The line between life and death is not as clear as once thought, now that developments in the science of resuscitation have made it possible to revive people even hours after their heart has stopped beating and they are declared dead, medical experts say.
"Historically, when a person's heart stopped and they stopped breathing, for all intents and purposes, they were dead," said Dr. Sam Parnia, an assistant professor of critical care medicine at State University of New York at Stony Brook. "There was nothing you could do to change that," Parnia told an audience at the New York Academy of Sciences last week.
However, in the process of unraveling mysteries of death at the cellular level, scientists have learned that death does not occur in a single moment, but instead is a process. It is actually after a person has died -- by our current definition of death -- that the cells of the body start their own process of dying. [After Death: 8 Burial Alternatives That Are Going Mainstream]
This process "could take hours of time, and we could potentially reverse that," Parnia said.
It was once thought that after the heart stops pumping blood throughout the body, a person has only few minutes before suffering permanent brain damage caused by lack of oxygen and nutrients getting to the brain cells. This notion, scientists now say, is outdated.
When the heart stops beating, the process of death is only beginning, said Dr. Stephan Mayer, a professor of neurology at Columbia University and a panelist at the discussion.
Brain damage from lack of oxygen to the brain comes in stages. Within seconds, brain activity is affected, but it isn't until several minutes later that sugar-deprived cells start going through the steps of programmed cell death.
"When somebody's been without oxygen, we know there’s a whole bunch of signals that are now starting to tell cells that it's time to die. So we have an opportunity to modify that programing just a little bit, to say 'wait put the brakes on,'" said panelist Dr. Lance Becker, a professor of emergency medicine at the University of Pennsylvania.
Some insights for how to halt the dying process come from case reports of people who were brought back to life with little or no brain damage after hours of a silenced brain and heart.
The key to these successful cases, in addition to good critical care, is hypothermia, experts say. Hypothermia is a state in which the body's core temperature is brought a few degrees lower than its normal temperature of 98.6 degrees Fahrenheit (37 degrees Celsius).
Studies have found that hypothermia seems to protect the brain by decreasing its need for oxygen and aborting activated cell death pathways. Still, there are limits -- although body-cooling techniques have improved recovery in many patients after cardiac arrest, there will be a moment when the damage is too much and it's too late to come back, the experts said.