lung expansion???

[Scuba]

Dr. Paul Thomas, you wrote:

If the chest wall and diaphragm did not move at all, as nature abhors a vaccuum an equal volume of blood from venous return fills the pulmonary capillaries - there will be a net transfer of 4.5 litres of blood from the peripheral circulation into the pulmonary circulation, which the body can cope with

The scope of the blood transfer described above would appear to me to be an event that seldom, or maybe never, is experienced by the human body unless subjected to the relatively extreme pressures encountered in un-natural human environments, such as the one the body is exposed to when diving. Correct?

If this is the case, are there any negative repercussion from repeatedly exposing the body to this type of change? Any reseach on this subject?

Do the physical demands placed on the body in order to be able to cope with this event, place some individuals with certain physical characteristics at greater risk of something going wrong?, aside from asthmatics.

Thank you for your good explanations, once again.

Peter

 

[mtdivegirl]

Part of research is knowing where to find the answers! Why subject yourself to searching and searching for something you dont know enough to really do research on when there is a group of highly knowledgeable people you can pose the question to?
I am not 5 years old asking inane questions. There is no reason to get frustrated with simple question asking. If you are annoyed dont respond. That simple!

Dr. Thomas,

Thanks again for your insightful answers. It makes even more sense now...and I don't even have a follow up question..go figure..but it looks like someone else did.

 

[The Iceni]

Originally posted by Scuba
Dr. Paul Thomas, you wrote:

The scope of the blood transfer described above would appear to me to be an event that seldom, or maybe never, is experienced by the human body unless subjected to the relatively extreme pressures encountered in un-natural human environments, such as the one the body is exposed to when diving. Correct?

If this is the case, are there any negative repercussion from repeatedly exposing the body to this type of change? Any reseach on this subject?

Peter

Ah! Peter I fear you may be confusing two things. The first is the horrifying (to me) changes to the pulmonary circulcation free- divers vountarily subject themselves to;- due to the massive relative pressure changes - and then there is scuba.

Quite honestly I fail to understand how anyone would subject their bodies to such a high risk environment voluntarily and it is not something that I would ever wish to do myself - that is apart from snorkelling to about 20 feet maximum. In scuba, because the breathing gas is supplied at near-ambient pressure the haemodynamic events I described occurring in free divers are absent.

I confess that free diving is not something that interests me greatly but I stongly suspect there will be long-. term implications but there is so little data on this specialist "sport".

 

[rcohn]

Originally posted by TwoBitTxn
The tracheal muscles that hold your air way closed are stronger than the pressure of the air trying to escape your lungs. The conscious effort to keep these muscles contracted can close off the air way long enough to result in lung over expansion.

TwoBit

The point of confusion I think I see in this thread is the question how can the closed glottis be strong enough to withstand the pressure of the expanding air on ascent? I believe the simple answer is that it only needs to be stronger than the alveoli in the lungs. As the air expands on ascent and the pressure within the lungs increases, the alveoli will rupture before the pressure would force the glottis to open. The expanding air can then escape into the lung cavity or bloodstream or elsewhere, relieving the pressure within the lungs that the glottis must withstand.

In engineering, this would be considered a design flaw, but evolution apparently did not have diving with compressed air in mind when the respiratory system developed.

Ralph
.

 

[rcohn]

Originally posted by Dr Paul Thomas
I confess that free diving is not something that interests me greatly but I stongly suspect there will be long-. term implications but there is so little data on this specialist "sport".

Some of us like freediving

I think the main long term effect on health is increased fitness and well being. I know of freedivers who have been diving for 40 years and their health appears to be fine. If you compare a random group of freedivers to a random group of scuba divers you will find the freedivers are more fit and much thinner on average.

By the way, the thing that apparently amazes the physicians who work the truly elite freedivers is the low heart rates (mid 20s) and cardiac arrhythmias that develop during their dives.

Ralph

 

[The Iceni]

Originally posted by rcohn


Some of us like freediving

I think the main long term effect on health is increased fitness and well being. I know of freedivers who have been diving for 40 years and their health appears to be fine. If you compare a random group of freedivers to a random group of scuba divers you will find the freedivers are more fit and much thinner on average.

By the way, the thing that apparently amazes the physicians who work the truly elite freedivers is the low heart rates (mid 20s) and cardiac arrhythmias that develop during their dives.

Ralph

Being a physician I admit to being amazed! I have also recently learned that Toothdoc (a medical moderator) used to be a keen free diver. Perhaps using free diving to illustrate pneumothoraces was not such a good idea on my part. I have clearly trodden on a few toes!.

Ralph, If I had an obligatory choice between free diving to 30 metres or making an emergency ascent form 30 metres after using scuba I would most certainly choose the former and that is despite the risks of "shallow water blackout"!

 

[Rockhound]

lung overexpansion can happen without the diver being aware of the process until it is too late. It is VERY easy to close off your glottis and suffer a serious expansion injury without being "forced" to exhale due to a sense of discomfort or a feeling of pressure. Your glottis is a very effective valve and quite competent at holding the pressure until something else gives way. The human body lacks the "wiring" to tell you things are going bad in your lungs until it is too late, so you won't even know what hit ya until it REALLY hit ya.


For those same reasons, divers suffering from conditions that might close or even impede their airways, like asthma, bronchitis or a chest colds should consider staying out of the water since they could injure themselves without even realizing it.


Having witnessed the consequences of lung overexpansion, I would not want you or anyone else to got through that on the mistaken assumption that such injuries are "mythical".

If you don't believe me, then do a little research on your own. There is a great deal of information out there for you to peruse that supports what you are being told by us and by your instructors. This information is not only anecdotal, but empirical-just go to the DAN site and do a little reading. Lung expansion injuries are real and they happen, unfortunately, all the time.

(Btw, it doesn't take much differential pressure, nor "much" of an injury to damage lung tissue (aveoli), or any other tissue for that matter.

As for how much expansion occurs on ascent, I remember making a free "out of air" (training) ascent from 50' once and being amazed at the volume of air I was able to "whistle" through pursed lips on the way up. It was like my lungs were "bottomless". I remember thinking that holding my breath for only a moment and stopping that outflow of air would do really bad things to my body very very quickly . It was a sobering experience, since I felt no sensation of pressure, but the volume of air varied with my ascent rate. When I "flared" at 15', I sank slightly and the volume just "stopped", again with no sensation of a pressure reduction. It was very disconcerting. I learned a lot from that training dive.

As for an unconscious diver being "immune" to the possibility of overexpansion, I would think that holds true most of the time, but not all of the time. When I took rescue training (back then it wa part of the basic class), we were taught to bring an unconscious diver to the service with regulator in place and the head tilted back. This would help keep an open airway. Unfortunately, if I remember correctly, a diver who had aspirated water might not have an open airway, even in this position, due to spasms in the trachea/glottis, but I am not sure (that was over 20 yrs. ago.) But, the training at the time suggested that an embolized diver might be better off than a drowned one.....

Oh, yea....don't worry....they don't do that kind of training anymore....(I hope).....

oh....and one final thing...about the relative safety of free diving: My ONLY serious injury in 25 years of fairly active diving happened about a month ago on a FREE DIVE to about 40'. (I posted some questions on this to the medical forum).

My ENT finally concluded that it was barotrauma to the inner ear. It turns out that only 2cm of barometric pressure change is necessary to cause a perilymphatic fistula (oval window rupture). Apparently, despite the lack of vertigo, pain and other differentials, that is what happened to me. I now have a sensorineural hearing loss that might be permanent.

So, you can get pressure injuries from free diving too, but not lung expansion injuries (for the reasons stated by others).

Go figure. Free diving is too dangerous for me, but i have been cleared to scuba dive. (heck, I went for 3 days AFTER the accident with no problems).

 

[rcohn]

Good luck with the ear, Rockhound.

Hearing loss seems to be the greatest risk for freedivers. I've learned from discussions on the Freedivelist that when a diver has a round window rupture, the ENTs usually tell him it is a rare and unexpected accident . However, from the number of freedivers reporting round window ruptures it doesn't appear to be that rare at all. Based only on the number of divers I've heard confessing they have lost all or partial hearing in one ear I would make a wild guess that prehaps around 10% of long term freedivers have the injury. Many report forced clearing (or not clearing) but some state that they were having no difficulty clearing and that it just happened. One beginner on the list ruptured the round window when he first started diving, but he did have great difficulty clearing.

Ralph

 

[BillP]

mtdivegirl once bubbled...
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. I am not looking for myth here...

mtdivegirl once bubbled...
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.

Howdy mtdivegirl:

I see that others have done a good job of explaining to you that lung over expansion is indeed not a "myth" promoted by PADI designed for "scaring people into doing what is necessary". IMHO dive training organizations are actually more likely to downplay the risks of barotrauma injuries in order to promote sales.

Pulmonary barotrauma (due to lung over expansion) is the second leading cause of death in the recreational diving community (after drowning). In fact, a study published by Powers et al in 1992 reviewing scuba diving fatalities suggests that pulmonary barotrauma may even be the leading cause of death in scuba divers since pathologists inexperienced with scuba diving fatalities seem to tend to attribute any death in the water to drowning. Pulmonary barotrauma doesn't have to be fatal. Lung over expansion with arterial gas embolism is a frequent cause for needing hyperbaric chamber treatment.

The diving medicine literature is full of information on lung over expansion injuries. I see where you asked for actual case reports so I have given you several references (see below). The list is far from complete, and I'm sorry that not all of them have abstracts to read, but if you're really curious you can probably find the articles in your nearest medical school library. I only included articles with actual case reports, per your request. I did not include any of the many, many articles that discuss lung over expansion injuries in general.

mtdivegirl once bubbled...
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.

Forgive me, but it would appear that these people in the "sciences" have either done a very poor job of explaining the physiology of lung over expansion to you, or they have inadequate knowledge on the subject. Since it seems that their information has caused you to be grossly misled on a very important subject I would humbly suggest that you not rely on them for diving related information in the future. It seems that your PADI text was a much better source.

HTH,

Bill

http://www.ncbi.nlm.nih.gov:80/entr...ve&db=PubMed&list_uids=11086673&dopt=Abstract

http://www.ncbi.nlm.nih.gov:80/entr...eve&db=PubMed&list_uids=9670439&dopt=Abstract

http://www.ncbi.nlm.nih.gov:80/entr...eve&db=PubMed&list_uids=9308145&dopt=Abstract

http://www.ncbi.nlm.nih.gov:80/entr...eve&db=PubMed&list_uids=8775407&dopt=Abstract

http://www.ncbi.nlm.nih.gov:80/entr...eve&db=PubMed&list_uids=8447807&dopt=Abstract

http://www.ncbi.nlm.nih.gov:80/entr...eve&db=PubMed&list_uids=2372179&dopt=Abstract

http://www.ncbi.nlm.nih.gov:80/entr...eve&db=PubMed&list_uids=2369396&dopt=Abstract

http://www.ncbi.nlm.nih.gov:80/entr...eve&db=PubMed&list_uids=3686745&dopt=Abstract

http://www.ncbi.nlm.nih.gov:80/entr...ieve&db=PubMed&list_uids=579394&dopt=Abstract

 

[jepuskar]

Talk about beating a subject to death. As a soon to be diver, I really could careless the physics behind lung expansion....nor would I even argue the point to anyone who thinks otherwise. I understand the relationship between volume, density, and pressure and it is quite obvious what would happen if holding your breath.

Its not worth questioning, nor is it worth the explanation from the Dr's. I mean, I was breaking out a medical dictionary for every other word.

In a nutshell this is how I look at it:

Gas expands as you ascend. Holding your breath...BAD. Cause lungs to go boom. You die. You dont dive no more. You dont post on scubaboard.com no more. You want to question this or provide more explanation to others? No need to. Have friends try this out in water. :/