Explain The Interaction Between The Key Components Of A Defibrillator
DEFIBRILLATOR
Definition
An electronic device that administers an electric shock of preset voltage to the heart through the chest wall in an attempt to restore the normal rhythm of the heart during ventricular fibrillation. Defibrillation is a procedure used to treat life threatening conditions that affect the rhythm of the heart such as cardiac arrhythmia, ventricular fibrillation and pulseless ventricular tachycardia.
The procedure involves the delivery of an electric shock to the heart which causes depolarisation of the heart muscles and re-establishes normal conduction of the heart’s electrical impulse. The machine used to deliver this therapeutic shock to the heart is called a defibrillator.
Defibrillators are key devices in maintaining …show more content…
proper cardiac function. A bit of background in cardiology will aid in the understanding of the role of defibrillators. First, ventricular fibrillation is a cardiac condition where individual heart muscles contract in a random, uncoordinated way. The heart seems to shiver, and blood circulation stops. The application of an electric shock to restore normal heart function is the only way to effectively treat a ventricular fibrillation and prevent death.
History
Key milestones occurred in the invention and development of the modern day defibrillator:
* In 1899 by French physiologists, Jean Louis Prevost and Frederic Battelli, were able to stop ventricular fibrillation in a dog by applying an electric shock to the animal's exposed heart. * In 1930, William B. Kouwenhoven, an American electrical engineer at Johns Hopkins University, and colleagues developed a closed-chest defibrillator that sent alternating current (AC) electrical shocks to the heart through electrodes placed on a dog's chest. * In 1947, Claude Beck, professor of surgery at Case Western Reserve University, first successfully resuscitated a human patient by internal cardiac massage and electrical defibrillation. * In 1961, American cardiologist Paul Zoll applied AC defibrillation to human patients in 1961. * In 1962, the direct current (DC) defibrillator was introduced by Lown and Neuman in 1962 provided greater reliability and safety. * In 1985, an implantable device, called the automatic implantable cardioverter defibrillator (AICD) to stop heart arrhythmias that was invented by Dr. Mieczyslaw Mirowski, of Johns Hopkins University received FDA approval. The device had dual tasks: the defibrillator jolts the heart out of ventricular fibrillation and the cardioverter shocks the heart out of an abnormally fast heartbeat. A heftier power pack is needed and so the battery is implanted in the patient’s abdomen. The major contribution of defibrillators is that have greatly improved the ability of patients to survive different cardiac conditions (heart surgery, heart attacks, etc.) where the heart can potentially go into ventricular fibrillation. Since the 1970s, most hospital emergency rooms have been equipped with electric defibrillators, and portable devices have becoming standard equipment for ambulances. A recent medical advance is the growth of automated external defibrillators (AEDs), lightweight, portable, user-friendly devices can be found in police cars, stadiums, etc. These devices can be used with minimal training; specifically, they provide audio instructions and visual prompts to walk the operator through the defibrillating process.
Scientific Principle Behind Defribillator
Defribillation is based upon the understanding that contraction of the heart, and the resulting circulation is under the control of electrical conduction system of the heart.
Defibrillation is based upon the understanding that contraction of the heart, and the resulting circulation, is under the control of the electrical conduction system of the heart.
The sinoatrial node, (SAN) located within the wall of the right atrium, normally generates electrical impulses that are carried by special conducting tissue to the atrioventricular node (AVN).
Upon reaching the AVN, located between the atria and ventricles, the electrical impulse is relayed down conducting tissue (bundle of HIS) that branches into pathways that supply the right and left ventricles. These paths are called the right bundle branch (RBBB) and left bundle branch (LBBB), respectively. The left bundle branch further divides into two sub branches (called fascicles).
Electrical impulses generated in the SAN cause the right and left atria to contract first. Depolarization (heart muscle contraction caused by electrical stimulation) occurs nearly simultaneously in the right and left ventricles 1-2 tenths of a second after atrial depolarization. The entire sequence of depolarization, from beginning to end (for one heart beat), takes 2-3 tenths of a second.
The SAN is known as the "heart's pacemaker" because electrical impulses are normally generated here. At rest, the SAN usually produces 60-70 signals a minute. It is the SAN that increases its rate due to stimuli such as exercise, stimulant drugs, or fever.
Should the SAN fail to produce impulses the AVN can take over. The resting rate of the AVN is slower, generating 40-60 beats a minute. The AVN and remaining parts of the conducting system are less capable of increasing heart rate, due to stimuli previously mentioned, than the SAN.
Problems with signal conduction, due to disease or abnormalities of the conducting system, can occur any place along the heart's conduction pathway. Abnormally conducted signals, or arrhythmias, result in alterations of the heart's normal beating. This is visualized on the electrocardiogram (EKG).
There are three major components to consider when studying a defibrillator: a capacitor, an inductor, and a power supply.
These three components will be explored in depth. Specifically, the interaction between these three components is what allows defibrillators to effectively restore proper cardiac rhythms.
I.) Capacitors: One of the key components of a defibrillator is a capacitor. The capacitor of a defibrillator stores a large amount of energy in the form of electrical charge. Then, over a short period of time, the capacitor releases the stored energy. The capacitor itself contains numerous components: a pair of metal plate conductors and an insulator. The insulator is in the middle of the conductors and does not loose electrons. On the other hand, conductors easily loose electrons and promote current flow.
When the switch is in position 1, direct current from the power supply is applied to the capacitor and electrons flow. Therefore current flows and a charge begin to build up on each electrode of the capacitor. Specifically, the lower plate is more negative and the upper plate is more positive. The build-up of opposing charges creates a potential difference across the plates (V) that opposes the electromagnetic force of the power supply
(E).
II.) Inductors: Defibrillators are needed to shock the heart back in regular rhythm. Thus, the current that is delivered must last for a several milliseconds. However, a discharging capacitor delivers charge and current very fast. Inductors, coils of wire that produce a magnetic field when current flows through them, prolong the duration of current flow. Specifically, inductors generate electricity that opposes the motion of current passing through it. This opposition is called inductance. Inductors typically have values of microhenries (µH). III.) Power Supply: Step-up transformers are transformers that increase voltage. In the case of defibrillators, step-up transformers are used to convert the main voltage of 240 V AC to 5000 VAC. A step-up transformer is used in defibrillators because this allows the doctor to choose among different amounts of charge. The control switch is calibrated in energy delivered to the patient (J), because this determines the clinical effect or physical impact that a patient will experience. As an additional energy source, many defibrillators also have internal rechargeable batteries.
TYPES OF DEFIBRILLATORS
There are four major categories of defibrillators:
1. Advanced Life Support (ALS) Units
ALS defibrillators, used by healthcare professionals in hospitals and ambulances, allow professionals to monitor the patient rhythm and manually intervene if it is determined that a shock is required. In addition, most of these units offer an Advisory or AED function, in which waveform analysis and shock recommendations are made based upon sophisticated algorithms contained within the device.
ALS units can be used with either paddles or electrodes, though the trend today is to use the defibrillation electrode as it is much safer for the rescuer and delivers the shock more uniformly and effectively.
A growing number of ALS defibrillators now also provide support for cardiac compressions. It has become exceedingly clear that good CPR is vital to improving resuscitation outcomes; it has also been determined that delivering good consistent CPR is difficult – even for highly trained professionals. Therefore, there is growing acceptance of the need for defibrillation products to not only be capable of delivering a shock, but also capable of assisting with delivery of optimal circulatory support.
2. Automatic External Defibrillators (AEDs)
SCA Survivor Stories and AED NewsThese units are designed for use by laypersons and basic life support-trained personnel. They are widely available in airports, schools, casinos and other public areas. They guide users through the application of the electrodes and automatically analyze the patient’s rhythm and either tell the rescuer to deliver a shock, or actually deliver the shock automatically. Many will also tell bystanders to start CPR, but only one AED, the ZOLL AED Plus currently coaches rescuers to deliver the correct rate and depth of compressions via the use of an accelerometer built into the electrode pad. As the importance of CPR delivery is increasingly realized to be a critical part of a successful rescue, this capability will most likely expand to other manufacturers.
3. Implantable Cardioverter Defibrillators (ICDs)
Type5These units are implanted directly into the patient’s chest and designed to protect those patients at high risk of sudden death. Generally, these are patients who have either a known medical condition that puts them at risk, or have actually experienced an episode of VF/VT. These products are beyond the scope of this website, and an in-depth discussion of these products can be found at the manufacturers' websites highlighted in the links to the right. 4. Wearable Defibrillators
These are an intermediate care option for patients with a short-term known risk of sudden death or who are not candidates for an implantable device. They are discussed more fully in the wearable defibrillator section of this website.
Resources:
The American Heritage® Dictionary of the English Language, Fourth Edition copyright ©2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
American Heart Association Official Website
http://www.resuscitationcentral.com/defibrillation/als-aed-icd-wearable-defibrillators/
Definition
An electronic device that administers an electric shock of preset voltage to the heart through the chest wall in an attempt to restore the normal rhythm of the heart during ventricular fibrillation. Defibrillation is a procedure used to treat life threatening conditions that affect the rhythm of the heart such as cardiac arrhythmia, ventricular fibrillation and pulseless ventricular tachycardia.
The procedure involves the delivery of an electric shock to the heart which causes depolarisation of the heart muscles and re-establishes normal conduction of the heart’s electrical impulse. The machine used to deliver this therapeutic shock to the heart is called a defibrillator.
Defibrillators are key devices in maintaining …show more content…
proper cardiac function. A bit of background in cardiology will aid in the understanding of the role of defibrillators. First, ventricular fibrillation is a cardiac condition where individual heart muscles contract in a random, uncoordinated way. The heart seems to shiver, and blood circulation stops. The application of an electric shock to restore normal heart function is the only way to effectively treat a ventricular fibrillation and prevent death.
History
Key milestones occurred in the invention and development of the modern day defibrillator:
* In 1899 by French physiologists, Jean Louis Prevost and Frederic Battelli, were able to stop ventricular fibrillation in a dog by applying an electric shock to the animal's exposed heart. * In 1930, William B. Kouwenhoven, an American electrical engineer at Johns Hopkins University, and colleagues developed a closed-chest defibrillator that sent alternating current (AC) electrical shocks to the heart through electrodes placed on a dog's chest. * In 1947, Claude Beck, professor of surgery at Case Western Reserve University, first successfully resuscitated a human patient by internal cardiac massage and electrical defibrillation. * In 1961, American cardiologist Paul Zoll applied AC defibrillation to human patients in 1961. * In 1962, the direct current (DC) defibrillator was introduced by Lown and Neuman in 1962 provided greater reliability and safety. * In 1985, an implantable device, called the automatic implantable cardioverter defibrillator (AICD) to stop heart arrhythmias that was invented by Dr. Mieczyslaw Mirowski, of Johns Hopkins University received FDA approval. The device had dual tasks: the defibrillator jolts the heart out of ventricular fibrillation and the cardioverter shocks the heart out of an abnormally fast heartbeat. A heftier power pack is needed and so the battery is implanted in the patient’s abdomen. The major contribution of defibrillators is that have greatly improved the ability of patients to survive different cardiac conditions (heart surgery, heart attacks, etc.) where the heart can potentially go into ventricular fibrillation. Since the 1970s, most hospital emergency rooms have been equipped with electric defibrillators, and portable devices have becoming standard equipment for ambulances. A recent medical advance is the growth of automated external defibrillators (AEDs), lightweight, portable, user-friendly devices can be found in police cars, stadiums, etc. These devices can be used with minimal training; specifically, they provide audio instructions and visual prompts to walk the operator through the defibrillating process.
Scientific Principle Behind Defribillator
Defribillation is based upon the understanding that contraction of the heart, and the resulting circulation is under the control of electrical conduction system of the heart.
Defibrillation is based upon the understanding that contraction of the heart, and the resulting circulation, is under the control of the electrical conduction system of the heart.
The sinoatrial node, (SAN) located within the wall of the right atrium, normally generates electrical impulses that are carried by special conducting tissue to the atrioventricular node (AVN).
Upon reaching the AVN, located between the atria and ventricles, the electrical impulse is relayed down conducting tissue (bundle of HIS) that branches into pathways that supply the right and left ventricles. These paths are called the right bundle branch (RBBB) and left bundle branch (LBBB), respectively. The left bundle branch further divides into two sub branches (called fascicles).
Electrical impulses generated in the SAN cause the right and left atria to contract first. Depolarization (heart muscle contraction caused by electrical stimulation) occurs nearly simultaneously in the right and left ventricles 1-2 tenths of a second after atrial depolarization. The entire sequence of depolarization, from beginning to end (for one heart beat), takes 2-3 tenths of a second.
The SAN is known as the "heart's pacemaker" because electrical impulses are normally generated here. At rest, the SAN usually produces 60-70 signals a minute. It is the SAN that increases its rate due to stimuli such as exercise, stimulant drugs, or fever.
Should the SAN fail to produce impulses the AVN can take over. The resting rate of the AVN is slower, generating 40-60 beats a minute. The AVN and remaining parts of the conducting system are less capable of increasing heart rate, due to stimuli previously mentioned, than the SAN.
Problems with signal conduction, due to disease or abnormalities of the conducting system, can occur any place along the heart's conduction pathway. Abnormally conducted signals, or arrhythmias, result in alterations of the heart's normal beating. This is visualized on the electrocardiogram (EKG).
There are three major components to consider when studying a defibrillator: a capacitor, an inductor, and a power supply.
These three components will be explored in depth. Specifically, the interaction between these three components is what allows defibrillators to effectively restore proper cardiac rhythms.
I.) Capacitors: One of the key components of a defibrillator is a capacitor. The capacitor of a defibrillator stores a large amount of energy in the form of electrical charge. Then, over a short period of time, the capacitor releases the stored energy. The capacitor itself contains numerous components: a pair of metal plate conductors and an insulator. The insulator is in the middle of the conductors and does not loose electrons. On the other hand, conductors easily loose electrons and promote current flow.
When the switch is in position 1, direct current from the power supply is applied to the capacitor and electrons flow. Therefore current flows and a charge begin to build up on each electrode of the capacitor. Specifically, the lower plate is more negative and the upper plate is more positive. The build-up of opposing charges creates a potential difference across the plates (V) that opposes the electromagnetic force of the power supply
(E).
II.) Inductors: Defibrillators are needed to shock the heart back in regular rhythm. Thus, the current that is delivered must last for a several milliseconds. However, a discharging capacitor delivers charge and current very fast. Inductors, coils of wire that produce a magnetic field when current flows through them, prolong the duration of current flow. Specifically, inductors generate electricity that opposes the motion of current passing through it. This opposition is called inductance. Inductors typically have values of microhenries (µH). III.) Power Supply: Step-up transformers are transformers that increase voltage. In the case of defibrillators, step-up transformers are used to convert the main voltage of 240 V AC to 5000 VAC. A step-up transformer is used in defibrillators because this allows the doctor to choose among different amounts of charge. The control switch is calibrated in energy delivered to the patient (J), because this determines the clinical effect or physical impact that a patient will experience. As an additional energy source, many defibrillators also have internal rechargeable batteries.
TYPES OF DEFIBRILLATORS
There are four major categories of defibrillators:
1. Advanced Life Support (ALS) Units
ALS defibrillators, used by healthcare professionals in hospitals and ambulances, allow professionals to monitor the patient rhythm and manually intervene if it is determined that a shock is required. In addition, most of these units offer an Advisory or AED function, in which waveform analysis and shock recommendations are made based upon sophisticated algorithms contained within the device.
ALS units can be used with either paddles or electrodes, though the trend today is to use the defibrillation electrode as it is much safer for the rescuer and delivers the shock more uniformly and effectively.
A growing number of ALS defibrillators now also provide support for cardiac compressions. It has become exceedingly clear that good CPR is vital to improving resuscitation outcomes; it has also been determined that delivering good consistent CPR is difficult – even for highly trained professionals. Therefore, there is growing acceptance of the need for defibrillation products to not only be capable of delivering a shock, but also capable of assisting with delivery of optimal circulatory support.
2. Automatic External Defibrillators (AEDs)
SCA Survivor Stories and AED NewsThese units are designed for use by laypersons and basic life support-trained personnel. They are widely available in airports, schools, casinos and other public areas. They guide users through the application of the electrodes and automatically analyze the patient’s rhythm and either tell the rescuer to deliver a shock, or actually deliver the shock automatically. Many will also tell bystanders to start CPR, but only one AED, the ZOLL AED Plus currently coaches rescuers to deliver the correct rate and depth of compressions via the use of an accelerometer built into the electrode pad. As the importance of CPR delivery is increasingly realized to be a critical part of a successful rescue, this capability will most likely expand to other manufacturers.
3. Implantable Cardioverter Defibrillators (ICDs)
Type5These units are implanted directly into the patient’s chest and designed to protect those patients at high risk of sudden death. Generally, these are patients who have either a known medical condition that puts them at risk, or have actually experienced an episode of VF/VT. These products are beyond the scope of this website, and an in-depth discussion of these products can be found at the manufacturers' websites highlighted in the links to the right. 4. Wearable Defibrillators
These are an intermediate care option for patients with a short-term known risk of sudden death or who are not candidates for an implantable device. They are discussed more fully in the wearable defibrillator section of this website.
Resources:
The American Heritage® Dictionary of the English Language, Fourth Edition copyright ©2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
American Heart Association Official Website
http://www.resuscitationcentral.com/defibrillation/als-aed-icd-wearable-defibrillators/