To be declared brain-dead, a person must have irreversibly lost function in all parts of his or her brain. That led to a whole class of people with warm bodies and circulating blood - who could even fight off infections or gestate a baby - but who had absolutely no brain function, said Leslie Whetstine, a philosopher at Walsh University in Ohio who studies the definitions of death. Once one part of the system failed, then the others would soon shut down as well, the reasoning went.īut the advent of the mechanical ventilator, which pushes air into and out of the lungs, created a new category called brain death, Bernat said. Until the 1950s, death was considered to be the point when any one of the vital functions - heartbeat, electrical brain activity or respiration - ceased. 'You're dead when a doctor says you're dead,' Bernat told Live Science.
