X-Message-Number: 7651
Date: Wed, 5 Feb 1997 11:20:44 -0800 (PST)
From: Doug Skrecky <>
Subject: Possible Solution to Visser's Problems

   I would like to suggest a possible solution to the problems that have
 been occurring with replication of the Visser technique. It seems that
 good viability requires that the rat hearts be retrieved from liquid
 nitrogen promptly, while prolonged immersion is lethal. I strongly
 suspect the problem is cracking and believe that an examination of the
 hearts used in the experiments will back me up in this. Switching to a
 two step fast then slow cooling rate should eliminate this problem. 
 Here's why: 
   If memory serves, rapidly cooled water undergoes a glass transition at
 -135 C, which is well above that of liquid nitrogen (-195 C). The large
 thermal stresses resulting from direct immersion in liquid nitrogen of a
 brittle object such as a rat heart cooled to below its glass transition
 temperature will often result in cracking, with consequent loss of
   Carotid arteries from rabbits have been observed to undergo cracking
 when cooled to -160 C, but remain crack free at -80 C. (Cryobiology 31: 
 506-515 1994) Here it seems is a solution to the replication problem with
 the Visser technique. In place of liquid nitrogen use a liquid such as
 alcohol cooled with dry ice (-78 C). Place the rat heart in an aluminum
 pouch and immerse this in the dry ice/alcohol mixture. After the heart
 has been quickly cooled in this solution, wrap it in insulation and then
 slowly cool with nitrogen gas till the temperature of liquid nitrogen is
 reached. Cracking should be eliminated and hopefully heart function

Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=7651