Posted by Kendall Raine on June 13, 2001 at 13:40:11:
In Reply to: Re: 160' on nitrox? posted by Steve on June 13, 2001 at 12:41:06:
First: lots of controversy here, particularly as IANTD early on touted reduced narcosis as one benefit of Nitrox. Second: I'm not aware of any empirical study on the relative narcotic properties of Nitrox versus air, but there is lots of literature on narcosis and the linkage to lipid solubility. Third: I'm a practitioner, not a theorist or physiologist.
That said, as gas property laws go, helium (non-narcotic)is one of the least soluable gasses while argon is much more soluable than say, nitrogen or oxygen. For example, one way to experience narcosis is to sit in 20 feet of water and breathe 15/85 argox. Based upon relative lipid solubility between oxygen and nitrogen, one could compute an equivalent narcotic depth by adjusting for the percentage of oxygen and nitrogen in the mix. Hence, END for EANx 32 > END for EANx 25 at the same depth. That's not what used to be taught, but that's what relative solubilities suggest should be true. Of course, nitrogen is inert and oxygen is metabolic, but no one has ever satisfactorily explained to me why this should make a difference. Based on personal experience, I'm less impaired on 15/20 trimix at 150 fsw than I am on EANx 27. Both have similar PN2's (PN2=3.60 ata for the 15/30 at 150 fsw and PN2=4.05 ata for EANx 27). That suggests that it's the cummulative effect of the solubility of the gasses, O2 and N2, which makes the difference. When I plan a dive, I compute my END assuming oxygen is narcotic and select the helium fraction to solve for max END.
Rather than babbling on, however, if you want more info on the research and chemistry of narcosis and the link to lipid solubility, I'll quote from Bennett and Elliot tomorrow. Let me know.