I've been following this discussion with interest as I have had several questions on this subject from divers and have been at somewhat a loss to give a reasoned answer.
One of my consultants (Dr. Ed Kay) has found some information that I feel might be valuable as follows:
"In a paper called "Structural determinants of the rigidity of the red cell membrane", (Nash GB, Gratzer WB) Biorheology. 1993 Sep-Dec;30(5-6):397-407. Review, the authors state "Although the stability and viscoelasticity of the red cell membrane are undoubtedly governed by the membrane's underlying protein skeleton, the mechanism by which this network controls elasticity is uncertain... It appears that elasticity may be regulated not only by the structure of the spectrin network, but also by its interactions with and freedom of motion relative to the lipid bilayer."
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Dr. Kay believes that the lipid layer is highly sensitive to oxidative stress and in Biochim Biophys Acta 1999 Oct 15;1421(2):306-16 Books, an article entitled "Membrane effects of nitrite-induced oxidation of human red blood cells" (Zavodnik IB, Lapshina EA, Rekawiecka K, Zavodnik LB, Bartosz G, Bryszewska M.) the authors found that an "increase in membrane rigidity have been shown as a result of
RBC oxidation".
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The studies he quoted suggest that Oxidative Stress consisting of Superoxide Radical damage and Lipid Peroxidation cause the dominant membrane effect.
It is not nitrogen that interacts with the lipids of a red blood cell but oxygen. This is the dark side of O2. Nitric oxide on the other hand has been shown to improve the membrane fluidity of erythrocytes. The addition of helium offers you more flexability to keep O2 levels below toxic range for extended exposure diving, but probably not because you have less nitrogen."
An exhaustive survey of Medline fails to bring up anything about the effects of nitrogen under pressure on the RBC.
Regards:
Ern Campbell