Larger gas capacity and increased DCS risk?

[SailNaked]

Lets just say that nitrogen is absorbed into the body at some unknown rate.
now lets say we are given the job by the Navy to come up with a way for divers to go below 45 feet without getting sick. Ok, lets assume that different parts of the body absorb and discharge the Nitrogen at different rates, we will call these compartments, maybe it relates to muscle and fat and organ tissue maybe not.

Ok so we will just assume that we have say 6 different compartments, and that they will saturate at 6 different levels and over 6 different times. lets just equally divide the compartments from say 15 minutes to about 2 hours. ok since we think that the more that a tissue or compartment absorbs the less that it can absorb we will just make the function easy and call it a half life, like the decay of isotopes, why not.

OK now we have a theory, lets try it out on some unsuspecting divers, the Navy is paying so we can use theirs.

Hmm, some of the divers did not conform to well to our new theory, lets change it a little to match the experimental data. we can adjust the limits of our compartments and the times a little, and bingo, bobs your uncle we have a system to allow the Navy to do some diving. Woop lets cash the check.

Now lets invent the Internet and act like this theory is actually true and argue about it. We still do not know the rate at which any part of our bodies absorb nitrogen or at what point the gas that comes out of solution or the mechanism for that is a problem for our bodies. but please discuss it on the Internet as that is what it is for.

 

[Rhone Man]

In calculating NDL limits for a dive, there are only two variables that I can see (at least with, say, the RDP tables): depth, and the amount of time spent at that depth.

Not to be pedantic, but there is a third variable - gas mix.

the concentration of nitrogen that a diver is exposed to during the entire dive is not really altered by how fast they inhale and exhale, so the fact that "more" nitrogen passes through their lungs doesn't affect how much nitrogen they're going to absorb.

In theory, you could limit your absorbtion of N2 by not breathing at all, and thereby limiting the amount of gas that can be absored to 79% of one lungful of air. This is why freedivers can go plummet down to 500' and shoot back up like a rocket and not get bent, whereas a diver on scuba doing the same and breathing continuously would be heading to the chamber (or more likely would embolise and die, but you see my point).

 

[reefduffer]

A number of previous posters have sort of talked around the edges of this, but here's some interesting reading. It turns out that some Uwatec computers model N2 loading including a metric of physical activity; briefly stated, it assumes that if you're more active you're absorbing N2 faster.

I don't dive one of these, I first encountered the concept trying to answer a question in this thread http://www.scubaboard.com/forums/co.../327300-computer-transmitter-nodeco-time.html and discovering that my first response was incorrect, given these computers.

UWATEC introduced workload-induced decompression algorithm compensation in 1995 with the Aladin Air X dive computer. ...

As as starting point, they use air consumption rate. Air consumption rate will affect no-deco time for this computer.

And for the Sol or others with a heart rate monitor, it can use that as the metric of exertion rather than air consumption.

Manual can be downloaded at GALILEO SOL - SCUBAPRO-UWATEC

The relevant description is section 2.9.5 starting on page 37.
That has a brief but informative description of what they're trying to do, which directly relates to the OP's question.

 

[veg123]

This is an interesting question, I have no idea what the answer is but I want to understand so I hope someone can help...

I would like to phrase the question differently.

Assumption: Its the same diver (this way we can rule out uncontrolable factors such as weight, fitness, smoker, drinker, etc.) Also assume the diver is hydrated to exactly the same degree on both dives and has eaten the same food and had the same amount of sleep the previous week on each dive.

Constants: everything about the profile is the same depth, time, gas mix, temperature, gear, stress, current, workload, etc.

Variable: Diver breaths more air on one dive compared to the other. This should be the only variable in equation

I'd have thought if more N2 passes through the lungs then absorption would be greater?

This is very theoretical and probably not possible to model. BTW I'm not trying to argue with any of the posts so far but I'd really appreciate an explanation as my understanding of gas isn't as good as some of you.

Thanks

 

[ianr33]

As as starting point, they use air consumption rate. Air consumption rate will affect no-deco time for this computer.

So you donate air to an OOA buddy and your NDL time decreases?

That makes a lot of sense.

 

[masska]

I do not want to disrupt this medical discussion, but keep in mind this:
deco tables and computer algorithms are so restrictive, that using 10 or 20% air more does not make problem.
this is example: US Navy tables gives 18m/sec as maximum rate of ascent, padi, cmas, naui etc..etc.. give 10m/sec, and as i heard even that will be changed to 9 m/sec.
So it is perfectly safe to ascent 18m/sec, but this is restricted to 50% to compensate for physical differences. if that is done with rate of ascent, dont you think this was also done with tables.

i have not mixed DCS with embolism... i`m just making a point