Pacemaker and Defibrillator

Operating principle pacemaker

It is an instrument that regulates the heart rate by means of impulses of external electrical stimulation when the sinoatrial area is affected whether it stops working or stops being reliable or if the triggering pulse does not reach the heart muscle due to the blockage of damaged tissues , the natural and normal synchronization of the action of the heart is altered.

Figure 1. Pacing pulses followed by the QRS complex of the heart

Pacemakers basically consist of two parts, where; the first is the electronic unit that generates the impulses of frequency and controlled amplitude and the second is the cable that transports the electrical impulses to the heart. The waveforms used for stimulation are round rectangular pulses of 1-3 ms duration with adjustable rates of 50-150 pulses per minute.

Types of pacemakers

The different types of pacemakers are based on the method of application of the stimuli to the heart, among these we find:

• External pacemakers: Used to restart the normal heart rhythm in cases of cardiac paralysis, in circumstances where short-term stimulation is considered adequate, while the patient is in the intensive care unit or waiting for the implantation of a permanent pacemaker . This handles pulses of 80 mA through 50-cm2 electrodes in the chest pulses of 80 mA through 50-cm2 electrodes in the chest, these can be delivered: continuously and by synchronous R-wave rhythm on request .

Figure 2. Block diagram of the external pacemaker

• Voltage pacemakers: are those in which the current in the circuit is determined by the available voltage during the entire duration of the impulse. The voltage output of the pacemaker remains constant and changes in resistance in the circuit will only influence the current..

• Current pacemakers: They are characterized since, throughout the impulse, the current in the circuit is determined by the internal resistance of the pacemaker.

• Current limited voltage pacemaker: This is primarily a voltage circuit, but the maximum current in the circuit is limited, which prevents a too large current pulse from circulating when there is low resistance in the electrode circuit. With these pacemakers, during the first part of the pulse, the current in the circuit is determined by the internal resistance of the pacemaker (constant current type) but during the second part of the pulse, the current in the circuit is determined by the available voltage ( constant voltage version).

Figure 3. Impulses of three different types of pacemaker as seen in the oscilloscope: (a) pacemaker of constant current type (b) pacemaker of limited current voltage (c) pacemaker

• Implantable pacemaker: The circuit is designed so that the batteries provide enough energy for a long period. Where its basic requirements are:

•  The components used in the circuit must be highly reliable.
• The power source must be able to supply sufficient power to the circuit for extended periods of time.
• The circuit must be covered with an inert biological material so that the implant is not rejected by the body.
• The unit must be covered in such a way that the bodily fluids do not find a path inside the circuit and, therefore, cause a short circuit in the batteries or a malfunction of the circuit.

In this class of pacemakers we find subtypes that are:

RESULTS

The following figures show the design of the system used to emulate a DEA team, first of all we have a patient simulator which is programmed through vectors in arduino, the signals are sent through a converter from digital to analogo in configuration. r2r, said signals (chosen 4, 2 for a patient in need of defibrillation and 2 in need of a pacemaker) were selected through a dip-switch where the main one would always be the original ecg signal of a patient in optimal states.

Thus in figure 1 is shown in the upper left the design of the converter from the resistances and its control for loading and unloading the capacitor, this had two stages controlled by relays, the first allowed the passage of current to the system and the second positioned the capacitor to perform its charge and after this it is brazing, at the same time a system was designed to deliver a train of pulses of 10ms for the detection of pacemakers, the former designed with an astable circuit 555, in The right part of the figure shows the design for the printed card and subsequent printing.

Figure 1. Schematic design for the aed equipment.

Once the circuit was implemented it was proceeded to it is proof and fine presentation, the system was connected through the arduino with the help of terminals of the pcb, the signal and out of this the patient's condition was selected, the coil of 30mH used for the purpose of the defibrillator, the capacitor of 1000uF allowed a storage of energy according to the needs of the practice, on the other hand the system counted on the distribution of the 555 to accionasrse according to the need of the patient.

Figure 2. Implementation of PCB for aed equipment