Regs and CO2 buildup

[Razorblade]

If you buy a reg for deep diving (say an Apeks ATX200), is it true that it's a good idea to use a big second stage (like the one to the Apeks TX100) ?? I was told that the bigger the second stage the better so your CO2 buildup is less because the gas you exhale diffuses more with the gas that comes in on your next inhale.
I'm interested to hear about people's opinions.

 

[Waterlover]

IMO It's not the size of the second stage that is most important(although a smaller one is my choice, less dead airspace). It's how you breath. A deep breath is more effective in getting good gas exchange than a shallow one.

 

[MikeFerrara]

In theory we want to reduce dead air space. Dead air space is a space that can hold exhaled breath. The gas in that space must be inhaled before you get fresh air. So...It would seem to me that we want a small volume between our mouth, the exhaust valve and the demand valve.

In practice I don't know what the volume difference would be between a "big" second stage and a "small" one or how significant it is.

Also notice that some second stages discharge the air almost right into your mouth essentially bypassing any old gas in the reg boddy. I think there is very little effective dead air space in most second stages.

 

[Genesis]

is that work of breathing is probably more significant than dead air in the regulator (in terms of difference between regs)

A smaller diaphram in the regulator means less area for the differential between ambient and you 'sucking' to act on, therefore, all other things being equal, a higher WOB.

So there is a trade-off - the "micro" regs may actually be far worse than the "small standard" ones, or even the "standard sized" ones.

I know of no studies that have been done on the actual CO2 retention under these conditions, nor do I have a good idea of how to design such a study without ending up with lots of "confounders" (things that change the results in non-obvious ways), making it nearly impossible to get "good" results.

 

[detroit diver]

Waterlover once bubbled...
IMO It's not the size of the second stage that is most important(although a smaller one is my choice, less dead airspace). It's how you breath. A deep breath is more effective in getting good gas exchange than a shallow one.

So, what you're saying is that it's not the size, but the depth that's important??:wacko: