SWB (if you are avoiding the barotrauma by exhaling).

 

[azapa]

to be honest, and this sounds dumber writing it than it does in my head, I I got the idea, and it's relaxing effects, watching seals jump in the water. I would notice that they would breath out a tiny bit and go on their way. I am very new to diving, and should not be trusted, but it really does seem to help me enjoy the experience a little more.

 

[trux]

Seals dive with empty lungs, so it is quite natural that they exhale after taking a breath. Well, the degree of exhale varies at seals - most of their short and shallow dives are aerobic, but when they go for a deep long dive, they go into complete anaerobic mode. With empty lungs the diving reflex kicks in faster and stronger, metabolism switches to the anaerobic mode, allowing for longer dive. Besides it the empty lung dives have other advantages in avoiding narcosis, reducing DCS (bents) risk, barotrauma, etc.

So the exhaling at seals is not really for relaxation, but rather natural exhaling, possibly also buoyancy control. If you do it at the beginning of the dive and it helps you to relax, there is probably no problem with it, but aside from the placebo psychological effect, it won't really help you unless you blow out relatively significant amount to get into the FRC mode (e-dive).

 

[trux]

EDIT: I forgot to mention (although I did mention it earlier above) - if you exhale not really at the beginning, but in the moment you are already in the struggle phase, then the exhaling may be really quite dangerous - not only because it increases the risk of the ascent blackout (SWB) due to the vacuum effect of depressurizing lungs, but also because the "relaxing" feeling of exhalation indeed partially suppresses the breathing urge (resp. the exhale urge because of high CO2) and you may not be able to correctly estimate the time to surface then.

So as I told, if you do it at the very beginning, then it is not an issue (though barely any help), but if you do it at depth, or during ascent, or in the struggle phase to suppress the urge of breath, then it is not really advisable.

 

[azapa]

thanks trux, I always read and appreciate your experienced comments. I will try to remove this "unique feature" from my dives. I guess we all want to be like seals

One goofy thing I have noticed as I have advanced is this: I can now do fresnel (yippee) but doing a mouth fill on the bottom (20M for me), sometimes If I don't bubble the air out of my mouth on the way up, it starts to hurt my ears as the pressure goes to my tubes. Should I be trying to swallow the air back to my lungs rather than wasting it, it feels very hard to do. Also on the same track: how can a not waste the air that has been equalized into my mask?? It just bubbles away at the skirt at the mo on the way up. My nose pocket in the mask is always too wet and snotty to think of breathing it in.

Bit of topic, but any help welcome. Thanks

 

[trux]

If you have your trachea closed, then there is no problem with releasing your mouth-fill. And also releasing a tiny amount of air from the lungs is certainly no big risk. Trying to keep the air, and pushing the mouth-fill back to lungs may be better, since it will increase the PaO2 in the lungs and facilitate the gas exchange that becomes to be inefficient at the end of apnea. However, we speak here about relatively tiny amounts of air, so I do not really know if the impact is considerable or can be quietly ignored. Possibly, if you need to struggle both psychically and physically to get the air back, it may in the end effect increase the oxygen consumption, so in that case relaxing and releasing the mouth-fill may be better. However, if you manage to drill it so that it is automatic and done with no effort or discomfort, then it may be better.

Though, if you use to pack, or if you feel strong overpressure on ascent, it may be the case I mentioned above, when the lung volume gets smaller due to blood shift, and there may be a risk of a light barotrauma - in that case a partial exhale may be necessary. Better though would be avoiding the necessity to exhale - not packing before the descent.

EDIT: As for the air in mask - many freedivers inhale the air from the mask when ascending. It can quite help a lot, depending on the mask and depth, there can be quite considerable amount of air (an oxygen) in it.

 

[diveoceanos]

Yes, that's what I described above. However there is also another theory (though unconfirmed) suspecting that some lung squeeze cases (barotrauma) may be caused during surfacing due to the overpressure, hence some exhaling may be needed in that cases. That is the case if you pack before diving, have a strong diving reflex with strong blood shift reducing the inner volume of lungs, and then surfacing faster than the blood shift can drop off. So ascending closer to the surface, the inner pressure in lungs will be higher than at the beginning (when it was already higher than the atmospheric pressure due to the buccal pumping). So in this case some exhaling would be necessary to avoid the barotrauma, but the risk of the ascent blackout (sometimes called SWB) remains, so you would need to reduce the dive length accordingly to reduce the risk. Paradoxically, the lung packing not only (possibly) increases the risk of a lung squeeze, but in fact also increases the risk of a SWB (if you are avoiding the barotrauma by exhaling).

What you are describing is highly interesting. As I understand there have not been any reports or anecdodal cases. Can you share the source of this information / theory?

P.S. Would it be more appropriate to use the term Lung Overexpansion Injury instead of Lung Squeeze? Squeeze as a term is being used to describe the decrease in volume in body air spaces which happens on descents.

 

[trux]

Yes, you are right; the term lung squeeze is indeed often wrongly used among freedivers. Generally, freedivers speak about lung squeeze at most lung/trachea injuries with bleeding. It was speculated (and I see it as rather probable) that large amount of lung squeezes are not at all caused by a barotrauma at negative pressures, but may have other reasons. Like for example the cases described in my previous post, or by other situations both on ascent or descent. From the discussions I saw here on DB, there were reported many cases of "lung squeezes" (correctly some types of barotrauma) even at shallow dives, and it was often in association with packing.

Some cases of ascent barotraumas (originally believed a "lung squeeze") were caused by some simple mechanical problems - for example I remember a DB member reporting such case of "lung squeeze". Only later when analyzing his dive he realized, that it was most likely caused by a belt that slipped on the ascent more than usually and remained then blocking his rib cage on the ascent. Since the lungs could not expand to the original volume, he suffered the barotrauma.

And today I am more and more persuaded about the correctness of the theory that many freedivers actually suffer an ascent barotrauma rather than negative pressure barotrauma. It is very logical. Unless like in the below linked thread where I did not yet have sufficient theoretical background and was rather defensive in the argumentation, today I am pretty persuaded it is quite correct and very much probable. Let's explain it again:

1. Freediver packs to the maximum on the surface. We know that already packing alone can cause lung injury, but let's accept that there is no problem at this moment and that the pressure inside lungs is still within secure margin.
   .
2. Freediver descents, in the first few meters, his rib cage is quite rigid because of the high pressure inside - already here he can suffer (and likely often suffers) a "lung squeeze" (in fact positive pressure barotrauma) if he compresses the ribcage or diaphragm by bending too much or by muscle pressure, increasing so the inner pressure further over the surface packed overpressure.
   .
3. At moderate depth, until reaching the negative pressure depth, the freediver is relatively safe - the inner lung pressure is equal to the outer pressure, and the rib cage is not in any extreme volume (neither too pressed, nor too inflated).
   .
4. At negative depth, there is the risk of the real lung squeeze due to bigger pressure outside than inside, but today it is well known that the body prevents this with blood shift. Blood pushed out of limbs and some parts of body due to vasoconstriction, floods into lungs (not inside the lung space, but into the veins and capillaries in alveoli) greatly reducing so the inner volume of alveoli containing air, and compensating so the pressure difference. The reliability of this mechanism is best demonstrated at FRC (empty lungs) divers who reach the negative depth very quickly after leaving the surface and proportionally often dive deeper than divers with full lungs, without any lung squeeze.
   .
5. Now, our diver starts the ascent. He is already in a progressed phase of the dive; diving response (including vasoconstriction) starts to kick in stronger and stronger. Due to the strong vasoconstriction, blood shifted to lungs has nowhere to go, so stays there still reducing the inner volume considerably. When the freediver reaches the surface, without exhaling, the volume of air is about the same as at the beginning, but the volume of lungs is still reduced due to the continuing blood shift and vasoconstriction, hence the pressure is bigger than after the initial packing, and can lead to an injury (not really a negative "lung squeeze, but a positive barotrauma).
   .
6. And of course, close to the surface, even if there were no blood shift at all remaining, the freediver's lungs are again quite pressurized, rib cage rigid, so some wrong movement or contractions during the ascent (very probable at this point of time) can easily increase the original overpressure over tolerable limit and cause barotrauma (that may be mistaken for a lung squeeze because of the symptoms)

I think it makes very much good sense. I also think that the risk is higher at divers using nose-clips. If you do not have it, at least some air from the depressurizing mask escapes (even if you try inhaling it back on ascent), reducing so the final volume of air at the end of the ascent.

There were also claims that the volume of air in lungs decreases during apnea due to the consumption of oxygen, but it is not really true. Oxygen is indeed being consumed, but the metabolism produces CO2 and water vapor so the final volume after the metabolic process is practically identical. Well, there may be some very fine differences (negative or positive), but unfortunately I did not manage to find any precise scientific data on this topic.

There are some interesting threads discussing the topic here:
http://forums.deeperblue.net/safety/66867-new-theory-about-risk-freediving-dcs-airtrapping.html
ImpulseAdventure - Freediving - Lung Squeeze
freediving - squeeze
http://forums.deeperblue.net/specialist-advanced/65690-depth-pressure-squeeze.html
http://forums.deeperblue.net/freediving-training-techniques/21577-how-safe-packing.html#post618592
http://forums.deeperblue.net/spearo-board/65190-spearing-lung-packing.html
http://forums.deeperblue.net/general-freediving/64645-packing-barotrauma.html

 

[diveoceanos]

There are some interesting threads discussing the topic here:
http://forums.deeperblue.net/safety/66867-new-theory-about-risk-freediving-dcs-airtrapping.html
ImpulseAdventure - Freediving - Lung Squeeze
freediving - squeeze
http://forums.deeperblue.net/specialist-advanced/65690-depth-pressure-squeeze.html
http://forums.deeperblue.net/freediving-training-techniques/21577-how-safe-packing.html#post618592
http://forums.deeperblue.net/spearo-board/65190-spearing-lung-packing.html
http://forums.deeperblue.net/general-freediving/64645-packing-barotrauma.html

Thanx for elaborating on and sharing of this info.

This link might also be relevant with lung injuries in general while BHD. The authors suggest a combination of negative intra-thoracic pressure due to the forced attempt to breath + voluntary diaphragmatic contraction (with mouth and nose closed) on the beggining of the ascent + increased blood volume and Blood Pressure in the pulmonary capillaries (blood shift and hemodynamic changes resulting in high BP) which all together form a stress failure of pulmory capillaries. The symptoms are similar to lung over-expansion injuries with alveolar edema and hemoptysis.

Hemoptysis Provoked by Voluntary Diaphragmatic Contractions in Breath-Hold Divers -- Kiyan et al. 120 (6): 2098 -- Chest

 

[Seal]

to be honest, and this sounds dumber writing it than it does in my head, I I got the idea, and it's relaxing effects, watching seals jump in the water. I would notice that they would breath out a tiny bit and go on their way. I am very new to diving, and should not be trusted, but it really does seem to help me enjoy the experience a little more.

Read some of Sebastien Murat's work (sorry if miss spelled)

He is working with exhale diving, or "Seal diving" if you will. Personaly I think his ideas are some of the best in sport.

 

[wjohnson100]

As far as whether lung volume decreases during a hold, I think it does to some extent because the O2 is consumed and CO2 (Same volume as O2) is produced, but not all of it makes its way into the lungs, hence the need to breathe. Just shake a coke bottle to see how much CO2 can be dissolved in water. There may be water vapor produced but I would bet that the air space in the lungs becomes saturated with moisture almost instantaneously (check the relative humidity of the air you breathe out, I bet before your mouth is closed on a hold, your lungs are at 100% relative humidity) and the volume of water vapor is actually quite small relative to lung volume, nowhere near the amount of CO2 and O2 involved. To get those kinds of concentrations of water vapor in the lungs you would have to have boiling water there, and that is certainly not happening. Anyway just check how you feel during a long static. Toward the end you feel like you have less air in your lungs. Something is causing that. One way to know for sure would be to do a Pulmonary Function Test with the air you have left at the end of a hold and compare that to your normal. Another way would be to measure the O2/CO2 concentrations of the air you breathe out at the end of a hold and compare it to the concentrations of O2/Co2 in the air. From that and using assumptions about lung volume you could calculate the change in volume during a hold relatively easily. If you have 7 liter lungs and O2 starts at 20% and ends at 15% with CO2 going from 2%-4%, then the relative change would be on the order of -3% of lung volume or about 200 CC, about the volume of 4-8 packs. For someone with bigger lungs the change would be even more. I am just guessing at all these numbers since I don't have my physics books handy.

Walt

 

[naiad]

As far as whether lung volume decreases during a hold, I think it does to some extent because the O2 is consumed and CO2 (Same volume as O2) is produced, but not all of it makes its way into the lungs, hence the need to breathe. Just shake a coke bottle to see how much CO2 can be dissolved in water.

I am almost certain that it does. If I start a long static with a full breath, I can often breathe in a bit afterwards before I breathe out, so there must be a bit of extra space. There is also some loss of buoyancy at the end of a dynamic.

Lucia

 

[aesthetic]

Sorry to disappoint you, but you won't lose any CO2. Better told you can blow out some air from your lungs, including some of the CO2, but it will not change the concentration (or the partial pressure) of CO2 in any way (unless you have a miraculous skill to blow out only CO2 ). And since for the gas exchange in lungs and blood, only the CO2 concentration plays a role, and not at all the absolute volume in your lungs, exhaling some air does not bring any physiological advantage.

As you wrote, you reduce the oxygen reserve, and in the same time the exhaling gives the body a false signal about ventilating air, which may suppress the urge to breath and can bring you into blackout. This effect may be amplified if you ascent and due to the decreasing pressure and expanding air in lungs oxygen is being removed from the the blood circulating through the lungs (ascent / depressurizing blackout also often called Shallow Water Blackout or SWB).

Besides it, by exhaling you also change your buoyancy and will need more effort to ascent. Also, exhaling is usually the sign of blackout, so buddies watching you may be alerted, but if you start doing it regularly and then once getting in real troubles they won't rush to help.

Better than exhaling during the apnea is learning to dive on empty lungs from the beginning. It has many advantages. I won't go into depth, since the topic was discussed here on DB very frequently, so I just advice you to use the search function above in the menu and look for threads about empty lungs diving, e-dives, or FRC dives, or threads about Sebastien Murat and his methods. You can also check this article: Fridykning

very useful information. thanks!