Science & Technology in Action

7th Edition

Defibrillators and How They Work

Boston Scientific

Defibrillators have been in use for about sixty years. The earlier machines were comparatively large and not really portable. Emergency portable defibrillators (also called AEDs or automatic external defibrillators) are today available in many public buildings, schools, clubs etc.
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Contains the full lesson along with a supporting toolkit, including teachers’ notes.

Lesson excerpt

The Normal Heart-Beat Cycle
The cardiac cycle has two distinct phases – the diastole phase and the systole phase. In the diastole phase, the heart ventricles are relaxed and fill with blood. In the systole phase, the ventricles contract and pump blood around the body through a system ofarteries.

These events are triggered by the sinoatrial node – a collection of modified myocytes that acts as the heart's pacemaker.

Ventricular Fibrillation
Normally the pulse rate (heartbeat rate) is appropriate for the body's oxygen demand. Problems can arise if the heart rate is too low or too high. If the speed is very high it can lead to ventricular fibrillation (VF) in which the heart muscle quivers and does not pump efficiently, if at all. This condition is generally fatal if not treated quickly.

Normal heart-beat can be restored by delivery of a controlled electric shock. This process is called defibrillation.

What is a Defibrillator?
Defibrillators have been in use for about sixty years. The earlier machines were comparatively large and not really portable. Emergency portable defibrillators (also called AEDs or automatic external defibrillators) are today available in many public buildings, schools, clubs etc. and small defibrillators can now be implanted surgically in patients with certain chronicheart problems.

Quiz questions

  1. The cardiac cycle has two distinct phases — the diastole phase and the systole phase. true
  2. The cardiac cycle is triggered by the sinoatrial node. true
  3. Normally the heart rate is independent of the body's oxygen requirement. false
  4. Ventricular fibrillation occurs when the heart rate is too low. false
  5. Defibrillation involves the delivery of a controlled electric shock. true
  6. Sensors in modern defibrillators can detect the cardiac rhythm and can deliver the most appropriate shock, if required. true
  7. A transformer is used to convert ac to dc. false
  8. The capacitance of a capacitor is inversely proportional to the area of the plates. false
  9. The energy delivered by the shock from a typical defibrillator is about 125 joules. true
  10. Defibrillators are also known as AEDs true