Waiting to exhale...

[Sweet Tooth]

Is it better to exhale the last few feet of your ascent so that you can inhale immediately upon surfacing or should you hold your breath until you surface?
I guess there are two schools of thought:
Exhale the last few feet of your ascent so the very first thing you do upon surfacing is inhale for a hook breath. You should be positively buoyant enough at that depth that the loss of air shouldn't make that much of a difference plus you're already moving upwards so the exhale shouldn't adversely affect your ascent.
Or,
Hold your breath until you surface. It takes less than a second to exhale so you're not wasting a significant amount of time after you surface before you inhale. You maintain maximum buoyancy during the entire ascent and exhalation bubbles are one of the signs of a diver in trouble so you don't want to give any false alarms.
Would there be any significant differences one way or the other for the pressure drop in your lungs? In other words is it more of a problem to reduce pressure by exhaling over a period of a few seconds coupled with the hydrostatic pressure drop of an ascent from 5' to zero or to experience the sudden drop of a rapid exhale at the surface?

Thanks

 

[vali]

my advice is that...it depends!!!
i don't sugest to exale until surfacing on a troubled water [waves]
and generally i think keeping your breath until head out of the water has some advantage
clearely more pozitive buoyance to help you GRAB THE BUOY, and the assurance that nothings go wrong if you don't appreciate allways the time to exhale untill the surface....

 

[ImmersionFD]

Sweet Tooth I keep bumping into you.


I don't think you will be surprised by my answer. We teach all our students to exhale the last bit of the dive so when your airway hits the surface you are instantly breathing in, so your getting 02 to the brain as quickly as possible.

As far as buoyancy is concerned if your weighted properly you going to be very positive at the surface, even if you were to exhale, so I don't think buoyancy is an issue.

Here is the way I look at it, the difference between a loss of motor control and a black out can be holding your breath for a couple of extra seconds. By making sure your getting oxygen to your brain a couple of seconds quicker you are increasing your safety. You could be turning a blackout into a loss of motor control, and possibly turning a loss of motor control into a clean dive. Oxygen is your friend!

 

[emdiesse]

Excuse my perhaps misunderstanding here however I don't nearly understand this sport as well as other however I have read that exhaling on a dive can contibute to shallow water blackout by making the partial pressure of oxygen in the lungs lower than the partial pressure of oxygen in the bloodstream causing oxygen to actually flow out the bloodstream and into the lungs.

Can anyone spread any light on this?

Is it safe to exhale just before you surface allowing you to inhale as soon as possible?

With my lack of an in depth understanding of the physiology behind this my guess is that exhaling on the surface and exhaling in the last metre or so of a dive ready to inhale on the surface isn't going to make too much difference?

Rather than exhaling fully out and then fully in at the end of a dive, would it be safer to wait to reach the surface and then exhale out and exhale in alternately and moderately until gradually reaching normal breaths.

Can a diver lose consciousness, even on the surface, of a dive if they fully exhale by reducing the partial pressure of oxygen in the lungs to lower than that in the bloodstream?

 

[Kars]

Ok, let's get some things clear here.

Firstly like Vali, I say it depends. I say it depends on wave and support (line or buoy stability). Naturally when the situation is unpredictable and tough you will avoid diving close to your maximum abilities, and work to have a bigger safety margin. Hence I say exhale at the surface upon securing your head above the water.

When the situation is good or ideal for a line dive personal best, then I recommend exhaling a bit (not much!) in the last 1-2m from the surface, to facilitate a big inhale at the surface.
I say a small exhale because exhaling drops the blood pressure that is supplying the brain just enough to remain conscious in some of those pb setting dives.
Therefore it is followed that upon surfacing one inhales fast and holds the air down while applying pressure on the lungs, tensing abdominal and chest muscles as to keep up the blood pressure for ~3 seconds, micro exhale - inhale hold 3, micro exhale - inhale hold 3, remove mask, Ok hand sign, slowly release saying "I'm ok", inhale, breath while keeping focus and awaiting the white card. So basically using hook-breath upon surfacing.

Hook-breaths surely has helped me a lot helping myself through near samba or samba situations, also in the pool.

I'm against exhales at greater depths, as well as deep exhales before surfacing, as the drop in lung pressure reduces gas-exchange and blood pressure, hampering O2 throughput to the brain. Resulting in shallow water blackout, or samba or BO at the surface.

Also another tip is NOT to constantly look up while your swimming/floating to the surface, this hampers bloodflow to the brain too. Take a quick glance to check for the platform/boat and sliding your upward open hand along the line, to hold it instantly when breaching the surface with the head worked for me very well.

Love, Courage and Water,

Kars

 

[trux]

I'm against exhales at greater depths, as well as deep exhales before surfacing, as the drop in lung pressure reduces gas-exchange and blood pressure, hampering O2 throughput to the brain.

Exhaling before surfacing has very little impact on the lung pressure or the PaO2. The pressure is given by the ambient pressure (the depth), not by the level of the lungs inflation. At fully inflated lungs, the pressure of the chest wall and the diaphragm is completely negligible in comparison with the ambient water pressure even when at surface. It means the the PaO2 will be practically identical at fully inflated lungs as at exhaled ones.

Still, there are arguments both for and against exhaling near the surface, and there are schools teaching either of the techniques. I do not think either of them is outright wrong or better. Although personally I tend to prefer a small exhale near the surface, I think it may be more important being consistent than selecting one method over the other.

 

[Kars]

Exhaling before surfacing has very little impact on the lung pressure or the PaO2. The pressure is given by the ambient pressure (the depth), not by the level of the lungs inflation. At fully inflated lungs, the pressure of the chest wall and the diaphragm is completely negligible in comparison with the ambient water pressure even when at surface. It means the the PaO2 will be practically identical at fully inflated lungs as at exhaled ones.

Still, there are arguments both for and against exhaling near the surface, and there are schools teaching either of the techniques. I do not think either of them is outright wrong or better. Although personally I tend to prefer a small exhale near the surface, I think it may be more important being consistent than selecting one method over the other.

Hi Ivo, thanks for chiming in, challenging and expanding the conversation.

In regard to the lung pressure remaining equal to the environmental (water pressure) coming up, I think I have to disagree. especially in the case of people who are tense or not very flexible. I think their muscles fighting the pressure, pushing out the chest and diaphragm and therefore creating a mild under pressure in relation to the water pressure. I diver feels crushed and out of air. When reaching the surface the air re expends and the lung volume increases to a comfortable level, meaning within muscle and chest flexibility range, at that moment the pressure difference is equal. Going further up, especially when packed and having a lot of bloodshift remaining, filling up lungvolume, the pressure inside the lungs in relation to the water pressure increases, one feels inflated, similar to packing on the surface. Granted the pressure difference won't be big, but I do think it's there.
Is it true that a (relative) over pressurised lung has a bigger gas exchange rate than an under pressurised lung?

I think there are more factors involved:

- The amount of bloodshift,
- Packing,
- maybe even more?

Anyway, when making a pb-level dive, things are different than making easier dives. My personal experience, is that a few times, doing pb's in CWT, I found that after surfacing my VC was temporary reduced by a substantial amount (measured by a Swedish Freediver doctor frequenting the Nordic Deep comp).
I have the idea that the bloodshift was not reabsorbed.
Packing in combination with remaining bloodshift can (overstress) the lungs and or apply to much pressure on heart and aorta, suppressing blood flow.

Exhaling at say 20m (to pick something extreme), I think may reduce or nullify the transfer of O2 from the lungs to the bloodstream. It will reduce buoyancy, it will drop blood pressure, dropping blood and therefore O2 throughput to the brain. If you need 20 seconds to reach the surface and inhale, than you still need after the inhale an additional 8 seconds for the fresh inhaled O2 to reach the brain.

In all, matching my personal experience, I think keeping the blood flow to the brain up is the main thing.


I'm sorry for the confusing blurry - all over the place - post, please feel free to clarify, correct or expend on my views. - Thanks.

 

[trux]

In regard to the lung pressure remaining equal to the environmental (water pressure) coming up, I think I have to disagree. especially in the case of people who are tense or not very flexible. I think their muscles fighting the pressure, pushing out the chest and diaphragm and therefore creating a mild under pressure in relation to the water pressure...

No, Kars, the pressure change, even with extreme packing is surprisingly very low. Although extreme packers can increase the lung volume by tens of percents, only very tiny part of it can be contributed directly to the higher pressure. Most of it is due to the expansion of the chest. I have a study with exact numbers somewhere, but not just at the hand (will try to find it later), but the pressure change is really absolutely negligible - somewhere around units of percent (if even). All that is easily compensated already with a water column of several decimeters (tens of centimeters). So the lung pressure or the PaO2 is really absolutely no issue here. What can play some role is the surface area of the alveoli that decreases at fully exhaled lungs, and the possible drop of blood pressure, but that would happen in a few seconds (when surfacing) anyway, so in fact the sooner you can inhale and raise the pressure (with a hook breath) the better. So from this point of view, partially exhaling just under the surface, inhaling and holding the breath (hook breath) for a while just after making the surface, seems to be the better solution. BUt as I told, the topic is rather complex, and there are many other aspects, so I respect both choices.

 

[Kars]

Thank you Ivo

Thanks also for the most honourable way you manage to present your information.

 

[trux]

I tried to find the study about the intrapulmonary pressures after packing, but still did not locate it. I just found one of my own quotes to the data from the study - it was related to the injuries related to packing, namely the pneumomediastinum. The packing was considered already pretty strong in that case, but the the cross-pulmonary pressure was only 0.041 bar, hence around 4% increase to the ambient pressure. That's compensated already by 40cm of water.

And I forgot to mention my habitual warning for those who use to pack before deep diving - for them exhaling shortly below the surface may be more important than to others. As shown by numerous studies, the packing alone is a maneuver posing considerable risk of injury. As I wrote, this overpressure is quickly compensated already with a very shallow depth. During the sink-phase (duck dive), when you compress your abdomen and chest, you increase the risk of an injury, but then you are quickly in a relative safety. The problem is at the ascent - if you do not exhale and come back to the surface with a closed epiglottis, you risk a serious barotrauma. That's because your lung volume may be considerably reduced by blood-shift, so although the air volume is typically 100-300 ml lower than at the beginning (due to the O2 consumption), the blood shift can be much bigger, hence the intrapulmonary pressure can easily surpass the critical level. So from this point of view, I think that at packing freedivers, partially exhaling ~1-3m below the surface is a quite wise choice.

 

[Kars]

Thanks Ivo!

As usual a great reply brought in an elegant and peaceful way

 

[emdiesse]

Cheers for the informative posts guys. Very helpful. The debate was an interesting one. I hadn't even thought of packing as increasing the pressue inside the lungs, however like you say a small column of water easily compensates for this packing. As I remember from scuba training the last 10 metres is the most dangerous since it's where the biggest pressure change happens. Which would have lead me to ask about whether a packer would be in danger to not exhale a little before the surface since the rate of expansion of there lungs would be fast at this point, faster than the rate of expansion of there lungs when they where packing. The very nature of this, to me, sounds dangerous.

I think really the general consensus seems that if you choose to pack you are likely doing yourself a favour by exhaling slightly before the surface to avoid barotrauma.

If you don't pack it appears a slight exhalation before the surface is favourable (for some) so that you can immediately proceed in hook breathing.

I'll have to do some reading on hook breathing, however I feel I understand it and to be honest, I somehow feel that this is something I subconciously have been doing after a breath hold.

It's nice to begin to understand the physiology of our bodies, and in a freediving context. It can only be in our interests to understand these effects in order to open a greater awareness to the way our bodies truely are feeling and to sympathise with what must be done in order to try and avoid blackouts, samba, etc

 

[vali]

i don't think that in freediving, packing can do barotrauma
in scuba: yes
because you allways inhale air at some pressure that change when ascending
but in frediving, keeping the same amount of air all the way down and up, is normal
the air in my loungs is a quantity that remain unchanged [just compress in descend and expand in ascend], but the same quantum....
anyway there are various factors...let's say only the air in the masq, who expand and go out...i-m shure that with all that air i let some air go out thrue my nose, but not before i-m shure that my exhale will die when i-m above the surface....

 

[trux]

I am sorry, Vali, but you are mistaken. With packing you can suffer a barotrauma already on the surface. There are numerous cases of several different barotraumatic injuries at freedivers documented in the scientific literature.

The next critical moment is the immersion - at a packing freediver, the lungs are already overfilled and the intrapulmonary pressure is close to the critical level. In the moment the diver performs his duck-dive, he compresses his abdomen, the intrapulmonary pressure rises, and can easily damage the lung tissue. This is speculated to be the reason why lung oedema is more frequent at packing than at non-packing divers.

And the next critical moment, as explained already in my previous post, is the ascent. You are wrong to think that the lung volume is constant. On one hand the organism consumes some O2, which is only partially replaced by the CO2 in the lungs - this leads to the reduction of air volume, hence to some reduction of the pressure. At an average person, the change is relatively small - somewhere around 100-300ml (depending the lung volume, the length of the apnea, the respiratory index, etc). But in the same time, there is also the blood shift (not only due to the hydrostatic pressure, but also due to the vasoconstriction of the peripheral vessels). It can reduce the lung volume by 1-3 liters. The blood partially retracts a bit from the lung vessels during the ascent with the decreasing hydrostatic pressure, but due to the progressing vasoconstriction not fully, and the lung volume will be smaller than at the moment of the immersion anyway. It means that the freediver has in the lungs practically the same amount of air (minus the 100-300ml), but the lung volume is much smaller (could be a liter or more). That would result in a much greater intrapulmonary pressure during the arrival to the surface than at the moment of the immersion (just after the packing). Hence a barotrauma is very well possible.

 

[vali]

thanks trux!!!
i didn't meant to say that the volume is constant
i wanted to say that if i go down with an A quantyty of air, i cannot return wit an A+n quantyty at the surface [like in scuba]

 

[trux]

i wanted to say that if i go down with an A quantyty of air, i cannot return wit an A+n quantyty at the surface [like in scuba]

Yes, but the quantity of air is not the only factor. The pressure is given A) by the quatity of air in the lungs (only slightly reduced at the end of apnea) and B) by the volume of the lungs (possibly much smaller than initially). So you are trying to fit practically the same amount of air in a much smaller container, which leads to a much higher pressure, of course. Hence the barotrauma is very well possible not only in scuba, but in freediving too.

 

[emdiesse]

Very interesting. There was me thinking it was something to do with how the lung expands during ascent (doubling in the last 10 metres). Leading me to think in a similar way to muscles contracting fast whilst lifting weight are at more risk of tearing and I thought in a similar way this fast expansion of a packed lung could react similar and tear when expanding faster.

Interesting to see that so many things are going on that we normally are completely oblivious to.

 

[Simos]

Interesting discussion guys - I prefer to not exhale until I surface. The main reason is that if you are so close to samba/BO that a couple of seconds will make a difference, you're already pushing too much. It's a slippery slope to take I think and temptation will always be there to start exhaling earlier.

In fact I am trying to learn to inhale a bit as I ascend to use the air in the mask. I don't know how to quantify this but the effects of inhaling the air that you would otherwise lose could counterbalance the second or so you get from exhaling underwater.

I guess if you've really over-done it and struggling on the ascend you always have the option to exhale a bit early so it's like an extra safety buffer.

Agree that for competition where you are trying to squeeze the last milimetre it might be a different story but that's no real diving anyway. Lol

In the sea you might even have cases where in the last few metres you see an obstacle like a boat or even swimmers etc and having your full breath makes it safer to wait a bit more before surfacing, change direction etc

 

[Sweet Tooth]

I finally get a chance to chime back in on my own thread:
I assume the decision whether to exhale at or below the surface is made to prevent the partial pressure of oxygen (PPO2) from dropping below a critical level.
Assuming .16atm to be the critical level, a diver who consumed 1/3 of the O2 in his lungs has reduced his percentage of O2 from 21% to 14%. That would translate to a dangerous PPO2 of .14atm at the surface. But even 5 feet down the 14% O2 would have a PPO2 of .16atm.
If the diver can create a 15% increase over atmospheric pressure in his lungs during his exhale, he should still have a "safe" PPO2 until the end of the exhale, but I don't know if the increase in pressure in the lungs would reach 15% or not though. If this is the case though, when he surfaces he could immediately inhale thereby exposing his lungs to a .14atm PPO2 for only a brief period of time before filling them with .21atm PPO2 air. Ok, the PPO2 in his lungs after the inhale would be less than .21atm due to the residual low PPO2 volume still in there, but the bottom line is our diver now has enough PPO2 to be safe.
Conversely, if the diver waits to exhale he will expose himself to a PPO2 of less than .16atm the last 5 feet of his dive. Even if the increased pressure during an exhale at the surface momentarily bumps the PPO2 up to .16atm he has still spent a couple seconds in dangerous hypoxia and will briefly enter that hypoxia again between exhale and inhale.
This made me think of a third possibility. Could our diver execute a val salva or similar type maneuver with a closed epiglottis and increase the pressure in his lungs that way until he exhales? That way he still has all of his original "air" until he surfaces and only creates a hypoxic state once between his exhale and inhale. The only drawback is that he does this a few seconds later than he would if he exhaled the last few feet of his ascent.

Thanks for all of the replies and I look forward to your thoughts.

 

[trux]

If the diver can create a 15% increase over atmospheric pressure in his lungs during his exhale,...

You cannot increase the PaO2 during the exhale. As explained above, the fact whether you have full or partially empty lungs has little effect on the PaO2 in them. It is given predominantly by the ambient pressure. You can increase it a bit by a voluntary diaphragmatic and thoracic pressure (which at prolonged apneas usually happens involuntarily anyway, and it is something we call "contractions"), but the increase of PaO2 is negligible (relative to the changes of the ambient pressure), and then it is impossible during the exhale. You would need to stop exhaling, closing the epiglottis, and then contracting again. However, since we are speaking about exhaling during the last few feet, we are speaking about the time-frame of around a single second, so you don't need to bother about any complicated maneuvres during such a short time.

Eric Fattah described using this method at deep dives, where he exhales pretty deep (at ~20m), which stimulates better the DR. I do not remember whether he keeps contracted, to keep the blood pressure up, but I think he wrote he did. However, I would really not recommend using this method to anyone. It is pretty extreme, and you have to have great experience with FRC diving, and have the safety perfectly assured by a reliable and an equally experienced buddy.

I would rather advise exhaling a bit (but not fully!) just below the surface, so that you can take a inhale just when arriving to the surface. If it happens within 5 feet from the surface (around a second), the early exhale can't cause any blackout. As explained the impact of the exhale on the PaO2 is more or less irrelevant, the main concern remains the drop of blood pressure, but none of it is critical in this time frame.