X-Message-Number: 6611 From: Brian Wowk <> Date: Thu, 25 Jul 1996 16:15:03 -0500 Subject: In-situ Brain Cooling In-situ deep cooling of the brain (proposed to -70'C) has been taking a harsh beating lately on sci.cryonics and CryoNet, ostensibly on thermodynamic grounds. However no numbers have been supplied to support this criticism. Here are some rough calculations. Assume (pessimistically) that the thermal conductivity of tissue is close to that of solid ice at about 2 W/mK. Assume an area in contact with the brain of 500 cm^2 and a temperature gradient of 100'C over one centimeter. This translates into a heat flow of 1000 watts into the brain. Now assume perfusion of the brain with cold cold perflurocarbon at 500 ml/minute = 8 ml per second. How much would this solution be warmed by absorbing 1000 watts during circulation through the brain? Answer: 30'C. Thus, arterial perfusion at -80'C would result in venous outflow at -50'C, and most of the brain staying at deep sub-zero temperatures. That's not to say that this isn't technically a very difficult model, only that it cannot be ruled out on thermodynamic grounds. In any case, it is expected that this post- cryopreservation dog-begging-for-a-biscuit (DBFAB) model will be the LAST step of the Project. Before this is even attempted expect, * Excellent ultrastructural preservation documented by light and electron microscopy studies. * Ex-vivo metabolic and EEG study documenting neurological survival. I agree there is no point in attempting a spectacular in-vivo demonstration until these first two milestones are reached. However ultimately an in-vivo model will be important. While the first two milestones will mark the transition from a dead brain to a living brain, only an in-vivo model will tell the subtle differences between a sick brain and a healthy brain. In addition to wanting our cryopreserved brain to be viable by conventional criteria, we also want it to be *healthy* if possible. *************************************************************************** Brian Wowk CryoCare Foundation 1-800-TOP-CARE President Human Cryopreservation Services http://www.cryocare.org/cryocare/ Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=6611