<P> Replacement of biological (susceptible to diseases) organs with mechanical ones could extend life . This is the goal of the 2045 Initiative . </P> <P> For cryonicists (advocates of cryopreservation), storing the body at low temperatures after death may provide an "ambulance" into a future in which advanced medical technologies may allow resuscitation and repair . They speculate cryogenic temperatures will minimize changes in biological tissue for many years, giving the medical community ample time to cure all disease, rejuvenate the aged and repair any damage that is caused by the cryopreservation process . </P> <P> Many cryonicists do not believe that legal death is "real death" because stoppage of heartbeat and breathing--the usual medical criteria for legal death--occur before biological death of cells and tissues of the body . Even at room temperature, cells may take hours to die and days to decompose . Although neurological damage occurs within 4--6 minutes of cardiac arrest, the irreversible neurodegenerative processes do not manifest for hours . Cryonicists state that rapid cooling and cardio - pulmonary support applied immediately after certification of death can preserve cells and tissues for long - term preservation at cryogenic temperatures . People, particularly children, have survived up to an hour without heartbeat after submersion in ice water . In one case, full recovery was reported after 45 minutes underwater . To facilitate rapid preservation of cells and tissue, cryonics "standby teams" are available to wait by the bedside of patients who are to be cryopreserved to apply cooling and cardio - pulmonary support as soon as possible after declaration of death . </P> <P> No mammal has been successfully cryopreserved and brought back to life, with the exception of frozen human embryos . Resuscitation of a postembryonic human from cryonics is not possible with current science . Some scientists still support the idea based on their expectations of the capabilities of future science . </P>

Lifespan extension has been scientifically achieved in in the laboratory