Prototype of a ventilator based on ATmega328Pmicrocontroller

Full Text

UDC 004.9

 

PROTOTYPE OF A VENTILATOR BASED ON ATMEGA328P MICROCONTROLLER

 

The first mention of artificial lung ventilation appeared about 5 thousand years ago. Initially, the ventilator process was used for children who were born with asphyxia and sometimes it was used if a person lost the ability to breathe independently. Nowadays, ventilators are widely in demand for anesthesia, especially for long-term surgical interventions. Lung ventilators are also used for acute respiratory failure to preserve human life.

Today the need for domestically produced ventilators has increased significantly because of the withdrawal of many foreign medical device manufacturers.  

Therefore, to eliminate this problem it is necessary to create a basic device for constructing ventilators. By studying the elements of the ventilator, design engineers will have an opportunity to create a modern high-quality Russian-made ventilator.

Project goal: to create a prototype of a ventilator to study its parameters.

 

The implementation of the project

The first task was to develop the principle of operation of the stand. It repeats the work of a real ventilator. After the power is supplied to the stand and the sensors are activated, the human mass value and the index value are manually adjusted by using potentiometers, which will be described below. Then, the motor, under the control of the driver and controller, begins to compress and decompress the AMBU bag, thereby supplying oxygen to the potential patient’s lungs.

The main factor of the ventilator, without which it would not be able to function properly, is the program by which all the components work in one cycle, but without a prescribed algorithm for the operation of the stand, it is impossible to create a program. The stand has two   parameters that can be changed, namely the patient’s weight and index. These parameters are needed to find the pulmonary minute volume (PMV). The value of the PMV can be found by Darbinyan's formula (formula 2) [2]. Formula 1 is used to calculate the respiratory rate needed. For a ventilator, the average respiratory volume for adults is 13 ml / kg, and for children 7 ml / kg. To find the respiratory volume of an individual, it is necessary to multiply the person’s weight by the value described above.

                                                                                               

where ν – respiratory rate, ;

       PMV – pulmonary minute volume;

       RV – respiratory volume.

                                                                                                            

  ,

 where PMV – pulmonary minute volume, ;

       m – human mass, kg;

       x – the index to find a more accurate MVB

       x = 2, if the person is older than 55 years old;

       x increases by 1 if the body temperature is more than 38 °с.

 

PMV (adult) =  + 1 + 2 = 18 л = 18000

ν(adult) =  = 12

PMV (child) =  + 1 = 1,294 l = 1294

ν(child) =  = 44

Thus, the parameters of artificial lung ventilation of a person weighing 150 kg and over 55 years old, as well as a child weighing 2.94 kg, were calculated. As a result of the research, the value of the respiratory rate of an adult was 12 breaths per minute. And the value of the child's breathing rate was 44 breaths per minute. The greater a person’s weight and age are, the lower the respiratory rate is. Therefore, to select the operating mode of the stand, only the patient's weight, age and body temperature will be needed. The minimum value of a person's weight will be set at 2 kg, and the maximum at 200 kg. The x index will be calculated from the values of the body temperature and the age of the person. The maximum index value is 8.

Once all the digital ports have been defined, the variables responsible for the patient's weight and the index ‘x’ are entered in the code. The program then uses the above formulas to calculate the respiratory rate from the index and weight. 

 

Printed circuit board

The circuit board was made by the author in the program "SPRINT LAYOUT 6.0". The board has an LCD display that will show  patient data, a controller, two potentiometers that are responsible for changing the parameters of the stand, two field-effect transistors, two 10 Kohm resistors, two220 ohms resistors, a CAMOZZI E521-11-10 distributor, and power. The analysis of the market of modern controllers shows that the microcontroller ATmega328P is the best option because the characteristics of this model are ideally suited to control the stand.

 

Fig. 1. The circuit board diagram

 

The general scheme of the stand

Compressed air is supplied to the stand, which is necessary for the operation of the pneumatic elements of the stand. The compressed air cylinder is shown under the number 6 in Figure 2. The main elements in the scheme of the stand are: pressure regulators models (PR1 and PR2) N1208-R00, pneumatic distributor (PD1) model E521-11-10- K12, pneumatic throttles (PT1 and PT2) of the PMCU 704-1/8-4 model and pneumatic cylinder (C1) of the 31M2A025A100 model. Also, two pressure gauges with an upper measuring range of 1 bar (RD1 and RD2) of the M043-F06 model are installed in the stand (Element 3 on the Fig. 2).

After powering up the stand, starting the program and setting the parameter values, a signal goes from the controller to the distributor, which is responsible for the operation of the pneumatic distributor. The signal changes the direction of the compressed air flow supplied to the distributor (4 in Fig.2). The air passes through various fittings (2 in Fig.2). Then, the air energy is converted into movement of the pneumatic cylinder output link consisting of a rod, a piston and a rod nozzle made on a 3D printer (5 in Fig. 2). The direction of the air flow changes the direction of the output link. The rod with the nozzle exerts pressure on the AMBU bag.

Fig. 2. 3D model of the stand (in the FUSION 360 program)

 

Program

  The signal is responsible for changing the compressed air flow. Special attention was paid to the program that is responsible for the interaction of pneumatic elements. Since an ATmega328P is the microcontroller in the project, the program has been implemented in the WIRING programming language. At the beginning of the program, two libraries are introduced: one for operation with the LCD screen, and the other for operation with a pneumatic distributor (P1). After that the types of pins are determined. Two of them are responsible for transmitting the signal to the distributor (OUTPUT), and the other two are responsible for reading information from the potentiometers (INPUT). The LCD screen parameters, such as screen brightness and the area for displaying characters on the screen are also introduced. The variable ‘timing’, which is responsible for storing the reference point, is simultaneously introduced.

In the ‘void loop’, 2 variables that are responsible for the patient's mass and the x index, respectively are introduced. Immediately, these variables are assigned maximum and minimum values. Next, 3 more variables are declared, responsible for PMV, RV and respiratory rate (frequency). These parameters were described earlier. Next, the conditions under which the direction of the compressed air flow is changed are described. The commands responsible for displaying information on the display are then created. A more detailed scheme, which shows  all the elements, is presented in Figure 3.

 

 

Fig. 3. The scheme of the stand

 

Results of the project

The constructed ventilator stand is capable of influencing the accelerated modernization of domestically produced ventilators. The stand will allow to construct a new generation of ventilators that are superior to their global counterparts due to a simpler design and relatively low cost. These advantages will enable a large number of medical institutions to purchase ventilators. The project has the potential to be used by various educational institutions as educational material. In the future, work on the project will continue and new parameters, such as the effect of pressure differentials on the operation of ventilators will be investigated. As technology develops, the project will continue to evolve and improve.

 

About the authors

Aleksei S. Vasilenko

Samara university

Author for correspondence.
Email: supervasilenko@yandex.ru
Russian Federation, 443086, Россия, Самара, ул. Московское шоссе, 34.

Svetlana Albertovna Avdeyko

Samara University

Email: asa210770@mail.ru

senior Lecturer of Department of Foreign Languages and Russian as a Foreign Language of Samara National Research University

Russian Federation, 443086, Russia, Samara, Moskovskoye shosse, 34

References

Supplementary files