Posted by BillP on June 25, 2001 at 22:35:59:
In Reply to: Blood Cell Rigidity posted by John Walker on June 25, 2001 at 19:43:10:
...at least as far as recreational divers are concerned. The studies that I found from the DDRC were very interesting, and I believe that they're the basis for the recommendations coming from the WKPP/DIR folks about nitrogen, helium, and cell rigidity. This study that John posted did indicate that nitrogen has more effect on cell rigidity than helium, but perhaps not in a way that is significant to typical recreational divers.
The dives in the study were SATURATION dives. I think it's fair to say that few of us are doing saturation diving. The effects MIGHT be found at shorter dive times, but we don't know because the researchers didn't look at those kinds of dive profiles.
They looked at the effects on what they considered "whole blood" which, because of the way the samples were handled, included some aggregates (clumps) of red blood cells and platelets which would affect the index of filtration. (See link below for further explanation.)
The effects of nitrogen were essentially the same at 15m (50ft) as at 30m (100ft). Are we to start diving heliox at say 30ft now?
There was some, uhm, "new math" in the study. A change from 4.3 to 7.5 is a 153% change? It doesn't alter the outcome of the study, but it does call other numbers into question in my mind.
The 174% "change" (7.5 is 174% of 4.3) is the biggest change they found in the study, but the researchers in the study had hypothesized in an earlier study that it would take a 200-300% change to significantly block blood vessels and cause the effects they were looking for. Nitrogen seemed to have more effect than helium, but neither seemed to have enough effect to cause the problem the researchers were investigating.
I had posted this here earlier, but you can read my interpretation of the DDRC studies at:
http://www.scubadiving.com/talk/read.php?f=1&i=293032&t=293032
if you're interested.
HTH,
Bill