Electrostimulator

Operating principle
It is a device designed to recruit muscle fibers by electrical impulses in an involuntary way. Where a stimulus is sent directly to the motor plate that causes a muscle contraction without receiving the previous order of the central nervous system. Its operation is through programs already integrated, focused on different objectives. The frequency in electrical stimuli is measured in Hz, depending on the frequency that we apply we will achieve one or the other result, according to our needs.

The types of waveforms required for electrodiagnosis are:

• Galvanic current for the qualitative and quantitative determination of galvanic excitability.
• Rectangular pulses to control nerve conduction as a function control.
• Exponentially progressive current to verify the capacity of adaptation or its loss as a symptom of the degree of degeneration and for the prognosis of the reinnervation of totally denervated muscles.
• Faradic current for qualitative and quantitative determination of faradic excitability.

Figura 1. Formas de onda de corriente normalmente empleadas en electrodiagnóstico y electroterapia: (1) galvánico (2) Faradic (3) exponencial (4) pulso rectangular con pendiente ajustable (5) surgido Faradic.

Figura 2. Diagrama esquemático de una unidad estimulante de diagnóstico / terapéutica [5] 

Types of electrostimulators

There are three types of electrostimulators which are:

• Transcutaneous Electrical Nervous Stimulation (TENS): These are designed to treat injuries through sensory nerve stimulation. They produce square wave form, have a pulse frequency range of 20-200 Hz, pulse width of 0.1 to 1.0 ms and pulse amplitude of 0-120 V with a maximum output current of 25 mA.

• Spinal cord stimulator: This is related to the use of electrical stimulation of the human spinal cord for pain relief. Applied electrical impulses develop an electric field in and around the spinal cord, which then causes depolarization or activation of a part of the nervous system that results in physiological changes.

• Magnetic stimulation: The pain is not very different from that induced by the stimulation of the peripheral nerves, but it is enough to limit its clinical acceptability. A magnetic pulse is generated by passing a short high current pulse through a cable coil. Where its advantage is that the stimulation is almost painless.

RESULTS

For the design of the electrostimulator, two oscillators were implemented with a monostable way, in the figure 1 it can be seen to the left of the schematic diagram of the circuit made and the right of the scheme the circuit design on pcb, can be seen a power transistor 3053 and a winding (for this case a transformer) which controlled the passage of current to the patient, the system was designed with the aim of pain therapy, emulating the well-known tens.

Figure 3. Schematics of the electro-stimulator

For the implementation it is possible to visualize in figure 2 the PCB circuit inside its corresponding structure, two output potentiometers were used as rotary controls, a led indicator and the system output connected to the patient, below this as a design issue was the transformer, the prototype was implemented with terminals in the pcb as an option for better development in case of unforeseen events.

Figure 4.  Implementation of the electro-stimulator as tens equipment.