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On the CNS clock, each time you take an air break it does some degree of resetting the CNS clock (also the pulmonary clock) The exact amount is not known but it is from experience both from diives and from chamber work an extensive amount. If you read the post George places they always emphasize that they take air (bottom mix etc) breaks every 20 minutes or so. Many of these air breaks are longer than the recommended 5 minutes. They also now decompress in a dry environment which is much more tolerant to oxygen tox than wet environments plus if they have a problem there is no threat of drowning. I would suggest as all of us have published on these nets various times that if you are doing a dive that on base line considerations exceeds the clock that you take the air breaks every 20 to 25 minutes. That these breaks be anywhere from 5 to 20 minutes in duration dependednt on how extensive the deco is. It is also wise to do as WKPP and have a dry environment or if not to switch to a full face unit where the higher po2 is used and then also ultilize safety divers to assist in the event of an o2 hit. This is the only safe way to run the clock up really high. Tom Mount At 12:12 PM 6/17/96 +0000, you wrote: >Hello Peter > > I am more interested in understanding what those guys (Rick, WKPP >folks, etc) do regarding the CNS clock DURING the long deco stops. In other >words, if we are going to stick this the current "CNS% clock wisdom", how can >we make loooooong deco schedules (more than 2 hours?) possible? > >>but...seriously folks, what evidence is there that the CNS clock "resets" >>rapidly at the surface as you indicate? I know the *theory* is that you >>consume O2 and are offgassed rapidly - but what if the effect is >>one of O2 on membrane stability? (Which seems more plausible). I don't >>know how you would measure that effect on cumulative dives, except >>empirically. Also the O2 clock assumes an equal increase of risk for each >>minute passed at a given pPO2 - risk analysis curves rarely look like that >>and the Navy model for CNS O2 toxicity (ref in the lists - it's Underwater >>Scuba Magazine - April issue) has a curve not a line. So?? > > I did some research on the subject and found the following text >searching on the "online" NOAA manual (Section 3.3 - Oxygen Poisoning), on >the same Underwater Scuba Magazine WWW site: > > >" At the present time, the most useful procedure for extending human oxygen >tolerance employs systematic alternation of hyperoxic and normoxic exposure >intervals to increase greatly the tolerable duration of exposure to a selected >level of hyperoxia. This procedure takes practical advantage of the empirical >observation that many early, subclinical effects of oxygen toxicity are >reversed more rapidly than they develop. Interrupted exposure as a means of >oxygen tolerance extension was innitially studied in animals (Clark 1983, >Lambertsen 1978), and its effectiveness was later demonstrated directly in man >(Hendricks et al. 1977). Although periodic interruption of oxygen exposure has >been a component of the U.S. Navy oxygen treatment tables (US Navy 1985) for >many years, its potential for oxygen tolerance extension has been only >minimally exploited to date." > > I'm interested in more info on this subject, via cientific studies (how >can we get a hold on the studies mentioned above?) or via practical >experiences. > Maybe Rick, Irvine and others that do long deco stops, and probably >"blow" their CNS% clock on those, can jump in and share with us their >experience on this theme. > >--- >Mauricio Henriques > Network Consultant Phone: +[55](21)297-1122 x.4715 > Digital Equipment Co. FAX: +[55](21)220-3324 > Brazil > > mauricio@va*.en*.de*.co* >--- >-- >Send mail for the `techdiver' mailing list to `techdiver@terra.net'. >Send subscription/archive requests to `techdiver-request@terra.net'. >
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