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 Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=2927