Dive Computer: why they don't take into account your breathing rate?

[darren_uk]

(Sorry if the Title is a bit obscure, I was trying to write a meaningful title within the character limit)


Considering those dive computers that wirelessly integrate with your tank's pressure:


These dive computers can measure your personal air consumption.


So they can measure both limits: running out of air and running out of deco.


QUESTION:


I learned from Oceanic at a dive show that despite the computers measuring your personal air consumption, nevertheless the deco is still working the same mathematical model without considering your air consumption (sorry, I've had a long day and I can't put it any simpler than that...)


But here's my query: If we consume more air (e.g. we're working hard) then the amount of nitrogen molecules going into our body is higher than if we were calm and breathed less: so why aren't dive computers giving us credit (longer no deco times) by taking into account a lower breathing rate, therefore less nitrogen molecules enter our bodies, and therefore half times are extended. Why does the dive computer that is measuring the gas consumed nevertheless continue to use constants and totally ignore the actual gas breathed?


Darren

 

[Thalassamania]

No, your analysis is incorrect. If you are working hard you have increased blood flow that is thought to increase the amount of nitrogen in the tissues, it has nothing to do with the number of nitrogen molecules going into your body, which is solely driven by the partial pressure of nitrogen. I believe that some AI computers have been built that added "safety factors" based on air consumption as a way to measure exercise level, a questionable concept.

Lynne's spot on comment from an earlier, similar, thread:

... if the reason the divers went through more gas was that they were working harder (less efficient, floundering around) then they might have absorbed more nitrogen, just because they had increased blood flow. We are taught that dives where one has worked hard at depth ought to be regarded as having taken place deeper than the actual depth, for precisely this reason.

It is entirely correct, however, that given equal exertion/perfusion, the rate at which gas is moved through the lungs does not affect the rate at which nitrogen is absorbed.

 

[CT Sean]

Same topic from a couple weeks ago: http://www.scubaboard.com/forums/ad...trogen-accumulation-time-vs-air-quantity.html

 

[Bubbletrubble]

Thal said it all.

This would be an excellent question to pose to students at the end of an Intro to Deco Theory course.
It would be a great assessment of what they've learned.

 

[Thalassamania]

He, he, he ... I've already added it to my final exam! In the form of a True/False: and why?

 

[reefduffer]

...
But here's my query: If we consume more air (e.g. we're working hard) then the amount of nitrogen molecules going into our body is higher than if we were calm and breathed less: so why aren't dive computers giving us credit (longer no deco times) by taking into account a lower breathing rate, therefore less nitrogen molecules enter our bodies, and therefore half times are extended. Why does the dive computer that is measuring the gas consumed nevertheless continue to use constants and totally ignore the actual gas breathed?
Darren

Some of the Uwatec computers do exactly that. See this thread http://www.scubaboard.com/forums/co.../327300-computer-transmitter-nodeco-time.html, post #8, where I summarized what I learned about the Galileo Sol as a result of (originally incorrectly) attempting to answer a question, and subsequent discussion. It includes a short excerpt from the Sol manual that addresses your query. Includes a link to the manual.

The rest of the thread, relatively short, provides some context.

 

[Hatul]

Yes the Galileo Sol offers the option of coupling workload from either heart rate or breathing to the algorithm.

Adam

 

[darren_uk]

No, your analysis is incorrect. If you are working hard you have increased blood flow that is thought to increase the amount of nitrogen in the tissues, it has nothing to do with the number of nitrogen molecules going into your body, which is solely driven by the partial pressure of nitrogen. I believe that some AI computers have been built that added "safety factors" based on air consumption as a way to measure exercise level, a questionable concept.

Lynne's spot on comment from an earlier, similar, thread:

Thanks Thal.


You're right: increased work load / increased blood flow is fundamentally what I was considering; increased breathing rate is just a symptom.

So the questionable concept is this one:
http://www.scubaboard.com/forums/co...uter-transmitter-nodeco-time.html#post5116877