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.

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

Hemodialysis Machines

GLOSSARY

Kidneys:                                               

The kidneys remove waste products from the blood and produce urine. As blood flows through the kidneys, the kidneys filter waste products, chemicals and unnecessary water from the blood. There are also products that help control blood pressure and regulate the formation of red blood cells.

Dialyzer:                                               
A machine equipped with a semipermeable membrane, which acts as a filter and is used to perform dialysis.
Pressure:                                               

Force exerting a gas, a liquid or a solid on a surface.

Flow:                                                     

Transport of a fluid across a certain area.

DEVELOP 

It is a technique that replaces the main functions of the kidney, by passing the blood through a filter, dialyzer),among these are:

• Facilitate the removal of toxic substances.
• Remove excess fluid accumulated in the body.
• Help control the pressure
• Arterial helps produce red blood cells.

 Figure 1.  Hemodialysis machine

There are two chemical physical processes included in the dialysis process:

1. Diffusion (depuration of solid substances)
2. Osmosis (osmotic ultrafiltration - water removal).

The operation of the hemodialysis machine focuses on the dialyzer that a cylindrical filter consisting of two compartments, the first is internally formed by hollow semi-permeable microporous fibers, where the blood is circulated; and the other compartment is that which is located within the hollow fibers and the walls of the dialyser since the liquid of the dialysis circulates there. In addition, it pumps and controls the blood flow of the patient through the dialyzer at a predetermined speed and pressure to guarantee effective clearances and the elimination of fluids in a specific period of time. Some machines also provide an ultrafiltration rate that measures the ultrafiltration rate in kilograms per hour. This allows the operator to calculate, predict and control fluid removal efficiently and accurately during dialysis.

 Figure 2.  Parts Hemodialysis machine

Figure 2.  Block diagram of hemodialysis machine

Parameters of a hemodialysis machine

1. The Hemodialysis machine must have at least:

   1.1 Volumetric ultrafiltration control.

   1.2 Automatic supply system for the concentrate mixture

   1.3 Ways to visualize hemodialysis parameters

   1.4 Energy requirement with lines to ground

   1.5 Security devices

       - Air intake detector device

       -Devices for pressure monitoring: In the arterial line: pre-pump and in the venous line: post-dialyzer.

       -Device for dialysate monitoring: Temperature, conductivity and for detection of blood leakage.

       -Alarms: all alarms must be visible and audible: Blood pressure, venous and transmembrane, blood leakage. Of the air detector, Conductivity, flow and temperature of the dialysate.

   1.6 The blood lines must be closed automatically if the circuit is interrupted

  1.7 Blood pump: You must have the option of being operated manually, blood flow in the range of 0 to 500 mL / min. 

    1.8 Heparin pump: With programming capability

Maintenance routine

There are preventive maintenance programs, which include detailed equipment examination, physical condition assessment, mechanical tests, calibrations, lubrication adjustments and safety inspections to ensure proper and safe operation. 

a) Daily inspection or each time the equipment is used Visual inspection before each session Procedure for cleaning after each hemodialysis session. 

b) Weekly inspection (or every 100 hours of work) 

c) Bi-monthly inspection. (or every 400 hours of work)

d) Semi-annual inspection (or every 1200 hours of work) 

e) Annual inspection (or every 2400 hours of work general maintenance and change of some components).

SIMULATION

The simulation was developed in the Labview software designed to perform programming by block diagram, in the panel you can see the use of the Roller pump which allows blood and heparin to flow into the dialyzer, without taking into account the control of the amount of blood extracted from the patient in relation to the amount of heparin delivered. Then, go through the bypass where there will be measured the pressure in which the dialysate is. Then in the lower part you can see the indicators of water, concentration and the degree of warming that the filtered blood can have in order to enter the patient again, where there will also be a blood pressure indicator already filtered. Based on the aforementioned, this simulation was implemented a variety of alarms in which they are:

• The one that indicates that the pH value in blood is not within the established range.

• The one that indicates that the quantity of water supplied is not in the established range.

• The one that indicates that the degree of the heater is not in the established range.

• Dialyzer pressure indicator is too high or too low.

NEWBORN INCUBATOR

GLOSSARY

Temperature:                                        

A magnitude that measures the thermal level or the heat that a body possesses.

PDI Control:                                           
(Proportional-integral-derivative control action), is a control mechanism that through a feedback loop allows to regulate speed, temperature, pressure and flow among other variables of a process in general.
P Control:                                              

(Proportional control action), gives a controller output that is proportional to the error, ie: u (t) = KP.e (t).

PD Control:                                            

(Proportional-derivative control action), this action has a forecast character, which makes the control action faster, although it has the important disadvantage that amplifies the noise signals and can cause saturation in the actuator. The derivative control action is never used by itself, because it is only effective during transient periods.

Humidity:                                              

It is the water vapor contained in the atmosphere.

DEVELOP 

A newborn incubator is a medical device used mainly to generate an ideal environment in which different variables important for the development of newborns are controlled.
The incubator consists of an aseptic chamber for premature babies, its air circulation system in the incubator is designed to give the premature baby an optimal atmospheric pressure, due to the careful control of the temperature and the supply of moisture and oxygen.

 Figure 1. Parts of an newborn incubator

In the incubators that work by thermal convection, the heat generated by the resistance system is transferred to a fluid in this case, which circulates in the incubation chamber, transferring the heat to the samples; The efficiency of this process depends on its flow patterns. In general, the air enters the incubator from the bottom and is heated in a compartment,
from which it flows to the incubation chamber, following uniform flow patterns, to finally go outside through a path located in the upper part of the incubator.

The basic equation that explains the behavior is:

q = hA (TW - Tθ)

where:
q = amount of heat transferred by convection
h = heat transfer convection coefficient
A = area through which the heat transfer is carried out
TW = temperature on the surface of the resistance

Tθ = fluid temperature
Some incubators also have fans that circulate the air, so the convection process is forced. In the diagram presented below, three design criteria used in the incubators are shown: thermal conduction, natural convection and forced convection.

Characteristics:

•Generally the cover is of simple or double acrylic that prevents the losses by radiation and facilitates the continuous observation of the patient.   

• It has different orifices that allow manipulation of the newborn and the entrance of ventilation equipment, monitoring and venous lines for the administration of medicines and parenteral nutrition.

• Modern neonatal incubators have electronic sensors and light screens that allow to continuously know the temperature and humidity ranges.

• They can also count on included scales that avoid excessive manipulation of the patient and filters to purify the air. It is also used in heavier children cribs with radiant heat sources.

Recommendations for use
1. Do not use an incubator in the presence of flammable or combustible materials, because inside the equipment there are components that in operation could act as sources of ignition.
2. Avoid spilling acid solutions inside the incubator. These deteriorate the internal materials of the incubation chamber. Try to handle substances whose pH is as neutral as possible. Avoid incubating substances that generate corrosive fumes.
3. Avoid placing containers on the lower cover that protects the resistive heating elements.
4. Use personal protection items when using the incubator: safety glasses, gloves, tweezers to place and remove containers.
5. Avoid standing in front of an incubator with the door open. Some substances emit fumes or vapors not recommended for breathing.
6. Calibrate the incubator at the installation site to verify its uniformity and stability.
7. Verify the operating temperature of the incubator in morning and evening hours, with certified instruments: thermometer, thermo pair, etc.
8. Record each nonconformity detected in the incubator log. Explain if corrective actions were taken.
9. Verify that the temperature of the incubator does not vary more than one degree centigrade (+/- 1 ° C).
10. Add a non-volatile microbial inhibitor, if a container with water is required to be installed in the incubator to maintain a certain amount of moisture.
Daily maintenance:
The daily care includes the attention of the accesses and the hermetic closures, as well as the ventilators and the anesthesia apparatuses, the incubator has to be checked completely twice a year, and the operation must be verified after each cleaning Observe if:
• It is heated to a fixed temperature and is capable of maintaining it.
• Excessive temperature alarm operates at the corresponding level.
• All quadrants give correct values.

RESULTS

For the elaboration of the incubator an air inlet fan and an air outlet fan were used to regulate the air circulation in the incubator, a sensor was also implemented to measure the relative humidity inside the incubator and another to measure temperature. For the increase and decrease of temperature and humidity, an analogous proportional power control was performed for the ambient and inversion resistance; characterizing each sensor so that the error of these is minimal. It should not be stressed that the model had three alarms, the first indicates if the dome is not fully closed, the second alarm is related to the temperature, whether it was below or above the set value and the last one is concerned to the percentage of humidity, also if it was below or above the established value.
In the design of the power stage of the incubator one of the parameters that greatly affected was the caliber of the wire used for the connection, this caused that the insulation of all was carbonized causing in turn that the heat transfer melted the internal contacts of the protoboard and short circuit between them which in the end results in an explosion of the circuit.
Another point that should be considered is the location of the sensors since this could influence the data collection. Since if they were near where the resistors were, they would have a very high value, but if they are located in the center of the dome, a measure could be obtained with a certain accuracy.

Figure 2. Design of newborn incubator

Figure 3. Disposition of  the parts of newborn incubator

Figure 4. Side view of design of  newborn incubator

CONCLUSIONS

In the development of the power stage of the incubator there are several recommendations for future generations, the Amperage that flows is enough and therefore a suitable wire gauge is needed to support it, in our case the circuit cables got too hot what caused that the rubber that covered them melted, it happened the same with the plastic material of the breadboard, it is so that at a certain moment there was the union of all the cables of the bt137 cables which caused a short circuit and the subsequent burst of the circuit.

In the implemented circuit a control was used for both parameters (temperature and humidity) could be controlled and varied in an analogous way, in spite of this, it was decided to leave the constant temperature and control the percentage of relative humidity of the incubator, in a moment to cause of the movement. the submersible resistance did not ignite at the moment that it had to, the error was solved but the capacity of control.

INFUSION PUMP

GLOSSARY

Infusion:                                                

It is the application of a drug to a patient using the intravenous route, that is, the application of a drug directly in the bloodstream. 

Volume:                                                 
It refers to the amount of three-dimensional space occupied by a liquid, solid or gas.
Sensor:                                                  

Device that detects and responds to some type of input from the physical environment.

Pressure:                                               
Force exerting a gas, a liquid or a solid on a surface.
Time:                                                     

Period determined during which an action is performed or an event takes place.

DEVELOP 

The infusion pump is a medical device capable of supplying medication, through its programming and in a controlled manner by intravenous (para-enteral infusions) or oral (enteral infusions) to patients who, due to their condition, require it.

Characteristics:

• Precision

• Ability to modify the variable maximum pressure limit speed

• Variable maximum pressure limit:

• Good protection against free flow

• Detection and alarm of any incident

• Ability to detect extravasation

• Possibility of reducing the pressure before solving an occlusion

• Maximum occlusion pressure alarm limits

• Track maintenance flow

Advantages of using pumps:

·    They allow a greater accuracy in the drip rhythm than the gravity systems through a flow regulating clamp.

·      They save time for the nursing staff, since with the use of pumps it is not necessary to regulate the drip flow.

·  They allow all kinds of solutions to be administered, blood and its derivatives, drugs and parenteral and enteral infusions. Adaptable to the needs of the patient, some of them are portable.

·      Infusion pumps unlike gravity systems that are regulated by a trolley device that is adjusted by the nurse, if the patient changes position or if there is a contraposition or resistance to the system, modifies the flow of solution creating errors of administration. There is a higher incidence of phlebitis, fluid overload, etc.

TYPES OF INFUSION PUMPS 

Linear peristaltic pumps: This type of pumps has undergone several modifications in its design that guarantee today levels of precision close to those of positive displacement. Current peristaltic linear pumps have pressure limitations and offer precise volumes of liquid delivery. Its operation is the use of a certain number of "fingers" that "milk" the liquid and makes it descend through a straight channel for its infusion in the patient.

 Figure 1. Linear peristaltic pumps

Figure 2. Peristaltic pump- Lineal system

Rotating peristaltic pumps: They are the most used using a rotor that pushes the rollers against a tube along a semicircular trajectory. Separation of plasma cells.

 Figure 3. Rotating peristaltic pumps

Figure 4. Rotary System

Syringe Pumps: Stanes have a motor (a gear reducer mechanism and a lead screw) that apply force to the plunger of a syringe containing the medication. The device is mainly suitable for applications that require the delivery of volumes limited by the size of the syringe.

Figure 5. Syringe pump

Figure 6. Principle of syringe pump

Implantable infusion pumps: The pump stores and releases prescribed amounts of medication. It is contained in a round metal casing approximately one inch thick and three inches in diameter; It weighs about six ounces. The main components are a miniature peristaltic pump, drug reservoir, battery, antenna and microprocessor. The pump is surgically implanted, usually in or near the abdomen.

Figure 5. Implantable infusion pumps

Figure 5. Parts implantable infusion pump 

Some recommendations:         

·  In a battery-operated pump, these should be replaced on a regular basis to avoid jeopardizing the safety of patients in the event of a sudden stop.

·   Pumps that do not have an integrated function of protection against free flow should be clearly identified and complemented by a training program on their management offered to users.

·   Pumps often have sudden deceleration or fall to the ground, so they must be inspected mechanically as part of a control and safety process.

RESULTS

   The block diagram shown in the upper part represents the infusion pump emulator equipment made, the quantity of doses and the delivery time were controlled from a keyboard, the optical sensors fulfilled the task of detecting bubbles, occlusion and lack of medication in the system and emit a visual and auditory alamar in case of any circuit failure, the above was transmitted to the microprocessor which controlled the peristaltic pump and finally all parameters could be displayed in the corresponding display, for the source was worked at 12V the power supply of the motor, for adjustments of the screen a voltage regulator was used to obtain only 5V as well as for the use of the sensors.

Figure 6. Block diagram of infusion pump emulador equitmet

   The schematic diagram made in proteus® allows to observe a large part of the components used in the development of the guide, the arduino® mega microcontroller allowed the appropriate development in front of the number of pins requested for the connection of the graphic display, the keyboard, the motor which was anchored to a structure to form the peristaltic pump, the optical sensors configured in such a way as to allow reading and handling of analogous data for their respective characterization in the program.

Figure 7. Schematic diagram of infusion pump emulador equitmet

  The final product is shown in the lower images, there was a container for the control module of the system, in which the keyboard can be seen on one side and the display on the front, the system had an internal audible alarm and with 4 visual indicators, leds in this case, which corresponded to the blue for on / off system, the green for the detection of bubbles in the system, the yellow for occlusion system in fault and finally the red to indicate lack of medicine in the container taken as syringes.

  The peristaltic pump is placed in a frame in high state and able exert force for operation across systems clamp, the system had two syringes appropriately marked to indicate the initial amount of medication and the end portion thereof.

Figure 8. Front view of infusion pump proposed

Figure 8. Side view of infusion pump proposed

   In the video you can see how the circuit works, for example the passage of medication (for this case water), which circulated at a certain speed from the input parameters, the system consists of a macro-drip which also it is evidenced in the taking and as a characteristic part the detection of bubbles and its audible and visible alarm (the LED on and off), for this case the obstruction alarm is not appreciated because the circuit is without interference nor the lack of medication alarm because there was enough in the containers for optimal operation.

CONCLUSIONS

   With the work done is concluded for the operation of the infusion pump (rotary peristaltic infusion pump) it is essential to obtain the proper occlusion of the hose (in this case a pump) to prevent fluid from circulating when the equipment is turned off. Also; a good connection between hoses must be taken into account to avoid leaks in the system and variations in the quantity of medicine delivered.

Laparoscopy - Electrosurgical Unit

DEVELOP

The laparoscopy tower is a set of equipment which is used in surgical procedures.

Image 1. The laparoscopy tower 

An electrocautery is an electronic equipment which is found in the laparoscopy tower, capable of transforming electrical energy into heat in order to coagulate, cut or eliminate soft tissue, choosing for this currents that develop at frequencies above 200 kHz since these do not interfere with the nervous processes and only produce heat.

Image 2. Parts the electrocautery

RESULTS

For the external design of the surgical electric scalpel the structure was designed (shown in the graph 1) which allowed:

1. change the ampli

Graph 1. Electrictical circuit

tude of each signal to perform the cut, coagulation or fulguration in the patient which is achieved with the red rotary knob.

2. For the frequency of each working signal of the electrocautery, a green rotary knob was used that directly controlled the increase or decrease in temperature.

3. A red LED indicating the electrode disconnected in Monopolar mode.

4. A blue LED that showed if the equipment was powered

The design of the interface is shown in the control and visualization system of the electrocautery, this interface was developed in LabVIEW® allows to activate or deactivate the control of the cutting and coagulation, in this way the corresponding graphs are exposed in Labview, green color for cutting, purple color for coagulation and finally red wine color for mix current.

The system is functional against its parameters, the device could not be proven to work in direct current, which caused that the coagulation cut is not performed correctly.

Graph 2. Prototype box 

Graph 2. Prototype box