X-Message-Number: 1383 Date: Tue, 1 Dec 92 12:03:42 PST From: ghsvax! (Hal Finney) Subject: CRYONICS: Technical Feasibility [Please forward to sci.cryonics] I enjoyed Ralph Merkle's paper on the technical feasibility of cryonics very much. It was quite thorough and covered a lot of material. One thing I was looking for, though, was more information on the question of whether freezing damage is too great to allow recovery. This is, in my opinion, the crux of the issue. In an ideal suspension, the cryonics team is able to begin work immediately once the patient's heart has stopped (and death pronounced by a cooperative physician). In this situation the patient is subjected to no more than a few minutes of warm ischemia. In my mind there is little doubt that if the patient could be miraculously preserved in exactly this state, that future medicine could revive them. But, we can't do that. Instead, we have to freeze them in liquid nitrogen. Now, recently I saw a message on CRYONET from Mike Darwin, former head of Alcor. He referred graphically to damage being done during the freezing process: "massive ice crystals displacing structures, cutting neuronal connections, and stirring the debris ahead of the growing ice fronts." This is an especially ominous description, coming from someone who has been in the forefront of the cryonics movement for two decades. I was hoping to find in Ralph Merkle's paper some information which would help me judge how much damage is actually done during freezing. If Mike Darwin is right, and ice crystals "stir" the cells into "debris" as they grow, then reconstructing the brain is going to be much more difficult than putting a jigsaw puzzle back together. Ralph did say that the percentage of water which freezes in an ideally perfused brain should be less than 40%, even at liquid nitrogen temperatures. And he said that some amphibians can be taken to a temperature at which 40% of the water in their own brains is frozen, and can spontaneously recover. So this is a hopeful sign. But 40% of water frozen is still a lot of ice. Where does this ice go? How does it fit? Wouldn't it have to go through the kind of growth process that Mike Darwin describes, growth which will tear up the brain internally? After all, people are not frogs. Maybe frogs have brain structures which allow these ice crystals to form without doing that much damage. Or maybe frog brains can tolerate damage, since they are presumably less complex than human brains. I'd like to see more discussion of the impact of freezing damage in terms of how much information is left to allow future recovery. If the information is there, as Ralph says, future technology may well be able to make repairs. But the kind of freezing damage Mike Darwin describes makes it sound as though the information is lost. Hal Finney [ Hal, thanks for your message. The October 1991 messages: 484 485 486 490 498 discuss the damage created by current cryonic suspension techniques (based on a talk by cryobiologist Greg Fahy). If anyone has more up-to-date information on that, please let us know. - KQB ] Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=1383