Now, I’m no scuba diver, but from what I remember in my schooling, the air was already in there from the descent. The increased pressure due to depth caused nitrogen to dissolve into the bloodstream, and when you came back up you had to wait at certain depths for a while to let the nitrogen to come out of solution. If you came up too fast, bubbles could form and that would lead to the bends.
And speaking from a common sense perspective, would the increased volume in the lungs go out the path or least resistance: your mouth?
Well, the “quantity” would be the same, but because pressure is decreasing, volume has to increase according the gas laws. (The number of molecules stays the same.) In the non-closed system of your lungs/throat/mouth the “excess volume” would escape when you exhale. I know you breathe slower while diving, but I doubt you’d be able to hold your breath when the pressure in your lungs is so great that oxygen/nitrogen can pass through the alveoli walls as actual bubbles.
Cecil’s talking about an embolism, not the bends. Actually, rereading, Cecil seems to be mixing the two.
If you’re breath-hold diving (no scuba), then the air in your lungs when you start descent is all that’s ever going to be there. Your lungs compress upon descent, according to Boyle’s Law - Pressure * Volume = k, where k is a constant. So as the pressure of the surrounding water goes up, the volume of the air in your lungs (and your lungs themselves) goes down. When you ascend, the air in your lungs expands, but only goes back to the volume it was when you started. So there’s no danger of an embolism.
If you’re scuba diving, then as you descend and breathe from your regulator, the air in your lungs is at the same pressure as the surrounding water, and your lungs maintain their normal breathing volume, since you have access to air at ambient pressure. If you then hold your breath and ascend, the air in your lungs expands as the pressure decreases, and ruptures your lungs, leading to an embolism. Which is why the very first thing they teach you in Dive Class is “never, ever, ever hold your breath while scuba diving”.
The bends, as in nitrogen bubbles coming out of solution as pressure decreases, has nothing to do with the increase in air volume in your lungs. It has to do with how saturated with nitrogen tissues become while you’re under pressure. If a tissue (like blood) is highly saturated, and you decrease the pressure quickly (by ascending too fast), the gases come out of solution faster than they should and form large bubbles. Which is why the second thing they teach you in Dive Class is “ascend slowly” - IIRC it’s 60 ft/min below 30 ft depth, 30 ft/min above 30 ft depth.
That description is very inaccurate, even if using the word “volume” informally.
The volume of air is the same, defined by the size of the lungs as they open and close while you breathe. The pressure in the lungs is higher, because the pressure outside the lungs is higher and the lungs have to overcome that difference. The mass of air in the lungs will be greater, which is “quantity” of air, because the air is compressed into a tighter density to match the pressure difference.
Second, the description of the greater air quantity pushing tiny bubbles into the blood vessels as you rise is also inaccurate. The air is not suddenly passing through the tissue. Rather, higher pressures mean greater mass of air means more gas absorbsion into solution. The blood has more air molecules dissolved in it at higher pressure. When the diver rises, the pressure reduces, that pressure that was keeping the gas in solution is no longer present, so some of the gas comes out of solution and forms bubbles in the bloodstream.
Cecil’s description is only vaguely accurate, in the sense that as you rise bubbles form in the bloodstream. But it is very inaccurate and highly misleading - not worthy of someone who promotes “the straight dope”.
Another question about the article:
How would treatment with pure oxygen save him? What constitutes “treatment with pure oxygen”? Is that giving him a gas mask feeding pure O2?
Or was it putting him in a hyperbaric chamber? That is using pressure to dissolve the gas in the blood stream, then slowly reducing the pressure to allow the gas to exit via the lungs, the same way to treat the bends (i.e. the situation with scuba diver listed above).
Or would putting a gas mask of pure oxygen have a similar effect, because the reduced presence of other gases in the lungs would lead the gas in the blood to be absorved out through the lungs?
I see muldoonthief snuck in on me, already talked about the bends, and described how Cecil’s description could be seen to make sense. In light of that, my objection is misdirected.
I guess that’s what rubbed me the wrong way is the general, vague way you can get embolisms from to fast an ascent. I agree with you Irishman, that inaccuracy doesn’t blend in so well with the other wise “straight dope” feel.
I didn’t get the thing with the oxygen treatment either, but I figured it was just a summary of a news article.
Yeah, the bends is nitrogen “undissolving” from the blood under reduced pressure - as what happens from opening a warm bottle of coke or beer. With the bends, IIRC the painful part is the tiny bubbles lodging in the joints where circulation is poor - it causes pain that makes you bend double. The lethal danger is bubbles on the brain - where they can create strokes by blocking the flow of blood.
Not only do you have to ascend slowly from diving, but there are charts that tell you how to stop for how long and what level in order to avoid even minor bends. (They also suggest not flying for 24 hours). IT’s something like ascend 30 or 60 feet then wait 5 to 15 minutes, or X minutes wait for every Y minutes at depth, etc. I have the book somewhere and I’m sure it’s on the internet if I cared to open a new tab.
For deep dives you have to plan out the whle thing so as to not to run out of air too soon. That’s more than half the written diving certification test.
If one were to hold one’s breath while ascending, the pressure would decrease and the volume of the air in the lungs would increase. It could rupture the alveoli, the small sacs where gas exchange takes place in the lungs . Since the lung tissue and vessels would be disrupted, you could force air into the vessels, resulting in an air embolism. Trapping the air in the alveoli makes this more likely, hence the problem with asthma.
Bubbles work their way the length of the intestines going southbound all the time. I think it’s easier for air to exit, but I don’t see why not… IIRC, the mechanism of the intestines is successive sections squeezing to push everything one direction to the final destination. I’m not sure you would pass air the wrong way, more likely you would get very large bubbles painfully stretching the intestines if they can’t pass, as happens normally with burritos.
But there is no “in” to your blood stream from the intestines unless you over-inflated the tube to the point where it burst, in which case air bubbles would be the least of the worries.