Myth or not? Deep air/oxtox

[Saturation]

You can find info in Bennett and Elliott, and a clear mention of that relationship in Bove's, Diving Medicine. Both from current edition as of this writing.

When deep air was fashionable and depths to 500' were reached attests to some phenomenon with PN2.

http://www.psai-philippines.com/history.html

http://www.travelsmart.net/article/101036/

More recent biological studies only came about:

http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=15322063&ordinalpos=21&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum

There is a danger in quoting that Rubicon abstract by Arieli dated 2003 regarding convulsion latency and PN2. It is later explained in this published paper, linked above, dated 2004, based on the same data.

http://archive.rubicon-foundation.org/1313

 

[H2Andy]

the papers I found (although they were work done in rats) suggest that increasing inert gas concentration -- regardless of what inert gas it is -- INCREASES susceptibility to oxygen toxicity

interesting

 

[H2Andy]

There is a danger in quoting that Rubicon abstract by Arieli dated 2003 regarding convulsion latency and PN2. It is later explained in this published paper, linked above, dated 2004, based on the same data.

ok, so it says:

"In contrast with nitrogen, no prolongation of latency to CNS oxygen toxicity was observed with helium, where an increase in helium pressure caused a reduction in latency."


so ...


nitrogen: prolongation of latency to CNS toxicity

helium: reduction in latency to CNS toxicity under pressure


?

(in rats, with individual succeptibility to narcosis playing a role)

 

[rjack321]

Generically, narcosis in toxciology means a non-specific CNS depression. In diving it has additional meaning. But returning to the toxicology definition for a moment is illustrative here. I.e. N2 being a CNS depressant, countering the stimulant effects of O2. Exley's autobiography has some interesting deep air history. At extreme depths 350-450ft they are essentially passing out, but not convulsing. Porbably because the CNS depressant effects are overriding the stimulate effects of the extreme ppO2.

 

[Dr Deco]

Hello readers :

If there is much to the oxygen/inert controversy, I might guess that it can be traced to carbon dioxide retention. CO₂ is a strong vasodilator in the brain; this increases blood flow and oxygen. Nitrogen in the lungs will result in a tendency to reduce lung CO₂ washout.

Helium on the other hand has such a low viscosity that gases more easily enter the lungs. Helium was once used as a treatment for breathing difficulties.:shakehead


Dr Deco :doctor:


The next class in Decompression Physiology for 2007 is August 18-19. :1book:
This class is at the USC campus in Los Angeles.
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[rjack321]

But wouldn't that suggest that deep air divers would be more susceptible to O2 tox? Since CO2 exacerbates O2 toxicity? The CNS depressant effects of N2 thus apparently override both the high ppO2 (>1.6) and the increased CO2 which is harder to eliminate on denser gases.

 

[daniel f aleman]

Whatever the science, 10 million dives have been made >250 ft on air with divers returning to surface alive and well, ready to do it again.

 

[rawls]

There was a very moving thread on The DecoStop recently where a young lady died,apparently due to oxygen toxicity

Ian...I read this thread and it was indeed a very difficult thing to read. We can hypothesize about how an oxtox hit occurs, but reading that thread literally broke my heart...

 

[emcbride81]

Wow...all I have to say is what do I need to read to understand what you all are talking about! I am not kidding either, this is fascinating!

 

[rawls]

Wow...all I have to say is what do I need to read to understand what you all are talking about! I am not kidding either, this is fascinating!

Read as much as you can about gas laws and relate it to physiology. At some point with more experience you may want to look into taking an advanced nitrox course. But above all read as much as you can. The more you learn the more you will be fascinated. And as you have already read, there is a wealth of info from very experienced divers here on the board. I am learning from them all of the time...