X-Message-Number: 5857
From: "Ralph C. Merkle" <>
Newsgroups: uk.legal,sci.cryonics,sci.life-extension
Subject: The Technical Feasibility of Cryonics
Date: Sat, 24 Feb 1996 18:56:08 -0800
Message-ID: <>

There have been several references to "The Technical Feasibility
of Cryonics" by Ralph C. Merkle, which appeared in Medical
Hypotheses, Vol. 39, 1992; 6-16. 

An extended version of this article is available on the web at:
http://merkle.com/merkleDir/techFeas.html.  This version
is more current than the version available at www.cryonet.org
(which was posted to cryonet some time ago).

Some comments:

1)  Radiation damage.  Background radiation is approximately 0.1
rads per year.  A "lethal dose" of radiation (by current criteria)
is about 600 rads.  Therefore, someone held in cryonic suspension
and exposed to normal background radiation levels will accumulate
what would today be considered a "lethal dose" in about 6000 years.

Most damage is "latent" until the cell divides ("cycles" or "renews").
Therefore, cells that do not divide are more resistant to damage.
The central nervous system is more resistant to radiation damage
than other tissues.  "There are no rapid renewal systems in
the CNS, but the glial cells and the endothelial cells cycle
slowly and can show injury.  The neurons are not injured except secondarily
or by doses of 50 Gy [5,000 rads] or more.  Very large exposures of
15 to 50 Gy [1,500 to 5,000 rads] can produce acute functional changes
and, at the highest doses, immediate death.  After 15 Gy [1,500 rads],
changes begin in four to five months and develop further over one to
two years."

If we assume that survival of the central nervous system is the important
consideration in cryonic suspension, and further assume that any dose
of radiation which is not immediately lethal by current criteria can be
repaired by future technology, then a person in cryonic suspension would
accumulate a "lethal dose" in about 50,000 years.

Reference:  Cecil Textbook of Medicine, 17th edition, James B. Wyngaarden,
Lloyd H. Smith, Saunders 1985, pages 2298-2297.

1 Gy (gray) equals 100 rads.  1 rad, or Radiation Absorbed Dose, corresponds
to 100 ergs per gram of absorbed radiation.  1 rem is roughly similar
to 1 rad.

Peter Mazur, a well known cryobiologist and critic of cryonics,
said:  "Cryobiologists are often asked how long cells can remain
viable at -196 degrees C, the temperature of boiling liquid nitrogen
(which is the usual cryogenic fluid).  The answer is clear -- more
than 1000 years. The reason is that direct ionizations from background
radiation are the only source of damage at such temperatures.
Ordinary chemical reactions cannot occur."[42]
 

42. "Stopping Biological Time: The Freezing of Living Cells" by Peter Mazur, 
Ann. N.Y.
      Acad. Sci. 541: 514-531, 1988

2) Ischemia.

"For many years, it was thought that irreversible cellular damage unavoidably
occurs after only a few minutes of complete cerebral ischemia. This opinion has
been modified during the past decade [omitted reference]. Provided that the
conditions for recovery are optimal, short-term restoration of brain functions

may be achieved after periods of ischemia lasting as long as 60 minutes..."[93].
"Most clinical and experimental studies suggest that the normothermic brain is

not able to withstand complete ischemia of >8 to 10 min. There is, however, firm
experimental evidence of functional and biochemical recovery of a substantial
part of the brain after complete cerebrocirculatory arrest of one hour [omitted

references]."[97]. "It turned out in fact that appropriate treatment of 
post-ischemic
recirculation disturbances led to recovery of energy metabolism and neuronal
excitability after complete cerebro-circulatory arrest of as long as 1 hour at
normal body temperature [omitted reference]"[95].

93. "Neurochemical Determinants of Ischemic Cell Damage" by
      Carl-Henrik Nordstrom, M.D. and Bo K. Siesjo, M.D., pages 49- 66; from
      "Protection of the Brain from Ischemia" edited by Philip R. Weinstein and
      Alan A. Faden, Williams and Wilkens 1990

94. "Hemodynamics of Postischemic Reperfusion of the Brain," by K.-A.
      Hossmann, M.D., Ph.D., pages 21-36; from "Protection of the Brain from
      Ischemia" edited by Philip R. Weinstein and Alan A. Faden, Williams and
      Wilkens 1990

95. "Post-ischemic resuscitation of the brain: selective vulnerability versus
      global resistance" by K.-A. Hossman; from Progress in Brain Research,
      Vol. 63, edited by K. Kogure, K.-A. Hossman, B. K. Siesjo and F. A.
      Welsh, 1985, pages 3-17

97. "Resuscitation potentials after prolonged global cerebral ischemia in
      cats" by Konstantin-Alexander Hossmann, MD, Ph.D., Critical Care
      Medicine, Vol 16, No. 10, 1988, page 964-971

It is important to note that these results are based on the use of presently
available medical technology.  It is reasonable to expect that substantially
better results will be feasible some time in the future, particularly if we
consider the major advances that are likely in future medical technology.
Some possible advances are considered in Nanotechnology and Medicine, available
at: http://nano.xerox.com/nanotech/nanotechAndMedicine.html

3)  Ethics.   To quote the American College of Physicians Ethics
Manual, "Each patient is a free agent entitled to full explanation and
full decision-making authority with regard to his medical care. John
Stuart Mill expressed it as: `Over himself, his own body and mind, the
individual is sovereign.' The legal counterpart of patient autonomy is
self-determination. Both principles deny legitimacy to paternalism by
stating unequivocally that, in the last analysis, the patient determines
what is right for him." "If the [terminally ill] patient is a mentally
competent adult, he has the legal right to accept or refuse any form of
treatment, and his wishes must be recognized and honored by his
physician."[92]

92. "American College of Physicians Ethics Manual. Part II:
      Research, Other Ethical Issues. Recommended Reading." by the
      Ad Hoc Committee on Medical Ethics, American College of
      Physicians; Annals of Internal Medicine, July 1984; Vol. 101
      No. 2, pages 263-267

4)  There are a great many other points I could make, but most have been
made already in http://merkle.com/merkleDir/techFeas.html.


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