Prism... nice!April 26 2004 at 11:16 PM
|Tanya (no login)|
It's true, -150 degrees would be better. Love the prism analogy, since it is highly reflective of reality. (Pardon a moment, while I crack myself up....)
The real barrier we have found to cryoprotective perfusion is not the 2-or-so hour time limit of ischemia, but rather the collapse of the blood-brain barrier. As long as the barrier is intact, we seem to have the ability to perfuse cryoprotectants. Once that barrier collapses, we seen significant swelling in both hemispheres of the brain. How bad the swelling is depends on multiple variables, like arteriosclerosis and whether or not the medications were administered or more factors besides. One of the advantages of the new protocol is that it has provisions for ensuring that the fluids going in are taken up to their fullest. Though this equilibration phase has added another five or so hours to the neuro procedure alone, the lack of cracking seems to justify the exhaustion. It's hard to emphasize the simple importance of cooling.
As a more direct reference, blood-brain barrier collaspes at around 16 hours. How well a transport does is reflected in whether or not we have the time to complete perfusion. Lab results show this trauma, but we can also see it when the brain bulges out of the burrholes. It's not paticularly scientific to gauge by the burrhole, but it's a measure we can directly observe. We're analyzing data to see if we can develop a more analytic explanation.
One of the problems we face is that so little of these complex chemical processes are understood. I feel particularly fortunate that there have been people willing to devote their lives and their careers to ensuring these problems get solved. Prolly our grandchildren will laugh at us.