Why Do My Lungs Get All Squishy?
March 9, 2011 8:35 PM Subscribe
Why, when going deep underwater, does the air in your lungs compress? I'm pretty sure we learned this in 5th grade...yet...I got nothing.
I'm reading A Short History of Nearly Everything by Bill Bryson- fun book about how things came to be the way they are. In it, he states,
"It isn't simply that we can't breathe in water, but that we couldn't bear the pressure. Because water is about 1,300 times heavier than air, pressures rise swiftly as you descend-- by the equivalent of one atmosphere for every ten meters (thirty-three feet) of depth. On land, if you rose to the top of a five-hundred-foot eminence -- Cologne Cathedral or the Washington Monument, say -- the change in pressure would be so slight as to be indiscernible. At the same depth underwater, however, your veins would collapse and your lungs would compress to the approximate dimensions of a Coke can."
Why is that? How is the gas in the lungs getting compressed?
I understand that when underwater, you have an absurd amount of weight pressing down on you- the column of water above you to the surface and the atmosphere above. With all that weight pressing against you, seems like if you go deep enough, you should just get compacted- all your hollow, gassy parts should just flatten out (Previous googling reminds me that gasses are pretty easy to compact, fluids not so much).
Seems to me, and here is where I know I am wrong- I just don't know WHY I am wrong.....that if you put something deep underwater in a sealed, rigid container, the molecules of air inside the container should be unaffected by the pressure....because how would the weight of the water get to them to compress them? And the human body, at least the lungs and veins should be somewhat like gas containers placed inside a somewhat rigid container? (Ears and sinuses don't seem as sealed off so I get why they might explode or implode, in order to try and equalize pressure).
Side Question for the Especially Special: When going to extreme heights or depths, such as in a plane or a submarine and they talk about keeping it "pressurized" most of the work keeping the structure from either exploding or imploding is the physical structure itself, right? Submarines are strong because of the incredibly thick plates, not because they have enough air pumped in them to mimic standard atmospheric pressure, right? (This is all predicated on what I think I understand: pressure always wants to equalize- high pressure to low pressure)
I'm reading A Short History of Nearly Everything by Bill Bryson- fun book about how things came to be the way they are. In it, he states,
"It isn't simply that we can't breathe in water, but that we couldn't bear the pressure. Because water is about 1,300 times heavier than air, pressures rise swiftly as you descend-- by the equivalent of one atmosphere for every ten meters (thirty-three feet) of depth. On land, if you rose to the top of a five-hundred-foot eminence -- Cologne Cathedral or the Washington Monument, say -- the change in pressure would be so slight as to be indiscernible. At the same depth underwater, however, your veins would collapse and your lungs would compress to the approximate dimensions of a Coke can."
Why is that? How is the gas in the lungs getting compressed?
I understand that when underwater, you have an absurd amount of weight pressing down on you- the column of water above you to the surface and the atmosphere above. With all that weight pressing against you, seems like if you go deep enough, you should just get compacted- all your hollow, gassy parts should just flatten out (Previous googling reminds me that gasses are pretty easy to compact, fluids not so much).
Seems to me, and here is where I know I am wrong- I just don't know WHY I am wrong.....that if you put something deep underwater in a sealed, rigid container, the molecules of air inside the container should be unaffected by the pressure....because how would the weight of the water get to them to compress them? And the human body, at least the lungs and veins should be somewhat like gas containers placed inside a somewhat rigid container? (Ears and sinuses don't seem as sealed off so I get why they might explode or implode, in order to try and equalize pressure).
Side Question for the Especially Special: When going to extreme heights or depths, such as in a plane or a submarine and they talk about keeping it "pressurized" most of the work keeping the structure from either exploding or imploding is the physical structure itself, right? Submarines are strong because of the incredibly thick plates, not because they have enough air pumped in them to mimic standard atmospheric pressure, right? (This is all predicated on what I think I understand: pressure always wants to equalize- high pressure to low pressure)
this is what I learned in dive class. the idea scared me shirtless: air embolism
posted by Redhush at 8:40 PM on March 9, 2011
posted by Redhush at 8:40 PM on March 9, 2011
Also: you're confused because pressure and weight are not the same thing. Pressure controls the volume of a gas, we use the weight as a shorthand to talk about pressure in a simplified way, but weight = mass * gravity, and that's only one component of pressure.
posted by zug at 8:41 PM on March 9, 2011
posted by zug at 8:41 PM on March 9, 2011
Best answer: And the human body, at least the lungs and veins should be somewhat like gas containers placed inside a somewhat rigid container?
That's the problem. You are not - not even close - to a rigid container. Try having someone sit on your chest and have you breathe normally. That's a small example of the same process. Humans are not rigid. They are squishy.
Other than that, inside a physically strong container is correct - submarines use atmospheric pressure plus lots of structure to maintain their shape under diving pressures and resulting forces.
posted by Brockles at 8:45 PM on March 9, 2011 [5 favorites]
That's the problem. You are not - not even close - to a rigid container. Try having someone sit on your chest and have you breathe normally. That's a small example of the same process. Humans are not rigid. They are squishy.
Other than that, inside a physically strong container is correct - submarines use atmospheric pressure plus lots of structure to maintain their shape under diving pressures and resulting forces.
posted by Brockles at 8:45 PM on March 9, 2011 [5 favorites]
Imagine that you have a big drum, open on top, that you then seal by stretching a thin membrane of rubber over the mouth. The membrane stretches taut over the drum, and pressure of the air inside the newly-sealed space is the same as before you put the rubber membrane on. Now, start piling sand in the middle of the membrane. It sinks in the middle, right? But the amount of air in there is the same even though the volume of the space it can occupy is decreasing, so the pressure goes up. In this analogy, the air is the contents of your lungs and the membrane is all your squishy soft tissues.
WHY I am wrong.....that if you put something deep underwater in a sealed, rigid container, the molecules of air inside the container should be unaffected by the pressure.
You're not wrong here, actually, the problem is that you're imagining the human body as a rigid structure when it is no such thing. The more rigid the container, the deeper you can go before it implodes (and the more spectacularly and catastrophocally it implodes when it finally does.)
posted by contraption at 8:48 PM on March 9, 2011
WHY I am wrong.....that if you put something deep underwater in a sealed, rigid container, the molecules of air inside the container should be unaffected by the pressure.
You're not wrong here, actually, the problem is that you're imagining the human body as a rigid structure when it is no such thing. The more rigid the container, the deeper you can go before it implodes (and the more spectacularly and catastrophocally it implodes when it finally does.)
posted by contraption at 8:48 PM on March 9, 2011
Best answer: begin to think of your body less like a rigid structure (say an airship, or steel building, submarine etc)... and more like a ziplock bag full of blood, guts, gas and some flimsy structures made of tissue. exert enough pressure on the ziplock back and pop! goes the weasel as it were. also, on preview, what brockles said!
posted by Bohemia Mountain at 8:49 PM on March 9, 2011 [1 favorite]
posted by Bohemia Mountain at 8:49 PM on March 9, 2011 [1 favorite]
Air is compressible; body parts, much less so. At greater depth/pressure, your body might keep the air in your lungs from being compressed quite as much as the air in a balloon, but your body will not be able to withstand the pressure, and the air in your lungs will be squished by you flexible rib cage.
If you put something underwater in a very strong container, the container will withstand the pressure, but something flexible like a balloon will be compressed. Human bodies are not built for withstanding high pressure.
posted by theora55 at 8:58 PM on March 9, 2011
If you put something underwater in a very strong container, the container will withstand the pressure, but something flexible like a balloon will be compressed. Human bodies are not built for withstanding high pressure.
posted by theora55 at 8:58 PM on March 9, 2011
I think I would qualify bohemia mountain's comment a bit: if the pressure on the ziplock bag were equal on all sides, it would not pop. If it were full of uncompressable solids and liquid, it would withstand pressure very well. Water, unlike air, is very difficult to compress. But now imagine that your lungs are represented by two ping pong balls in that bag. If the pressure on that bag (equally, on all sides) started to increase, the ping pong balls would certainly start feeling the pressure and eventually compress, or worse, collapse under the pressure.
What does sound weird in the Bryson quote is that veins will collapse. Veins are full of liquid and should not themselves compress under water pressure.
posted by holterbarbour at 9:07 PM on March 9, 2011
What does sound weird in the Bryson quote is that veins will collapse. Veins are full of liquid and should not themselves compress under water pressure.
posted by holterbarbour at 9:07 PM on March 9, 2011
Response by poster: Oh you fabulous people with your visual metaphors! Alright- people are squishy and going deep enough underwater like having somebody sit on our chest, which is really like a ziplock bag full of goo. This is most definitely where I went wrong....I assumed we were much more rigid than we are- picturing someone sitting on my chest is really helpful in showing just how squishy we really are...and it sounds incredibly uncomfortable. Ugh.
I knew it would be something incredibly simple- yet you would be surprised how many scuba diving websites and high school physics pages I waded through where nobody reminds you how gooey and smooshy we are....
posted by Bibliogeek at 9:08 PM on March 9, 2011
I knew it would be something incredibly simple- yet you would be surprised how many scuba diving websites and high school physics pages I waded through where nobody reminds you how gooey and smooshy we are....
posted by Bibliogeek at 9:08 PM on March 9, 2011
Response by poster: I was assuming that veins would collapse because they are full of gassed-up liquids? So...under pressure, they would squish out the gasses and compress down quite a bit...eh?
posted by Bibliogeek at 9:12 PM on March 9, 2011
posted by Bibliogeek at 9:12 PM on March 9, 2011
Of course, when you dive using SCUBA equipment you're able (unless something goes horribly wrong) to fill your lungs up with as much air as you like, you just inhale until your lungs feel full. When you do this at great depth, you are indeed going to have much more air in your lungs (by mass, since more molecules are occupying the same space under the heavy pressure) than you would at the surface. It feels perfectly comfortable since the pressure is equalized, but has a couple of interesting side effects (other than the bends, which are not interesting as much as horrifying):
With all those high pressure gases (if you're breathing plain air, mostly nitrogen) jostling against your tissues and being absorbed in ways they normally aren't, you're liable to experience Nitrogen Narcosis ("Rapture of the Deep") if you dive to great depths. The exact mechanism is apparently still up for debate, but the result is a euphoric intoxication similar to nitrous oxide, which is obviously a very dangerous thing to start spontaneously experiencing when you're wearing a belt of lead weights deep underwater.
A safer and more mundane side effect is that if you start to ascend while holding a lungful of air, you'll find that it expands as the pressure around you lessens. This is theoretically dangerous in the sense that if you forcefully held your breath while rapidly ascending you could rupture something, but in practice you feel a tremendous urge to exhale as the air in your lungs expands. It's a strange feeling to be able to keep breathing out and out for much longer than your lung capacity should allow.
posted by contraption at 9:15 PM on March 9, 2011 [1 favorite]
With all those high pressure gases (if you're breathing plain air, mostly nitrogen) jostling against your tissues and being absorbed in ways they normally aren't, you're liable to experience Nitrogen Narcosis ("Rapture of the Deep") if you dive to great depths. The exact mechanism is apparently still up for debate, but the result is a euphoric intoxication similar to nitrous oxide, which is obviously a very dangerous thing to start spontaneously experiencing when you're wearing a belt of lead weights deep underwater.
A safer and more mundane side effect is that if you start to ascend while holding a lungful of air, you'll find that it expands as the pressure around you lessens. This is theoretically dangerous in the sense that if you forcefully held your breath while rapidly ascending you could rupture something, but in practice you feel a tremendous urge to exhale as the air in your lungs expands. It's a strange feeling to be able to keep breathing out and out for much longer than your lung capacity should allow.
posted by contraption at 9:15 PM on March 9, 2011 [1 favorite]
When I did my advanced certification dive ages ago, we went down to a depth of 100 feet. Our dive teacher had us do some fun puzzles at depth to show how compromised our faculties were (some not at all, others more so). One of the cool things he did was bring down some raw eggs. He cracked one open and we watched it come out of the shell and float in front of us. First it was a random blobby shape and then it compressed into a fairly perfect sphere with the yolk floating right in the middle. The pressure all around it kept it together. He then took his dive knife and sliced it right through the middle. For a second it was two semi-circular halves and then both re-ordered themselves into spheres with half yolks in each center. I thought it was such a great and fun visual way to show how pressure acts.
posted by amanda at 10:02 PM on March 9, 2011 [1 favorite]
posted by amanda at 10:02 PM on March 9, 2011 [1 favorite]
I think you are also missing another important dimension: gas diffusion into liquid. At depth, most of your gaseous cavities (beside the lung) disappear because the gas just get diffused into the liquid tissue surrounding that pocket. Said air pockets collapse; and once they collapsed, your body become fully liquid, which isn't very compressible. Sure, your tissue membrane may be stretched a bit, but if it was gassy before, perhaps it was used to being stretched. Furthermore, I don't think we human have any gas cavities that are air-tight (not gas permeable); so most of those cavities either out-gassed or diffused. Fish has an air-tight cavity, the gas-bladder. I suppose they have mechanism to maintain volume during ascent; or they may just blow-up like balloon.
The only gas cavity in your body that you absolutely must maintain is your lung. You do this by forcefully blowing it up using high-pressure gas in your air tank. Which is why it's dangerous to scuba, I suppose. Also, if you ascent rapidly from depth; all those diffused gas will reappear and cause all sort of trouble.
posted by curiousZ at 11:39 PM on March 9, 2011
The only gas cavity in your body that you absolutely must maintain is your lung. You do this by forcefully blowing it up using high-pressure gas in your air tank. Which is why it's dangerous to scuba, I suppose. Also, if you ascent rapidly from depth; all those diffused gas will reappear and cause all sort of trouble.
posted by curiousZ at 11:39 PM on March 9, 2011
So, as a deep free diver and a scuba diver, I can tell you, you can go as deep as you want with out any problems related to pressure. Pressure is really never an issue. Your body is mostly liquid and does not compress much. Your air spaces compress with little issue, your ears need to be equalized. But crazy deep divers pack their ears with water before they go down. Your body is basically a big bag of water.
Real problems come in with breathing air at depth. With those compressed bubbles entering your body, having them grow as you ascend can kill you.
Contraption is right with all the science stuff. Contraption, is wrong about the practical side of things. I have watched people people with excruciating pain from corking out from 15ft. I have watched people pop their lungs. Always breath normally on scuba and never hold your breath for any reason.
Nitrogen narcosis is weird stuff, I feel nothing until after 110ft. But after that, weird stuff. Its like being on drugs, but you swim up and it goes away instantly, no after affects. Cousteau said it felt like the deep was calling to him, like he needed to swim down. I have only felt this once. Its this really weird feeling to look at your gauges and watch the needle plummet towards the red with each breath and feel a nagging feeling that something is wrong. You know you have to go up, everything in your head says go up. But the idea of going deeper feels like looking at a hammock and a cooler full of beer on a hot summer day. You know you need to mow the lawn; but damn it would be nice to sit and forget your worries.
posted by Felex at 12:02 AM on March 10, 2011 [1 favorite]
Real problems come in with breathing air at depth. With those compressed bubbles entering your body, having them grow as you ascend can kill you.
Contraption is right with all the science stuff. Contraption, is wrong about the practical side of things. I have watched people people with excruciating pain from corking out from 15ft. I have watched people pop their lungs. Always breath normally on scuba and never hold your breath for any reason.
Nitrogen narcosis is weird stuff, I feel nothing until after 110ft. But after that, weird stuff. Its like being on drugs, but you swim up and it goes away instantly, no after affects. Cousteau said it felt like the deep was calling to him, like he needed to swim down. I have only felt this once. Its this really weird feeling to look at your gauges and watch the needle plummet towards the red with each breath and feel a nagging feeling that something is wrong. You know you have to go up, everything in your head says go up. But the idea of going deeper feels like looking at a hammock and a cooler full of beer on a hot summer day. You know you need to mow the lawn; but damn it would be nice to sit and forget your worries.
posted by Felex at 12:02 AM on March 10, 2011 [1 favorite]
Answer to Side Question: Generally speaking, yes, that is correct.
posted by coffeefilter at 12:12 AM on March 10, 2011
posted by coffeefilter at 12:12 AM on March 10, 2011
Response by poster: Doing some more reading around, I found this explanation of why and how nitrogen bubbles form during a dive, which helps explain where the gas goes when it is compressed and why it can be so awful for those places. You divers be crazy, basically.
But gas can't compress forever, even if it is diffused out into various organs and blood streams...with enough pressure (is there enough, even at the bottom of the ocean?), does it just get pushed out of the body completely? Through any convenient openings? Or fizz out through the skin?
Hearing more about this just brings up more questions- Nitrogen narcosis? Gas-bladders? HOW DO THEY WORK? I have to stop reading general science books, I end up doing more research than reading...
posted by Bibliogeek at 12:15 AM on March 10, 2011
But gas can't compress forever, even if it is diffused out into various organs and blood streams...with enough pressure (is there enough, even at the bottom of the ocean?), does it just get pushed out of the body completely? Through any convenient openings? Or fizz out through the skin?
Hearing more about this just brings up more questions- Nitrogen narcosis? Gas-bladders? HOW DO THEY WORK? I have to stop reading general science books, I end up doing more research than reading...
posted by Bibliogeek at 12:15 AM on March 10, 2011
Under enough pressure... gas becomes liquid.. and then a solid.
During the BP Oil disaster there was a lot of talk about the methane crystals clogging things up.
This is methane, in solid form due to temperture (low) and pressure (high) at a depth of 5000'.
posted by j03 at 3:50 AM on March 10, 2011
During the BP Oil disaster there was a lot of talk about the methane crystals clogging things up.
This is methane, in solid form due to temperture (low) and pressure (high) at a depth of 5000'.
posted by j03 at 3:50 AM on March 10, 2011
. I have watched people people with excruciating pain from corking out from 15ft. I have watched people pop their lungs. Always breath normally on scuba and never hold your breath for any reason.
Well, I'll be damned. You sound like a much more experienced diver than me. My dive instructor gave us the warning not to hold our breath on the way and explained why, but couched it in the reassurance that it was difficult to hurt yourself this way in practice, and that's something I've found to be born out by experience, since the pressure buildup makes me feel like I need to exhale long before anything starts to hurt, and anyway you should never really ascend fast for the expansion to take you by surprise, since going up that fast puts you potentially at risk for other problems previously mentioned. After reading your comment, though, I'll never again minimize the potential for injury. 15 feet? That's nothing!
posted by contraption at 10:30 AM on March 10, 2011
Well, I'll be damned. You sound like a much more experienced diver than me. My dive instructor gave us the warning not to hold our breath on the way and explained why, but couched it in the reassurance that it was difficult to hurt yourself this way in practice, and that's something I've found to be born out by experience, since the pressure buildup makes me feel like I need to exhale long before anything starts to hurt, and anyway you should never really ascend fast for the expansion to take you by surprise, since going up that fast puts you potentially at risk for other problems previously mentioned. After reading your comment, though, I'll never again minimize the potential for injury. 15 feet? That's nothing!
posted by contraption at 10:30 AM on March 10, 2011
15' is an extra .45 atmospheres, so your lungs are holding 50% beyond their capacity (1 atmosphere = 33 feet)
posted by misterbrandt at 9:08 PM on March 10, 2011
posted by misterbrandt at 9:08 PM on March 10, 2011
This thread is closed to new comments.
volume (of a gas) = particles of gas * a constant * temperature / pressure
As you surmised, all the weight of the water exerts extra pressure on gases (there is a 'normal' pressure on gasses at sea level, too, which is exerted by the collective mass of the atmosphere pressing down on us).
Pressure goes up, volume goes down, all else being equal.
posted by zug at 8:38 PM on March 9, 2011