Holding your breath on ascent...

[pjones]

The difference between trying it on land and actually doing it in the water is your chest volume and diaphragm.
On land what you're doing is "opening" your diaphragm as far as you possibly can, there by increasing your chest cavity to it's fullest. So that tight sensation you feel is your chest, not your lungs.
Your alveoli in you lungs probably don't have as many nerve endings as your chest, maybe even none, zip zilch etc.
Keep in mind that an over expansion injury from a breath hold ascent injures the alveoli first, not your diaphragm or chest. So this is probably why no one feels it happening until after their alveoli rupture.

I see what your saying. I figured my experiment would have a flaw to it. I'm not too sure of the operation of the alveoli to know if the sacs fill with air or absorb oxygen. It would make more sense to me if they filled with air because then I can picture them popping like balloons. Anybody familiar with how those little fellas go about completing their daily chore?

 

[pjones]

Have you ever done the experiment of filling a plastic bottle at 10 meters below, seal it and let it surface. You will be amazed what the expansion of air can do!

Does it explode?
I did the Dry Ice/Water in the pop bottle experiment and was quite impressed with the sound it produced. Holly mother of god its LOUD! I videoed it but its not as impressive when played back on speakers of any size. It sounded much like a bomb so we wrapped up real quick and departed quite fast. :nuke: --> -->

 

[Acanthurus]

In simple terms, air exchange occurs in the alveoli. When we breath in there is more O2 than CO2 in the alveoli so the O2 leaks into the capillaries and binds to red blood cells and CO2 goes into the alveoli and is exhaled. The purpose of breathing is to keep the oxygen concentration high and the carbon dioxide concentration low in the alveoli so this gas exchange which is very fast,can occur!

Hope this helps

 

[Rhone Man]

When I did my first dive (aged 9) I misunderstood the instructions from my Dad to never hold my breath particularly whilst ascending, to always hold your breath whilst ascending. Kids, eh? They never listen.

Well, I did my darndest, but I just could not hold it in and I eventually expelled the air in a great plume of bubbles. I felt a huge amount of pressure on the inside of my chest up to to the time of breathing out, but so far as I have ever been able to tell, I never suffered any injury from the experience.

Mind you, 9 year old bodies are much more resilient to injuries (as my own son seems determined to prove regularly...). I suspect if I did the same with a 38 year old body, I would not nearly be so fortunate.

 

[Herk_Man]

To have the problem in an aircraft you would have to have a rapid/sudden decompression (hull breach) at a high altitude and you would have to be holding your breath when it happened. As a pilot we do periodic training in altitude chambers. One of the exercises is dealing with a rapid decompression and I've never had a chamber tech warn anyone not to hold their breath. There is just a much higher pressure gradient in water than there is in air. So probably not a huge factor.

 

[Thalassamania]

Interesting: Delayed-onset cerebral arterial gas embolism in a commercial airline mechanic.

 

[Herk_Man]

Interesting: Delayed-onset cerebral arterial gas embolism in a commercial airline mechanic.

Yep. Not saying it couldn't happen. But it also sounds like this was a little different injury and it was due to repeated frequent exposure to rapid decompressions.

 

[pjones]

In simple terms, air exchange occurs in the alveoli. When we breath in there is more O2 than CO2 in the alveoli so the O2 leaks into the capillaries and binds to red blood cells and CO2 goes into the alveoli and is exhaled. The purpose of breathing is to keep the oxygen concentration high and the carbon dioxide concentration low in the alveoli so this gas exchange which is very fast,can occur!

Hope this helps

I'm still slightly unsure of the process that occurs in a lung over expansion scenario. If the alveoli were to expand and pop then I would expect blood to be coughed up by a victim. I've never heard of blood being expelled as a result so is it that the pressure in the lungs collapses the alveoli rendering them useless?

 

[TSandM]

Remember that the alveoli are one cell thickness from a capillary, which is also small enough to carry blood cells single file. Although there may be a few blood cells that escape into the airspace, while the air is escaping into the blood, it is not a significant volume. And the patient may not even have a cough.

 

[NIT-LVR]

Yes Alex....Going up in an aircraft would increase the volume in a sealed flexible vessel(your lungs).Boyles Law.....it is no different than an ascent in the water.Exactly the reason why we do not fly after diving.However......I really gotta challenge anyone to hold their breath for a long enough time to incur a lung expansion injury in an airplane.......unless your maybe cruising around in an F-18...