Abstract: Based on the forced oscillation principle,a small-scale forced oscillation pulmonary function measurement system with multi-frequency compound mode is designed.Sine signals of four different frequencies (5,10,15,20 Hz) are superimposed as forced oscillation excitation sources,and the superimposed excitation source signals are output to the loudspeaker through the power amplifier circuit by the STM32F407 processor,generating oscillating airflow to act on the human respiratory system.The flow and pressure signals collected by flow sensor and pressure sensor are processed by variational mode decomposition algorithm to extract pure forced oscillation signals effectively.The experimental verification of airflow resistance measurement and adult repeatability respiratory impedance measurement shows that the system is stable and reliable,and can accurately obtain human respiratory impedance parameters,which is suitable for early detection and evaluation of clinical respiratory diseases.

Key words: forced oscillatory pulmonary function measurement system, STM32F407, variational mode decomposition, respiratory impedance measurement