A big tank could bend you????

[Dyno Bill]

I have to say that although I have been diving for quite a while and have enjoyed diving in tons of neet places I learn a lot from reading the articles from the scientifically advanced posters. I just need to know whos theory is actually acurate. I am of the belief that when someone is working hard he or she will absorb more nitrogen that someone who is leisurely kicking around a rock. The deeper, colder and harder you work the more you will absorb. So I have always felt that the consumption rate is an indicator of nitrogen absorpiton as in the faster the breath cycles the faster the absorption and that doesnt take into consideration the age and physiology of an individual. Thanks for the lessons.
Bill

 

[Zept]

jbd said...
What I am suggesting is that if you put 100 N2 molecules on one side of a cell membrane and there are zero molecules of N2 on the other side then to achieve equilibrium the mebrane will "let through" 50 N2 molecules so you end up with 50 on each side. Lets say that is the case with Walter on his dive. I on the other hand put 200 molecules on one side of the cell membrane. To achieve equilibrium the membrane will "let through" 100 molecules. Now I have 100 on each side; twice as much as Walter in this case. IMHO this would put me at a higher risk of DCS.

No.

You don't put 200 molecules on one side of the membrane. You put 100 molecules, just like Walter. A few of them transfer across, but not nearly as many as 50. The rest you breathe out. Then you take in another 100. Your lungs don't see 200 molecules at once, they see 100, then another 100, then another 100, and so on.

Zept

 

[Charlie99]

Dyno Bill once bubbled...
The deeper, colder and harder you work the more you will absorb. So I have always felt that the consumption rate is an indicator of nitrogen absorpiton as in the faster the breath cycles the faster the absorption and that doesnt take into consideration the age and physiology of an individual. Thanks for the lessons.
Bill

Deeper -- yes you will absorb more N2.

Colder -- no. But the cold screws up your circulation to the extremities, making later offgassing as your ascend more of a problem.

Harder work -- this increases blood flow to some areas, effectively shortening the halftimes. If you are then inactive while ascending/deco'ing, then your offgassing halftimes are slower than the original ongassing times and you need to do more deco than in a normal situation.

Faster breath cycles --- No, this does NOT change N2 loading.

 

[jbd]

good point about 100 per breath vs 200 and true only some molecules are passing through at a time, but it still seems as though by breathing twice as fast as Walter I am keeping that 100 molecule level present at the membrane for more time than Walter is thus allowing more molecules to pass through in a given time frame. Lets say that Walter's respiratory cyle is 10 seconds and that in that time 7 N2 molecules cross the membrane. With my two breaths in that same 10 seconds could it be that I move 11 molecules across the membrane? I think that its possible since there's the need for homeostasis to be established.

If I do move 11 molecules to Walters 7 then I will be moving more molecules into the various body tissue from the blood thus giving me an overall larger N2 loading than Walter got from the dive.

BTW folks I'm using Walter in this scenario because I know he has much more experience than I do which allows me to be the "hoover"

 

[JimC]

even if yuor breathing twice as fast, you will end up with the same amount of gs in your longs averaged over the a time period.

Here is a time scale:

(0) Walter starts inhailing, (0)You start inhailing
(1/2)Walters lungs are 1/2 inhailed, (1)Yours are full and start exhaling
(1)Walters lungs are full and starts exhaling, (0)Yours are empty and start inhaling
(1/2)Walters lungs are 1/2 exhaled, (1)Yours are full
(0)Both empty(0)

Total for both is 2.


Logic is funny that way. Twice the gas passed though your lungs, but over time you had the same amount in them.



Back to the original question.

The body tisues absorb nitrogen carried by blood. The blood is a liqud which picks up gas from the lungs and carries it in solution to the body. Nitrogen saturates into blood very, very quickly, which is why we get bent at all. To much nitrogen, to fast. Blood gets supersaturated and starts to form bubbles.

Solubility of nitrogen into the blood is controlled by 2 factors.

The solubility of a gas in a liquid depends directly upon its partial pressure and inversely upon the temperature of the solvent. The temperature in the human body is basicaly constant, so we can ignore it here. (Henry's Law)

The other factor to this is how little nitrogen we are talking about. Aproximatly 1.5liters of the stuff to completely saturate at each ATM. A normal adult lung can holds 4-6liters of gas, 80% of which is nitrogen (air) and always has 1-2liters of gas, even after a full exhale.

So, we have 4-5 times enough nitrogen to kill us in ONE breath.

Quantity is not the problem.

 

[jonnythan]

jbd once bubbled...
good point about 100 per breath vs 200 and true only some molecules are passing through at a time, but it still seems as though by breathing twice as fast as Walter I am keeping that 100 molecule level present at the membrane for more time than Walter is thus allowing more molecules to pass through in a given time frame. Lets say that Walter's respiratory cyle is 10 seconds and that in that time 7 N2 molecules cross the membrane. With my two breaths in that same 10 seconds could it be that I move 11 molecules across the membrane? I think that its possible since there's the need for homeostasis to be established.

If I do move 11 molecules to Walters 7 then I will be moving more molecules into the various body tissue from the blood thus giving me an overall larger N2 loading than Walter got from the dive.

BTW folks I'm using Walter in this scenario because I know he has much more experience than I do which allows me to be the "hoover"

The main point that I think you're missing is that both you and Walter will have very very close to the same concentration of N2 in your lungs at all times. If you're at 66 feet on air, you will have 2.37 atm of N2 in your lungs, and so will Walter. No matter how long you hold your breath, that number won't drop significantly. It's not like your body will absorb so much N2 that your exhaled breath will have 2 atm of N2. If the absorption rate were that fast your body would become saturated in a matter of minutes. This is just guessing, but I'd say that your exhaled breath may contain 2.36 atm of N2 vs Walter's 2.35 N2. That's basically like you swimming 3 inches above him for about half the time.

Edit: Also keep in mind that the longer you're down there, the slower the N2 absorption rate is.

 

[Dr Deco]

Dear Readers:

Air Consumption and DCS

This topic comes up frequently on SCUBA BOARD. The breathing rate (ventilation rate) in and of itself will not determine the amount of nitrogen absorbed (dissolved) by the tissues. Since nitrogen is not very soluble, only a small amount of what is in the alveoli (the gas exchange portion of the lung) will actually be transferred into the lung capillaries. The nitrogen concentration in the alveoli is essentially unchanged, even if you were to “skip breathe” or even hold your breath.

Activity

Insofar as one breathes faster because of, for example, nervousness or anxiousness in the water, the nitrogen carried to the tissues is the same. The amount in a tissue is determined by the local perfusion (blood flow) in the tissue. If, however, the diver is exercising heavily (e.g., swimming against a current), the heart rate will increase and the local perfusion will increase in the muscle and tendons and ligaments (by the “muscle pump,” local regulators such as carbon dioxide, and neural control). In this case, increased air consumption, because of increased activity, will lead to more tissue nitrogen.

Dr Deco :doctor:

Please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[NAM001]

how does reduced breathing rate and using a nitrox mix differ in absorbsion rate. are the differences unable to show since the co2 drives breathing.

never mind stupid question breathing rate will not change the n2 level in the lung only the co2 and o2, and breathing will not change the gas absorbsion rate, only the mix will do that. sorry


curious