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---------- Forwarded message ---------- Date: Tue, 18 Jun 1996 11:13:27 -0700 (PDT) From: "Peter N.R. Heseltine" <heseltin@hs*.us*.ed*> To: HeyyDude@ao*.co* Subject: Re: CNS Clock Values Kevin, Leaving aside the issue of whether one guy's parabolas are another guy's curves, ;-) I have two questions/concerns with the concept of the CNS clock and it's rapid "reset" 1. Each minute on the clock has the same toxicity value as the minute before. This isn't the way drug/human toxicity usually works. e.g., taking 100 aspirins is not twice the toxicity of taking 50 aspirins. 2. As best I can find, the reset values were taking from guinea-pigs who were pressurized in a chamber. Nowhere can I find data on, say DLCO perfusion/exchange studies in humans, which would be the modern way to assess impairment to gas transfer. So I have trouble relating this to some physiologic aspect of the toxicity. As in 1., recovery time for a human membrane usually requires (a) electrical restabilization, i.e., some "recharging" of lost or ionic imbalance or (b) in extreme cases, cell regeneration. As the effect in ventilated patients takes days to abate (albeit they do already have underlying respiratory problems) it doesn't seem logical that the toxicity would be linear - like a clock. Whaddye say? Peter Heseltine On Sun, 16 Jun 1996 HeyyDude@ao*.co* wrote: > Peter, > > In all of my training (NACDS, Technical Mixed Gas Rebreather Diver - TDI, > Technical Rebreather Diver - NAUI, Scuba, etc..) I have learned that the > Oxygen toxicity "clock" resets extremely quickly. Were it in a "curve" it > would be quite a parabola with a very high gamma. > > The bottom line really comes down to this: No matter how many OTU's you > might gain while diving, unless you are in a saturation mode, it is damn near > impossible to overexpose yourself to O2 when keeping your maximum PPO2 to > below 1.4. > > If you don't believe me, then do the math yourself. Figure how long you > would have to be underwater with a maximum PPO2 of 1.2-1.4 to get your OTU's > to a dangerous level. I can tell you it is going to be longer than you've > got gas, or in Richard Pyles and my case, scrubber in your rebreather. > > Unless this is merely a wonderful exercise in "what if" you are really > wasting your time worrying about it. Besides, if you are doing the kind of > dives which run your O2 clock up high enough to even be INTERESTED in it, > then you are doing some diving that we would ALL like to hear about. > > If you still don't believe me, talk to guys who are pushing the O2 limits to > the max already, and don't give a crack about O2 clocks, like George Irvine, > and Richard Pyle. > > Take care, > > Kevin > HeyyDude. >
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