AI Computers - No-Decom Time based on Breathing?

[edwinh]

I have a question about Air Integrated Computers.

Non-AI coms calculate the no-decom time based on depth and time at depth.

Are there any AI computers that calculates the no-decom time based depth and breathing rate? Gas saturation under pressure occurs if there is gas exchange in the lungs. So the lesser one breaths, the longer should the ndt be. In other words, the faster/more you breath, the faster you should get saturated, eh?

If the AI computer only shows tank pressure and air left without using breathing information in the algorithms, what's the plus of having an AI other than to have the entire SPG on your wrist?

 

[outlawaggie]

I have a question about Air Integrated Computers.

Non-AI coms calculate the no-decom time based on depth and time at depth.

Are there any AI computers that calculates the no-decom time based depth and breathing rate? Gas saturation under pressure occurs if there is gas exchange in the lungs. So the lesser one breaths, the longer should the ndt be. In other words, the faster/more you breath, the faster you should get saturated, eh?

If the AI computer only shows tank pressure and air left without using breathing information in the algorithms, what's the plus of having an AI other than to have the entire SPG on your wrist?

The AI I'm looking at calcs deco time or amount of air time based on breathing. It shows how much time you have left based on which ever calulation is the shortest.

 

[Scubaroo]

Gas saturation under pressure occurs if there is gas exchange in the lungs. So the lesser one breaths, the longer should the ndt be. In other words, the faster/more you breath, the faster you should get saturated, eh?

I think this logic is flawed - the nitrogen you breathe is not metabolised, so gas exchange (ie breathing) does not affect the rate of nitrogen uptake. There's always nitrogen in your lungs to be absorbed into the bloodstream at a reasonably constant rate relative to the ambient pressure in your lungs (ie relative to depth). You mightn't have realised it when you typed it, but you're implying that skip breathing extends NDLs, which is bunk.

There's a number of docs on the board who could answer this part of your question correctly.

Following this logic through, the rate of breathing should not be used to calculate NDLs or decompression obligations.

outlawaggie,

If you're referring to a Suunto AI computer by any chance, the "remaining air time" displayed is based on your breathing rate, and only shows when it's less than your "remaining NDL". Remaining NDL is based on nitrogen loading. They're not related. One has to do with how much gas is in your tank, the other on how much nitrogen is in your body.

Disclaimer - I'm not a diving doc, hyperbaric technician or dive computer designer, so read this post with that in mind. I could be wrong.

 

[MyDiveLog]

I have an Oceanic Datamax Pro+ (console) and a VT Pro (wrist). Both are air integrated and calculate a theoretical remaining dive time based on the lesser of the air consumption rate or the NDL time.

 

[edwinh]

I think this logic is flawed - the nitrogen you breathe is not metabolised, so gas exchange (ie breathing) does not affect the rate of nitrogen uptake. There's always nitrogen in your lungs to be absorbed into the bloodstream at a reasonably constant rate relative to the ambient pressure in your lungs (ie relative to depth). You mightn't have realised it when you typed it, but you're implying that skip breathing extends NDLs, which is bunk.

That is one way to interpret what I typed, but it's not what I meant directly.

I'll try to put it in a simpler way.

Diver A huffs and puffs throughout the entire dive - let's say the consumption is 30SLM.
Diver B breaths slow and easy - the consumption is 11SLM.
Both divers dive for 1 hr with the same dive profile.
Who would be more N2 saturated at the end?

 

[Firefyter]

That is one way to interpret what I typed, but it's not what I meant directly.

I'll try to put it in a simpler way.

Diver A huffs and puffs throughout the entire dive - let's say the consumption is 30SLM.
Diver B breaths slow and easy - the consumption is 11SLM.
Both divers dive for 1 hr with the same dive profile.
Who would be more N2 saturated at the end?

Scubaroo's answer still holds:

the nitrogen you breathe is not metabolised, so gas exchange (ie breathing) does not affect the rate of nitrogen uptake. There's always nitrogen in your lungs to be absorbed into the bloodstream at a reasonably constant rate relative to the ambient pressure in your lungs (ie relative to depth).

 

[paulwlee]

A diver who exerted himself may be more saturated, but not because he breathed more gas. The increased circulation may result in the tissues absorbing more nitrogen from the blood.

AFAIK, no computer takes this into account. (I vaguely recall there being one in the past, but not any more.) It will be overly complicated, and moreover the best the computer can do is to just add some hodgepodge conservatism factor when it thinks the diver is exerting himself.

Now with that out of the way:

There are two advantages of air integrated computers.
One, it computes remaining gas time based on current consumption. Two, it stores the beginning and ending pressures so you can log them, and it also gives you the surface air consumption (SAC) rate if you download it to a PC.
Another benefit, only for hoseless computers, is that you have the gas info on the wrist, so it is slightly more convenient to check.

For me, number two and three make a difference. Number one (remaining air time) doesn't really matter. So it's mainly about a little convenience, but I still like it. I wouldn't have gotten a non-hoseless AI computer, though, as I like my instruments on my wrist.

 

[scubatoys]

Actually the Uwatec Smart Pro does do that... It watches breathing rates, and if the breathing rate goes up, it will shorten available Nitrogen time - assuming you are now in a strenuous situation. It will also back off it's allowable times based on other UW behavior, like saw tooth profiles, etc.

Neat?? Oh yes... Necessary?? IMHO No... The darn thing is so conservative to begin with - I feel making it even more so is way overkill.

We had some guests over to the house a few weeks ago - and some had little kids, so I went out and bought one of those pool alarms. You mount it on the side of the pool, and if anyone touches the water - a loud alarm goes off. It turns out my pool alarm is about the same algorithm as Uwatec and Suunto computers.

 

[miketsp]

That is one way to interpret what I typed, but it's not what I meant directly.

I'll try to put it in a simpler way.

Diver A huffs and puffs throughout the entire dive - let's say the consumption is 30SLM.
Diver B breaths slow and easy - the consumption is 11SLM.
Both divers dive for 1 hr with the same dive profile.
Who would be more N2 saturated at the end?

Your logic is flawed. 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.

PS: Just found the thread:
http://www.scubaboard.com/t64178.html

 

[strider]

Actually the Uwatec Smart Pro does do that... It watches breathing rates, and if the breathing rate goes up, it will shorten available Nitrogen time - assuming you are now in a strenuous situation. It will also back off it's allowable times based on other UW behavior, like saw tooth profiles, etc.

I was just going to ask about the Uwatec Air Z nitrox. My buddy and I were both diving identical Air Zs and he has amazing air consumption, not the best shape but breathes less than me. I noticed that I acquired more deco on the computer and the little lung icon popped up every now and then.
It's always great having knowledgeable people around to answer these questions, thanks Larry.
Justin