Two questions for diving science nerds only

[shakeybrainsurgeon]

I am not trying to spread disinformation, that's why I qualified the story by saying it was at best incompletely relayed or, at worst, diver folklore. Thanks for the info, re: ditching weights --- these are tidbits that aren't easily found in books and are best not learned from experience.

The thread has gotten a little off track --- the original issues were how fast can a diver ascend uncontrollably and can that ascent rate, even in an unpanicked diver breathing normally suffer lung barotrauma simply by virtue of being unable to equalize pressure in the chest during rapid ascent because of anatomic limitations of the airway. The impression i get is that, under the right conditions, ascent rates greater than 200 fpm may be possible, but whether this causes barotrauma alone may be impossible to know because ascending divers may hold their breath and if they do so even for a few seconds, they may get AGE.

These are not arcane issues, given that rapid ascent is a leading cause of injury and death. The only reason to relate anecdotes like he one i repeated is to try an establish a dialogue about similar episodes of people who corked to the top wih no ill effects. What they have in common might be useful in preventing injury in others, or it may be that these divers have some idiosyncratic resistance to DCS

 

[Gary D.]

I know first hand that a person in “GOOD CONDITION” can make one 100’ buoyant assent after another without any ill effects.

We used to climb into the 100’ lock of the tower and rapidly equalize it. We then put on an inflatable vest with what I would guess is 50# lift. Slip into the water column inflate it with an external air hose and let go.

Roughly 30 seconds later we were on the surface giggling like school kids ready to do it again. So back down the outside of the tower for a repeat and a repeat and a repeat. Most of us would rather do that than go on Liberty.

The velocity, even with that much lift was only enough to get us out of the water to about our shoulders and we were as streamlined as one could get. It was just our body, trunks and the vest with nothing else to slow us down.

So thinking someone can breach the surface without a rocket pack of some type I will have to say is another episode for Myth Busters and it will be busted. IMHO I call BS to that one.

As far as the medical aspects involved with diving, like anything else, we are still learning. Will we ever know the answers to everything in diving? My guess is nope they never will because way to many variables.

Why can a group of divers do something almost identical and some come out fine while others suffer a variety of injuries from AGE to Bent? Just a simple thing like diet can mean getting bent or not. Physical condition and age seems to have a factor on the out come.

Some will say it’s age. Some will say it’s physical conditioning. But what is the risk comparison between an older diver in good condition and a young obese diver. I’ll bet the older diver in good condition can do things safely that could prove fatal to the younger obese diver.

I don’t think there is a single right or wrong answer to any medical conditions related to diving. It’s just like driving fast or running stop signs. You might do it and get away with it for a long, long time but someday you just might be putting your signature on the ticket or crashing.

Gary D.

 

[Kim]

These are not arcane issues, given that rapid ascent is a leading cause of injury and death.

I don't think for a moment that you are trying to be flippant or something of that order. I do think you might be delving too deep. It strikes me that someone with limited training and experience in an environment where they can't get air might automatically hold their breath to preserve what air they have. It's the wrong thing to do but actually quite understandable IMO. I've never heard of anyone suffering AGE because they ascended so fast that they couldn't expel air fast enough from their lungs to keep up with the expansion that occurs. In fact, as I understand it, as long as your airway remains open it would be impossible to do as the pressure build up would always have a release path. As taught for CESA/ESA you have to consciously breath out. This guarantees that the airways remain open, thus ensuring an escape path for excess pressure of expanding gas.

 

[shakeybrainsurgeon]

I don't think for a moment that you are trying to be flippant or something of that order. I do think you might be delving too deep. It strikes me that someone with limited training and experience in an environment where they can't get air might automatically hold their breath to preserve what air they have. It's the wrong thing to do but actually quite understandable IMO. I've never heard of anyone suffering AGE because they ascended so fast that they couldn't expel air fast enough from their lungs to keep up with the expansion that occurs. In fact, as I understand it, as long as your airway remains open it would be impossible to do as the pressure build up would always have a release path. As taught for CESA/ESA you have to consciously breath out. This guarantees that the airways remain open, thus ensuring an escape path for excess pressure of expanding gas.

Thanks Kim. I like to delve deep (don't we all that's what diving is for). The fact that the airway is open doesn't guarantee freedom from barotrauma. The air can only flow so fast through the airways and, even then, it exits by pushing against the lung tissues. Consider an expanded balloon --- open ithe top and try to push the air out faster, it will only exit at a maximum rate through the opening no matter how hard you compress it and continued squeezing may break it, even with an open egress. Moreover, the increased flow of air through the outlet of the balloon can only be generated by increasing the pressure of the balloon itself.


Which offers the path of least resistance for air exiting the lung at a 2 atm gradient --- an open trachea or the flimsy aveoli? I don't know.

Barotrauma is more of a problem in clinical medicine than in diving --- in patients with pulmonary disease on ventilators, small amounts of positive pressure is needed to ventilate lungs stiffened by disease. Pressures well below that experienced even at 10 feet of submersion can damage or drop a lung. One post above mentions feeling the air rush out of his lungs as he ascended -- this feeling may have been due to increased airway pressure.

I agree, though, that this is all overly academic, since it seems we can do little more in a rapid ascent scenario other than keep the airway open. From the case reports I've read over the last several years, the cause of AGE was not determined...in fact, many cases diagnosed as AGE weren't autopsied or were autopsied by pathologists with no knowledge of dive medicine. The diagnosis of AGE was made by later review of the medical file by DAN's people. Thus, whether such a thing as "open glottis barotrauma" due to excessive ascent rates remains speculative.

But speculation makes life more interesting.

 

[ZenDiver]

Human Physiology is wonderful thing. There are never any guarantees. I have heard of people blowing off 30 mins of deco with no ill effects and on the other side a person embolizing in 5 feet of water at the pool. You may be able to run the same dive profiles for years and then one day you get bent running the same profile you have run for years. I have heard of people getting bent at the Living Seas Aquarium at Epcot in only 35 feet of water. Crazy stuff....you can never know. You hear of people getting bent on a bounce dive of less than 10 minutes or some one diving on air (21%) to depths of 400 plus feet, well above the 1.4 ppo2 recommended.

As far as shooting to the surface at rocket speeds....."today" you might get away with it. There are no guarantees that you will get away with it tommorow.

 

[SNorman]

I can expell almost all the air in my lungs in about 1 second. I can't imagine needing to blow out air any faster than that.

 

[shakeybrainsurgeon]

I can expell almost all the air in my lungs in about 1 second. I can't imagine needing to blow out air any faster than that.

That is correct. Healthy airways can exhale about 70% of lung volume in one second. But not everyone has healthy airways. What you're talking about is the FEV1 or the forced expired volume fraction in one second. An asthmatic or a smoker with obstructive airway disease may take five times longer than you to exhale their lung volume and that may not be fast enough if the ascent is very rapid. And remember, if even one of the many bronchi is too narrow, that section of lung may not equalize, and a pneumothorax or AGE could result. There are countless air passages in the lung that all must allow adequate equalization, not just the glottis and trachea, and the more rapid the decompression the more likely that some small compartment will be slow to equalize and rupture. Think of the lungs as a hundred little ears --- if you bob up like a cork, what is the probability that all of those little ears will adequately equalize in every diver? If even one "pops" like an eardrum, it could be curtains for you.

 

[Puffer Fish]

Does the above analysis qualify me for "nerd" status?

Yes, it does.


The speed of accent would obviously be primarily effected by:

1 Buoyancy.

2. Resistance.

Obvously, resistance would be effected by you position in the water, and I'm sure it would vary by 1 or 2 hunderd percent.

Buoyancy would be effected by:

BC or BPW - capacity and % full. If the accent starts a depth, and there was already significant air in the bag, at some point, the bag will begin to vent.

Capacity to hold air. How big of a bag.

Wet Suit/Dry suit. With either, the buoyancy would increase as depth went down. A dry suit would be very inflated by the time one reaches the surface. This would increase buoyancy, but also effect resistance.

Maximum buoyancy of suit. A 3mm is not equal to a 7mm.

If you shoot a sausage to the surface from depth, they max out at something around 200 - 250 ft/minute, so would expect a human to be a bit slower.

Problem is, one would be going the fastest in the last thirty feet, and would be accelerating a bit.

Is it possible to exhale fast enough - would depend on several things, but if you are head up, looking up, and your lungs were full going into the final 30 feet, then I would be very surprized if you could.

If you are looking down, your lungs were no where near capacity, then it should be easy.

Note: Looking down would result in lower pressure around the mouth area, looking up would increase the pressure.

There are a lot of people that have managed to do just that without injury, but I don't know the odds. It may not be that good.

 

[Puffer Fish]

That is correct. Healthy airways can exhale about 70% of lung volume in one second. But not everyone has healthy airways. What you're talking about is the FEV1 or the forced expired volume fraction in one second. An asthmatic or a smoker with obstructive airway disease may take five times longer than you to exhale their lung volume and that may not be fast enough if the ascent is very rapid. And remember, if even one of the many bronchi is too narrow, that section of lung may not equalize, and a pneumothorax or AGE could result. There are countless air passages in the lung that all must allow adequate equalization, not just the glottis and trachea, and the more rapid the decompression the more likely that some small compartment will be slow to equalize and rupture. Think of the lungs as a hundred little ears --- if you bob up like a cork, what is the probability that all of those little ears will adequately equalize in every diver? If even one "pops" like an eardrum, it could be curtains for you.

I have seen 3 uncontrolled accents from over 50 feet in my life, and luckily none resulted in any known lung damage. But that is way to small of a population to draw anything from it. There have been a fair number of people that were injured, but do not know if they were really trying to exhale as fast as possible.

 

[SNorman]

That is correct. Healthy airways can exhale about 70% of lung volume in one second. But not everyone has healthy airways. What you're talking about is the FEV1 or the forced expired volume fraction in one second. An asthmatic or a smoker with obstructive airway disease may take five times longer than you to exhale their lung volume and that may not be fast enough if the ascent is very rapid. And remember, if even one of the many bronchi is too narrow, that section of lung may not equalize, and a pneumothorax or AGE could result. There are countless air passages in the lung that all must allow adequate equalization, not just the glottis and trachea, and the more rapid the decompression the more likely that some small compartment will be slow to equalize and rupture. Think of the lungs as a hundred little ears --- if you bob up like a cork, what is the probability that all of those little ears will adequately equalize in every diver? If even one "pops" like an eardrum, it could be curtains for you.

Cool, got it. One questoin, when you say 70%, is the majority of the 30% that's left in air spaces that you can't fully expel? Because, after about a second I really can't expell any more air. And that's after inhaling as much as possible first.