Hibernation

Artificial hibernation in humans, 'suspended animation'

The main goals for hibernation would be the delaying aging and to minimize the psychological challenges like boredom and loneliness of long stretches in space and also reducing food requirements.

Hibernation state could help prevent serious side effects from low gravity, such as changes in spinal fluid flow that diminishes eyesight.

metabolism dramatically slows during hibernation, heart rates and blood pressure also decreases.

Sleep vs hibernation

A common definition of hibernation is a long-term state in which body temperature is significantly decreased, metabolism slows dramatically and the animal enters a coma like condition that takes some time to recover from. By this definition, bears don't hibernate, because their body temperature drops only slightly and they awake relatively easily. Not everyone accepts this particular definition, we'll use the term hibernation to describe any long-term reduction in body temperature (hypothermia) and metabolism during winter months.

hibernation basically a really long nap? No. These animals aren't just sleeping, they're undergoing physiological changes that can be very drastic.

Sleep, by contrast, is a mostly mental change. There are physiological aspects of sleep that are similar to hibernation, such as a reduced heart and breathing rate and lowered body temperature, but these changes are very slight compared to hibernation. Sleep is also pretty easy to break out of -- if you're awakened from even your deepest sleep, you can be fully awake within several minutes. Sleep is primarily characterized by changes in brain activity. In fact, the brain waves of hibernating animals closely resemble their wakeful brain wave patterns, though they're somewhat suppressed. When an animal awakes from hibernation, it exhibits many signs of sleep deprivation and needs to sleep a lot over the next few days to recover.

Entering a deep unconsciousness

Some animals hibernate naturally with ease particularly through winters such higher animals as bears, squirrels and hedgehogs. Yet periodically, hibernating animals will rouse from their torpor state for half a day, raising their body temperatures back to normal, animals still don’t eat or drink during these periods.

Reducing metabolic rate

Animals such as the fat-tailed lemur can drastically drops its metabolic rate when food supplies dwindle. The poorwill is the only species of bird that truly hibernates. It drops its body temperature up to 60 degrees Fahrenheit and can live up to 100 days on 10 grams of stored body fat.

Induced hypothermia

Doctors have employed therapeutic hypothermia—lowering body temperature by a few degrees for several days—to help keep patients with brain injuries or epilepsy in suspended animation.

NASA has done some preliminary research into therapeutic hypothermia for a space-travel hibernator for a mission to Mars, but prolonged hypothermia is terrible for health: blood clots, bleeding, infection, and liver failure may occur. Understand the biology of natural hibernators most likely will be preferable to induced hypothermia.

Coma state

A coma is a prolonged state of unconsciousness, effectively a shutting down of brain function. During a coma, a person is unresponsive to his or her environment. The person is alive and looks like he or she is sleeping. However, unlike in a deep sleep, the person cannot be awakened by any stimulation, including pain.

An induced coma , also known as a medically-induced coma, a barbiturate-induced coma, or a barb coma, is a temporary coma (a deep state of unconsciousness) brought on by a controlled dose of a barbiturate drug, usually pentobarbital or thiopental, the main thing about a drug-induced coma, as opposed to a coma, is that it's reversible. But there are many possible dangerous side effects, even after short times they include experiencing vivid nightmares and very disturbing hallucinations.

We are still a long way off from any sort of Human hibernation, but interesting research is actively being worked on.