Posted by mike on May 18, 2001 at 14:35:31:
In Reply to: I know nothing about this topic posted by JRM on May 14, 2001 at 17:01:53:
Not to flame, but there are a few problems /w/ the above referenced article. It is not primary PEER REVIEWED scientific literature, it is part of a SALES PITCH for medical equipment (the same sort of device they used when i blew my knee out BTW)! Also, there are some serious, serious typographical errors. At times, it seems the author forgot to put the "er" in so hypERoxia became hypoxia, and the result was that the sentence(s) contradicted each other (guess that's what we get /w/ touchy-feely education). I had to read it about 2 to 3 times (which is typical for "primary" scientific literature, which this is NOT) before the problems as they relate to us divers all coalesced. the question(s) and/or point(s) that come to my mind are as follows:
1) hemoglobin molocules in RBCs (there are about 280,000,000 of the little buggers per RBC) do the "molecular heavy lifting" of binding to oxygen.
1.1) as hemoglobin binds to oxygen, its structural properties MAY change. Is this in fact the case? A simple literature search at the CSULB or Cal Poly Pomona or UCI library should turn up the answer.
1.2) if and when the hemoglobin (all 280 million of 'em) changes in its structural characteristics, the entire RBC could experience a temporary stiffening (temporary that is, until the RBC gives up its oxygen in some capilary in some muscle or tissue somewhere in the body)
1.3) the "RBC stiffening" caused by oxygen loading (i ASSUME that that is simply binding to O2 in the lungs, which is what the durn things are supposed to do) MAY not be to the same degree hypothesized as it regards RBC rigidity due to hydrostatic pressure or simple N-pressure (again, there is speculation piled atop speculation piled atop still more speculation here, and it's starting to smell bad).
1.3.1) the RBC stiffening that was mentioned, appears to be somewhat normal, with RBCs carrying oxygen from the lungs.
1.3.2) the "abnormality" may arise when there is already so much oxygen in the surrounding tissue, that the normal mechanism whereby hemoglobin gives up its oxygen, fails and the hemoglobin simply keeps the O2 while the RBC continues on its merry way (pushing and shoving because it's stiff and can't flex a little?) through the capillary, and ultimately, back to the heart.
1.3.3) perhaps the stiff, O2 carrying RBC may just sit in the capillary until blood pressure/oxygen demand increase to the point that it is shoved along, or it gives up its O2, becomes more supple, and continues on through in a normal fashion: again, just speculation on two possible outcomes
2) The rats in question were given 100% O2 as a breathing mixture i assume. I further ASSuME that this occurred at STP (standard temperature and pressure) so that the ppO2 was 1.0 ATM in their little plexiglass box in their little lab in some little R&D facility somewhere.
2.1) That may not neccessarily be the same as a 1.0 ATA ppO2 using 32% 'trox at 62 fsw off of Redondo Cyn.
2.1.2) Unless they're hanging on deco /w/ pure O2 ar 20 feet, divers using EANx still have the other gas(es) in their breathing mixtures (we hope) and these gasses could help maintain more of an osmotic gradient (the gradient created when different concentrations of dissolved gas/ions/whatever are separated by a thin membrane, that may or may not let the respective substances through)
2.1.2.1) the last point is on shaky ground, the other gasses may be insignificant and there may be hyperoxic conditions in the tissue and on the RBCs regardless....nonetheless, just a thought
3) so concluding, my questions are that 1) the RBC rigidity from O2 loading may be insignificant, compared to what could be caused by N (and we await the research on that one) 2) it may not even be an issue /w/ divers on elevated ppO2 with other gasses in the mix. 3) i got a tank of 36% sitting by my front door right now and boy am i pissed that the surf is kickin up 'cause i really wanted to go looking for halibut off of PV instead of sitting at this stupid computer! grrrr!