new theory about risk in freediving (dcs/airtrapping)

[naiad]

Originally Posted by bubestube

thus, in the case of the ascending freediver who has not packed, there is NO risk of volume trauma while ascending.

But the available space may have decreased due to blood shift, so there is still a problem of increased volume for the amount of space available.

[bubestube]

Originally Posted by naiad

But the available space may have decreased due to blood shift, so there is still a problem of increased volume for the amount of space available.

no! since the available (non compressible) space is reduced due to blood shift the air has no other option (cause air IS compressible) than to not increase volume as desired maintaining
a higher pressure (pressure x volume = constant) even though ambient pressure (water pressure) is already lower. in other words, you now have a relative postive pressure situation (in relation to the baseline
- the moment after you took your last breath)
in your lungs, just like the trumpet player. if you wait at the given depth and give the blood time to exit the chest cage
space becomes available for the air to expand into, thus reducing the relative pressure to zero again.

so, to rephrase your sentence :
But the available space may have decreased due to blood shift, so there is still a problem of increased PRESSURE.

italic = wrong info


but as already mentioned, pressure is not a problem at all.


bube

[trux]

Bube, I am afraid you have it wrong. Say you have 5 liters lung capacity at surface, and residual capacity of 1 l. At -50m, the residual capacity is reached, and it is then filled due to the blood shift, further compressing the air in the lungs to the ambient pressure. So far you are right there is no pressure problem (assuming the blood shift really works, and that it works as fast as you descend).

At -100m, you have only 0.5 l of air in the lungs compressed to the ambient pressure of 10 bars, and the remaining 0.5 l of your residual capacity is filled with blood plasma. So far, so good.

Now you start ascending, but faster than the reverse blood shift can receive the plasma from the lungs. Let's say you are now at -50m but still have 5 liters of atmospheric air compressed to 5 bars (it means to 1 l), but you also have 0.5 l of plasma in the lungs. Still, there is no problem - it takes all together just 1.5 l - much less than your 5 l lung capacity.

However, as you ascend to the surface, the air goes on expanding to its original 5 l, but there still may be up to 0.5 l of liquid in the lungs (well, probably less - hopefully some got already absorbed in the meantime). Now you are in real troubles - the pressure is indeed higher than it was originally when you started the descent. The difference would make 10% if no reverse blood shift occurred at all yet in that moment. I hope though that the reverse blood shift is faster, hence the difference would be lower.

If you packed before the descent, the difference in the lungs volume before and after the dive, hence the difference of surface pressures, would be already quite important and could indeed cause injury or embolism.

[bubestube]

Bube, I am afraid you have it wrong. Say you have 5 liters lung capacity at surface, and residual capacity of 1 l. At -50m, the residual capacity is reached, and it is then filled due to the blood shift, further compressing the air in the lungs to the ambient pressure. So far you are right there is no pressure problem (assuming the blood shift really works, and that it works as fast as you descend).
At -100m, you have only 0.5 l of air in the lungs compressed to the ambient pressure of 10 bars, and the remaining 0.5 l of your residual capacity is filled with blood plasma. So far, so good.

trux, first of all, I think you are mixing a few things up here. I reckon you mean 5 litres total lung capacity and 1 litre residual VOLUME (or did you mean 1 litre functional residual capacity?). Further, at -100m you have an ambient pressure of 11 bar (11 atm) and your lung (gas) volume will be 0.45 l (you just forgot the 1 atm at sea level).
But anyway, let's stick to you example cause the numbers are even.

Now you start ascending, but faster than the reverse blood shift can receive the plasma from the lungs. Let's say you are now at -50m but still have 5 liters of atmospheric air compressed to 5 bars (it means to 1 l), but you also have 0.5 l of plasma in the lungs. Still, there is no problem - it takes all together just 1.5 l - much less than your 5 l lung capacity.

again, let's pretend you meant 90 and 40 meters. apart from that, I am still with you.

However, as you ascend to the surface, the air goes on expanding to its original 5 l, but there still may be up to 0.5 l of liquid in the lungs (well, probably less - hopefully some got already absorbed in the meantime). Now you are in real troubles - the pressure is indeed higher than it was originally when you started the descent. The difference would make 10% if no reverse blood shift occurred at all yet in that moment. I hope though that the reverse blood shift is faster, hence the difference would be lower.

OK, after having read my previous posts I must admit that they are a bit confusing content-wise (even wrong at some points) - thanks for bringing that up. so let's make it as clear as possible:

Of course, in your extreme example of (permanent) reduced lung volume at depth (lung volume -0.5 l, the shifted blood), the freediver would have a total lung volume of 5.5 litres (5 l gas and 0.5 l blood) when surfacing. Or, if volume expansion were to be restricted to the 5 l, the diver would have a pressure of around 100 cmH2O in his lungs. In other words, another 0.5 l of space is required. That these 0.5 l can be housed without lung rupture is quite propable. It has been observed that lung packing can inrease VC up to 39% (The Lung at Depth, Ed. C.E.G Lundgren and J.N. Miller, Volume 132, page 576). In your example (VC of 4 l) that would be another 1.59 l, so 0.5 l extra should not be problem. However, this VC increase effect due to packing is in all likelihood achieved partly by blood being driven out of the chest cage. In your example you assume that this will not be the case (or only marginally). I on the other hand think that the rate of blood shift into the chest while descending is similar to the rate of blood shift out of the chest while ascending (because the driving force of this blood shift is pressure difference, negative during descent and positive during ascent). Depending on your heart rate on ascent, this extra blood can be pumped out of the thorax quickly. Besides, it has been calculated that a freediver would take up as much as 700 ml N2 during a single dive to 90 m (page 572, same book - thus DCS certainly an option during extreme and/or repeated freediving). Whatever the exact numbers, you will surface with less than 5 l of air after such a dive because there has been some net N2 uptake. So... in summary, your scenario seems very unlikely to me.

If you packed before the descent, the difference in the lungs volume before and after the dive, hence the difference of surface pressures, would be already quite important and could indeed cause injury or embolism.

well... it certainly increases the chance of lung rupture but already while doing it at the surface. Or do you have any references for the slowed down return of the shifted blood during ascent?

so again:

VOLUME damages the lung,
PRESSURE influences haemodynamics (bad enough, I guess packing is responsible for many surface black outs).

bube

[Mullins]

I had a lung function test done the other day at a navy hospital here in Auckland. Packing got me an extra 34%, or 3.6L on top of my VC. Based on this I asked about the possibility of lung overexpansion when returning to the surface (one of the dive docs there is reputedly very experienced and has some, though not much, experience with freedivers). He said it should be a non-event, given that a fair proportion of the gas taken down is used for respiration and not exchanged back into the lungs. I guess it might be an issue if a diver aborted at a shallow depth for some reason then came rocketing back up without using much of his/her oxygen.

What you say about volume, rather than pressure, damaging lung tissue sounds right (to a layman). One thing - do you know whether residual blood shift would affect the whole lung surface area evenly? If not, 500ml or 1L of residual shifted blood might distort the shape of a lung trying to return rapidly to 139% of its VC, creating damaging volume in the area less affected by blood shift. NB: this is just a thought and is quite probably *******s.

[Mullins]

My, what a touchy text-censor...

[Mullins]

Just noticed something:

in your extreme example of (permanent) reduced lung volume at depth (lung volume -0.5 l, the shifted blood), the freediver would have a total lung volume of 5.5 litres (5 l gas and 0.5 l blood) when surfacing

This makes it sound like the blood is actually in the lungs. I thought that shifted blood stays in blood vessels, packing out the space around the lungs and allowing them to compress further in what would otherwise be a rigid container (the chest cavity once diaphragm/ribcage have reached their non-pathological elastic limit), rather than (the lungs) remaining at RV on a deep dive even while ambient pressure increases.

I.e. Chest cavity RV remains the same despite increasing ambient pressure, while blood shift from the extremities contributes some of this volume and thus lowers potential lung (airspace) RV, allowing lung & ambient pressure to remain 1:1 and avoid a damaging gradient.

If the blood is in the lungs, as you imply, it would indeed cause high volume rather than high pressure on return to the surface. If it is in the blood vessels around the lungs, it would simply restrict them (the lungs) from expanding and cause high pressure (hence my question above re. uniformity).

[trux]

Originally Posted by bubestube

VOLUME damages the lung,
PRESSURE influences haemodynamics (bad enough, I guess packing is responsible for many surface black outs).

Thanks for your analysis and the corrections. Unfortunately you focused on unimportant or deliberately simplified details, but do not seem to be willing to accept the fact that volume and pressure are very much bind together. Although lungs (+the surrounding body) are flexible, there are limits on both extremities of the volume, resulting so in overpressure or underpressure in the lungs, and leading hence possibly to an injury or embolism.

In the moment the ambient pressure is higher than the pressure inside lungs (descent), the lungs (volume) are being compressed to equalize the pressures, and oppositely when the inside pressure is higher than outside, then they expand. Due to this effect, the pressure difference outside and inside is pretty much close to zero, but only until the moment when the max or min volume limit is reached. In that moment the pressure difference starts to grow (no more the volume though) and can lead to injury. In this way it makes no sense to claim that it is caused by the volume and not the pressure, as well as it nonsense to tell that it is causes by the pressure and not the volume, because there would be no overpressure or underpressure if there were no volume limits, and there would be no volume change if there were no pressure gradient.

In the discussed case though the situation is more complex, because we have several additional factors changing both the volume and the pressure: the initial packing increases the inner pressure, the blood shift reduces the volume, and there may be also some differences due to a different level of gas dissolving in the blood. Especially nitrogen, as you wrote too. Unlike the doctors of Mullins, I do not think that "fair proportion of the gas taken down is used for respiration and not exchanged back into the lungs" - oxygen may be transformed into CO2, and the volume of gas dissolved in blood may vary in different moments of the dive, but I wonder whether the difference is really important.

So depending on several factors, specifically the speed of the ascent, the speed of the reverse blood shift, and the speed of nitrogen and CO2 releasing, the resulting overpressure in the lungs may be higher than the initial one caused by the packing. This is just a speculation - I do not know the specific speeds, so am unable to tell when (or whether at all) it happens, but think that such possibility is rather realistic and should be taken into consideration.

Unlike bube, I am with wolleneugebauer and others in this thread who expressed their worries that extreme packing can lead to problems other than just a BO. Sorry, bube, but by claiming that packing (pressure) cannot damage lungs or cause embolism, you are virtually telling that you can attach compressor to your mouth and put as much pressure into your lungs as you want, without causing any damage. You certainly realize that it is nonsense, and I hope that you realize that by extreme packing (or the consequent overpressure at surfacing as described here), the overpressure inside lungs can indeed reach dangerous levels.

[Mullins]

There seems to be some confusion over whether blood shift contributes volume to the lungs themselves, or to the chest cavity around the lungs. I'd humbly suggest that it is this confusion that is putting Trux and Bube at odds.

If the blood shift increased the volume inside the lung cavity then pressure would indeed influence volume directly, as Trux is saying, meaning that a diver would be at risk returning to the surface with residual blood shift on top of their 139% VC (gas exchange stuff notwithstanding).

However, I gather that bloodshift contributes volume between the lung and the walls of the chest cavity. This would be different. In this case, when the diver ascends the lung would only be trying to expand back to its 139% VC, so the lung tissue itself would not be under too much stress. However, it would be trying to do so inside a chest cavity that already contained 500-1000ml of incompressible blood plasma. This would cause high pressure in the chest cavity, not high lung volume. The chest cavity would be under stress, as it would now be forced to contain fully inflated lungs + the bloodshift volume. In this case you'd presumably expect diaphragm/intercostal injuries...?

Can anybody out there give a good mechanical account of how and where bloodshift occurs? It seems like quite an important point to me. I may be off the mark when I suggest it is better conceived as a process that fills the space between lung and chest wall rather than entering the lungs themselves - it may be somewhere between the two, i.e. plasma swelling the capillaries throughout the lungs, not actually entering the airspace but contributing to their volume nevertheless. That would make it very tricky to determine whether residual bloodshift could contribute to over-inflation injuries, time to send a monkey down...

I definitely agree that it would be possible to seriously injure oneself by overpacking - you can certainly generate a fair bit of pressure.

I think the contention that gas volume drops significantly over the course of a breathhold is pretty difficult to refute, Trux. Most divers would notice their buoyancy decreasing during a dynamic swim, for instance.

[bubestube]

Originally Posted by trux

Thanks for your analysis ..., but do not seem to be willing to accept the fact that volume and pressure are very much bind together. Although lungs (+the surrounding body) ...to an injury or embolism.

Hey, basically you accuse me of denying Boyle's law? I am sorry if
I gave you this impression but it seems to me that you have only read my final statement (Pressure... Volume...) in my last post and neglected everything I have written before. This is very unfortunate because I think I have more or less confirmed what you have said before. I just added some info on why I don't think that even with your extreme example I don't think barotraumas during ascent will be a problem for the free diver.

In the moment the ambient pressure is higher than the pressure inside lungs (descent), the lungs (volume) are being compressed to equalize the pressures, ... if there were no pressure gradient.

I agree with most of it but still have to stick to my VOLUME claim. Here is why (although I think we more or less mean the same thing and that this is only about some sort of misunderstanding):
Because of Boyle's law the gas pressure in the lung during ascent will be equal to the ambient pressure as long as the lung has enough room to expand into (let's make it a FRC dive where you really start with a pressure of zero at surface). If the lung for whatever reason cannot expand freely anymore (your not returning blood taking a volume of 0.5l) the pressure will start to rise while the volume gain slows down (this is an important point, there still IS volume gain but not unrestricted anymore, hence pressure goes up). A pressure volume curve demonstrates this sequence nicely.

This will go on until the lung tissue is stretched to its limits due to increasing VOLUME!!!(pressure will of course also rise – see p/v curve) At the microscopic level, the cells (endothelial and pneumocytes) are basically stretched until they rupture. It is like a rubber band pulled out till it tears. In the unrestricted lung (thorax opened) this critical volume will be reached at 70 mmHg, if the thorax is confined (closed thorax) the lung ruptures at about 110 mmHg (The Lung at Depth, Ed. C.E.G Lundgren and J.N. Miller, Volume 132, page 315). So… to repeat, it is the spacial displacement that causes the rupture. It has per se nothing to do with pressures (you can also rupture the lung due to overinflation with no or slightly negative pressure differences by putting a human into an iron lung).
To clarify further, if you inflate a balloon with 1l at a depth of 10 m and let it ascend it will burst because of the volume expansion (to keep Boyle’s law satisfied). If you, on the other hand, put this balloon at -10 m in a metal container (that can withstand pressures of more than 2 bar) in which the balloon just fits in, and take it up to the surface, it will not burst because volume expansion has been limited through the container. However, the pressure in the balloon will be doubled at the surface but this increased pressure causes no damage to the rubber wall of the balloon. Same with humans going to a depth of 20 m with scuba gear, they will have a pressure of 3 bar in their lungs – nothing happens, no ruptures (the ambient pressure being the metal container here). Like I mentioned before, trumpet players generate a pressure of 150 cmH2O hundreds times a day without experiencing barotrauma (http://www.chestjournal.org/cgi/content/full/116/suppl_1/9S-a).

In the discussed case though the situation is more complex, because we have several additional factors changing both the volume and the pressure: the initial packing increases the inner pressure, the blood shift reduces the volume, and there may be also some differences due to a different level of gas dissolving in the blood. Especially nitrogen, as you wrote too. Unlike the doctors of Mullins, I do not think that "fair proportion of the gas taken down is used for respiration and not exchanged back into the lungs" - oxygen may be transformed into CO2, and the volume of gas dissolved in blood may vary in different moments of the dive, but I wonder whether the difference is really important.

Let’s leave packing out for the moment (will discuss it later). In my previous post I gave you the reference of the N2 net uptake (700 ml) at a dive to 90 m. This would already be substantial to answer your question of importance. Further, assuming you don’t have a respiratory quotient (RQ, volume of carbon dioxide released divided by volume of oxygen consumed) of 1 (which would mean you only utilize glucose for energy generation) but rather a normal 0.8, you would loose some more gas during the dive because you extract more O2 and return less CO2. Resting O2 consumption is about 3.5 ml/min/kg (245 ml in a 70 kg person). So having a RQ of 0.9 would mean 24.5 ml of net gas absorption per minute. Even though I don’t know what the O2 demand during a free dive is, it seems to me that this consumption mechanism further reduces the gas volume. Finally, gas will be taken up and stored in the blood/tissues. This applies to all 3 gases (N2, CO2 and even O2 to a small extend). Having said all this I must conclude (and agree with the doctors of Mullins) that you definitely won’t surface with the original amount of gas you inhaled at your last breath. Also, the difference may also be quite substantial. In other words, you’ll “loose” gas on your dive which protects you against ascending barotrauma.

So depending on several factors, specifically the speed of the ascent, the speed of the reverse blood shift, and the speed of nitrogen and CO2 releasing, the resulting overpressure in the lungs may be higher than the initial one caused by the packing. This is just a speculation - I do not know the specific speeds, so am unable to tell when (or whether at all) it happens, but think that such possibility is rather realistic and should be taken into consideration.

OK…, I agree…, like you said, depending on the several factors (worst case scenario: maximum pack and a blood volume that refuses to leave the thorax on ascent) there definitely is a chance of barotrauma during ascent. The key factor here is the reduction of intrathoracic blood (the shifted blood) on ascent (gas is not the problem, rather protective as explained above). And like I mentioned in my previous post, I don’t think that this will be a big problem unless you ascend with your heart beating only a few times. It has been shown (same book page 560) that cardiac output increases during the ascent, especially due to increased stroke volume (the chest trying to get rid of the shifted blood).

Unlike bube, I am with wolleneugebauer and others in this thread who expressed their worries that extreme packing can lead to problems other than just a BO. Sorry, bube, but by claiming that packing (pressure) cannot damage lungs or cause embolism, you are virtually telling that you can attach compressor to your mouth and put as much pressure into your lungs as you want, without causing any damage. You certainly realize that it is nonsense, and I hope that you realize that by extreme packing (or the consequent overpressure at surfacing as described here), the overpressure inside lungs can indeed reach dangerous levels.

Well… why do I get the impression that you are putting words into my mouth?
Shall I quote myself? I said more then once that packing can be dangerous because overstretching the lung may result in rupturing lung tissue. I even find that to be very realistic when watching how much force is put into this packing procedure. But not assuming your worst case scenario mentioned above, the major thread of packing already develops at the surface, haemodynamically (black outs) AND due to the consequences of lung rupture. It certainly is not a good idea trying a deep free dive having just torn your alveolar-capillary membrane at parts because of packing.

Sorry, bube, but by claiming that packing (pressure) cannot damage lungs or cause embolism, you are virtually telling that you can attach compressor to your mouth and put as much pressure into your lungs as you want, without causing any damage. You certainly realize that it is nonsense, and I hope that you realize that by extreme packing (or the consequent overpressure at surfacing as described here), the overpressure inside lungs can indeed reach dangerous levels.

Well… I hope from what I have explained above you will now understand what I mean with VOLUME trauma. But just for the fun of it I’ll take up your compressor example. Let’s say your compressor is capable of generating 6 atm. Then I will be delighted to put the compressor tube into my mouth after having descended to 50 meters. Get my point?

So… to summarize, Yes, in theory, there may be a risk of barotrauma on ascent IF you go up super fast (with only a few heart beats, but at the same time super fast would mean a higher workload (if you don’t use an air balloon for ascent) with consequently higher heart rate and higher cardiac output) not allowing the heart to pump the shifted blood out of the thorax. But I honestly don’t think that this is a realistic scenario. But to be on the absolute safe side, maybe take at least 10 seconds for the last ten metres.


bube

[bubestube]

Originally Posted by Mullins

Can anybody out there give a good mechanical account of how and where bloodshift occurs?

Well… the book I am referring from (The Lung at Depth, Ed. C.E.G Lundgren and J.N. Miller, Volume 132) talks about intrathoracic blood pooling. I understand that as blood inside the thoracic cavity (the blood vessels there should also be much more compliant to taking up extra blood due to negative pressures). In theory, whether the blood pools inside the thoracic cavity (increasing the volume of the lung tissue, heart… = what I think) or outside the visceral pleura (resulting in a sort of “bulging in” of the latter into the thoracic cavity reducing the volume) does not matter at all in terms of truxe’s dilemma of no or only little reverse blood shift. As soon as the ambient pressure falls below the gas pressure inside the lung, the lung will expand until pressure equalizes no matter what (this leading to ruptures). This is because neither the rib cage nor the abdominal contents can restrict the volume expansion of the lung before it reaches the point of stress failure.

bube

PS.: just found another reference confirming blood pooling inside the lung (inside pulmonary circulation)
http://www.ncbi.nlm.nih.gov/entrez/q...=pubmed_docsum

[trux]

Thanks once more, bube, for the detailed explanation. However, again, you just concentrate on unimportant and well known facts that no one argues about. What I was initially not agreeing with you, was the following claim of yours (quoted below), and I still do not agree with it. Also, the sentence about packing and slow reverse blood shift "this will cause no damage since the higher pressure cannot be translated into a greater VOLUME" actually denies the Boyle's law that you described yourself so well - both at the initial pre-dive packing, and at the post-dive surfacing (you admitted the liquid is inside the lungs, hence it does not reduce the lungs tissue volume).

Though, if I interpreted well your later posts, with your current analysis, you actually withdrew your original claim, or didn't you?

Originally Posted by bubestube

... so, in my opinion, the answer is NO, no high pressure lung damage due to a too fast ascent. even if it takes the shifted blood longer to leave the chest cage again refusing the air in the lung to "claim" its appropriate volume (according to the ambient pressure), the remaining blood still restricts the available volume in chest cage. so ,YES, the gas pressure in the lung may be a bit higher than expected (according to the ambient pressure) because of the "slow returning blood", but this will cause no damage since the higher pressure cannot be translated into a greater VOLUME.

So let's clear your original claim, now, without lengthy details - do you agree that such injury can indeed happen in extreme cases, or do you still deny such possibility even remotely?

On my mind, extreme packing, hence extreme PRESSURE (and consequently extreme VOLUME - if you prefer) either before the dive, or upon a fast resurfacing with a delayed reverse blood shift can cause lung damage or micro embolism.

I do not think that it can happen easily - we would see it much more often among freedivers, but I would much more prefer seeing serious scientific real-life measurements, than excluding such possibility just because it does not look probable in theory. I'd like to see some more specific numbers based on reality, than just excluding such possibility theoretically.

I think that claiming that packing cannot cause any embolism or lung damage, like you did, only based on a theoretical analysis, is very dangerous. And it is the more dangerous because you accompanied your claims with a lot of "scientific speech" creating the impression to an average reader that you are very well familiar with the topic, and that your facts are perfectly correct and safe.

Although I have no proof that the embolism or lung damage can actually happen, or that it ever happened, if people follow your claim instead of being more vigilant with packing until the issue is seriously researched, it may lead to some ugly accidents.

So let me say it clearly - I am not trying to attack your knowledge (you apparently know much more than average freediver about the physiology and the physics of freediving). I am just trying to make clear that your claims are not necessarily compatible with the more complex reality, and that people should do better to be really careful with packing until more research is done.

[bubestube]

Originally Posted by trux

Though, if I interpreted well your later posts, with your current analysis, you actually withdrew your original claim, or didn't you?

Yes, it was wrong info (like I have indicated (italic = wrong) I was thinking of deleting them first but thought this is a better way of correcting myself).
Basically, forget everything I have written before (though lots of it is still valid) and just take my last 2 posts (from the very long one onwards).

However, again, you just concentrate on unimportant and well known facts that no one argues about.

You keep repeating yourself here and I am not sure of how to interpret this since I thought I had elaborated on all the factors that are involved in your scenario. If I left one out, please tell me so...

So let's clear your original claim, now, without lengthy details - do you agree that such injury can indeed happen in extreme cases, or do you still deny such possibility even remotely?

I have already answered that, so I am just going to quote myself:

Originally Posted by bube

OK…, I agree…, like you said, depending on the several factors (worst case scenario: maximum pack and a blood volume that refuses to leave the thorax on ascent) there definitely is a chance of barotrauma during ascent. The key factor here is the reduction of intrathoracic blood (the shifted blood) on ascent (gas is not the problem, rather protective as explained above). And like I mentioned in my previous post, I don’t think that this will be a big problem unless you ascend with your heart beating only a few times. It has been shown (same book page 560) that cardiac output increases during the ascent, especially due to increased stroke volume (the chest trying to get rid of the shifted blood).

So… to summarize, Yes, in theory, there may be a risk of barotrauma on ascent IF you go up super fast (with only a few heart beats, but at the same time super fast would mean a higher workload (if you don’t use an air balloon for ascent) with consequently higher heart rate and higher cardiac output) not allowing the heart to pump the shifted blood out of the thorax. But I honestly don’t think that this is a realistic scenario. But to be on the absolute safe side, maybe take at least 10 seconds for the last ten meters.

On my mind, extreme packing, hence extreme PRESSURE (and consequently extreme VOLUME - if you prefer) either before the dive, or upon a fast resurfacing with a delayed reverse blood shift can cause lung damage or micro embolism.

I find it difficult to argue against something that is refered to as being "extreme" although it is actual numbers we are talking about. What is extreme pressure, what is extreme volume? I gave you references of lung pressures (trumpet player, stress failure pressures etc.) and volumes (39% increase during packing, also Mullin confirmed this number from personal experience). So maybe we should stick more to the actual numbers and figures than to personal feelings and impressions.

I do not think that it can happen easily - we would see it much more often among freedivers, but I would much more prefer seeing serious scientific real-life measurements, than excluding such possibility just because it does not look probable in theory. I'd like to see some more specific numbers based on reality, than just excluding such possibility theoretically.

Who would not like to see real-time live measurements? Although I got the impression that a lot has already been measured in simulated chamber deep dives and apparently your scenario has not yet been identified as a possible problem.

I think that claiming that packing cannot cause any embolism or lung damage, like you did, only based on a theoretical analysis, is very dangerous. And it is the more dangerous because you accompanied your claims with a lot of "scientific speech" creating the impression to an average reader that you are very well familiar with the topic, and that your facts are perfectly correct and safe.

First, I am always only expressing my oppinion. I never claim anything. As you may have noticed, I am rather careful with absolutes and tend more to talk about probabilities. I also have corrected myself (earlier posts of mine).
Besides, I think the average reader is still responsible and mature enough to understand that the issues being discussed here are to be taken completely at own risk.
Secondly, I express my oppinion based on scientific facts. The stuff I quote has actually been measured and performed. It is therefore valid to draw conclusions from this data. So it is not just pure theory I am speculating about.
Thirdly, I am very familiar with the topic.

Although I have no proof that the embolism or lung damage can actually happen, or that it ever happened, if people follow your claim instead of being more vigilant with packing until the issue is seriously researched, it may lead to some ugly accidents.

So let me say it clearly - I am not trying to attack your knowledge (you apparently know much more than average freediver about the physiology and the physics of freediving). I am just trying to make clear that your claims are not necessarily compatible with the more complex reality, and that people should do better to be really careful with packing until more research is done.

Again, I don't think I have ever claimed anything here and I am sorry if anybody got the impression that I did.
Also...I am puzzled why you keep saying that I don't think packing is dangerous. Even in the post where I got some things wrong I have always stated that packing creates substantial risks.

After having re-read my long post I think I have elaborated on all the important factors concerning your inhibited reverse blood shift scenario.
Based on scientific facts I came to the conclusion that under normal circumstances your scenario does not seem very propable, that as long as you ascent with your heart beating, it does not make sense why the shifted blood should not leave the thorax. But as I have already mentioned in one of my previous posts, I always refer to healthy lung conditions. There are indeed situations that surely increase the chances of injury during ascent (pneumonia, asthma, aspiration...). Apart from that I have clearly explained how packing could lead to lung ruptures while doing at the surface, and that this could have serious consequences if the dive procedure is continued.

bube

PS.: However, I have found one unusual case of apparent pulmonary barotrauma and fatal air embolism. A diver attempted twice to swim across a 25 yard pool at about 6 ft of depth. After the second try , he immediately developed symptomes (dizziness, headache, "tingling all over").Autopsy revealed large amounts of air in the right heart and cerebral vessels. It was assumed that either air has shifted within the lung to a compartement that became relatively full at depth, was closed off before ascent, and then became distented to the point of rupture during ascent. Or, alternativley, very forceful inhalation to total lung capacity might have caused lung rupture by overdistension of a weak area in the lung (The Lung at Depth, Ed. C.E.G Lundgren and J.N. Miller, Volume 132, page 574).

[bubestube]

So... let's come back to the original issue:
I do not think that air embolism has caused the symptoms wolle has mentioned in his first post:

Originally Posted by wolle

furthermore I know 3 examples that freedivers had symptoms like dsc without deepdives. the symptoms are coming directly after or while performances with over-packing!
fortunately all symptoms (blindness, hemiplegia, syncope, kaleidoscope viewing, tachycardia etc.) wear gon after 20 minutes...

Rather, these symptoms sound very much like the ones of people suffering from TIA's (Transient Ischemic Attack) which is caused by local hypoxic episodes in the brain (symptoms depend on where the hypoxia occurs). wolle has described that these severe symptoms were reversible. The fast recovery (20 min) on the other hand argues against air embolism as being the cause. To suffer from such severe symptoms (hemiplegia) large areas of the brain must have been affected. Hence, it must have been a rather large embolus (air) that has plugged brain vessels. If this was the case I seriously doubt that these symptomes could wear of in such a short amount of time with no further lasting effects.
Therefore, I think the most likely cause of these symptoms was hypoxia due to restricted brain perfusion initiated by haemodynamical alterations (positive pressure in the lung compressing the alveolar capillaries).
The mean pulmonary capillary pressure (normal circumstances) is around 7 mmHg (pulmonary artery systolic/diastolic/mean pressure: 25/8/15 mmHg). So…in theory as soon as the pressure in the lung exceeds this pressure lung perfusion comes to a halt. Of course it is not all that easy (different parts of perfusion regions in the lung, cardio-vascular compensation etc.) but to keep it simple, let’s say intrathoracic pressure has profound effects on haemodynamics (heart rate, cardiac out put, blood pressure). Just inflating the lung to its total capacity generated an airway pressure (after vocal cord closure and relaxation) of around 22 mmHg. The same individual generated a pressure of 43 mmHg after packing (VC increase by 26%). In other words, resistance to pulmonary blood flow almost doubled after packing compared to normal conditions. Another interesting report concerning this issue comes from Paul Kotik (http://www.deeperblue.net/article.php/744/19/3). He packed while being extensively monitored. Echo revealed that his right heart collapsed after having stuffed 35 packs of air. Amazingly though, he stayed conscious during this procedure.
To cut things short, haemodynamics are profoundly altered during breath holding, especially after packing. Having said that combined with what I have mentioned above, I come to the (my) conclusion that the severe symptoms mentioned by wolle in his cases are more likely of haemodynamic origin than due to air embolism. Tanya’s pre-dive black out (http://forums.deeperblue.net/showthread.php?t=63554)
for instance is a good example of what I think was a pure brain perfusion problem that resulted from compression of the pulmonary circulation due to high lung pressure after packing.

bube

[pat fish]

It is quite common for advanced freedivers to slow down on the last meters of the ascent and exhale underwater.