Do recreational dive computers factor in air consumption rate when calculating nitrogen loading?

[RonR]

Ok, so what I'm getting is that computers don't factor in air consumption. You can be a huge air hog or a sipper and the nitrogen loading it calculates will be the same for each case if the dives and ascents were identical, despite one person ending the dive with, say, 500 psi and the other with 1500 psi (I actually had this happen - instabuddied with the boat's divemaster and he came up with 500 psi and me with 1500 psi). I would assume that the heavier breather would have taken in more nitrogen, but I guess it doesn't make that much of a difference in recreational diving?

What about with tech diving and mixed gas? Or is replacing nitrogen with helium or hydrogen only done to eliminate nitrogen narcosis?

The heavier breather is not taking in more nitrogen. Nitrogen absorption for a given mix is a factor of time and pressure, and has nothing to do with metabolism or SAC rate. Off-gassing or bubble formation may be affected by exercise level (including after you get out of the water), among many other factors (hydration, age, fitness, body fat %, etc.).

I don’t see any way an AI computer could infer exercise level by air consumption alone- you could be a 92 lb woman breathing really hard, or a totally relaxed 350 lb NFL player barely sipping air, both with the same SAC. The computer has no way to know from gas use alone.

Measuring heart rate can provide a good indicator as to how hard you are working, but exactly how that should be factored into decompression calculations is um, unclear. Most divers know to be a bit more conservative on strenuous dives, or if they are cold, or tired, or subject to other factors that may increase DCS risk. You know more about how you are doing than the computer can.

Computers provide very broad brush guidelines for generally safe profiles, I think you are expecting a level of precision that just is not there.

Ron

 

[broncobowsher]

Of the 4 computers I have not a single one has any idea how hard I am breathing.
Time, pressure, and knowing what you are breathing (typically just air). That is all any of the calculations go off of. Don't expect anything more, they really are that simple.

 

[gcarter]

Ok, so what I'm getting is that computers don't factor in air consumption. You can be a huge air hog or a sipper and the nitrogen loading it calculates will be the same for each case if the dives and ascents were identical, despite one person ending the dive with, say, 500 psi and the other with 1500 psi (I actually had this happen - instabuddied with the boat's divemaster and he came up with 500 psi and me with 1500 psi). I would assume that the heavier breather would have taken in more nitrogen, but I guess it doesn't make that much of a difference in recreational diving?

What about with tech diving and mixed gas? Or is replacing nitrogen with helium or hydrogen only done to eliminate nitrogen narcosis?

The heavier breather may have taken more nitrogen into their lungs, but they have breathed it right out again. What is important is the absorption rate, not the breathing rate. Breathing more heavily simply wastes more gas without changing absorption.

 

[wetb4igetinthewater]

Really, nobody is going to have a wired AI computer on a sidemount tank.

I wouldn't be so sure: Steve Bogaerts

 

[JohnnyC]

I wouldn't be so sure: Steve Bogaerts

I'm not seeing a wired AI computer, did I miss it? Wireless AI is not uncommon on sidemount, but I'd be willing to bet the number of people using something like a Cobalt 2 is a fraction of the number of people using either 2 transmitters or standard SPG's.

 

[tursiops]

I wouldn't be so sure: Steve Bogaerts

That post clearly shows and discusses transmitters for pressure, not wires.

 

[wetb4igetinthewater]

I'm not seeing a wired AI computer, did I miss it? Wireless AI is not uncommon on sidemount, but I'd be willing to bet the number of people using something like a Cobalt 2 is a fraction of the number of people using either 2 transmitters or standard SPG's.

He's using Perdix AI's with the diluent and oxygen cylinders for his CCR.: Edit: my bad. I misread your post. It never would have dawned on me for people to use wired dive computers with sidemount, so I read that as using transmitters, as some folks can't grasp the concept of how reliable Shearwaters are.

 

[boulderjohn]

So nitrogen loading is pegged to metabolism? And the individual differences in metabolic rates among relaxed divers isn't enough to demand compensation by the computer?

I wrote my earlier post in a hurry and from a phone, so it was not as clear as it should have been.
One of the factors affecting nitrogen ongassing and offgassing is perfusion--the blood flow carrying the nitrogen to and from the tissues. The harder you work, the more the blood flows. If you are working hard during the dive, your blood will be flowing more. You may also be breathing harder. If you are going through your gas faster because of that, then, yes, it will affect your nitrogen saturation. If you are just a heavy breather, then no, it will have no effect.

 

[Lorenzoid]

I wrote my earlier post in a hurry and from a phone, so it was not as clear as it should have been.
One of the factors affecting nitrogen ongassing and offgassing is perfusion--the blood flow carrying the nitrogen to and from the tissues. The harder you work, the more the blood flows. If you are working hard during the dive, your blood will be flowing more. You may also be breathing harder. If you are going through your gas faster because of that, then, yes, it will affect your nitrogen saturation. If you are just a heavy breather, then no, it will have no effect.

I think blood perfusion may be what the OP meant by "metabolism." There may be differences in blood perfusion among individuals, and there is certainly a difference based on how much you're exerting yourself at the moment.

 

[yle]

I would assume that the heavier breather would have taken in more nitrogen, but I guess it doesn't make that much of a difference in recreational diving?

Seems your confusion stems from a fundamental misunderstanding of what happens to all that nitrogen that's in the air "consumed" by the diver that goes through their tank faster. For example, you and your buddy start a dive with 3000 psi. You finish with 1500 and your buddy finishes with 500. It is true that your buddy removed far more nitrogen (as part of the air) from his tank.

But the nitrogen didn't stay in his body. He exhaled it into the water. That's why he went through his air faster: his body's not actually "consuming" the excess air, he's just exhaling it into the water.