Medical Applications User Guide (pdf) - Freescale Semiconductor

Defibrillators
11.1
Automated External Defibrillator (AED)
An AED is a portable device used to restore normal heart rhythm to
patients in cardiac arrest by delivering an electrical shock to a patient
through the chest wall. Cardiac arrest is an abrupt loss of heart
function. This medical emergency occurs mainly because of ventricular
fibrillation.
Ventricular fibrillation is a condition where there is an uncoordinated
contraction of the ventricles in the heart, making them tremble rather
than contract properly. The urgency of ventricular fibrillation requires
that the heart must be defibrillated quickly, as a victim’s chance of
surviving drops by seven to 10 percent for every minute a normal
heartbeat is not restored.
An MCU or MPU calculates whether defibrillation is needed and a
recorded voice indicates whether to press the shock button on the
AED. This shock momentarily stuns the heart and stops all activity,
giving the heart an opportunity to resume beating effectively.
The charge is generated by high-voltage generation circuits from
energy stored in a capacitor bank in the control box. The capacitor
bank can hold up to 7 kV of electricity. The shock delivered from this
system can be anywhere from 30 to 400 joules.
62 Medical Applications User Guide