Posted by MHK on June 15, 2001 at 11:05:54:
In Reply to: Re: STEVE- Meyer-Overton hypothosis posted by Steve on June 14, 2001 at 23:01:17:
Most manuals teach the settled principles and the basics.. Oxygen narcosis is far from a settled principle and it's likely that you'll need to look further than a course manual for added details in this subject area..
Clearly there is a greater body of research and a more well-settled principle with respect to toxicity and Nitrogen narcosis. As Kendall correctly points out, based purley on the lipid solubility issues, a case can be made that oxygen is more narcotic than nitrigen. However, that's purely theoretical.. Our real life experiences tell us differently, and as I noted, the scientists can't form a consensus on the matter.
My thinking, ( as I MINE, not anyone else's and certainly not a peer reviewed study) is that I'm not convinced, even in light of the lipid solubility issues, that 02 is more narcotic, or even narcotic in the first place.. It's by-in-large a rhetorical arguement to my diving since I'll keep my P02's at 1.4 and I'll adjust the mix with helium so as to render the problem moot. But I think you should consider the following:
It's going to get technical here....
Oxygen pressure in the blood is called the PaO2: partial pressure (P) of oxygen (O2) in the arterial blood (a). At sea level and breathing air (21% O2), normal PaO2 is about 80 to 100 mm Hg. This means that the oxygen pressure in the blood, by itself, will support a column of mercury 80 to 100 mm high. Because air pressure falls with altitude, the normal PaO2 also falls with altitude. In Denver, for example, the normal PaO2 is only 65 to 85 mm Hg. On the summit of Mt. Everest PaO2 has been estimated in air-breathing climbers to be only about 28 mm Hg! (Any lower and the climbers would not have lived to report the ascent.)
If a healthy person inhales 100% oxygen at sea level, nitrogen in the lungs and tissues is replaced by the pure oxygen. This "washout" of nitrogen by 100% oxygen is reflected in a much higher PaO2, about 600 mm Hg at sea level. (During the washout with 100% O2 at sea level, the blood nitrogen pressure actually falls from about 573 mm Hg to almost zero.)
While PaO2 goes up markedly with 100% oxygen, the actual number of oxygen molecules in the blood goes up only slightly. A PaO2 of 600 mm Hg puts only about 7% more oxygen molecules into the blood than a PaO2 of 100 mm Hg, even though the oxygen pressure is six times higher.
Accordingly, the percentage increase in Pa02 doesn't mean that the same percentage increase in 02 molecules ( o2 content), and as such MAY [emphasis added] discount the pure result of a comparitive analysis with respect to teh lipid solubility.. Again, that conclusion is my own and you can feel free to do with it what you wish, or take it for what it's worth, but based on our real life experiences (and assuming you stay withing recognized P02 oxtox limits, 1.4) I'd just as soon take my chances with 02, as opposed to N2.. This is strictly speaking to narcosis comparisons and should be in no way confused with OxTox concerns which should dictate the mix... In other words, OxTox trumps narcosis...
Later