Answer to Question #110214 in Physics for Mukelo Madolo

Question

Test 2

Explain what a defibrillator is and how it works.

Answer 1

As the name suggests, defibrillation stops fibrillation, the useless trembling that a person's heart muscles can adopt during a cardiac arrest. Simply speaking, a defibrillator works by using a moderately high voltage (something like 200–1000 volts) to pass an electric current through the heart so it's shocked into working normally again. The patient's heart receives roughly 300 joules of electrical energy (about as much as a 100 watt incandescent lamp uses in three seconds).

The defibrillator consists of an electric supply unit and two metal electrodes called paddles that are pressed very firmly to the patient's chest using insulating plastic handles. The important thing is getting the current to flow through the heart, so where the paddles are applied is crucial. One way of applying them is to put one paddle above and to the left of the heart and the other slightly beneath and to the right; another method involves placing one paddle on the front of the body and the other round the back. In order for the electric current to flow properly, and to reduce the risk of skin burns, the electrodes have to be applied close enough together. They must also make good electrical contact with the skin, so a solid or liquid conducting gel is usually applied to the patient's chest first.

In units designed to be used by less-trained people in public places, sticky, self-adhesive electrode pads are often used instead of paddles for safety and simplicity: once the pads are stuck on, the operator can stand well clear of the patient's body and that reduces the risk of their getting an electric shock.