Are there any forms of suspended animation? If you consider how animals hibernate during winter, that’s a natural example. However, if we reference the science fiction concept of stasis—where an individual is placed in a pod and frozen to endure an interstellar voyage—then it’s more of a fantasy.

That said, there are several realistic applications, particularly if we can address the challenges of preserving human tissues through freezing.

For decades, the possibility of employing cold temperatures to slow down biological processes has been recognized, and we’ve recently started using this method as a critical life-saving intervention.

For instance, patients experiencing a heart attack can undergo what is formally termed “suspended animation for delayed resuscitation,” wherein they are rapidly cooled to induce hypothermia. This process slows bodily functions and safeguards vital organs, especially the brain, albeit at the cost of disrupting blood circulation.

This approach significantly reduces the chances of brain damage and proves incredibly effective, allowing individuals to survive without treatment for up to 90 minutes.

This form of suspended animation entails dropping body temperature to approximately 59°F (15°C), compared to the usual 98°F (37°C). Temperatures below this threshold can result in cellular death.

Once the temperature dips below freezing, the large volume of water within cells turns problematic. Ice forms and expands, creating sharp crystals that can damage delicate cells and blood vessels.

Those who have suffered frostbite can attest to the harmful effects of extreme cold on body tissues. Completely freezing a person would be fatal.

Nevertheless, we successfully freeze human embryos, which can remain frozen for as long as 19 years before being thawed and developing into healthy infants.

Embryos typically freeze at an early stage when they consist of only a few cells, and they survive thanks to prior preparation. Protective agents are used to draw out water and prevent the formation of ice crystals.

These embryos are then rapidly frozen in a tank of liquid nitrogen at -196°C (-320°F), allowing for prolonged storage in suspended animation.

North American Wood Frog employs a similar strategy to survive winter. As the temperature drops, it can inundate its cells with glucose (a natural antifreeze), effectively freezing itself until both heart and brain functions cease.

The frog’s organs are encased in ice, yet the glucose inhibits ice crystals from forming within its tissues.

As temperatures rise, it gradually thaws and resumes normal activity. This process is a complex challenge for humans; every body part would necessitate risky water extraction and chemical solutions.

Hibernation represents a different strategy. Small rodents, such as mice and hedgehogs, permit their body temperatures to drop significantly, leading to a marked decrease in breathing and heart rate.

Larger mammals don’t need to reduce their body temperatures as drastically. For example, American black bears may drop from 36°C to 30°C (96°F to 86°F), reducing their metabolic rate by about 25%. This is usually sufficient to avert bone and muscle loss resulting from prolonged inactivity.

Being frozen is far from ideal, and for large mammals, it may be more advantageous than suspended animation through a hibernation-like state.

This article responds to the inquiry (from Safia Hall via email) regarding whether suspended animation has ever been realized.

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