Coma is a deep and prolonged state of unconsciousness resulting from disease, injury or poisoning. The word coma usually refers to the state in which a person appears to be asleep but cannot be awakened.
Persistent vegetative state refers to another form of altered consciousness in which the person appears to be awake but does not respond meaningfully to the outside world. In this condition, the person's eyes may be open and there may be some yawning, grunting or other vocalizations. In both cases, the patient is alive, but the brain does not function fully.
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