We don't know how to do that yet for long periods of time. It would be nice to be able to knock people out somehow, like hibernating bears, and travel to the stars packed like popsicles, but our understanding of how to get the human body to do this is, so far as I have ever heard, not there yet. Nor does it seem that it is within grasp in the near future. There are many animals that can hibernate for months and years, perhaps we will eventually find out how to put humans in such a state, and prevent the aging process too. It sounds like a tall order to me, but it is our only option for interstellar travel, and possibly even travel inside our own solar system.

In modern heart surgery, it is common to chill anesthetized patients to far below the usual 98.6 degrees. By using chilled blood pumped into the veins at temperatures below 60 degrees F, patients biological processes slow down and open-heart surgery can be performed. Clinically, the brain is nearly flat-lined and there is of cource no heart beat so you are really dead by all legal accounts, yet these patients can be revived after 3-5 hours. There are, however, measurable long-term consequences whoich begin with a well-documented state of befuddlement that seems to go away after a few weeks. In fact, anyone placed on a heart-lung machine seems to go through thie and it is called 'pump-head syndrome'. The problem is that long term studies show a marked decline in certain cognitive and memory-related functions. This method of artificial suspended animation seems to have its own substantial risks.

A study from Duke University, published in the New England Journal of Medicine in February, 2001, confirms what many doctors have suspected, but have been reluctant to discuss with their patients: A substantial proportion of patients after coronary artery bypass surgery experience measurable impairment in their mental capabilities. In the surgeons’ locker room, this phenomenon (not publicized for obvious reasons) has been referred to as "pump head."

In the Duke study, 261 patients having bypass surgery were tested for their cognitive capacity (i.e. mental ability) at four different times: before surgery, six weeks, six months, and five years after bypass surgery. Patients were deemed to have significant impairment if they had a 20% decrease in test scores.

This study had three major findings

Cognitive impairment does indeed occur after bypass surgery. This study should move the existence of this phenomenon from the realm of locker room speculation to the realm of fact.

The incidence of cognitive impairment was greater than most doctors would have predicted. In this study, 42% of patients had at least a 20% drop in test scores after surgery.

The impairment was not temporary, as many doctors have claimed (or at least hoped).

The decrease in cognitive capacity persisted for 5 years.

The mental impairment was not due to the patients' age (which averaged 61). The results from the Duke study were compared to results from a similar study among patients of the same age who did not have bypass surgery. The decline in mental capacity in those who had bypass surgery was 2 -3 times higher over five years than in patients who did not have surgery.

The authors could not say what, exactly, caused the impairment in mental capacity. The most common speculation is that the mental changes are due to the showering of the brain with tiny particles (microemboli) related to the use of the bypass pump (the heart/lung machine, that oxygenates and pumps the blood while the heart is stopped during surgery.) If this is the case, then newer surgical techniques such as “beating heart surgery” (in which the bypass pump is not used) should help to minimize the problem. The Duke study was completed prior to the use of such procedures.

Doctors have reacted to the Duke study with mixed feelings. While most believe the Duke study was extremely well designed, many criticize it saying that "in my hospital we don't see this," or that surgical techniques have improved in the 5 years since this study was done, or that publicizing this study will discourage patients from getting necessary surgery. This was taken from the About Heart Disease web site.

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