When are you dead? It’s not an easy question to answer.
In fact, of the two great certainties in life, death and taxes, the former is actually harder to work out than the latter.
One way to define death is to look for behaviors and organs that have stopped working. But that doesn’t necessarily mean someone is dead. The heart can stop temporarily and start up again. The body may be completely unresponsive but revive later. There are thousands of accounts of people “coming back to life” after being wrongly pronounced dead or, worse, buried alive.
Physicians distrust using the activity of heart and lungs as indicators of death, and over the past 100 years or so have turned to the concept of brain death. These days many countries use loss of function of the brain stem as their definition of death. This is the situation when the body can no longer carry out actions controlled by the autonomic nervous system, such as breathing, on its own.
It can still leave us with some very troubling decisions to make. I remember a tragic case in the United States where a 33-year-old Texan woman, Marlise Munoz, suffered a stroke and was declared brain dead. However, she was 14 weeks pregnant and even though the fetus was not thought to be alive, doctors kept her on a life-support machine that artificially ventilated her.
An awful legal battle ensued and, in the end, the life-support was withdrawn. Many similar cases make the news, often when there is a conflict between what the doctors are saying about the patient, and what the family want desperately to believe.
Now new research has made our understanding of the end of life even fuzzier. We know that more than 1,000 genes not only remain active in cells of dead bodies, but that some genes actually switch on when the body is dead. By studying mice who have just died, scientists have now found that cells in the kidney, heart and liver continue to operate even 24 hours after death.
“The study certainly opened our eyes to how parts of the body continue to provide an environment for molecular activity in the hours after death,” says Sandrine Claus from the University of Reading, United Kingdom. “It was particularly interesting to note that the heart was one of the organs that saw the most activity over 24 hours after death when we traditionally think of the heart ‘stopping’ at the point of death.”
The most widely accepted description of death is permanent cessation of the critical functions of the organism as a whole. But this definition immediately begs the questions: What is “critical’? And what does it mean to say “the organism as a whole”?
We know that cells continue to produce compounds for a day after death, so it looks like we need a new definition. “If cells continue to display molecular activities, the irreversible nature of death may be what characterizes the condition,” Claus tells me.
Claus’ colleague Alain Oregioni says it’s not too much of a stretch to think that cells will go on working independently as long as they have energy and enough warmth for chemical reactions to happen.”We were amazed to find that even after a mouse is dead, most of its cells are active and still fighting to compensate for lack of oxygen,” he says. “Understanding these changes could help improve both organ transplants and forensic investigations in the future.”
These discoveries are part of a new field, called thanatometabolomics — from Thanatos, the name given to the personification of death by the ancient Greeks. Oregioni also says that death is more than just the end of living: It is also an irreversible state.
But since sometimes animals (including humans) can be revived after the blood circulation has stopped for some time, the study of thanatometabolomics — cell activity that continues after death — may be able to work out more precisely were the boundary is between resuscitation and irreversible death.
“This could be done for each organ, which would be useful for transplants,” Oregioni says. “It is also possible that the information gathered would then help improve resuscitation of a whole organism.”
It could mean that scientists and doctors have to record multiple times of death. For example, a pathologist might use rigor mortis to determine how long someone has been dead. The temperature of the body can also be correlated to the time since death.
To be more precise, however, we could look at cellular and genetic activity. Some organs may remain “alive” long after their body has irreversibly died.
Rowan Hooper is managing editor of New Scientist magazine. He tweets at @rowhoop and his book, “Superhuman: Life at the Extremes of Our Capacity,” is out now, published by Simon & Schuster.
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