From: kqb@cbnewsl.cb.att.com (kevin.q.brown)
Subject: Re: Possible thawing process
Organization: AT&T Bell Laboratories
Date: Fri, 18 Dec 1992 16:33:43 GMT
X-Crossposted-To: cryonics mailing list

    ------------------------ Forwarded Message ------------------------

> Date: 18 Dec 92 02:12:29 EST
> From: Mike Darwin <70023.3041@CompuServe.COM>
> Message-Subject: Re: Cooling Fluids Debate (CRYOMSG # 1168)
> Date: 12/17/92

     I would like to make the following comments about the debate  between 
Edgar Swank and Richard Schropel (CRYOMSG #1168).

     First,  this  idea is not a new one.  In fact, the use of  gases  and 
liquids  as  perfusing agents and heat exchange agents has  actually  been 
explored both in practice and in theory.  I believe Cravahalo, et al.  did 
extensive calculations on rates of heat transfer with both fluid and gases 
and  found both to be disappointingly low.  However, the real  utility  in 
the  use of these agents may be to minimize intravascular  ice  formation.  
The  first reference that I know of reporting success  with  intravascular 
perfusion  of  helium during freezing was that of Guttman,  et  al.  which 
appeared  in  Cryobiology 6:32-36 (1969).  Guttman  and  colleagues  froze 
sections  of  canine  bowel to dry ice  temperature  using  intra-arterial 
helium  gas perfusion, warmed and reimplanted them with the bowel  showing 
some signs of peristalsis and regeneration of some of the mucosa.    Later 
Guttman  tried the same technique with canine kidneys, reporting  positive 
results.  Unfortunately several other groups, including David Pegg's group 
at the MRC, were unable to reduplicate the renal work.  Pegg and  Jacobsen 
also  tried gas perfusion to minimize histological damage during  freezing 
and  reported dissappointing results, including problems with  gas  emboli 
(Jacobsen,  I.A.,  et al., CRYOLETTERS  6:227-232 (1985).   These  kidneys 
also  revealed extensive intratubular and intraglomerular  bleeding  which 
the controls (frozen in the absence of gas perfusion) did not demonstrate.

     Thus, the best that can be said is that the jury is still out on  gas 
perfusion.  However, I feel it merits more attention and it will be one of 
the areas we investigate.

     As Edgar has correctly speculated alcohol is an unsuitable fluid  for 
vascular perfusion.  It readily dissolves into tissue water, it is  toxic, 
and  it  dissolves out fats.  I launched an extensive search for  a  safe, 
nontoxic  cooling  fluid.   After  evaluating  many  materials,  including 
freons,  the  one  I settled on was a  polymer  of  dimethylsiloxane:  Dow 
Corning  polydimethylsiloxane  200.   Little did I  know  that  this  very 
material  had  been  perfused through kidneys circa  1968.   None  of  the 
kidneys was evaluated long term, but they did make urine acutely and  they 
perfused  well  (Linn, B., et al., "Organic liquids as  preservatives  for 
organ  storage" in ORGAN PERFUSION AND PRESERVATION, ed. John  C.  Norman, 
Appleton-Century-Crofts,   New   York,  1968).   They   also   found   the 
fluorocarbon FC-75 workable.  Both have pour points below -120xC and  both 
remain pump-able down to dry ice temperature.

     Will  these agents help to minimize injury by reducing  intravascular 
ice  formation?   I don't know.  However, there is an experiment  I  would 
like  to  do:  Perfuse a large  organ or small animal with  one  of  these 
fluids,  connect  the  fluid-filled vasculature to  a  pressure  gauge  or 
manometer filled with the same fluid and read any developed pressure  upon 
freezing.

     Rich  is  quite  right about the  "short-circuit"  problem  with  gas 
perfusion.  I've observed it first hand in my limited experience with  the 
technique  (perfusing  dog heads).  In fact, you never get all  the  fluid 
out, there are always un-gas perfused patches of tissue.

     As  to  going down to liquid nitrogen temperature, as far as  I  know 
there  is no reason to do this.  All the interesting events are over by  -
80xC.   Once you are down to -80xC, and certainly by the time you  are  at 
the  glass transition point (TG) of the water cryoprotectant  mixture  you 
are  using you can cool at as leisurely a rate as you like.   Indeed,  you 
may  not want to cool much below TG unless you want the organ to  fracture 
into pieces. 
Newsgroups: sci.cryonics