Consumption and Nitrogen Absorption

[RICoder]

I realize there are a lot of variable that go into nitrogen absorption and thus how to dive without getting bent. However, in review of the charts I have, what I see absent is the rate of air consumption.

My question, thus, is since I tend to consume air pretty quickly sometimes (relatively speaking), am I absorbing more nitrogen, and hence getting more saturated than my dive buddy? Maybe I should rephrase and ask if my consumption rates should lead me to limit my time at depth.

I'm eager to hear any and all responses. The more technical the better.

 

[Charlie99]

The basic answer is that increased air consumption does NOT mean that you will absorb more nitrogen.

Think of a sponge. It doesn't matter if it is in a sink or an ocean, it absorbs the same amount of water. Your body absorbs only a tiny, tiny fraction of all the N2 that you inhale and exhale.

There is a slight correlation between air consumption rate and N2 uptake. The link is that if you are exercising hard, then your circulation will be higher, and this effectively reduces the time constant of some tissues. There are some Uwatec dive computers that try to guess from your breathing pattern & rate whether or not you are working hard, and will adjust the deco calculations a bit.

Again, the reason you don't see SAC factored into the dive tables is that it doesn't really have a material effect.

Charlie

 

[DepartureDiver]

ditto ... what Charlie said

 

[RICoder]

thank you...yet another deep dark mystery solved here at SB!

 

[Dr Deco]

Hello RICoder :

Gas Uptake

One must always bear in mind that gas is taken into the tissues from the capillary blood. That is the exchange point. What occurs in the lungs is not of great relevance since the lungs were designed to allow the maximum degree of gas exchange.

An athlete performing at maximum physical capacity will not find that oxygen exchange or carbon dioxide elimination is limited in the lungs. The limiting processes are in the tissues themselves.:wavey:

Dr Deco :doctor:

 

[miketsp]

This was extensively discussed on a recent thread.
The N2 takeup depends on the pressure gradient at the interface which in turn depends on the PP of the N2 in the lung.
The quantity of N2 absorbed in the lung is negligable in comparison to the volume of N2 present so the PP reduction of the N2 is also negligable.
End result is it doesn't matter if you're breathing hard or shallow, the N2 takeup rate is the same.


See this thread:
http://www.scubaboard.com/t64178.html

 

[RICoder]

Thanks doc...and everyone else.

It seemed, to me, at the time, a logical conclusion that breathing affected up take. Having heard all of this, I see how it works. At the end of the day, more knowlege makes you a safer diver. I appreciate it.