X-Message-Number: 6906
From: Brian Wowk <>
Date: Sun, 15 Sep 1996 02:54:07 -0500
Subject: Cooling Rate issue

Bob Ettinger writes:
 
> On the question of the Visser method possibly not being compatible with 
> slow cooling/warming:
 
> As I understand it, Mrs. Visser first tried rapid (but not "flash")cooling
> because that would be most convenient, if it worked--and it did. I know of 
> no reason why slower cooling would not work also--and there are theoretical
> and empirical reasons to think it will.
 
        There is a large literature on the dependence of freezing injury
on cooling rate; it is a core issue of cryobiology.  Even my home  
science encylopedia (Van Nostrand's) contains the following observation:
 
        The advantages of rapid freezing by cryogenic systems,
        including reduced tissue damage and improved quality, have
        been summarized many times, including reports by Merryman
        (1956) and Sills (1969).
 
I highly recommend the review article by Mazur (Mazur, Peter,
Freezing of living cells: mechanisms and implications, Am. J.
Physiol. 247 (Cell Physiol. 16): C125-C142, 1984) for a discussion
of this issue.
 
        The mechanics of ice crystal formation, cell membrane distortion, 
osmotic stress, and CPA toxicity all critically depend on the cooling 
rate.  Consider that in the early 1970's, Luyet and Rapatz recovered
whole frog hearts from dry ice temperature, and also from liquid
nitrogen temperature if they traumatically stretched the heart to
maximize heat transfer (Volume 11, Biodynamica).  Fast freezing  
can work wonders at reducing cryoinjury.
 
> Remember also that Mrs.Visser's single pig heart experiment was
> partly successful. 
 
        As was your own work in demonstrating bioelectrical activity 
in glycerolized brain tissue thawed from -196'C.  Still, we know
that glycerol by itself will never achieve reversible brain preservation.
 
> The IMPORTANT thing is that the Visser method is NEW and HAS produced
> dramatic results and ipso facto is worthy of a LOT of further work.
 
        It is an extension of similar work previously reported for 
small amphibians to small mammals, with a cooling rate that is not 
scalable to large organs.  While it is certainly new and interesting,
statements like "the most significant event in cryobiology since 
Frog sperm was frozen in 1948" and "perfect cryopreservation of every 
organ in the human body in TWO YEARS FLAT" are indefensible based on what 
has been disclosed thus far.  A demonstration of successful heart
recovery after *slow* cooling (an easy and cheap experiment now that
Alcor already has the Visser rat heart model up and running) would
generate much more well-justified enthusiasm.
 
***************************************************************************
Brian Wowk          CryoCare Foundation               1-800-TOP-CARE
President           Human Cryopreservation Services   
   http://www.cryocare.org/cryocare/

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