Design And Implementation Of Non-invasive Ventilator Based On Humidity Trigger Mode

Non-invasive ventilator is an important medical equipment for the treatment of respiratory diseases such as severe and critical illness of new type of coronary pneumonia,obstructive sleep apnea hypopnea syndrome and chronic obstructive pulmonary disease.In the assisted ventilation mode,the traditional non-invasive ventilator triggers mechanical ventilation of the ventilator by detecting changes in the airway flow,pressure,or diaphragm myoelectricity caused by the patient’s breathing.Because the flow and pressure are greatly affected by the output airflow of the ventilator,these two triggering methods cannot achieve higher-frequency breathing triggering.However,the diaphragm muscle electrical triggering method is contact measurement,and the patient’s comfort is poor.Therefore,it is of great significance to design a non-invasive ventilator with a new trigger method to achieve highfrequency respiratory triggering and improve the therapeutic effect of mechanical ventilation and the comfort of patients.This paper proposes a new humidity triggering method.The ultra-fast humidity sensor is placed in the breathing mask,and the humidity signal that changes rapidly in the mask caused by the patient’s breathing is used as the basis for triggering the mechanical ventilation of the non-invasive ventilator.According to the functional requirements and performance indicators of the non-invasive ventilator,a non-invasive ventilator based on the humidity trigger method was designed.The system is composed of humidity sensor,breathing circuit,BLDC fan,main control module and upper computer.The main control module is used to collect respiratory humidity signals and airway pressure signals,and send the data to the upper computer.The host computer processes the humidity signal,judges the patient’s breathing action through the respiratory humidity trigger algorithm,sends pressure control instructions,and controls the main control module to drive the fan to output the corresponding airway pressure to realize the respiratory trigger function.The main control module uses STM32F407 of the Cortex-M4 series as the control core.It uses its mounted pressure sensor and corresponding acquisition circuit to collect pressure and humidity data,and sends it to the host computer through the serial port circuit,and at the same time receives control instructions from the host computer.Using the complementary PWM output function of the main control chip,through the motor drive circuit,the sensory brushless DC fan is driven in a six-step commutation manner,and the duty cycle of the fan speed is controlled by the incremental PID control algorithm to realize the output Specifies the function of pressure.The upper computer program is developed based on MATLAB,which can perform functions such as ventilation parameter setting,system start and stop control,and real-time data viewing.The host computer receives data through the serial port,uses the FIR digital filter to filter the humidity signal,and realizes the judgment of the patient’s breathing movement through the humidity change rate trigger algorithm,and realizes the functions of judging abnormal breathing status and calculating breathing parameters.Finally,the ventilator system was tested,including the debugging of PID control parameters,the test of the ventilator’s humidity trigger mode,and the test of the abnormal breathing state detection function.The test results show that the non-invasive ventilator designed in this paper can accurately trigger mechanical ventilation through respiratory humidity triggering,can achieve high-frequency respiratory triggers,and achieve a better human-machine synchronization effect;in terms of pressure control,the specified output can be relatively stable Pressure,and has a faster pressure switching speed,can meet the treatment needs of mechanical ventilation.