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> Thanks for the detailed post -- it was thought provoking. However, your
> suspicions are correct. I AM thinking it is symptomatic of O2 toxicity. As
> you know, you can experience toxic O2 symptoms two ways: 1) high exposere
> over time as in several dives, or 2) very high ppO2 on a single exposure.
Even the CNS toxicity ("very high ppO2 on a single exposure") is a
function of time. It's just that the times are generally much shorter.
> Your supporting argument that the effects were exacerbated while at rest does
> not support you theory, in fact it supports the opposite. Heavy physical
> exertion dramatically increases metabolism of oxygen, therefore consuming
> considerably more oxygen that otherwise would lead to toxicity.
That may sound good in theory, but in reality CNS O2 toxicity convulsions
are MUCH more likely to occur during periods of exertion, regardless of
the drop in O2 concentration due to metabolism. That's one of the main
reasons why patients lying motionless in chambers can tolerate much higher
PO2 than divers should expose themselves to.
> I do agree with one point though. I believe the experience you and others
> have described are a combination of factors. Probably some combination of O2
> toxicity, N2 narcosis, and possibly CO2 toxicity--depending on your breathing
> pattern while exerting at depth. Also, as you know, specific O2 toxicity
> levels within individuals is dynamic. This serves to account for the varience
> in symptoms you describe on different occasions.
Agreed - especially the CO2 toxicity. However, I think you can treat O2
narcosis as separate from O2 toxicity, because I'm pretty certain they
operate by different physiological mechanisms. From what biochemistry I
learned as an undergrad, I'm pretty sure even pulmonary O2 toxicity and
CNS O2 toxicity operate by different physiological mechanisms as well.
> Obviously it is difficult to determine exactly what is happening without
> proper scientific research.
Perhaps impossible...but as a scientist by profession, I can say with
confidence that scientific methodology is not always the best way to learn
about how things work.
> I have never personally
> experienced the phenomena you describe, and I am not an expert in physiology,
> so maybe I'm not qualified to comment.
Given the type of diving you do, you are CERTAINLY qualified in my book!
> However one thing that IS certain is
> that bad things happen when diving deep on air. This is a practice that I
> feel strongly opposed to, just as I am opposed to diving caves with only one
> light, or not using a guideline. I believe you may be able to survive it --
> but why take the chance. The US Navy plans dives with a ppO2 of no greater
> than 1.2 ATA. There are rare instances of divers taking O2 hits with as
> little as a 1.5 ATA ppO2.
I COMPLETELY agree with everything you said...except I am not as opposed
to others doing deep air dives if they want to. With a few rare exceptions
early-on, I gave up deep air diving (deeper than 200 feet) the day I made
my first trimix dive. With the rebreather, I'll likely never expose myself
to an END greater than 130 feet again (Yes, that means I now do 150 foot
dives with trimix). All of the experiences I described in my posting
occured before any of this tech-diving stuff existed. I'm neither
embarassed about these experiences, nor proud of them. I learned a hell
of a lot about diving from them, however, and in cases where the things I
learned may be useful or informative to others, I have no reservations
about sharing some of these experiences.
> Lets bite the bullet and establish 1.4 ATA as the maximum safe ppO2 at depth
> for ALL divers. With increasing availability of He and other substitute inert
> gasses is is not really a big deal to encourage everyone to get their mix
> ticket. In the beginning mix was used to extend the bottom. Maybe now it's
> time to sell mix tickets for the sake of safety. There is no need to live on
> the edge when we don't have to.
Yup, totally agree. 1.4 ATM is what I use. I used to bump it up to 1.6 on
decompression, but lately I've just been sticking with 1.4 for the whole
dive. Not much difference in decompression times, so why risk it?
> I wasn't around when the subject of deep air was "beat-to-death" as you put
> it so I am grateful for this discussion. I know, as everyone does, how George
> feels about this issue. Regardless of whether or not you like his style he is
> right on this one. Just this week a diver died who was rumored to be diving
> deep on air in Lake Wausee, WI.
>
> 1.4 is the new max ppO2 at depth. All in favor say Aye!
Aye!
Aloha,
Rich
Richard Pyle
deepreef@bi*.bi*.ha*.or*
*******************************************************************
"WHATEVER happens to you when you willingly go underwater is
COMPLETELY and ENTIRELY your own responsibility! If you cannot
accept this responsibility, stay out of the water!"
*******************************************************************
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