Study of the Generation System-Induced Degradation of Airflow Signal for FOT Applications

In the forced oscillation technique (FOT), a pressure generator typically delivers a sinusoidal airflow to the patient through an oscillator circuit, which modulates the frequency of the voltage supplied to a speaker. When the speaker-generated airflow interacts with the respiratory system, it causes a forced response in pressure and airflow. This forced response is useful in modeling the system's characteristics using a transfer function. However, system components may degrade the produced signal, compromising the transfer function analysis. This paper investigates an FOT system equipped with a speaker and a pneumotachometer to examine interference with the generated airflow signal. This investigation explores how the generated signal behaves under variations in frequency and amplitude. As a metric of signal degradation, we analyzed the percentage of the signal's energy at its natural frequency and the percentage dispersed among its first harmonics.