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electro-stimulator

Muscular Electrostimulation

BackGround

The application of an electrical current escapes from depolarizing the membrane of the muscular or nervous fiber and artificially produces its excitation.

Figure 1: Principle of selective stimulation of the denervated musculature 

It is a technique that involves applying an electric shock directed at a particular muscle, to produce a controlled contraction. It is a therapeutic means, since it controls the work of the muscular fibers with an aim: to repair damaged tissues, to avoid degenerations and / or to avoid traumatisms.

Electrotherapy, employing low-volt, low-frequency impulse currents, has become an accepted practice in the physiotherapy departments. The biological reactions produced by low-volt currents have resulted in the adoption of this therapy in the management of many diseases affecting muscles and nerves. The technique is used for the treatment of paralysis with totally or partially degenerated muscles, for the treatment of pain, muscular spasm and peripheral circulatory disturbances, and for several other applications. Different types of waveforms are used for carrying out specific treatments.The most commonly used pulse waveforms are discussed below. 

Figure 2: Different types of waveforms

Galvanic Current: When a steady flow of direct current is passed through a tissue, its effect is primarily chemical. It causes the movement of ions and their collection at the skin areas lying immediately beneath the electrodes. The effect is manifested most clearly in a bright red coloration which is an expression of hyperaemia (increased blood flow). Galvanic current is also called direct current, galvanism, continuous current or constant current.

Faradic Current: Faradic current is a sequence of pulses with a defined shape and current intensity. The pulse duration is about 1 minute with a triangular waveform and an interval duration of about 20 minutes. Faradic current acts upon muscle tissue and upon the motor nerves to produce muscle contractions. There is no ion transfer and consequently, no chemical effect. This may be used for the treatment of muscle weakness after lengthy immobilization and of disuse atrophy.

Surging Current: If the peak current intensity applied to the patient increases and decreases rhythmically, and the rate of increase and decrease of the peak amplitude is slow, the resulting shape of the current waveform is called a surging current. The main field of application of the Faradic surge current is in the treatment of functional paralysis. The surge rate is usually from 6-60 surges per minute in most of the instruments. The ratio of interval to the duration of the surging is also adjustable so that graded exercise may be administered. This type of current is usually required for the treatment of spasm and pain.

Exponentially Progressive Current: This current is useful for the treatment of severe paralysis. The main advantage of this method lies in the possibility of providing selective stimulation (Fig. 1) for the treatment of the paralysed muscles. This means that the surrounding healthy tissues even in the immediate neighbourhood of the diseased muscles are not stimulated. The slope of the exponential pulse is kept variable.

Analgesic currents stimulation sensitive afferent nerve fibers. Excitomotor currents stimulation of motor efferent fibers.

The type of frequency selected is the key to indicate to the body what type of fiber to activate essentially:

Table 1: Frequency types and their effects

TENS (Transcutaneous Electrical Nerve Stimulation)

Figure 3: Analgesic electrotherapy application

Depolarization of the peripheral sensory nerves to cause, fundamentally, pain reduction.Electrotherapy by TENS modality presents different modalities such as:

• Conventional or high frequency
• Low frequency
• Low frequency in trains or gusts
• Brief or intense

High frequency: Place the electrodes directly on the area painful or also on nervous path, trigger points, acupuncture points, dermatome, contralateral limb. Tickling sensation.

Low frequency: On a muscle of the myotome belonging to the same metamera as the origin of the pain or at the motor point of the muscle. Visible muscular contraction (without movement).

Precautions:

• Proper preservation of electrodes.

• Wet and well rinsed pads

• Good electro-leather contact

• Good skin condition (erosions and wounds)

Contraindications TENS:

• Pacemakers, stimulators (Parkinson's, incontinence)

• Anesthesia or hypoesthesia of the skin.

• Lack of patient cooperation (elderly, children)

• Neoplasms.

• Infections and acute inflammatory processes.

• Precordial zone, carotid sinus, larynx.

• Pregnancy (relative contraindication).

• Gynecological pathologies (metrorrhagia), in applications ABS.

• Epilepsy (relative contraindication).

• Osteosynthesis and metallic stents (non-compensated pulses).

Desing

The design of the electro stimulator is composed of a LM555 timer which will allow us to generate square pulses at different frequencies by the capacitor located in the threshold and potentiometer located in the Discharge, using the equation

And so with the help of this formula and putting a capacitor of 100µF and an R1 100Ω is calculated The value Of the potentiometer to obtain frequencies between 6Hz and 100Hz, and thus it was obtained that the potentiometer should be of 1kΩ getting

Already obtained the frequencies we proceed to manipulate the intensity of operation, this was made daring of a optocoupler, which in turn allowed to make protection to the patient because it performs an isolation of lands, to regulate the intensity It is made by a potentiometer located in the collector of the phototransistor that composes to the optocoupler, for the isolation is done locating the negative part of the diode towards the ground of the circuit and the transmitter of the phototransistor to another Earth, obtaining So the following convention.

Frequency	CORREINTE
6Hz	0.05 mA
100Hz	27th

Results 

In figure four and five, the output signal generated by the circuit implemented with a 555 circuit can be observed. The output frequencies are between 6 and 104 Hertz. To increase the amplitude of the generated signal, an optoacolator powered with 15 volts is used. In this way, a variable current between 0.05 and 0.27 mA is generated. When the signal is amplified with the optocoupler, a small frizzing occurs in the negative part of the signal, as shown in figure 6.

Figure 4:  Signal out of 555.

Figure 5: Signal out of 555.

Figure 6: Signal out optocoupler. ,

Because there was a bad coupling of impedances, when the output signal of the optocoupler was induced to the patient the signal deformed a little, the signal went from being measured to becoming a triangular signal, although this change only occurred at high frequencies, this is due to the impedance of the patient that responds to the change in the frequency of the induced signal. As a solution for the coupling of impedances between the generator circuit of the signal Tens and the patient, a reducer transformer can be used, in addition, to generate an optimal impedance coupling, a circuit of protection to the patient is also being generated. In the implanted circuit an optocoupler was used for the protection of the patient, which is an optimal circuit to generate the protection of the patient, but it is not optimal to generate the coupling of impedances between the patient and the circuit. As the signal is deforming, it was losing its pain treatment properties, so when it reached high frequencies the patient felt itching or tingling.

Figure 7:Figure 8: Output signal with pateint.

Figure 8: Output signal with pateint.

Figure 9: Figure 8: Output signal with pateint.

Conclusions

The signal generated, which is a continuous square wave for treatment of pain through TENS electro-stimulation, is deformed when the circuit is connected to the patient and frequencies greater than 50 Hz are configured, this deformation is possibly generated by the impedance of the patient, for To solve this type of problems, a coupling of impedances between the circuit and the patient must be carried out, for this a transformer can be used, such that the patient is totally isolated from the circuit.

Bibliography

• Webster, J. G.(2006). Encyclodedia of Medical devices and instrumentation. John Wiley & sons, Inc.Khandpur, R.S. 2014. Handbook Of Biomedical Instrumentation, Third Edition. India. McGraw Hill Education.
• Barbara H. Estridge, Anna P. Reynolds, Norma J. Walters (2000). Basic Medical Laboratory Techniques. Cengage Learning.

DEFIBRILLATOR AND PACEMAKERS

DEFIBRILLATOR AND PACEMAKERS

BackGrounds

PACEMAKER

It is a small device operated with batteries. Notice when the heart is beating irregularly or very slowly. This is the correct message.

Figure 1: Transcutaneous pacemaker

Figure 2: External Pacemaker

External pacemakers are employed to restart the normal rhythm of the heart in cases of cardiac standstill, in situations where short-term pacing is considered adequate, while the patient is in the intensive care unit or is awaiting implantation of a permanent pacemaker. Frequently, external pacemakers are used for patients recovering from cardiac surgery to correct temporary conduction disturbances resulting from the surgery. As the patient recovers, normal conduction returns and the use of pacemakers is discontinued.

The pacing impulse is applied through metal electrodes placed on the surface of the body. Electrode jelly is used for better contact and to avoid burning of the skin underneath. An external pacemaker may apply up to 80-mA pulses through 50-cm electrode on the chest. This procedure is painful and therefore is used only in an emergency or a temporary situation. The pulses may be delivered:

• Continuously: When it is felt that the heart rate is below the pre-set value. The impulse frequency is independent of the electrical activity of the heart.

Figure 3: Continuous Pulse

• On demand R: synchronous wave stimulation. Normally, the pacemaker does not work, but it is activated when the heart rate falls below the normal or preset value. In such a situation, a beat-to-beat examination of the time interval between two R waves is performed. When this interval exceeds the preset value, the pacemaker becomes operational.

There are three types of pacemakers based on the type of output waveform  These are:

Voltage Pacemakers: 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 from the pacemaker remains constant and changes of resistance in the circuit will influence only the current.

Figure 4: Voltage Pacemaker

Current Pacemakers: In current pacemakers, throughout the impulse, the current in the circuit is determined by the internal resistance of the pacemaker.

Figure 5: constant current type pacemaker

Current Limited Voltage Pacemakers: This is primarily a voltage circuit, but the maximum current in the circuit is limited, preventing too large a current impulse to circulate when there is a low resistance in the electrode circuit. With these pacemakers, during the first part of the impulse, the current in the circuit is determined by the internal resistance of the pacemaker (constant current type) but during the second part of the impulse, the current in the circuit is determined by the voltage available (constant voltage version).

By download

Single phase: it has a current that is carried out in only one direction, which means a high dose of shock in three shocks of 200, 300 and 360 joules.

Biphasic: these are more advanced defibrillators. This means that they need up to 40% less energy and consequently produce less myocardial damage. It is a double current, because it changes polarity during the crash, with an administration of three shocks of 150. They are more efficient defibrillators and have lower energy expenditure.

Figure 7: Defibrillation by download

Type of user

Manuals: must be used by qualified personnel due to their complex functions. Only trained health personnel are authorized to use it in Europe.

Automatic: these types of defibrillators apply the discharge without prior notice, which is very dangerous for the person assisting the victim. They are increasingly disused by this aspect, but their DEA terminology is still used, since they were the only external defibrillators used in the past.

Semiautomatics: these are types of defibrillators for public use, which warn at the time of discharge and indicate that you have to separate from the patient by pressing the button that will activate the defibrillation. They are devices that require little training by the user. The device indicates the steps to be followed through sound and visual instructions.

INTERNAL DESFIBRILLATOR

Internal defibrillator or DAI (implantable cardioverter defibrillator), is the one that is implanted in the person, There are several types of DAI:

Monocameral DAI: acts only in a cardiac chamber with a pulse generator and an electrode in the right ventricle.

Bicameral DAI: acts in two chambers of the heart with a pulse generator and two electrodes, one the right ventricle and one in the right atrium.

tricameral DAI: acts in three chambers to treat ventricular arrhythmias and heart failure.

Figure 8: Internal Desfibrillator

Desing

In Figure 9 we observe the electrical circuit diagram used to perform an asynchronous pacemaker at 60 hertz and a defibrillator with two different discharge levels. To generate the pulse, the Arduino Uno board was used, a logical one (5 volts) was generated for 40 milliseconds and a logical zero (0 volts) for 960 milliseconds. At the output of pin two of the arduino a voltage divider was coupled with a potentiometer and a fixed resistance, in this way the amount of voltage supplied to the patient is varied. To simulate the patient a wave generator is used, the simulated ECG signal enters a non-inverting adder amplifier circuit with gain one, together with the generated pulse that comes from the Arduino Uno board. To create the different discharge values for the defibrillator, capacitors connected to a diode in series were used, so when loading and unloading, different load values were generated, since depending on where the selector was located, the patient received more or less voltage, that is to say, the more capacitors I had in series, the more charge they evicted, therefore, the more charge they released. Finally, to select the mode, a three-position selector is used to choose the mode: pacemaker, defroster or off.

Fugure 9: Electrical diagram of the pacemaker and the defibrillator.

Results

After carrying out the previous theoretical consultation of the operation of a pacemaker and a defibrillator, it was carried out its implementation which consisted of two parts. The first one is the pacemaker, which had an operation that consisted of an asynchronous one, that is, the stimulation is done at a constant frequency in this design was made at a frequency of 60 ppm which is equivalent to a frequency of 1 Hz because the pathology that was wanted to regulate are bradycardia, the pulse was sent by a microcontroller, Arduino each pulse has a duration of 40ms this is to what is established in the manuals, later to generate the pulse as shown in figure 1 psterior to this was done to show the pulse on the ECG signal obtained from the generator at a frequency of 500mHz as shown in figure 2.

figure 1,2

the second part was to perform the defibrillator which consists of making a discharge to different jouls, these charges were made by loading and unloading a capacitor and a discharge time calculated by means of the equation 1

t = R * C

t = 10k * 4,7uF

t = 40ms

this means that the discharge time is 40 ms as recommended in the bibliography, the charges were 12.8V and 13V

loading to nd unloading was done manually with the help of a push button. The results can be seen in figure 3 and 4.

figure 3

figure 4

Conclusions

An asynchronous pacemaker can bring different problems such as uncoordination between ventricles and atria, waste of the battery, blood flow does not depend on exercise, among others. Even in some patients it can cause fibrillation, for this reason only used externally because they are used when they are in a medical center and its use is transient.

Ventricular fibrillation (VF) is the initial rhythm in up to 90% of adult CRPs, the only effective treatment of VF is defibrillation.

It can be concluded that a defibrillator is currently very important because it can reverse some deadly damage to the heart for this reason today it is looking to improve it, that is why it is important to understand its operating principle when the time comes to manipulate it, let's know how.

BIBLIOGRAPHY

Lifetime; types of defibrillators, (2017), taken online from: https://www.desfibrilador.com/desfibrilador/tipos-de-desfibriladores/, consulted: 05/12/2019.
Webster, J. G. (2006). Encyclodex of Medical devices and instrumentation. John Wiley & sons, Inc.
Daneri, P. (2007). Electromedicine Diagnostic and Intensive Care Equipment. Editorial HASA.