lung expansion???

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mtdivegirl

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I have had a talk with a few people in the "sciences" and have begin to question the validity of "lung over expansion" or bursting. From what the text says you would suffer from lung over expansion if you do not continuously breathe while ascending from a dive. However, your body would naturally force the air out of your lungs before they could even get to over expanding, no?
So...my question (beside the one about the theory of it all) is, have you ever seen someone with lung over expansion caused from diving? I am not looking for myth here... I want to know if you have actually seen it or suffered from it.
 
The first time you see a guy with his mask full of blood and other crap laying dead on a boat deck you'll believe.

Questioning the basic safety premises of diving will get you killed fairly quickly. Yes, DSC is real too.

Tom
 
I dont question the validity of DCS. I understand the properties of nitrogen and its related effects on the body. I am specifically concerned with lung over expansion (even though the two are grouped together in most course work).
I am asking purely on a level that is medical not emotional. I am not advocating people hold their breath..i am not considering a test of this theory either. But, the human body is an amazing thing and the theory is that your body would force the air out of your lungs no matter what you tried to do. PADI seems to like to work from the premise of scaring people into doing what is necessary. I want to know a medical case.. a case study published somewhere or a case from an actual doctor who treated someone for lung over expansion after a dive.
 
Originally posted by mtdivegirl
I want to know a medical case.. a case study published somewhere or a case from an actual doctor who treated someone for lung over expansion after a dive.

Ok. First, it doesn't take very much pressure to damage the lungs. The muscles involved in holding your breath are stronger than the walls of your lungs.

First up is personal experience. There was one time that I was diving stupidly, zig-zagging over huge boulders [10-20 ft] when my depth was 40-50 ft. For a few days after it hurt to take a deep breath, and I'm not positive, but I'm sure I hurt my lungs on those ascents.

But that's not what your looking for.

Ok. Read "Terrible Hours" by Peter Maas, which is the story about the sinking of the Squalus during it's sea trials. Swede Momsen got involved in the rescue, and it was the first submarine rescue with the use of the Momsen's lung.

Why read it? Because it discusses a few deaths that occurred in Momsen lung training, where students died 3 ft from the surface. The reason they died is because they held their breath and were killed by collapsed lungs due to lung over-expansion injuries. It doesn't take a lot to damage a lung, I believe you can do it by holding a full lung of air and ascending 3-6 ft when your down less than 33 fsw.
 
Here's a couple threads:

http://www.scubaboard.com/t11967/s.html
http://www.scubaboard.com/t11203/s.html
http://www.scubadiving.com/talk/read.php?f=1&i=522718&t=522718
http://www.scubadiving.com/talk/read.php?f=1&i=520613&t=520613

There's enough accident reports out there to keep you busy for quite a while. Maybe go check out http://groups.yahoo.com/group/divingaccidents/ while you're at it.

You're going down a road that has no good end. Whoever told you that this can't happen is a fool. Lung tissue is very delicate.

Tom
 
Different question on same subject.

I assume that the reason lung over expansion injury doesn't occur during a normal ascent with normal breathing is because we are starting from a low gas volume in lung as opposed to a lung already at or near full volume, and the increase in pressure is minimal with the distance traveled during a normal breath. Nevertheless, giving the fact that this injury could occur within a pressure drop equivalent to aproximately 4 ft in shallow water, could this injury occur on a long, slow inhale and a normal ascent?
and a rapid ascent? I am not reffering to breath holding at all, just normal breathing as ones ascends. ( maybe an out of control ascent )

Is it better to take shorter breaths on a normal ascent? In an out of control or otherwise rapid ascent?
 
While you're breathing your airway is open. That's the key, keep breathing :)

I don't know the detailed mechanics or physiology of it. I'm sure one of the Docs will pick up this thread soon.

Tom
 
Originally posted by mtdivegirl
However, your body would naturally force the air out of your lungs before they could even get to over expanding, no?

That would be true if the diver was unconcious and rising through the water column and providing there would be no physical airway obstructions. Basically an unconcious diver will not embolise. The body would be totally relaxed and airway open so expanding air could vent out.

So...my question (beside the one about the theory of it all) is, have you ever seen someone with lung over expansion caused from diving?
Yes, both concious and unconcious. It's not a pretty scenario.
 
Originally posted by mtdivegirl
However, your body would naturally force the air out of your lungs before they could even get to over expanding, no?

That would be true if the diver was unconcious and rising through the water column and providing there would be no physical airway obstructions. Basically an unconcious diver will not embolise. The body would be totally relaxed and airway open so expanding air could vent out.
 
Hi Scuba,

Can I speak as someone who has actually treated several patients with pneumothoraces during my time as a "resident" on the chest ward of my teaching hospital? While the causes differ the effects of, and the treatment of, a tension pneumothorax is the same.

Forgive me lecturing, but feel this is so important I have to get the message across.

The terms burst lung and lung over expansion are somewhat misleading as this is only a part of the complete picture.

First of all I do agree, the rib cage is a pretty solid pyramidal structure, but had you not noticed that there is a very large flap of soft muscular tissue holding the lungs and mediastinum in place within the chest cavity;- the diaphagm. OK it is muscle, but believe me it is not stong enought to maintain intrathoracic pressure very much above or below ambient pressure. (You cannot snorkel below about a foot of water. This suggests that it cannot vary the intrathoracic pressure more than +- 0.03 bar ambient.). In addition a large proprtion of the chest cavity is filled with blood in the pulmonary circulation which is effectively in direct contact with external pressure through the great veins and arteries in the abdomen (and neck).

The lungs are floating in the chest cavity, in an ambient pressure environment. They are isolated from the chest cavity itself by the pleura (a very, very thin membrane) and the walls of the airways and the alveoli. It is easier to demonstrate than to describe but in effect the airways of the lungs are like lots of little condoms connected together to one opening at the level of the trachea. They are like a baloon suspended in an evacuated solid jar by the nozzle through the top. Because of the near vaccuum in the jar air fills the balloon pressing it against the sides..

To complicate matters the jar contains a piston at the bottom. When the piston goes down the baloon expands as air enters through the nozzle at the top to keep the air within it at ambient pressure and visa versa.

I will not discuss other causes of pneumothorax but this is what happens during an ascent when you hold your breath. (Or you have an asthma attack or other obtruction to exhalation.)

The gas within the airways is a fixed mass and will either increase in volume as the external pressure is reduced or it's RELATIVE pressure will increase if the volume remains constant.

What happens is a bit of both. The increased relative pressure forces the blood within the pumonary circulation into the lower pressure environment of the abdominal cavity as the airways expand against the reducing external pressure. The airways can almost double in size as the blood vessels shrink. Such changes will take place in much less than 1 bar, or from 10 metres to the surface.

In time when the relative pressure increases to more than 0.03 bar the expanding lungs will force the diaphragmatic piston downwards into the abdominal cavity, which remains at ambient pressure at all times.

The walls of the airways and the alveoli are very thin and can stretch to a certain extent. However they are not designed to expand to more than twice their natural size so at the weakest point the lining will tear. This is as if the baloon were to be punctured, and it allows the high pressure gas in the lungs into the space between the lungs and chest wall. The lungs relax as they shrink against their inherant elasticity. Unfortunately since there is no longer a near vaccuum to keep them inflated almost ALL the air within them moves into the pleural cavity.

Once the air is in the space between the lungs and the chest wall it has nowhere to go. It cannot get back into the airways because they have collapsed. In consequence as the ascent continues the relative pressure of the air within the pleural cavity increases.

So scuba NO!
your body WILL NOT force the air out of your lungs before they could even get to over expanding,
. The increased pressure will simply close the unsupported airways. This is what happens in asthma.

It does not take much to work out that if the pneumothorax occurs at 30 metres the pressure within the chest could exceed 3 bar at the surface. ie 45 psi and more than that of a car tyre! Not only is this sufficent to stop all chest movement and compress the unaffected lung, this is more than enough to stop all venous return to the heart.

You cannot perform your proposed long slow inhale during the whole of an acent as it is not physically possible. If you are trying to inhale as the ambient pressure rapidly reduces all that happens is there may be little or no air movement at all or it will move out of the lungs through the open glottis that's OK then!. The danger, of course, is you will be actively attempting to inhale more and more (as the regulator does nothing) and actively overinflate the lungs to their natural maximum size.

Then what would happen if you were to hold your breath?

When they first attempted submarine escape the, if I remember correctly, the Davy aparatus allowed the excapee to take a beath. Many years ago I ascended from the bottom of the Navy's training tank (60 feet) and was able to forcibly breath out all the way the the surface.

I do not think this drill is done nowadays for obvious reasons.

I hope this explains the danger!
 

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