ExternalDefibrillatorsAutomate 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.
Descriptionof the devices:The kitconsists of paddle electrodes, power control unit, cables, connectors and somevarious accessories. They are made individually and assembled together througha process called integrated production process. Figure 1. The figureabove represents the symbol of AED as well as the figure of the portabledevice. Construction Details:Biocompatibleraw 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 functiondepending on the variety of environmental conditions.
The components requiredconsists of:· Controlbox· Capacitorbank· Inputbuttons ( power control, energy select control, charge button, and an energydischarge button)· Batteries· Electrodes ControlsThe controlbox contains power generating and storage circuits. The charge that flows tothe patient is produced by high voltage that is being stored in the capacitorbank. The capacitor bank can withstand up to 7kV of electricity. The circuit elementsof a simple defibrillatorTo startwith the fundamentals of a defibrillator, figure 2 below is a depiction of acircuit for a simple defibrillator.Figure 2When theswitch is connected to point A above, the connection flows from capacitor tothe power source. Current starts flowing to the capacitor until the capacitorhas the same amount of voltage to the power source (Vo). From this pointonwards, the current will stop flowing as the capacitor has reached its totalcharging limit. When theswitch is then connected to point B, the connection stops flowing from powersource and capacitor.
The capacitor begins to discharge and electrical currentis transferred through the paddles of the heart. There is a need for thedelivery of the current to the heart to last for milliseconds in order for theheart to completely depolarize. The purpose of the inductor is to elongate thetime of the current flow by inducing a voltage that goes against the currentflow.
ElectrodesElectrodesare the appliances used to deliver the current energy to the heart of thepatient. 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 increasingthe speed of the shock as well as improving defibrillation technique. Paddlesize correlates to the current flow. Larger paddles have the tendency toproduce a lower resistance and allows current to flow to the heart. Hence,larger paddles are highly recommended.
Most paddles that are being used have adiameter of 8-13cm, and paediatric paddles, which are smaller.Since skinis a bad conductor of electricity, a gel must be used to form a connecting bridgebetween the patient and the electrode. Without this gel, the amount of currentflowing to the heart is reduced. Furthermore, there is a possibility that itmight burn the skin. There are a wide variety of gels and pastes for thispurpose. They are made of cosmetic ingredients such as lanolin or petrolatum.
Chloride ions may be one of the essential requirements to form the connectionbetween the skin and the electrode. Most of these materials are similarcompounds used for different medical devices such as ECG scans.Battery Batteriesare known to be containers of chemical reactions. In defibrillators, many typesof batteries are being used. They are classified under the chemical reactionsthat contained in them and include lead-acid, lithium, and nickel-cadmiumsystems.
These batteries can usually be recharged by an outside power supply,and when not in use defibrillators are being plugged in. Extremities in temperaturemay lead the batteries to be affected negatively. Hence, defibrillators arerequired to be stored in controlled environments. Batteries will be worn outover time and are required to bereplaced. This is crucial as batteries are intuitively corrosive andpotentially toxic. Automated external defibrillatorsThis deviceis equipped with sensors that are installed to the chest and determine ifventricular fibrillation is ongoing during that time. Once detected, the deviceprints out a command to deliver an electric shock. These advancements intechnology has vastly reduced the training required to use a defibrillator andhave saved countless of lives.
Assembly of the externaldefibrillatorMaking the batteries· Onetype of the battery is called lithium battery. The design of the device led thebatteries to connect to a number of cells. For this device, the cells arecomposed of sulfur dioxide and lithium metal.
Due to it being in a condition ofoxygen free, the lithium is moulded into a solid case with sulfur dioxide beingadded next.· Thecell is sealed airtight to prevent the sulfur dioxide gas from flowing out andmoisture from flowing in. Per battery design, wired in series are the fourlithium cells that are organised in packed holding. A fuse with the value of 8Aare mounted on each cell due to safety precautions. Once pressure builds up toohigh, a vent that is installed on every cell can be used to release thepressure. Function: Application:Thesedevices are traditionally implanted on the upper chest beneath the collarboneabout the size of a stopwatch.
This battery powered device are connected to theheart with a lead; a thin flexible wire. An internal defibrillator can sensewhen the heart is beating too fast called tachycardia. The device sends smallharmless electrical pulses to the heart to regulate the heart rate. If therapid heart rate continues, the defibrillator will produce a necessary life-savingshock to provide the heart a normal rate.
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