X-Message-Number: 2049 Subject: CRYONICS: patient storage Date: Thu, 01 Apr 1993 17:51:37 -0500 From: "Perry E. Metzger" <> I've been following the discussion about high temperature patient storage for a while, and only started thinking about this seriously in the last day or two after it was obvious that people are talking about actually building such units soon. I hope I don't insult anyone by bringing up topics that have already been hashed out a million times before -- my apologies in advance if I do. I have several question, some simple minded, some not. I imagine that everyone involved has already thought of all these things -- I am more running on the assumption that you have and that I simply somehow missed the discussion. 1. a simple-minded question. I was under the impression that you could buy commercial freezer units that operated at the temperatures in question. Wouldn't it be simpler and cheaper either to buy such units, or, if they are too small, to commission a manufacturer of such units to build extra-large units? Again, I would understand that such a solution would be dismissed out of hand if such units did not exist, but my understanding is that they do exist, at least for storing cell samples. Also, given that people build such units, would they not have far more experience in what sort of insulation systems are most efficient for them, since they do this for a living and we are merely amateurs? 2. Another issue I haven't seen addressed too much is this: precision of temperature regulation. The systems that have all been mentioned thus far sound like they would expose patients to relatively large temperature swings compared to the "stay at the boiling point of LN2 forever plus or minus a few tenths" system that we have now. Does anyone know if such swings might in and of themselves induce damage in the patients? If no one knows, isn't this something to do experiments on? Also has anyone actually done experiments on mammalian brain tissues to determine the extent of cracking damage at LN2 temperatures? I know that autopsies on the bodies of post-suspension neuroconversions have been done, but I haven't heard about tests on actual brain tissue thus far, and that is, after all, what we are preserving. If only to know how bad the problem for the existing patients is, it would be useful to know precisely how bad the problem is for brain tissue. 3. Lastly, it seems that people have dismissed using a working fluid other than liquid nitrogen out of hand. It would seem, however, that other fluids do exist with an appropriate boiling point and that they are not considered primarily because of expense or toxicity. However, it is unnecessary to actually expose the patients or employees to the working fluid or to consume it -- one could simply use the liquid in a closed recirculating system to exploit its boiling as a way of very stably maintaining patients at a desired temperature. Patients could be surrounded by dry gas or by a liquid with a suitably low freezing point. Is this impractical in some way that I haven't thought of? Perry Metzger Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=2049