X-Message-Number: 1489 Subject: CRYONICS - Re: Gas perfusion From: (Edgar W. Swank) Date: Tue, 22 Dec 92 16:51:00 PST I'd like to thank Mike Darwin for publicly commenting on mine and Rich Schropel's ideas in CRYOMSG 1465. His very informative commentary prompts some further questions. I'm glad Mike has determined some candidates for "safe, nontoxic cooling fluids", Dow Corning polydimethylsiloxane 200 and FC-75. Are both these fluids miscible with water? If not, is there a problem using them to "wash out" water-based cryoprotective fluids? That is, are "pockets" of water-based fluids left inside the circulatory system? Are these fluids more volatile than water? Higher vapor pressures and lower boiling points at given ambient pressures? If so, then it seems that a good answer to the "short-circuit" problem when transiting to a gas would be to surround the subject with a (partial) vacuum. (note: keep circulatory system at same or only slightly higher pressure). At some pressure and temperature Y (below 0xC) organic fluid will vaporize and will easily mix with/be washed out by circulating helium. If organic fluid is more volatile than water, then this procedure should not result in excessive removel of (solid) water through sublimation (freeze drying). Once organic fluid is washed out, vacuum may be gradually released. Circulating He may then be used to cool all the way to LN2 temperature. Hopefully, since cooling is even, and strains can be absorbed by flexure of open circulatory system, gross fractures will be avoided.? Since circulatory system is clear, this process can be reversed in an attempt at revival. i.e., warm with circulating He to temp Y, apply vacuum, washout He with organic fluid vapor, release vacuum, vapor condenses (no bubbles), continue to warm via circulating organic fluid to above 0xC, washout organic fluid with water-based cryoprotectant, washout that with blood or blood substitute, etc, warm to 98.6xF and try rescucitation. The object is to try to use a clear circulatory system to duplicate what already works for single cells and early zygotes, which are routinely preserved in LN2 with good survival rates. I don't completely understand Mike's comment: 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. The interest in LN2 is for long-term storage. Referring to Hugh Hixon's article from CRYOMSG 15, -80xC is clearly too warm for long-term storage (1 second of body temp decay takes 17 minutes). I would guess -164xC (L Methane) is the warmest useable (1 sec at body temp = 42 years) long-term storage temp. LN2 is overkill (24 Million yrs.), but is used because it's economical. This is not to say that a "round trip" suspension/revival to -80xC would not be a monumental accomplishment. I would guess that what you need that you don't already have to perform the above experiment is a vacuum chamber suitable for a cannulated small animal. Any idea what such a tool would cost? You didn't comment on use of trehalose as a water-based cryoprotectant. Seems to me this is worthy of investigation as it's likely to be less toxic than either glycerol or DMSO. -- (Edgar W. Swank) SPECTROX SYSTEMS +1.408.252.1005 Silicon Valley, Ca Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=1489