The Defibrillator

Figure 1. Early Commercialized Defibrillator (Source)

Brief: Another tool commonly associated with the medical care field is the defibrillator. But to understand the device itself we must first take a look at the underlying principle of defibrillation. Defibrillation is a therapeutic dose of electric current to the heart to depolarize a critical mass in the heart muscle, allowing the body to return to a natural pace. In the previous post referring to the galvanometer, Galvani discovered that electrical currents can cause muscle contraction in 1791. However, the application of electricity in the field of medicine was primarily to confirm whether or not a person was truly dead. Eventually in 1850, Karl Ludwig applied the current to a dog's heart and made it quiver. There are currently 2 types of defibrillation devices: Automated External Defibrillators (AED) and Implantable Cardioverter Defibrillators (ICD). 

Figure 2. Sample ICD (Source)

The Automated External Defibrillator was created as a result of the introduction of computers to the manual external defibrillator. An onboard computer takes the time to judge the right amount of voltage to deliver to the patient and discharged. The AED is designed so that a regular person without much medical training can use it as well. Because of its simplicity, the AED cannot treat patients as accurately or as quickly as a Manual External Defibrillator paired with a trained professional. The more invasive alternative the ICD consists of a shock generator and wires with electrodes on both ends. The generator is implanted into the chest with a series of wires being fed through the atria or ventricles of the heart. When the ICD detects a heart irregularity, it delivers a small charge to the heart to restore equilibrium known as cardioversion. Emergency personnel began training in defibrillation in the 1960's and the first AEDs were created in the 1980's. 

Figure 3. AED Available for Public Use (Source)

Use: Implantable defibrillators often had their own regulation requiring no action for them to function. Generally, external defibrillators consist of 2 paddles representing the positive and negative leads connected to a charge pack. An AED would require the paddles to read the patient for a few seconds while the computer makes the necessary calculations. The paddles are removed from the chest of the patient and allowed to build a charge. A tone would play indicating the AED is at optimal charge at which point the user places both paddles on the chest of the patient to discharge it. Manual versions of the external defibrillator are controlled by a specialist but fundamentally operate the same with the exception that it can be tuned to a wider variety of currents and voltages.

Additional Information: General, Defibrillation, General 2,