General air-integrated question-how does 'it' know your N2 load?

[scubafanatic]

I own 3 Oceanic DataMax Pros (air-integrated/non-Nitrox).....and on my last weekend's dive trip to Cozumel all the other divers used little wrist-watch style computers (not air-integrated) whereas I used an air-integrated computer on a hose.

My question is this: does my air-integrated computer actually use my air consumption data in determining my N2 loading ? All the other divers used computers that 'input' depth and time to calculate N2 loading, but couldn't care less how many psi got burned, or how what sized tank was used............so, is my computer the 'same' as the non-air-integrated models in that it only uses depth and time to calculate N2 loading? ....or, does my air-integrated computer actually incorporate my real air consumption into it's N2 loading 'projections'?

The reason I ask is, what would happen if during a dive I used a pony bottle.....or breathed off a divemaster's octo (which I did for a little while on 2 dives)....would these situations 'throw-off' my air-integrated computer's N2 loading 'projections'?

Thanks,

Karl

 

[scubasean]

Dr. Deco, in a different thread, recently said:
====================
The amount of inert gas (nitrogen that you dissolve in your body is really basically a function of pressure. The deeper (and longer) you are underwater, the more nitrogen you will acquire. The breathing rate has really little to nothing to do with it per se. Sometimes a diver will breathe faster because s/he is working harder (swimming against a current, for example). When this is the case, the heart rate is fast and more blood is pumped to the tissues. This will result in increase nitrogen loading, but basically because of the blood flow. A diver who is nervous and breathes faster will take “on board” more nitrogen.

In addition, nitrogen is inert in the body and is eliminated by the blood to the lungs. It is not “burned up” in the body. Only oxygen is involved in a chemical reaction (unless you are a nitrogen-fixing bacterium).
====================

So, if I understand it correctly, Nitrogen loading should be determined using the tables...i.e. Nitrogen loading is a generally function of pressure and time rather than rate of consumption.

Therefore, my guess is that your computer would calculate your loading without using your consumption. A way to determine this would be to dive exclusively off of a pony for a dive, and see what your comp said about loading for that dive.

Increased heart rate obviously wouldn't be considered by tables, computers, etc.

 

[scubafanatic]

Thanks scubasean,

...yeah, I guess I could do a pony dive and see if my computer notices any N2 loading even though I'm not breathing off my main reg set.......assuming the pony would even last long enough to get any N2 loading at all to show up on the bar graph before I emptied the pony.

There's nothing at all in the owner's manual on this subject.......which seems like a big omission.

It's a pretty serious question......looks like I'll have to run it by my nearest Oceanic dealer this week to be 100 % certain.

Karl

 

[agstreet]

scubafanatic once bubbled...
Thanks scubasean,

It's a pretty serious question......looks like I'll have to run it by my nearest Oceanic dealer this week to be 100 % certain.

Karl

Yes, it's a serious question, but if you have to "run it by your nearest Oceanic dealer" you don't understand the physiology enough to understand the answer.

Why do you have the impression that the amount of air you breathe has anything to do with inert gas loading of tissues? If this was the case, why don't tables take into account gas consumption? How would anything but an air integrated computer ever work?

Gas consumption is a function of how much oxygen you need to keep your body functioning. It is a totally seperate issue from intert gas loading of tissues, which is purely a function of time and pressure. While different people can vary *widely* in the amount of oxygen they need, most people are reasonably consistant in their tissue loading. If this weren't the case, how could a small woman diving with an Al 67 stay down the for same time as a really big guy breathing off a steel 120 (assuming the same profile), yet neither gets bent and both start their surface interval with about the same level of N2 tissue loading?

 

[scubatexastony]

so I dug up a dive I did in the local lake using my pony gas....(30ffw) don't freak out, pups.... I have a cobra and vyper and the cobra dl shows ongassing even though no air was being used.... if that helps any!

tony

 

[ZoCrowes255]

That's a good question and one that I never really thought about...and now I know

 

[RichLockyer]

Without sufficient surface interval, record-attempting freedivers can get bent.

The N2 in your lungs will be absorbed by the blood, and by the tissues in the body, whether or not you add more. N2 absorption is STRICTLY a function of depth and time, since N2 is not metabolized.

 

[scubafanatic]

....well, agstreet......most of the responses so far indicate my question is a legitimate question........looks like a finer point that more than a few divers have over looked.

It seemed possible that an air-integrated computer incorporated a more 'advanced' algorithm since it has more data to work with.

Dive tables are gross approximations of N2 loading.......non-air-integrated computers are a significant improvement in reflecting 'reality'...so it seemed possible that an air-integrated computer might further 'fine-tune' the algorithm, allowing the widest possible dive envelope.

As far as most people being reasonably consistent in their tissue loading......what explains the substantial differences between different computer brands.......some are a lot more 'conservative' than others......apparently there's wide disagreement within the industry as to the most 'correct' algorithm.

Interesting about the cobra, scubatexastony........at least the cobra isn't using air consumption in it's model....based on the discussion so far I'd lean toward agstreet's explanation.

I guess it's just as well, since I was worried using a divemaster's octo would confuse my computer and lead it to underestimate my N2 loading.

Karl

 

[Cave Diver]

I posed a similar question just out of my BOW class.

I was thinking about those people who had "undeserved hits" i.e. they dove within the tables, seemed to do everything right, yet still got bent.

I wondered if breathing rate could have affected it. If you have two divers at the same depth for the same amount of time, and one used twice as much air as the other, would they absorb twice as much nitrogen?

I posed that question to numerous people and the general consensus was that breathing rate did not affect nitrogen loading. As previous answers have already stated it is strictly a matter of depth vs time.

You are not alone out there!

 

[scubafanatic]

...thanks Cave Diver and RichLockyer! .....looks like the consensus view is that air-consumption isn't part of the equation...purely depth and time (and, of course, the gas mix).

I'm expecting to do some dives where a pony may be a good idea, and if I go that route it's good to know using a pony won't distort my computer's N2 loading projections.

(my charter boat prohibits doubles.......and it's impractical to try to get doubles in Cozumel either....so I may bring a pony or 2 on those 2 trips for 2-tank-dive days)

Karl