The ventilator is a mix of electronic circuits and mechanical air circuits. Its general structure is composed of nine parts: oxygen source, solenoid valve, mixed air device, pressure limiting valve, humidifier and temperature control circuit, airway resistance meter, breathing valve, signal box, and solenoid valve control circuit. The following introduces them one by one:
(1) “Oxygen source”
It is an oxygen storage device designed to provide the patient with the oxygen they need to inhale. Usually supplied by high pressure oxygen cylinder or compressed air.
(2) Solenoid valve
The solenoid valve is an on-off valve for the “oxygen source”. The difference between it and the mechanical regulating valve is that it is electrically controlled, that is, by controlling the on and off of the solenoid valve coil current to control the opening and closing of the valve, so as to make the air flow or cut off. Its working principle is somewhat similar to ordinary relays.
(3) mixed air
The air mixing device uses the principle of reducing the lateral pressure of the high-speed fluid, and injects oxygen from the high-speed nozzle to generate a negative pressure area. The air pressure on both sides is greater than the negative pressure area, and the air is involved in the high-speed flowing oxygen.
(4) Pressure limiting valve
The pressure limiting valve is a gas pressure limiting device that ensures that the gas is output at a certain pressure. When the machine leaves the factory, it is generally adjusted to a height of 6kPa (60cmH2O). If the output air pressure of the machine exceeds this value, the gas will be automatically released to ensure the safety of the patient.
(5) Humidifier and temperature control circuit
It is a constant temperature device with constant temperature water and gas can enter and exit. The device can avoid the stimulation of the patient’s lungs by cold air, avoid dehydration of the respiratory tract mucosa, and play the role of humidification, filtration and warmth similar to the human respiratory tract. The temperature control circuit is a circuit used to adjust the water temperature in the humidifier and keep it constant.
(6) Airway resistance table
This table is a device used to indicate the resistance of the patient’s airway. From the airway resistance and the pressure of the oxygen source, the oxygen content (excluding the oxygen content in the air) and the tidal volume can be calculated respectively.
(7) Breathing valve
It is a device that uses pneumatic methods to drive two valves to realize the organic combination of three signals of exhalation, IC chip decryption and inhalation, and negative air pressure. When inhaling, the inspiratory valve is opened, and the machine supplies air to the patient in one direction. When exhaling, the inspiratory valve is closed, and the exhaled gas is discharged through the expiratory tract.
(8) Signal box
The signal box is composed of a pair of sealed electrical contacts driven by a sensitive elastic diaphragm. When the suction negative pressure reaches a certain value, the contact is disconnected, and the signal box outputs a pulse signal. In this way, the patient’s inhalation negative pressure is converted into an electrical signal, and input to the “solenoid valve control circuit” to realize the control effect on the solenoid valve.
(9) Solenoid valve control circuit
It is a logic control system composed of pulse digital circuits, which is used to control the on or off of the solenoid valve. Finally, through the air circuit, the required breathing frequency, the machine-controlled breathing of the breathing-to-breathing time ratio, the synchronized breathing, and the automatic conversion between active and passive breathing are realized.