Medical general, the most basic design of a

Devices Report

B device – Defibrillators

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of the device


In general, the most basic design of a defibrillator is
made of a few key components. Controls, power supply and the electrodes

Electrodes transmit energy to the heart of the patient.
There are many types of electrodes like disposable electrodes, hand-held
paddles and even internal paddles. Generally, electrodes with a bigger contact
area means lesser resistance which also means more current can flow to the
heart. Naturally the surface of the skin is not a good conductor of
electricity, thus a special gel must be placed between the electrodes and the
skin. It is also to reduce as much burning of the patient’s skin.

Controls refer to the control box where it is made of a
light piece of insulating material and circuitries to generate and store power
using capacitors. Typically, the control box also holds user input knobs and
buttons such as energy select control, energy discharge button, power control
for any adjustments. Some have special controls for different segments such as
for disposable electrodes or internal paddles.

The power supply is needed to power the device. Some
defibrillators make use of a battery. A large majority of the battery used are
lithium batteries and can be recharged but must be replaced after some time.
Most defibrillators are stored where temperatures are controlled, and the
batteries aren’t affected by the elements and temperatures.

Figure 1: A picture of an
external defibrillator kit showing the control box and the electrodes 1


A defibrillator is a device that stops or counter
ventricular fibrillation using a therapeutic shock when a person is under
cardiac arrest or having conditions that affects the heart and its rhythm. In
simple terms, the heart needs to be pumped in an orderly sequence, having a
ventricular fibrillation means the pace and sequence is disturbed and the heart
will probably be preceded with a cardiac arrest

Figure 2: Shows the mechanism of action of defibrillator 3

Figure 2 shows a relatively simple circuit that is not
electronically controlled. Most defibrillators are generally similar in concept
but there are variations and complexities in different types of defibrillators.
As the switch, is set in position 1, the power supply charges the capacitor. Once
it is charged the switch is set to position 2. Both paddles need to be pressed
to ensure there is a flow of current. Since depolarization of the heart
completely will take several milliseconds of the current flow, the inductor is
put in place to prolong the exponential discharge of the capacitor.