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>David, > >Well, you don't like my hypothesis - can you come up with an >alternative one or do you discount the anecdotal observations it >attempted to address? I forget what these anecdotal observations were. I was just pointing out that aterial bubble trapping is an old theory that is neither established as fact or particularly likely to be the case. >#This is not so. There is little (or no?, comments Prime Ra?) evidence that >#bubbles trap in the arterial circulation. One workers calculations suggest >#that the bubble, which would be tubular in shape, would need to extend >#through three generations of arteries before they would trap. > >Firstly, if bubbles were to lodge at all I would imagine them to do so >in arterioles/capillaries: I didn't mean to imply they could get >trapped in the arteries themselves. If this trapping can't happen, >then how does the lung normally trap the so-called "silent bubbles" >present in the pulmonary artery? The pulmonary arterial pressure is much lower than the systemic arterial pressure. >Secondly, lack of evidence don't always mean something ain't true. > >#Bubbles are a problem if untrapped, they activate the complement and kinin >#systems and damage the blood vessel endothelium. > >That's why I said simplistically, and I didn't suggest that bubble >trapping was the only factor involved. >Were your assertion correct, then why would arterial bubbles be >considered more of a problem (PFO and the like) than venous ones per >se? Are the complement and kinin systems only activated on the >passage of bubbles through capillaries? I suspect these systems are activated by venous bubbles (the first to form) and this accounts for the 'flu' like symptoms of mild DCI. Possibly endothelial damage and associated opening of the blood brain barrier is more damaging in the cerebral arterial vessels where the higher blood pressure will promote extravasation etc. than where the bubbles form in veins. Possibly cerebral venous vasculature is not a site of significant de novo bubble formation, but this is unlikely. I will foward this to Prime Rat to comment as he is more expert in this area. regards, David Doolette ddoolett@me*.ad*.ed*.au*
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