The increased swelling and pressure can also push the brain out of its normal space within the skull, damaging or destroying the brainstem. The brain stem controls breathing, heart rate and blood pressure. Parts of the brainstem help maintain consciousness and carry messages from the body to the brain. The brainstem is also involved with controlling movement, speech and swallowing. Coma is a decrease in brain function and there is a chance a person may regain consciousness.
Brain death is the irreversible absence of all brain function.
There is no chance of recovery with brain death. I have always understood that when an individual dies, the heart stops beating. The human heart has its own pacemaker. It doesn't need the brain to make it beat. As long as the heart has a supply of oxygen and blood, it continues to beat.