Physicians could not reliably diagnose death in all cases until the early nineteenth century when a new technology, the stethoscope, was invented and medical scientists began to understand cardiorespiratory anatomy and physiology. Ironically, it was the introduction in the late twentieth century of more new technologies, such as the mechanical ventilator, that once again caused uncertainty about the definition and determination of death.

Before life-sustaining technology was introduced, critical vital functions such as heartbeat, breathing, and brain activity were so interdependent that when one function ceased, they all did. For example, when a person suffered a massive heart attack and cardiac arrest, breathing and consciousness were lost almost simultaneously because the heart pumps nutrient rich, oxygenated blood to the brain and the rest of the body. If a person stopped breathing, say from drowning, heartbeat and consciousness were almost immediately lost for the same reason...