Automate External Defibrillator (AED),
is a device that delivers shock to the heart and passes through the chest wall.
This shock allows the heart to proceed back into a regular, healthy rhythm.
of the devices:
consists of paddle electrodes, power control unit, cables, connectors and some
various accessories. They are made individually and assembled together through
a process called integrated production process.
Figure 1. The figure
above represents the symbol of AED as well as the figure of the portable
raw materials, meaning that they do not harm or is toxic to the living tissues.
The materials must be non-toxic, inert, sterilisable, and ability to function
depending on the variety of environmental conditions. The components required
buttons ( power control, energy select control, charge button, and an energy
box contains power generating and storage circuits. The charge that flows to
the patient is produced by high voltage that is being stored in the capacitor
bank. The capacitor bank can withstand up to 7kV of electricity.
The circuit elements
of a simple defibrillator
with the fundamentals of a defibrillator, figure 2 below is a depiction of a
circuit for a simple defibrillator.
switch is connected to point A above, the connection flows from capacitor to
the power source. Current starts flowing to the capacitor until the capacitor
has the same amount of voltage to the power source (Vo). From this point
onwards, the current will stop flowing as the capacitor has reached its total
switch is then connected to point B, the connection stops flowing from power
source and capacitor. The capacitor begins to discharge and electrical current
is transferred through the paddles of the heart. There is a need for the
delivery of the current to the heart to last for milliseconds in order for the
heart to completely depolarize. The purpose of the inductor is to elongate the
time of the current flow by inducing a voltage that goes against the current
are the appliances used to deliver the current energy to the heart of the
patient. There are various types of electrodes such as the hand-held paddles,
internal paddles, and self-adhesive, pre-gelled disposable electrodes.
Generally they favour disposable electrodes as they have the benefit of increasing
the speed of the shock as well as improving defibrillation technique. Paddle
size correlates to the current flow. Larger paddles have the tendency to
produce a lower resistance and allows current to flow to the heart. Hence,
larger paddles are highly recommended. Most paddles that are being used have a
diameter of 8-13cm, and paediatric paddles, which are smaller.
is a bad conductor of electricity, a gel must be used to form a connecting bridge
between the patient and the electrode. Without this gel, the amount of current
flowing to the heart is reduced. Furthermore, there is a possibility that it
might burn the skin. There are a wide variety of gels and pastes for this
purpose. They are made of cosmetic ingredients such as lanolin or petrolatum.
Chloride ions may be one of the essential requirements to form the connection
between the skin and the electrode. Most of these materials are similar
compounds used for different medical devices such as ECG scans.
are known to be containers of chemical reactions. In defibrillators, many types
of batteries are being used. They are classified under the chemical reactions
that contained in them and include lead-acid, lithium, and nickel-cadmium
systems. These batteries can usually be recharged by an outside power supply,
and when not in use defibrillators are being plugged in. Extremities in temperature
may lead the batteries to be affected negatively. Hence, defibrillators are
required to be stored in controlled environments. Batteries will be worn out
over time and are required to be
replaced. This is crucial as batteries are intuitively corrosive and
Automated external defibrillators
is equipped with sensors that are installed to the chest and determine if
ventricular fibrillation is ongoing during that time. Once detected, the device
prints out a command to deliver an electric shock. These advancements in
technology has vastly reduced the training required to use a defibrillator and
have saved countless of lives.
Assembly of the external
Making the batteries
type of the battery is called lithium battery. The design of the device led the
batteries to connect to a number of cells. For this device, the cells are
composed of sulfur dioxide and lithium metal. Due to it being in a condition of
oxygen free, the lithium is moulded into a solid case with sulfur dioxide being
cell is sealed airtight to prevent the sulfur dioxide gas from flowing out and
moisture from flowing in. Per battery design, wired in series are the four
lithium cells that are organised in packed holding. A fuse with the value of 8A
are mounted on each cell due to safety precautions. Once pressure builds up too
high, a vent that is installed on every cell can be used to release the
devices are traditionally implanted on the upper chest beneath the collarbone
about the size of a stopwatch. This battery powered device are connected to the
heart with a lead; a thin flexible wire. An internal defibrillator can sense
when the heart is beating too fast called tachycardia. The device sends small
harmless electrical pulses to the heart to regulate the heart rate. If the
rapid heart rate continues, the defibrillator will produce a necessary life-saving
shock to provide the heart a normal rate.