Lungs underwater
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i use my lungs every day, every minute for 31 years. But just could not believe in those numbers in that book.
Our lungs are essentially gas bags with one main attachment point called the lung root or hilum where the air and blood flow in and out. There's some minor connections to the rest of the body, but nothing that keeps it stretched out to a fixed volume.
The vast majority of the volume of the lung at ambient pressure is airspace. So since the exterior of the lung isn't fixed in place, as the air in the lung compresses during freediving, the lung itself is going to compress. It really is the balloon situation.
The vast majority of the volume of the lung at ambient pressure is airspace. So since the exterior of the lung isn't fixed in place, as the air in the lung compresses during freediving, the lung itself is going to compress. It really is the balloon situation.
I think I understand why you were concerned. Your chest wall and ribs are a modestly rigid container. So it was hard to imagine them being compressed so much.
You are correct. They aren't. At some point, the soft abdominal contents push up against the diaphragm and make up for the resistance of the chest wall to further compression.
But the lung volume really does compress to 1/5 of its original at 40 m. Your alveoli are like tissue paper and will not tolerate any shearing action. It's why scuba divers are advised to never hold their breath. The same is true in reverse, upon compression. Your lungs simply have to compress to 1/5 of their original volume at that depth, because of physics. Fortunately, the difference between our maximum inspiratory volume and our residual volume is about 6:1. And fortunately, our abdominal contents slide under the rib cage to help out with anything beyond that.
Diving Doc
You are correct. They aren't. At some point, the soft abdominal contents push up against the diaphragm and make up for the resistance of the chest wall to further compression.
But the lung volume really does compress to 1/5 of its original at 40 m. Your alveoli are like tissue paper and will not tolerate any shearing action. It's why scuba divers are advised to never hold their breath. The same is true in reverse, upon compression. Your lungs simply have to compress to 1/5 of their original volume at that depth, because of physics. Fortunately, the difference between our maximum inspiratory volume and our residual volume is about 6:1. And fortunately, our abdominal contents slide under the rib cage to help out with anything beyond that.
Diving Doc
tarponchik
Contributor
I can't even imagine what happens to the lungs of sperm whales who dive deeper than 3,000 ft!
Wrong logic. Inverse logic.
Why would the air in the lungs compress? The air in my scuba tank does not compress during a dive. I can clearly see how the SPG shows a constant pressure even when I dive from 1 ATM to 2 ATM. The pressure drops with time but depth does not affect cylinder pressure. This has something to do with the STEEL cylinders.
The air in my lungs would then retain its pressure. PV/T=constant and as my body temp is contant, so PV=contant. Volume goes down, pressure up, or vice versa. At depth there will be an external overpressure (caused by the weight of the water) that compresses the body - and hence the air inside. When the volume has shrunk and pressure increased accordingly (to match the external pressure) an equilibrium is reached.
And oh, it's not my rib cage but my belly that is giving way. The soft tissues.
(I have tried to compress my rib cage during some tight crawling and no, it's not that compressible.)
Scuba diving is different because then we breathe compressed air at the ambient pressure.
We aren't submarines or scuba tanks. Changes in ambient pressure affect us directly. Most of what we are made of is incompressible liquid which is why we don't dramatically shrink or grow with pressure changes. But the volume of air in our internal spaces absolutely does. This is why free and scuba divers have to equalize. Unlike our lungs, our sinuses are not free to contract as the air in them compresses (and we aren't filling them with ambient pressure gas from a regulator in the case of scuba). This causes pain and eventually tissue damage if you do not add enough air to equalize the interior pressure with ambient.
Yes. You are correct.
The nostrils connect with the water and the water pressure causes increased pressure in the nose/mouth/eustachian tubes. Equalization makes sure that pressure changes do not affect the ears or other voids.
How does the external pressure affect the lungs, if one is breath-holding? Is the trachea closed and the pressure enters the body trough the soft tissues (belly)(hence, more pressure and squeezed lungs) or does it somehow get from the mouth down to the lungs (less air volume inside)?
My theory was that the rib cage does not get compressed (and I know it will not). I then assumed that trough the soft tissues below the rib cage pressure could squeeze the lungs. Are you saying it happens through the nose and trachea instead? I'm actually interested...
The nostrils connect with the water and the water pressure causes increased pressure in the nose/mouth/eustachian tubes. Equalization makes sure that pressure changes do not affect the ears or other voids.
How does the external pressure affect the lungs, if one is breath-holding? Is the trachea closed and the pressure enters the body trough the soft tissues (belly)(hence, more pressure and squeezed lungs) or does it somehow get from the mouth down to the lungs (less air volume inside)?
My theory was that the rib cage does not get compressed (and I know it will not). I then assumed that trough the soft tissues below the rib cage pressure could squeeze the lungs. Are you saying it happens through the nose and trachea instead? I'm actually interested...
I'm not sure I understand what you mean by where "the pressure enters the body". The pressure is everywhere.
But the abdomen is the answer to the question as to what moves to fill up the interior space vacated by the lung. Just like when you are breathing. As you breath in and out the abdomen contracts and extends. So a freediver starts at the surface with a full breath and extended abdomen, as he or she descends it will contract. When you get too deep for the normal exhaled state, as Diving Doc says above, "fortunately, our abdominal contents slide under the rib cage to help out with anything beyond that." If you go too deep for the abdomen to compensate, the remaining void gets filled with fluids squeezed out of surrounding tissues. This is generally not good for you.
Diving Deep: Pulmonary Barotrauma in a Free Diver — Brown Emergency Medicine is a great article that covers all of physics in the context of a real freediver who ended up in the author's emergency room. For example, here's the article answers your pressure entering the body question, "The body behaves as a liquid and follows Pascal’s law; pressure applied to any part of a fluid is transmitted equally throughout the fluid. When a diver submerges, the force of the tremendous weight of the water above is exerted over the entire body."
But the abdomen is the answer to the question as to what moves to fill up the interior space vacated by the lung. Just like when you are breathing. As you breath in and out the abdomen contracts and extends. So a freediver starts at the surface with a full breath and extended abdomen, as he or she descends it will contract. When you get too deep for the normal exhaled state, as Diving Doc says above, "fortunately, our abdominal contents slide under the rib cage to help out with anything beyond that." If you go too deep for the abdomen to compensate, the remaining void gets filled with fluids squeezed out of surrounding tissues. This is generally not good for you.
Diving Deep: Pulmonary Barotrauma in a Free Diver — Brown Emergency Medicine is a great article that covers all of physics in the context of a real freediver who ended up in the author's emergency room. For example, here's the article answers your pressure entering the body question, "The body behaves as a liquid and follows Pascal’s law; pressure applied to any part of a fluid is transmitted equally throughout the fluid. When a diver submerges, the force of the tremendous weight of the water above is exerted over the entire body."
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