If I breathe in deeply, hold it, pinch my nose, and relax my chest, I can feel my lungs getting smaller. Or do they? Is it placebo I am feeling, or can I actually feel the air being removed? Is there a doctor or intelligent person who can tell me how much oxygen is in the air and then how much of it we absorb? I think I heard somewhere that when we exhale, there is still 16% O2 in our breath. That’s why CPR works. Is the amount pulled out sufficient that I would be able to detect it, or is it just my chest relaxing even more?
Thanks!
The oxygen you absorb is replaced by the carbon dioxide that you exhale. I’m not sure how it balances out, but I expect the in-out volume is equal (though exhaled air might actually weigh a bit more).
Can any physiologists confirm what I just said?
I don’t claim to be either one, but I’ll make a stab at answering.
It isn’t correct that when oxygen is absorbed into the blood the total amount of gas in your lungs decreases. The mechanism is as follows.
The blood returned to your lungs by the veins is deficient in O[sub]2[/sub] and has an excess of CO[sub]2[/sub]. The air on the other hand has O[sub]2[/sub] and is deficient in CO[sub]2[/sub].
The blood and the air constitute a continuous medium as far as the gasses are concerned. The lung tissue is a membrane that blocks the large molecules of the blood but passes the small molecules of the gasses.
The partial pressure for O[sub]2[/sub] is low in the blood and high in the air and that differential pressure causes the O[sub]2[/sub] to go through the membrane into the blood. Conversely the CO[sub]2[/sub] partial pressure is high in the blood and low in the air, and that differential forces the CO[sub]2[/sub] into the air.
So the oxygen that was in the air in the lungs is replaced by carbon dioxide and the volume of gas in the lungs remains about the same.
The air in the lungs retains some O[sub]2[/sub] and the blood retains some CO[sub]2[/sub] because once the partial pressures are equalized the exchange of gasses between blood and air stops.
I don’t have any idea what your are feeling. It is possible that you are able to relax your diaphram which would give the lungs more space and you would feel a lowering of pressure in the lungs. There might also be some subtleties that I know nothing about.
I’m about 90% sure that what you are actually feeling is your diaphragm relaxing and the rest of your upper body slumping down when you relax, which does sorta feel like your chest is shrinking.
The part about the gas volumes written above is right; if we absorbed gases from the atmosphere without releasing the same amount, we’d all have swollen up like balloons and popped within the first hour from when we were born :eek: .
Try this: take your deep breath of air, close off your throat/mouth, and relax. Now keeping your air intake clamped off, try breathing in again - feel your chest and shoulders rise up a bit? I suppose it is your lungs or chest cavity expanding and shrinking a bit, but from your diaphragm trying to create the vacuum, not oxygen being sucked into the bloodstream.
Were you going to say sucking chest wound?
The atmosphere contains about 21% oxygen and exhaled air contains about 16% oxygen.
Of the oxygen you actually take in, some ends up in water (which leaves the body in a variety of ways), and some ends up in carbon dioxide (which you exhale). By the ideal gas law, a given number of molecules of any gas will have the same volume, and oxygen and carbon dioxide both contain two oxygen atoms per molecule, so the portion of the oxygen which gets combined with carbon would not contribute to a volume change.
If we approximate that human “fuel” is C[sub]x[/sub]H[sub]2x[/sub], then twice as much oxygen would combine with carbon as with hydrogen, so about a third of the oxygen you take in with each breath would be removed from the gas volume. Since the oxygen you take in is about 5% of the air, this means that the change in volume of your lungs would be less than 2%. If you hold your breath for longer, and thus take out more of the oxygen, you might decrease the volume of gas in your lungs by up to 7%, which probably still isn’t noticeable.