Posted by MHK on October 26, 2004 at 14:55:57:
In Reply to: Was this diver using a rebreather? posted by Elaine on October 26, 2004 at 14:44:01:
I disagree to a certain extent. Open circuit divers are very suceptible to C02 build-up's. While for sure Rebreather divers have a greater chance, open circuit divers are by no means immune to C02 retention. Again, this issue is subjective and varies from dive to dive, depending on any number of variables and conditions. I don't have enough facts in the instant case to do a detailed analysis, but to the extent he was breathing air, as opposed to Nitrox or Triox, it's likely the gas would be denser, which would mean more difficult breathing. I have no idea how this diver's regulator was preforming, but it's certainly something I'd look at in the post dive analysis. In my mind, the largest variable, which is doubtful we'll ever know, is the level of physical excursion. Certainly gas density and reg performance are contributory factrs, but my sense is that the largest contributing factor would likely be the physical excursion level.
It's possible to retain as much as 65% of the prior breath when experiencing Dypsnea. With that level of retention, and the physiological desire for 02 the diver will continue to breath more and more rapidly, and retain more and more C02, and the results are manifest. Again, I can't state for certain if this is what happened in the instant case, but my consider judgement is that it played a huge role. Bennett & Elliot have written extensively on C02 retention, as it relates to open circuit divers. You may want to look at DAN's website to find some of the papers that they've offered.
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