X-Message-Number: 5084 Date: Wed, 1 Nov 1995 01:03:02 -0500 (EST) From: Ben Best <> Subject: Back to high pressure tactics Robert Ettinger's "mildly hyperbaric freezing" suggestion is similar to what I presented as potential use of pressure number (2) on page 20 of my piece "High Pressure Cryonics" in the Autumn 1994 issue of CANADIAN CRYONICS NEWS. In discussing this idea I raised the point about heat of fusion (as Brian Wowk has done). In the Winter 1995 issue of CANADIAN CRYONICS NEWS I experienced the "firing squad" in the form of a letter from Dr. Fahy in which he said (page 9) "rapid freezing is utterly different from vitrification", adding "Even a passing familiarity with phase diagrams would have prevented this absurd idea from appearing in print." But Robert has not argued that this procedure might cause vitrification, he has instead offered it to "reduce freezing damage". I can't say for certain that his idea would not *reduce* freezing damage, but it is an open question as to whether the reduction great enough to be worth the effort. Water is not very viscous at freezing temperatures, and I'm not sure that the effects of a rapid pressure change would be propagated through the liquid rapidly enough to reduce crystal formation or to reduce the damaging effects of ice crystals. The reason that Audrey Smith was able to turn 60% of hamster brains into ice was that *slow* freezing allowed the pure ice to form *outside* the cells. It is intracellular freezing that does the most damage. And, of course, intra and extra cellular fluids are not pure water, but are salts -- which depress freezing point. NaCl has a eutectic temperature of -21.6C and CaCl2 has a eutectic temperature of -55C. None of these points mean that Robert's suggestion would be of no value, but they do imply that they might not be as valuable as an initial uncritical examination of the idea might lead one to believe. Robert added that "this procedure might be combined with a relatively low level of cryoprotectant perfusion". Why a "low level"? With a good level of cryoprotectant, the "freezing point" (closer to vitrification temperature) would be considerably lower and the liquid would be considerably more viscous. Thus, the use of this technique could give us a "freezing" which causes some level of damage mid-way between freezing with cryoprotectant and vitrification. I think the heat of fusion would be lessened -- and in any case would not be great enough to eliminate the benefit under these conditions. I think the main problem with these high pressure methods is that they could involve extremely awkward procedures requiring extremely expensive equipment. The work of Dr. Fahy on kidney vitrification without this expensive overhead is so promising that is would be a shame to blow vast amounts of money on equipment to somewhat *reduce* damage when the same money has the potential to *eliminate* freezing damage and maybe even retain viability. -- Ben Best () Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=5084