THE CONCEPT OF BRAIN DEATH

Brain death represents death of the organism and not merely death or necrosis of the brain in a living body. The organism is an aggregation of living cells, although an aggregation of living cells does not necessarily constitute an organism. An organism exists only when the cell aggregation is under the control of modulating systems such as the central nervous system (CNS), the endocrine system, and the immune system. After any one of these systems ceases to function, death is inevitable unless artificial measures can be taken. The physiologic significance of brain death and cardiac death are essentially equal, and both represent an irreversible loss of communication between the control center and peripheral cells and tissues, as well as loss of modulation of an aggregation of cells. Without these systems, harmonious functioning of individual cells as constituents of the whole organism ceases. Because total and irreversible elimination of immune or endocrine function is not a phenomenon of reality, in contrast with the CNS, the concept of endocrine or immune death does not exist.

Previously, cessation of respiration was equivalent to immediate death of the organism, but artificial ventilation can now prolong the life of a body for a certain period. Various functions are believed to reside in the hypothalamus and brainstem—the endocrine, autonomic, and immune functions, as well as others that are unknown. The brainstem also contains the main tracts for neural communication between the control center and peripheral tissues. All the motor outputs from the hemispheres have to travel through the brainstem, as do all the sensory inputs to the brain except sight and smell. Each of these functions of hypothalamus and brainstem can be monitored precisely and provided artificially. Autonomous respiratory function of the lower brainstem constitutes the border between life and death, and the need for mechanical devices to supply respiratory functions is defined as representing death of the individual. Possibly, most of the brain functions vital to life could be replaced with computers and drugs and the circulatory functions maintained for months or years. The endocrine system is an example. Administration of arginine vasopressin prolongs the cardiovascular functions for months in brain-dead patients. ^{[11] [12]} The only function advance technology cannot provide is that constituting humanity or personality, both of which are possibly products of the telencephalon.

The traditional concept of death has used the cessation of cardiac and respiratory functions as its basis because of acceptance of simple and nonmedical concepts—that life begins with the first inspiration after birth, that death comes with the last expiration, and that cardiac activity ceases within a few minutes of the last expiration. In contrast, the current concept of brain death adopts the conclusions of modern biologic science—that the CNS, including the brainstem, is the control center for the living organism, that cessation of CNS functions represents cessation of the harmony of life, and that without CNS control, the living organism is nothing more than an aggregation of living cells.