X-Message-Number: 1913
Date: Mon, 8 Mar 93 01:14:42 CST
From: Brian Wowk <>
Subject: CRYONICS Oxygen Utilization

Marvin Minsky:
 
> In article <> > 
 (Terry Ford) writes:
 
>> If you drain the blood of someone, and refill them with that other liquid,
>> would that not stop all brain activity;therefore, killing the person
>> clinically?
 
> We might be able to replace the blood by an alternative
> oxygen-carrying fluid that is also cryoprotective.  
 
        Brain electrical activity stops dead (reversibly) at about 20'C 
(70'F) for biochemical reasons unrelated to oxygenation.  Residual 
cellular metabolism persists almost all the way down to freezing, but is 
so low below 15'C (a typical temperature at which blood is replaced) 
that oxygen needs are met by dissolved gas alone.  Below 10'C 
cardiopulmony support is not required because the brain is so subdued by 
hypothermia that it doesn't use oxygen at all.
 
        This effect, by the way, is how neurosurgeons achieve a 
bloodless field in certain types of brain surgery: They deeply cool the 
patient, then shut down circulation for an hour or more.
 
        Just in case any confusion remains about this point, there is no 
question that cryonic suspension ultimately "kills" the patient 
clinically.   In fact, so does hypothermic neurosurgery.  Rather than 
preserving brain function, the goal of both procedures is to preserve 
enough brain *structure* so that the patient can be revived at some 
future point.   
 
                                                --- Brian Wowk

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