Posted by BillP on May 11, 2001 at 10:18:44:
In Reply to: Re: Red blood Cell Rigidity???? posted by Steve on May 11, 2001 at 07:31:17:
Sure thing, Steve. You can read an abstract of the study that Bill Mee quotes at:
http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9789336&dopt=Abstract
Remember that (according to my understanding of their assertions) Bill Mee, George Irvine, MHK and apparently Jarrod Jablonski (according to MHK) are claiming that increased partial pressure of nitrogen causes red blood cells to become rigid. George Irvine goes on to claim that adding helium to the breathing mix alleviates this problem. He also claims that the effect is ONLY found at depth and goes away once the diver surfaces. MHK adds that the problem is significant in the recreational diving range so recreational divers should change their behavior to avoid the effects.
Look at the abstract of the study. The study does not look at the effects of the partial pressure of nitrogen. It looks at the effects of HYDROSTATIC pressure. Not the same thing at all. The study goes on to say that this effect of hydrostatic pressure is to cause increased aggregability (NOT rigidity) of RBC's. Aggregability is NOT the same thing as rigidity. This effect was found when the RBC's were examined at the surface (1 ATA) after the dive. (They didn't look at the cells at depth.)
What is not explained in the abstract, but can be found in the full article is that the divers in the study were compressed to 36 ft on air (ppN2 ~1.6 ATA) but all further compression was done on HELIUM. The authors of the study looked at the effects of hydrostatic pressure after several (I think at least 2) hours at 66' (where the ppN2 was now less that 1 ATA and essentially in the "normal" range) and again after more hours at 300'. In this study they found that increased hydrostatic pressure enhances the aggregability of RBC's in divers. The authors specifically state that they believed that any effects seen were NOT the result of the partial pressure of any inert gas.
My point about the study is, if the partial pressure of nitrogen was essentially normal when the effect was found, how can you say that the effect is caused by the partial pressure of nitrogen? And if the effect is found at a normal and even reduced partial pressures of nitrogen, but at elevated partial pressures of helium, how could someone claim that the effect is NOT caused by helium or that helium alleviates the effect? In otherwords, the study did not look at the cause or the effect Bill Mee claimed, and it does not support his findings, so why is it the only study I've seen any of them cite? It's an interesting study, but it looks to me to be irrelevant to the points they are making.
I'm at a computer where I don't have the link to the techdiver mailing list archives where Bill Mee cited this study as his source, but if you like I can get it later tonight.
HTH,
Bill