X-Message-Number: 2927
Date: Thu, 21 Jul 94 17:58:03 CDT
From: 
Subject: SCI.CRYONICS Ischemia

     The extraordinary excerpt below is from page 271 of the
1991 edition of the "Texbook of Medical Physiology" by
Arthur C. Guyton.

     ...4 to 5 minutes of circulatory arrest causes
     permanent brain damage in over half the patients.
     Circulatory arrest for as long as ten minutes almost
     universally destroys most, if not all, of the mental
     powers.

          For many years it was taught that this detrimental
     effect on the brain was caused by the cerebral hypoxia
     that occurs during circulatory arrest.  However,
     experiments have shown that, if blood clots are
     prevented from occurring in the blood vessels of the
     brain, this will also prevent the very rapid
     deterioration of the brain during circulatory arrest.
     For instance, in one animal experiment, all of the
     aminal's blood was removed from the blood vessels at
     the beginning of circulatory arrest and then replaced
     at the end of the circulatory arrest, so that no
     intravascular blood clotting could occur.  In these,
     the brain was able to withstand up to 30 minutes of
     circulatory arrest without any permanent brain damage.
     Also, administration of heparin or streptokinase prior
     to cardiac arrest was shown to increase the
     survivability of the brain two to four times as long as
     is usually the case.  Therefore, it is likely that the
     severe brain damage that occurs following circulatory
     arrest results mainly from permanent blockage of many
     small or even large blood vessels by blood clots, thus
     causing prolonged ischemia and eventually death of the
     neurons.

This sounds to me like a pile of nonsense!  If this was true
then why doesn't all tissue become necrotic after a few
minutes of ischemia?  Comments?

                                        --- Brian Wowk

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