Automated external defibrilator and pacemaker

Glossary:

Cardiac WaveForm: Characteristic electrical signal, that allow recognize the electrical heart function.

Image1. heart waveform.

Power: The power is the rate that energy is consumed.

Energy: The energy is the cuantitive propiety that can be transfered from an object to other.

Automated External Defibrilator (AED):

The Automated External Defibrilator is a medical device that analyze and look for defribillable rhythms, the device notify to the rescuer and if is necessary apply the shock.

Actually exist 2 kind of  defibrilators, monophasic defirbilator and biphasic defibrilator.

The monophasic defibrilator use current in only one way, for this is necessary a high energy near the 200, 300 and 360 joules.

The biphasic defibrilator use double current, in other words the current travel from one electrode to other and return to the first electrode. 

Image2. Current travel respresentation.

The main parts of a defibrillator are :

1.  On / Off button.
2.  Shock button.
3.  Display.
4.  Electrode connector.
5.  Battery indicator.
6.  Piece to load.

image3. AED interface.

PaceMaker:


The pacemaker is a little device that sense when the heart have a irregular or slow  beat,  then the pacemaker send a signal that correct the heart beating.

The pacemaker is located under the patient skin, generally is under the collarbone.

Image4. Pacemaker implanation.

Circuit desing:


To develop an AED is necessary consider the voltage that we can use, the capacitor charge and discharge time.

Image5. Simple AED circuit.

To calculate the charge time its necessary use the following fromula:

To load 63% : T = Rs*C

To load 99% : 5*T = charge time

where charge time > 2 seconds. 

The AED allow deal 3 discharges with different energy, to this the device uses different load times.

To calculate the discharge time its necessary use the same formula but use less time. Discharge time is between 10 and 50 miliseconds.

To our desing we use a voltage multiplier to get higher voltage.

image6. Voltage mutiplier.

At the output we use a relay to switch the power supply and the patient. In the next image we can see the proteus simulation of our circuit:

Image7. Proteus schematic circuit.

You can get the proteus file here: AED Proteus PCB

Image6. PCB AED circuit.

You can get the arduino code from here: Arduino code for AED

We obtained the next results.

Image7. Defibrilator model.

Image8.  Ventricular tachycardia.

Image9. Normal ECG signal.