X-Message-Number: 2906
Date: 17 Jul 94 23:38:31 EDT
From: Mike Darwin <>
Subject: SCI.CRYONICS Circle of Willis

Steve Harris' points are by and large valid ones.  But I don't think the

situation is quite so black as he paints it (yes, there is a disagreement here).
Anatomical variations will affect the degree of collateral circulation to the
occipital area of the brain, but my experince has been more rosy than Steve's
speculation suggests.

First of all, when I have perfused rabbit and even dogs' heads in isolation I

often don't even bother to ligate the vertebrals.  The trick here is to maintain
the pressure in the circle of willis at 40-60 mmHg *even with the loss down the

vertebrals*.  The vertebrals are fairly small caliber vessels and it is possible
to get good global brain perfusion using this technique.  In the intact human
you have the added advatage that you can tie off the distal carotids and
jugulars so that you create (and admittedly rather large capacitance) reservoir
which will fill and reach equilibrium pressure.  Greg Fahy has used this
technique successfully as well with both rabbit and dog heads (isolated).

One thing which puzzles me is Steve's repeated references to "Alcor's
experiences with dogs bearing this out.  I'm not sure what he is referring to

here.  He is apparently away for the weekend so I was unable to phone him up and
ask him -- and I didn't think it worth paging him over!  Perhaps he'll see this
message and clarify it in print or give me a call.


Having said this, I would still advocate aortic arch perfusion where possible --
and with the help of a mortician this might be possible in Australia.  Clearly,
for both the reasons Steve cites and for those I cite, it is the most
conservative and the safest course of action.  However, when confronted with a
situation where you are faced with very long delays before reaching such
capability, or are given the option of doing cryoprotective perfusion and

freezing earlier rather than much later, I would opt for early cryopreservation.

Even assuming the worst case, that you fail to perfuse the occipital brain you
will still be ahead in my opinion (depending upon what sort of person the
patient was).  Judgement, intellectual function, and what we commonly refer to

as humanity seem to be primarily forebrain and midbrain functions.  The occiptal
lobes are primarily (although by no means exclusively) involved in visual
processing.  If I had to choose (speaking personally) between a hit on one of
these two broad areas, I'd pick the hindbrain rather than the forebrain.  And I
am a highly visual person.

One of things I regretted after posting my message was that I didn't weigh in
print more carefully the tradeoffs.  Yes, there are *very* good reasons for
using the aortic root when you can.  But, and this was my point, you may not
always be able to do that without paying some other kind of price which may be
higher.  Tough choices, huh?


Mike Darwin

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