X-Message-Number: 1465
Date: 18 Dec 92 02:12:29 EST
From: Mike Darwin <>
Subject: Re: Cooling Fluids Debate (CRYOMSG # 1168)
> From: Mike Darwin
> Re: Cooling fluids debate
> 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.
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