DEFIBRILLATOR - PART 2

Hi friends!!!

In our previous blog we have discussed about the concept of defibrillator.

Check out for this blog:

DEFIBRILLATOR – PART 1.

https://biomedicalviews.blogspot.com/2020/05/defibrillator-part-1_31.html?m=1

Our today’s content is the extension of PART 1 and we are going to discuss about types of defibrillator.

Let’s get into the topic with a defibrillator definition.

WHY DEFIBRILLATOR?

Defibrillator is an electronic device used to deliver electric shock to the patients to restore the rhythm of the heart. The basic function of the heart is to pump the blood and there is a term called VENTRICULAR FIBRILLATION which means abnormal heart rhythm where the ventricles of the heart quiver instead of pumping the blood normally. So to avoid this issue electric shock is given using defibrillator machine.

Image courtesy: Wikimedia Commons

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WHAT ARE THE TYPES OF DEFIBRILLATOR?

During defibrillation, the current that goes through the heart changes over time. And OSCILLOSCOPE is used in defibrillator circuit to study the flow of current over time. It plots the graph of current over time.

The following are the types of defibrillator.

MONOPHASIC DEFIBRILLATOR

Monophasic defibrillator is one of the types of defibrillator in which the  discharge of current flows in one of the two directions (forward direction or reverse direction) as shown in the image below.

Oscilloscope waveform for current flowing in forward direction and reverse direction.

As you can see in both of the above waveform, oscilloscope has never gone below the baseline 0. It means the discharge of current has taken place in only one of the two direction.

Monophasic defibrillator circuit includes inductor in the circuit to reduce the peak current discharge and spreading it over a longer time.

BIPHASIC DEFIBRILLATOR

Biphasic defibrillator is one of the types of defibrillator which discharges the current in both forward and reverse direction.

These types of defibrillator has four stages Forward current, Switching interval, Reverse current, Truncation as shown in the image below.

Similar to monophasic defibrillator, initially current is discharged in forward direction. During this time switch 1 and 4 are turned ON. However before the complete discharging of the capacitor, these two switches are turned OFF. Now there is some current still left in the capacitor to discharge. After switching off the 1 and 4 switches, defibrillator now turns ON the 2 and 3 switches.

The time gap between turning OFF of 1 and 4 switches & turning ON of 2 and 3 switches is called switching interval. This interval is for the purpose of proper turning off of 1 and 4 switches & proper turning on of 2 and 3 switches.

After switching interval, the remaining current in the capacitor is discharged in reverse direction. In reverse direction current gradually decrease and reaches the baseline. But only half of the reverse direction discharge has suitable high current to cause defibrillation of heart. The remaining low energy current can cause further problem in fibrillation of the heart. So in order to avoid low energy current near baseline, discharge of current is suddenly truncated.

During truncation, switch 1 is turned ON. Now the current flows through switches 1 and 4, this creates the short circuit and excess current is dissipated in the form of heat.

 Now I hope you have acquired fair amount of knowledge about types of defibrillator. 

Check out for DEFIBRILLATOR – PART 1 in the link given at the top of this page.

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