No-Limits Question

[Billextreme]

rxcnc2,

There are many world record holders in training, and even more behind the computer. And that it is more or less why AIDA exist - but then we have some extremely good freedivers out there who do not want to excel in official forms.

No Limits have no limits. It's more about mankind adaptation over long time, patience, sustainability, passion and commitment. And then of course you have to add pure motivation, hard-core performance and money - then also the technical expertise and equipment. (perfect logistics)

Herbert’s next NL dive, probably an 800ft dive, will add less than 20 seconds to his 214m dive and this will not be close to any of Herbert’s limits, nor the 3 extra atm. A 305 meters No Limits dive will be a big step, but not close to any limits. According to more "sophisticated calculations" in Herbert’s case, his dive-stile will cover a 365m dive before there are any doubts. To know is that when people do this kind of depths/dives, the mental status is the key factor.

How do you get a mental status that is sufficiently strong to bring you down to those depths? Well, first of all you need some good training behind your back, training that convince you that the dive time will be NO PROBLEM (this means that you should be able to hold your breath the same time as the dive will take, but with empty lungs on the surface) Then the training need to convince you that the equipment, set-up and the crew incl safety is in perfect order to handle the dive even if unpredictable things happen. Then you have to trust that your body and brain can deal with the effects of the gas exchange (or no gas exchange and/or mix of both) in those depts. And last you have to train the pain-threshold to a level when you still smile when it feels like your going to implode and soon die.

Questions:
Speed down? How fast can a sled freefall? Both theoretically and then practically? In Herbert's 214m dive he was over 3m/s but normally most of the NL divers is around 2m/s. Will it be possible to freefall faster then 4 to 5 m/s?

Then I'm curious about VWT, how deep can you go and still be able to make the surface with a white card? The easy part is to go down, but it is possible to pull up from let say 160m. How long would a 160 VWT dive take?

/B

 

[Arjen]

Questions:
Speed down? How fast can a sled freefall? Both theoretically and then practically? In Herbert's 214m dive he was over 3m/s but normally most of the NL divers is around 2m/s. Will it be possible to freefall faster then 4 to 5 m/s?

Well, the deeper you go, the faster the sled has to freefall.

If we take the 305 meter dive Herbert is going to make eventually, because in my mind there is no doubt that he is going to do it, the difference between a 2m/s descent speed and a 4m/s descent speed are hugh. That would be 2 minutes 32 seconds compared to 1 minute 16 seconds in a descent. The time gained in a faster descent, can be used in the probably necessary decompressionstops at the end of the dive. And you want to minimize the time you spend in the deep as much as possible because of the O2 toxicity, the narcosis and the risk of DCS.

It's the same for ascend speeds. You want those high as well untill around 40 to 50 meters. After that it would probably be good to ascend in a sort of decompression stop mode. A slower ascend from 50 to 20, a short stop at 20, slow to 15, short stop at 15, slow to 10, hang for at least a minute at 10 and after that as slow as is possible from 10 to the surface. A bit like a tech diver would do after a deep dive. To get as much time as possible in the last parts of the dive, you need the speed in the first part of the dive. Even if you can hold your breath as long as the Herberts in this world.

 

[superhornet59]

Wait, I'm sorry, why is narcosis becoming an issue as we go deeper? Once the gas exchange between lungs and blood stops, shouldn't the concentration of nitrogen in the blood plateau at that point? I agree this may already be at or past the point where narcosis is a problem, but it shouldn't get any *worse* after this point unless time is a factor (I wouldn't know, I've never gone diving that deep whether scuba or apnea). Is it?

 

[efattah]

Gas exchange is predicted to stop around 215m+, which hasn't been reached yet.

But the deep narcosis is primarly caused by CO2 production, which continues even after gas exchange stops.

 

[trux]

Well, to tell the truth, scientists agree, the narcosis process is not fully understood yet. One hypothesis is that it is caused by direct pressure of gas molecules on nerve synopsis - in that case the gas exchange has little to do with it - once the molecules are present (dissolved) in the tissue, they'd have the same effect. And, as Eric wrote, CO2 is a very important factor at narcosis too. It is a well known trigger/amplifier, and some sources suspect it as a direct narcosis factor as well. That makes it the most important factor in deep apnea dives, of course.

BTW, I suspect that in Herbert's case the gas exchange stopped before 215 m, because he practicaly dove on empty lungs. Or, more precisely, on lungs emptied at ~20 m, which means the lungs were likely as well as completely collapsed probably much earlier than before he reached the bottom plate.

 

[rxcnc2]

BTW, I suspect that in Herbert's case the gas exchange stopped before 215 m, because he practicaly dove on empty lungs. Or, more precisely, on lungs emptied at ~20 m, which means the lungs were likely as well as completely collapsed probably much earlier than before he reached the bottom plate.

I think empty lungs means with about 1-2.5L of air still in (at 1 atm), which is the so-called residual volume: air we are not able to exhale. Besides, if he blew at 20m (3atm) 1.5L (bottle volume) of air, this would mean 4.5L at 1atm which is hardly the full lung volume for Herbert I think esp. after packing.

Of course you are right about the basic point, i.e. very little gas left to echange. Unlike the deep technical divers which are probably the most studied case.

 

[trux]

Yes, when we speak about diving on empty lungs, it actually means "emptied" and not physically perfectly empty, and of course everyone knows that there is still some residual volume in the lungs after that point anyway. No one would argue about that. However, if you empty your lungs at 10% of your target depth (regardless if only partially), it is pretty much clear that the lungs will collapse much quicker than if you dive with full lungs, hence that the gas exchange drops or stops much earlier in the dive.

And that was the point of my comment. It is not so much about the remaining volume of the gas available, but more about the colpased alveoli - most of the air will remain in less collpasible trachea and bronchi, where there is quite little gas exchange. It means, at such freediver, the nitrogen trapped in that space has much reduced chance to get into the blood.

 

[Fitz-Clarke]

I agree with previous comments that breath-hold time is not a major limiting factor in no-limits depth. The limiting factor so far has been having the skill and courage to go deep and risk the unknown. Herbert is going into uncharted territory where anything could happen. I have a few comments:

(1) Herbert’s 214 m dive does not invalidate my theory at all. I have simulated this dive in my computer model. Here are some numbers. We can assume 12 litres at the start of the dive. He stops briefly at 22 m where lung volume is 3.6 litres. He appears to blow about 1.0 litre into the coke bottle in the video. This is consistent with his impression at that depth that all his air is blown out down to an airway pressure of zero relative to ambient. He transfers a small volume of air back into his upper airway, then the rest of the air in the bottle is seen to bubble away. This is not the same as a true exhale dive because it still leaves 2.6 litres in the lungs and lower airways at this depth. At this point, 24 percent of alveoli are collapsed. More alveoli collapse as he goes deeper, and remaining air moves into the more rigid airways. If he did not use the bottle, his lungs would collapse around 268 m (see Figure 10 in my paper). With exhalation into the bottle, collapse happens around 196 m. It is therefore conceivable that his lungs collapsed on this dive. Even if my model is a bit off because of inaccurate lung volume data, it just means he goes into a regime where he is extracting oxygen from the blood store, not the lungs.

(2) His large initial lung volume delays collapse until much deeper than would be experienced by someone with average lungs. When the last alveoli collapse, there will be an increase in negative tracheal pressure that may be quite uncomfortable, depending on tracheal stiffness. This could become one limiting factor. It will be very interesting to see how his airways feel if he reaches greater depths.

(3) The thoracic blood shift actually has very little effect on collapse depth because it reduces the negative pressure drop in the chest by only a very small amount compared with the huge change in ambient pressure, and has negligible effect on the rate of lung gas volume reduction and therefore collapse depth.

 

[efattah]

(3) The thoracic blood shift actually has very little effect on collapse depth because it reduces the negative pressure drop in the chest by only a very small amount compared with the huge change in ambient pressure, and has negligible effect on the rate of lung gas volume reduction and therefore collapse depth.

I'm not sure I understand this comment. In my case, even if I'm flexible from multiple days of diving, if I try a full negative (100% exhale) dive at the start of a dive session, I reach the point of discomfort in my chest around 11m. On the 2nd dive, the discomfort happens around 14m. 3rd dive, around 19m, 4th dive around 24m, 5th dive around 27m, 6th dive I can reach 30m, and so far I haven't tried more than that. With each successive dive, my chest feels more and more 'engorged' and my ability to inhale decreases with each passing dive, until at the end I'm total unable to take a full breath, and doing so makes me cough. My residual volume also seems to decrease as indicated by my mouthfill depth on an FRC dive, which becomes deeper and deeper with each passing negative.

 

[aquaholic21]

Hey guys!

I originally posted this on another thread but havnt really gotten any feedback so I figured Id post it here too since it fits in here.

I had a few things I was wondering if I could get cleared up though... for one, what happens during a lung collapse? Is all of the air in the lungs gone or is there just an extremely small amount left? Does this sort of event damage the alveoli in any way?

And also, what is FRC? I looked it up and one of the answers was Functional Residual Capacity. But what exactly does that mean?

Lastly, i saw that lung volume capacity plays a role in what depth your lungs would collapse. Is it the greater your lung capacity, the deeper your working lung depth?

Thanks!

 

[Fitz-Clarke]

That is an interesting observation Eric. I don’t know why that happens. I doubt it is related to blood shift because that would require adaptation of elasticity in the cardiovascular system, which is unlikely to that degree. You are probably seeing slow adaptive changes in the mechanics of the chest wall that involve the ribs, diaphragm, and abdominal muscles, and maybe lung elasticity. These are the main determinants of airway pressure. Even a small change in chest or diaphragm compliance could have a very significant effect on airway pressure. You are probably getting some alveolar or airway edema that is causing the tight feeling after the deeper dives. It would be interesting to study that.

As for my statement that blood shift has little effect on collapse depth, this is because collapse depth is essentially governed by Boyle’s law which depends only on initial gas volume and the change in ambient pressure. Lungs collapse when all the initial gas volume is pushed into airways external to the alveoli that remain open at depth. Boyle’s law does not care how much blood is in the chest. Even a large blood shift of one litre into the chest reduces the negative intrathoracic pressure by maybe 20 cm H2O at most. This is negligible compared with the change in ambient pressure of 10,000 cm H2O at 100 m depth that governs gas compression and determines collapse depth. That small change of 20 cm H2O is very significant in terms of comfort in the airways allowing you to go deeper, but it does not affect actual lung collapse depth significantly.

 

[Ulf]

Even a large blood shift of one litre into the chest reduces the negative intrathoracic pressure by maybe 20 cm H2O at most.

Wouldn't that depend entirely on the RV?

 

[Fitz-Clarke]

As for the other questions asked, what I mean by lung collapse is when all the air in the alveoli and small collapsible airways is compressed sufficiently that they close completely and displace all remaining air into the larger more rigid airways like the trachea and mainstem bronchi. Some air can be trapped in alveoli if the small feeding airways happen to close first. This air gets absorbed into the alveolar capillary blood. There must be a small amount of air left of perhaps 0.3 to 0.5 litres in the rigid airspaces. This cannot disappear completely because the rigid trachea and sinuses would have to collapse, and this would generate a very large and painful negative pressure relative to ambient causing squeeze.

To my knowledge, alveolar and small airway collapse itself does not cause any damage. This happens everyday in operating rooms when patients have heart surgery and they are put on bypass pumps for a few hours. The lungs are allowed to collapse when the chest is open. They are reinflated easily with positive pressure ventilation as long as healthy surfactant is present to keep surface tension low. Interestingly, diving animals have different surfactant properties than humans that allow easy spreading over the airway and alveolar surface to facilitate repetitive opening and closing.

FRC is just the relaxation volume of the chest. When you relax your chest muscles completely with the glottis open, you are at FRC. It is the equilibrium volume between lung stretch wanting to collapse the lung inward, and rib cage elasticity wanting to sping the chest outward. FRC is typically about 2.5 to 3.0 litres for an average person.

Yes, high initial lung volume increases collapse depth.

 

[aquaholic21]

Awesome! Hopefully someday I'll be good enough to worry about these things! haha Its nice to be able to talk to someone doing some research on these things!

 

[Ulf]

At what depth could you expect lung collapse if you dive on RV?
Could you collapse the lungs by reverse packing?

 

[cebaztian]

On the 2nd dive, the discomfort happens around 14m. 3rd dive, around 19m, 4th dive around 24m, 5th dive around 27m, 6th dive I can reach 30m, and so far I haven't tried more than that. With each successive dive, my chest feels more and more 'engorged' and my ability to inhale decreases with each passing dive, until at the end I'm total unable to take a full breath, and doing so makes me cough. My residual volume also seems to decrease as indicated by my mouthfill depth on an FRC dive, which becomes deeper and deeper with each passing negative.

This, Eric I find very interesting. I know you dont advocate full breaths or packing, but for those of us who uses that method to optimize our depth we have a choice to make.
1) The kind of warm up you describe above (maybe not so extreme) which in my experience reduces RV (well probably prepares the body for bloodshift) AND reduces TLC. OR...
2) Go for the higher TLC (with pack) and be more moderate with warm ups that reduces TLC.

Depending on: TLC, ability to pack, and the ability for the kind of warm up you describe, one method should be better than the other. In my case since I am a lousy "packer" and have no impressive TLC (7.8) - I believe I should go for the reduced RV method.

Sebastian
17 on my third

 

[Fitz-Clarke]

In answer to your question, RV does not affect collapse depth either. Rigid airspace volume does. RV is the lowest lung volume you can achieve by a maximal forced expiration. It is determined by the strength of expiratory muscles to squeeze against a stiff rib cage. It is a dry land test of chest wall stiffness and respiratory muscle strength. If anything, RV is just an indirect measure of chest wall stiffness (rib cage and diaphragm). It has nothing to do with the lung itself. People used to think RV was some kind of anatomical limit on the lung, but it is not. The lung can collapse to zero without injury. It normally doesn’t get there because the increasingly stiff chest wall at low volume prevents collapse.

Now you go free diving and your muscles are relaxed and you have a very high hydrostatic pressure that is much stronger than your expiratory muscles. The chest gets compressed far below RV. The lungs do not even notice this, so RV itself doesn’t limit anything. If your RV is say 2.5 litres instead of 1.4 litres, it just means your chest becomes stiff at the higher volume, and you will draw a higher negative chest pressure at depth from perhaps -20 down to -40 cm H2O. This results in a greater passive blood shift into the chest. High RV means you will experience a more negative airway pressure unless you can move sufficient blood into the chest. But collapse depth is not affected. My point is that RV affects the degree of negative airway pressure, which may be very important, but not collapse depth.

If you start a dive at RV of 1.2 litres, and assume your rigid airspace is 0.4 litres, you would need to dive to 1.2/0.4 = 3 atm or 20 m to reach collapse depth. But as I said above, you would have a very uncomfortable negative airway pressure.

 

[Fitz-Clarke]

Is it possible to reverse pack to collapse depth? That is a great question. The answer is probably not. Only one study has looked at airway pressures during reverse packing, by Loring et al. Reverse packing by four elite divers in a dry lab found they got nowhere near this low volume before they experienced high negative airway pressures that were limiting. They only got about 0.3 to 0.4 litres out below RV. The problem is that when the volume drop is relatively rapid, as it is in reverse packing, expiratory airflow causes many of the alveolar ducts to collapse first, trapping air in the alveolar sacs. This is caused by a fluid dynamic phenomenon that I suspect is not seen to the same degree during a diving descent where the decrease in volume is much slower, and air flow within the lung is very small resulting in less air trapping.

 

[rxcnc2]

The lung can collapse to zero without injury.....

The chest gets compressed far below RV.

I didn't know that the first statement is true, interesting. About the second statement, I always thought that blood shift replaces the volume between the maximum compression permitted by the chest and the RV. But you say that it's even more. So if a person has say 7L TLC and 1.5L RV, how much are the lungs actually compressed at great depth and how many liters of blood are involved in the blood shift? I think it's ok to have no air in the lungs (O2 is in the blood) for a couple of minutes, but it's not ok to have no blood left for the brain.

Thanks.

 

[aquaholic21]

and btw...if anyone else got a bit lost in all the terms and stufff...I found this on wiki and it helped a lot!

[ame=http://en.wikipedia.org/wiki/Lung_volumes]Lung volumes - Wikipedia, the free encyclopedia[/ame]