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On Fri, 9 Aug 1996, Robert Wolov wrote: > The problem initially seems that the theories involving lipid solubilities > are based on an inert gas model....and again O2 isn't an inert gas. The > more chemically active electrons of O2 (especially O2 radicals) have > effects on the lipid bilayer that an inert gas (by definition) will not. We > know clinically that effect is profound or you wouldn't get convulsions. > (we also know chemically that the radical form of O2 literally tears up the > lipid bilayer) > > That doesn't mean there can't be a narcotic effect, just that there are > additional chemical and physiologic factors to take into consideration when > dealing with O2. I'm also lulling myself into the assumption that the > narcotic effect of O2 is probably of such relatively small effect (when > compared to the much greater volume of inert gas, be it N2 or other) and > it's narcotic effect that it probably is getting swamped out. Now that's > only my assumption. I'm sure Bill Hamilton's thinking and findings are > based on far better experience and knowledge. Thanks, Robb - I made a mistake in suggesting lipid solubility was really a factor. It may have been molecular weight - I can't remember which correlative factor was used to theorize that O2 had twice the narcotic potency as N2. Regardless, it is not the theoretical stuff that has led me to believe that O2 plays a role in narcosis - it is the fact that whenever I have breathed an enriched-air nitrox mixture with a PO2 greater than about 1.6atm at a depth in excess of about 180 feet (i.e, in conjunction with a PN2 > than about 5atm or so), the narcosis has been clearly more severe than it would have been under the same conditions on air. But the relationship is complex. I once breathed pure O2 at a simulated depth of 220 feet in a chamber (accident), and felt a narcosis level similar to what I would have felt breathing air instead. In other words, it seems to play some role in narcosis, but not necessarily a bigger role than an equivalent amount of nitrogen. My worst narcosis/depth ratios (for a given set of conditions ofr other known variables) have been in situations with both high PO2 and high PN2. > What worries me is what do you do if O2 *IS* a significant narcotic at > depth? There are alternatives to N2. But what do you choose instead of O2? Like I said in one of my posts, the narcotic effect of O2 as I have experienced it seems to only be noteworthy when the PO2 is in excess of about 1.6atm. Because none of us should ever breathe oxygen at higher partial pressures (except for treatment of DCS symptoms), then most of us probably do not have to worry about any potential role of oxygen in causing or enhancing narcotic symptoms. In other words, as long is the PO2 is kept at a safe level, I don't think we need to find a less narcotic substitute for it on deep dives. ;-) Aloha, RIch
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