Book cost over a $100!Quote:
Originally Posted by adam0321
How about a short summary.
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Book cost over a $100!Quote:
Originally Posted by adam0321
How about a short summary.
the variance is particularly interesting to me...for example, if we were tested to 2.5 ppo2 for 30 minutes would that indicate that we would most likely not seize when doing deco on o2 at 20'.
I'd rather not find out that either of us are sensitive to longer exposures to normal tech type ppo2's in the water. However if the variance is very large and that someone could seize at 1.6 for 20 minutes after sustaining 2.5 for 40 minutes on another day that would obviously negate any worthiness of testing.
In the water you already have a history of oxygen exposure and activity during the dive. Perhaps a more accurate O2 test in the can would be starting with a typical long exposure at lower levels to a certain OTU point and then crank it up.
I do know from personal experience about what my 'sensitivity' is pulmonary wise and when I need to take breaks from 100%.
Perhaps the OP should find that first.
Here are some references regarding oxygen sensitivity:
http://archive.rubicon-foundation.or...en+sensitivity
The Rubicon repository has a searchable database and is a phenomenal resource, largely underused by divers unfortunately. Take a peek!
Dive safe,
Celia
I agree.Quote:
Originally Posted by FW
FWIW, a former student who is a long practicing MD specializing in Hyperbaric Medicine and and active (non cave) diver told me a while ago he believes there is an anesthetic affect of the PN2 (Nitrogen Partial Pressure) that may reduce the toxicity effect in water. I'd like to hear other opinions as to this theory of his. It may go a long way to explaining the causes of in water incident that may or may not have been seizures that can be attributed to P02.
His theory was based on early diving to depths in the 260 - 300 ffw range on air and long exposures to P02 of 1.8- 2.1 that either rarely produced or produced no evidence of what appears to be toxicity issues. Yet, I've interviewed two people that took 80% and the other 100% to greater than four atmospheres for less than a couple of minutes and both stated they felt physical symptoms that alerted them to the mistake.
I got the same impression after researching this incident: http://www.cavediver.net/forum/showt...The-Crack-quotQuote:
Originally Posted by Ken Hill
I think it's reasonable to say that currently the evidence neither supports nor refutes the theory that additional inert gas affects the toxicity of oxygen at a given PO2. Lanphier in his early work with the US Navy believed nitrogen increased the incidence of CNS O2 toxicity, but that has not been confirmed by other studies. Donald, who probably knew more about oxygen toxicity than any other diving physician, believed that inert gas had no effect. There is no good scientific evidence (to my knowledge) that nitrogen reduces the incidence of oxygen toxicity at a given PO2. Narcosis may reduce the subjective awareness of the early symptoms, which could explain the anecdotal reports Ken mentions.Quote:
Originally Posted by Ken Hill
There were definitely a lot of swimming cave dives to those depths (and greater) on air without incident.Quote:
Originally Posted by Ken Hill
Quote:
Originally Posted by apitkin
Hi Andrew,
I recall his use of the phrase "anesthetized" the brain which would reduce the awareness and recollection of symptoms. Causes attributed to incidents in the early days of cave diving were almost always anecdotal and the subject of those incidents were also the "experts" of their day. Using that as a basis we have relied on inaccurate recollection or perception but it has served us well.
What amazes me is before there were "professionally trained people," you and others, there seemed a lack of reporting on O2. Everyone knew about narcosis and it's effects and the guidelines drummed in to every basic diver. However, with regard to P02, my personal thought is that any dive plan above 1.2, is risky. I personally use a 1.0 set point.
I don't trust the analysis of a lot of the old accidents since new awareness of P02 could point to other factors. We are helped by this because of dive computers recording accurate run time and P02 levels. But the anecdotal evidence still lingers. For example, Hal Watts told me that he dove the grotto to 240 ffw every morning on air. Hal said he kept a pretty close routine, same sleep, same breakfast, same frame of mind and there were days when he was aware of severe narcosis even before he got half way down into the sink. Then the story of a Navy Chief, Sibitsky?? who was awarded the Navy Cross for his effort to run a down line on the Squalus in 1939. The Navy used him in a study when he was a young sailor to help them when developing tables. They were never able to bend the guy despite depths and duration that bent plenty of others. I believe they threw his stats out as they skewed the findings!
I think Steve Berman said it best. "every one only gets only so much deco they can blow off, some more than others!" I think this could also be true of 02. I could also be inclined to believe those affected by toxicity have not come back to give us their version of what happened.
Keep up the good work.
/Ken