[extropy-chat] Cryonics without comprehensive brain disassembly?

[Eugen Leitl]

On Tue, Apr 20, 2004 at 10:38:59AM -0700, Robert J. Bradbury wrote:

> Eugen, is there any good data on precisely precise brain
> decay per unit time with a flat-line EEG?  I'm not talking
> about ischemia-reperfusion injury -- I'm talking about what
> actually causes the flat-line (e.g. severe comas) and the
> limits to dealing with it.

Stopped blood flow (e.g. through wall-current induced heart arrest) results in flat EEG
after some 15-20 seconds: http://www.usyd.edu.au/su/anaes/lectures/cerebprot/
Some sedative drugs and hypothermia help here, too. (Assisted shutdown of
cerebral metabolism by itself is a good idea, since preventing some damage
pathways and reducing the amount of damage in general).
 
> I would imagine one could have problems with ATP synthesis
> and perhaps the proteosome and other methods of proteins
> being degraded but is isn't clear to me that either of
> those contribute directly to a flat-line so long as the
> brain has sufficient nutrients.  This may be a question

Due to brain's very high metabolism rate both oxygen and glucose content collapse at
stopped blood flow. If perfusion is to be maintained, you need to use
drug-assisted shutdown and/or hypothermia to flatten the
electroencephalogram.

> along the lines of "what precisely is required to reboot
> a brain?".  A different way of looking at it would be

The operational attractors are robust (it'd better be, evolution is a harsh
taksmaster) and resume cleanly, when reperfusion is restored (temperature is
elevated (notice that heart starts fibrillating if it's too cold, which is
not a good state to be in for long), sedative drugs are degraded or leave the system).

> *what* precisely would contribute to a loss of the
> neuronal structure in the brain in a flat-line condition
> but one that has sufficient resources to maintain the
> neuronal structure?

If you reperfuse after a prolonged ischemic episode, electric 
activity immediately goes way above normal. This is both a symptom and a
reason for some of the brain damage. Most of the damage cascades manifest 
some 2-3 after the insult. You can keep down the activity and block some 
of the damage pathways with drugs, administered before and/or after.
 
> I'm thinking along the lines of we may currently have the
> technology to preserve the brain structure but we don't know

If the system can no longer homeostate itself, and it's still above
vitrification temperature, it's going to degrade. I.e., you better bring it
back quick (before it's too far gone to be able to resume), or you try to
bring the system as quickly as possible into a stable state. Right now, the
best way to do that is to perfuse and vitrify.

> enough (yet) to perform a reboot (similar to the fact
> that decades ago we didn't know how to restart a heart
> that stopped beating).  In that case there is a clear
> alternative to cryonics that might make Brett and/or
> others happy.

People in coma are slowly going. How long can you leave a person on the
ventilator? Maybe half a year max. Maybe a bit longer, but not much.
Technology doesn't yet advance at a pace where individual days or weeks
matter. As such, coma only gives you a brief respite, slowing the damage
somewhat.

There's no real alternatives to cryonics, unfortunately. We all wish there
was a stasis field, or something, but that doesn't appear to be possible
according to our current knowledge of physics.

Treat above with caution: I've forgotten a lot, and I never knew much about
this area of medicine to start with.

-- 
Eugen* Leitl <a href="http://leitl.org">leitl</a>
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