X-Message-Number: 26201
From: "Brian Wowk" <>
Subject: Recent Suspended Animation Research
Date: Thu, 19 May 2005 07:20:41 -0700

    Questions have been asked about the recent Science paper, and related 
Scientific American article, discussing a suspended animation breakthough. 
The subject has been discussed extensively on the Imminst website.  In my 
opinion, the implications of this work as it currently stands have been 
overstated.

    The researches used H2S to inhibit the cell energy producing enzyme 
cytochrome oxidase.  This is the same mechanism as cyanide poisoning, except 
that H2S "poisoning" is apparently more easily reversible.  When the energy 
producing ability of cells is inhibited, animals can no longer obtain normal 
body temperature.  Their temperature falls to match that of the environment. 
This is no surprise.  In a cold state, the animals require less energy and a 
lower metabolic rate to stay alive.  This is also no surprise.  In fact, the 
metabolic reduction claimed at +11 degC is similar to what would be expected 
had the animals been simply cooled to that temperature by the methods of 
conventional clinical hypothermia.  (The world record for human hypothermia 
survival is +7 degC, by the way.)  This highlights the greatest weakness of 
the Science paper: no controls.  They did not show that metabolic inhibition 
and cooling facilitated by H2S gives better results than what would be 
obtained by a combination of anesthesia, paralytic drugs, and cooling by 
conventional means.

    If we suppose that this approach does give better results in mice than 
ordinary cooling, there are still many questions about the extendability of 
the work to larger animals.  For example, even if you turn off all energy 
production inside a human, a human will only passively cool at approximatley 
one degree C per hour (the rate at which a dead body cools in room air).  A 
human with metabolism that is merely inhibited will cool even slower, which 
leads to questions of whether cells will have sufficient energy to maintain 
basic housekeeping (homeostasis) in a high temperature state with their 
metabolism inhibited.  To implement this protocol in a human, it would have 
to be done either very slowly, or with the aid of conventional heart-lung 
bypass cooling.  If the latter, then we get back to the question of whether 
H2S is actually providing a protective effect, or merely facilitating 
cooling that we can do more expeditiously by other means.  In other words, 
does H2S actually reduce *the need for energy*, or merely inhibit the body's 
*ability to produce energy*.

    There are a host of pathologies known to afflict large animals in 
ultraprofound hypothermia, ranging from blood cell agglutination (why 
hemodiluation is used in clinical hypothermia), altered ion balances, and 
cardiac arrythmias.  It would be a miracle if simply inhibiting one energy 
producing enzyme could address all these problems and more.  Stranger things 
have happened, but it hasn't been shown yet.

    It's remarkable that a simple molecule can reversibly inhibit biological 
energy production.  At a minimum, this should be useful to treat malignant 
hyperthermia.  But it is premature to call this work a "suspended animation 
breakthough" based on what has been reported so far.

---Brian Wowk 



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