nitrogen accumulation ? time vs air quantity.

[eternaljonah]

hi i have a question
lets say there are 4 people going down to 35 meters/110 feet and we stay down for 11min they all go down together and stayed at the same level.

now diver one still has 140 bar , diver two has 100 bar and diver three has 80 bar and diver four( was not paying attention) is down to 40 bar so on the accent diver one and four share air.

now at the end of the dive all diver have been down for 25 min( slow accent) but every diver has used a very different amount of air, would the divers whom consumed more air not naturally have nitrogen in their blood then those whom used 1/3 the amount of air...

if diver one (lets say) has 1/3 the amount of nitrogen in his blood the diver four would he not be able to stay longer on the second dive or need less of a surface interval.....

......... thanks ..........

 

[Thalassamania]

No, the driving force of nitrogen going into the body is partial pressure not breathing rate.

 

[TSandM]

Thalassamania is basically right, although if the reason the divers went through more gas was that they were working harder (less efficient, floundering around) then they might have absorbed more nitrogen, just because they had increased blood flow. We are taught that dives where one has worked hard at depth ought to be regarded as having taken place deeper than the actual depth, for precisely this reason.

It is entirely correct, however, that given equal exertion/perfusion, the rate at which gas is moved through the lungs does not affect the rate at which nitrogen is absorbed.

 

[ScubaBB]

No, the driving force of nitrogen going into the body is partial pressure not breathing rate.

... and time

 

[eternaljonah]

thanks,
so if i understand right the amount of air used is not important for calculating the amount of nitrogen absorbed but effort is, so a 10min dive with the current would result in less nitrogen absorbtion then a 10 min dive against the current.

 

[Thalassamania]

That second order consideration is covered in the cold and arduous rules for tables.

 

[cloudflint]

Think of it like a big motor that cools its self by drawing water in from a river. Regardless of how fast or slow the water is pouring through the river the motor is going to draw in water at the same rate regardless. If the motor has to work harder, it will have to draw in more water which isnt a problem so long as there is enough water in the river.

Your lungs are like the river and your body is like the motor, so long as there is adequate flow through your lungs you will take in gas at a constant rate depending on pressure and exertion no matter how fast the gas is flowing. You just need to make sure you have enough gas flowing in and out of your lungs so that your body has enough to draw in.

 

[boulderjohn]

The amount of air used seems to make a difference if you use the reductio ad absurdum thought process, in which you take a concept to its logical extreme to magnify the effects. The rate of nitrogen absorption by the tissues is based on the difference in the mount of nitrogen in the air being breathed and the amount of nitrogen in the blood and tissues. The greater the difference, the faster the rate of absorption.

To go to the absurd extreme, if one diver were to do the entire bottom time of a dive on one breath, there would indeed be a big difference, because over the minutes that diver was doing that one incredibly breath, the nitrogen levels in the lungs and in the blood would move toward equalization--there would not be as much more nitrogen in the air as in the blood and tissues. Consequently, the rate of nitrogen transfer from the air to the blood would drop significantly.

The more normal difference in breathing rate between two divers, however, is not significant enough to have any measurable effect. The air in the lungs is being refreshed constantly from the air in the tank with each breath, so both divers are essentially at the same level constantly.

 

[Thalassamania]

The amount of air used seems to make a difference if you use the reductio ad absurdum thought process, in which you take a concept to its logical extreme to magnify the effects. The rate of nitrogen absorption by the tissues is based on the difference in the mount of nitrogen in the air being breathed and the amount of nitrogen in the blood and tissues. The greater the difference, the faster the rate of absorption.

To go to the absurd extreme, if one diver were to do the entire bottom time of a dive on one breath, there would indeed be a big difference, because over the minutes that diver was doing that one incredibly breath, the nitrogen levels in the lungs and in the blood would move toward equalization--there would not be as much more nitrogen in the air as in the blood and tissues. Consequently, the rate of nitrogen transfer from the air to the blood would drop significantly.

The more normal difference in breathing rate between two divers, however, is not significant enough to have any measurable effect. The air in the lungs is being refreshed constantly from the air in the tank with each breath, so both divers are essentially at the same level constantly.

John,

I don't think your analysis is correct. Under standard conditions there is about 100 ml of nitrogen in you at the surface. Contrast this with the approximately 4800 ml of nitrogen in your lungs at full inhalation. Now, making some perhaps unwarranted simplifying assumptions like constant temperature and a complete lack of diffusivity from the blood out in to the tissues, then at say, 99 feet, you could at most (e.g., at total saturation) quadruple the nitrogen in circulation, to about 400 ml, reducing the nitrogen in your lungs to 4500 ml. This is equivalent to an fN2 drop from 78% to 73% (ignoring, of course the respiratory consumption of oxygen, which would serve to raise the fN2 and thus reduce the 5% change).

Now if we look at your thought experiment of a diver doing his entire bottom time on one breath: I do not think that there would be much of a difference, even if the dive were long enough to reach saturation (e.g., 12 hours), rather than a dive that is measured in minutes. The nitrogen levels in the lungs and in the blood would, as you state, move toward equalization, but equalization at saturation consumes less than 5% of the available Nitrogen in the lungs. Consequently, the rate of nitrogen transfer from the air to the blood would NOT drop significantly.

 

[DiveNav]

I think by now we lost the OP