X-Message-Number: 6611
From: Brian Wowk <>
Date: Thu, 25 Jul 1996 16:15:03 -0500
Subject: In-situ Brain Cooling

	In-situ deep cooling of the brain (proposed to -70'C)
has been taking a harsh beating lately on sci.cryonics and
CryoNet, ostensibly on thermodynamic grounds.  However no
numbers have been supplied to support this criticism. 

	Here are some rough calculations.  Assume
(pessimistically) that the thermal conductivity of
tissue is close to that of solid ice at about 2 W/mK.
Assume an area in contact with the brain of 500 cm^2
and a temperature gradient of 100'C over one centimeter.
This translates into a heat flow of 1000 watts into
the brain.

	Now assume perfusion of the brain with cold
cold perflurocarbon at 500 ml/minute = 8 ml per second.
How much would this solution be warmed by absorbing 
1000 watts during circulation through the brain?
Answer: 30'C.  Thus, arterial perfusion at -80'C 
would result in venous outflow at -50'C, and most of
the brain staying at deep sub-zero temperatures.

	That's not to say that this isn't technically
a very difficult model, only that it cannot be ruled
out on thermodynamic grounds.

	In any case, it is expected that this post-
cryopreservation dog-begging-for-a-biscuit (DBFAB)
model will be the LAST step of the Project.  Before
this is even attempted expect, 

	* Excellent ultrastructural preservation
	  documented by light and electron microscopy
	  studies.

	* Ex-vivo metabolic and EEG study documenting
	  neurological survival.

	I agree there is no point in attempting a spectacular
in-vivo demonstration until these first two milestones are
reached.  However ultimately an in-vivo model will be
important.  While the first two milestones will
mark the transition from a dead brain to a living brain,
only an in-vivo model will tell the subtle differences
between a sick brain and a healthy brain.  In addition to
wanting our cryopreserved brain to be viable by conventional
criteria, we also want it to be *healthy* if possible. 

***************************************************************************
Brian Wowk          CryoCare Foundation               1-800-TOP-CARE
President           Human Cryopreservation Services   
   http://www.cryocare.org/cryocare/

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