Mechanical Ventilator

The mechanical ventilator is a equipment that is used to provide air and gases artificially to the respiratory system so there are two types of ventilators in function to mode of work with pressure: the first one is the negative-pressure that create a flow of air similar to pressure obtained of preural cavity in inspiration by distention of the diaphragm, expandind the intra-thoracic volumen and dropping the pressure inside the lung, its generate that flow of atmosphere goes to lungs.

Image 2. Illustration of negative pressure ventilator.

The mechanical ventilator is composed by three subsystems: breathing circuit, monitoring system and ventilation system and its composed by electrical, pneumatic and mechanics systems that works in group.  The pneumatic  system is the tubes, electromechanical valves and the source of flow of air; the eletromechanical valves work to manage and control differents pressures in the systems and it ensure the correct flow in a only one direction, the tubes connect the ventilador and created air to patient.

Image 3. Pneumatic system in mechanical ventilator.

The pressure control is developed by a group of sensors with their respective electronic aconditioning that are measuring in real time the flow, volume, pressure, and in sophisticated devies another vitals signs and another electronic system work in cojunction with the pneumatic system to open or close the valves and supply the requeried air according to the ventilation mode of work.

Ventilation modes

Existing four elemental principles of functionating in function of mechanism of cycles of inspiration and expiration

• By pressure: In this classification the ventilator have to sustain the same pressure (set previously) in the airways while the inpiration valve is open and the inspiratory flow is finished.
• By time: The period of every inpirations is constant and the pressure and volume is varied.
• By volume: Is the best mode because it keeps the correct volumens in patients and evite generate another troubles and patologies, so the volumen is preselected and the pressure varies.
• By flow: Is when the phase between inspiratory and spiratory cycle is determined by a value less than a flow determined.

The other ventilation modes are determined by the requirement of ventilatory function (total or partial), so they are in the next diagram:

Image 4. Ventilation modes

Design of a mechanical ventilator

Used Circuits

• Materials

• opto-coupler 4N35
• transistor 2N2222
• TIP 41C
• heat sink
•  220 ohm Resistances  

First we had to design a power circuit that can provide the compressor with enough current and voltge. Likewise we made a second power circuit, with the same characteristics, to control the valve that allow the passage of air.

Ventilation system


To simulate the mechanical ventilator, we choose a 12VDC compressor as a source of air, then we use a pressure sensor MPX5100DP to control the system pressure, and we choose a 12VDC bidirectional valve to provide air to our artificial lung.

Image 6. Electronic assembly of mechanical ventilator with arduino and labview.

Graphical interface

We used LabView to made the mechanical ventilator interface, in LabView we used the arduino interface, that allow get information of the analog pins of arduino, also we can route data from pc to Arduino to turn on/off the compressor and the valve.

Image 7. Graphical interface of mechanical ventilator

First we had to initialize the arduino interface, then we used a case cicle to do a iterative program, then we use the MPX5100DP datasheet to know the voltage-pressure convertion, also we initialize the compressor and valve turned off.

Image 8. Initializing program.

 Then we use a Case cicle and  flat sequence to start self-test cicle. The cicle was design to detect leakages, bad funtion of the compressor, or artificial lung failures.

Image 9. Self-test cicle.

 The program was made to do the CPAP mode, where the compressor always were on and the valve was controlled for the chosen pressure. 

Image 10. CPAP mode

Finally we start the controlled pressure ventilator, where the compressor were on until the system pressure reach the chosen pressure.

Image 11. CPV mode

So here is a little video with the functionating system of mechanical ventilator:

Bibliography:

1. Myer Kutz: Biomedical Engineering and Design Handbook, Volume 2. DESIGN OF RESPIRATORY DEVICES, Chapter (McGraw-Hill Professional, 2009 2003), AccessEngineering
2.  Coursehero.com. (2018). Modes Of Ventilation - Janeen Jordan MD TACS Fellow an opening must be attempted in the trunk of the trachea into which a tube of reed or cone should be. [online] Available at: https://www.coursehero.com/file/14858334/Modes-Of-Ventilation/ [Accessed 27 Feb. 2018].
3. Bing.com. (2018). Citar un sitio web - Cite This For Me. [online] Available at: http://www.bing.com/cr?IG=B725E12EB386485EB6772EE1AC5E1133&CID=214984E4788A6A6E00368F4779256BC5&rd=1&h=NZlTrWvPHwuE3xTCo4CPZM-BNf9zEQz-wVGUOke3l6w&v=1&r=http%3a%2f%2fbiomedica.webcindario.com%2fManuales%2frespimeradores.pdf&p=DevEx,5050.1 [Accessed 27 Feb. 2018].
3.