Cryonics

Cryonics (from Greek κρύος 'kryos-' meaning 'cold') is the low-temperature preservation (usually at −196°C) of people who cannot be sustained by contemporary medicine, with the hope that and restoration to full health may be possible in the far future.Cryopreservation of humans is not reversible with present technology; hope that medical advances will someday allow cryopreserved people to be revived.

Cryonics is regarded with skepticism within the mainstream scientific community and is not part of normal medical practice. It is not known if it will ever be possible to revive a cryopreserved human being. Cryonics depends on beliefs that death is a process rather than an event, that clinical death is a of death rather than a diagnosis of death, and that the cryonics patient has not experienced information-theoretic death. Such views are at the speculative edge of medicine.

Cryonics procedures can only begin after legal death, and cryonics "patients" are considered legally dead. Cryonics procedures ideally begin within minutes of cardiac arrest, and use cryoprotectants to prevent ice formation during cryopreservation. The first corpse to be cryopreserved was that of Dr. James Bedford in 1967. As of 2014, about 250 bodies were cryopreserved in the United States, and 1,500 people had made arrangements for cryopreservation after their legal death.

Long-term memory is stored in cell structures and molecules within the brain. In surgeries on the aortic arch, hypothermia is used to cool the body while the heart is stopped; this is done primarily to spare the brain by slowing its metabolic rate, reducing the need for oxygen, and thus reducing damage from lack of oxygen. The metabolic rate can be reduced by around 50% at 28 °C, and by around 80% at 18 °C or profound hypothermia. By keeping the brain at around 25 °C (considered deep hypothermia), surgeries can stretch to be around a half-hour with very good neurological recovery rates; stretching that to 40 minutes increases the risk of short term and long term neurological damage.

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