Adaptive Excitation Signals for Low-Frequency Forced Oscillation Technique Measurements in Patients

The low-frequency forced oscillation technique (FOT) has a high diagnostic potential for the detection of respiratory diseases. However, it is not yet widely accepted in clinical practice, partly because the natural breathing frequency usually interferes with the measurement, thus requiring patient-unfriendly breathing maneuvers. The presence of a subject’s breathing generally results in patient-unfriendly measurement protocols. These are needed to extract the important low-frequency information about the subject’s respiratory system. This work presents a technique enabling the application of low-frequency FOT during spontaneous breathing. This is accomplished by adding an external visual stimulus to encourage the subject to synchronize his/her breathing to the measurement apparatus, in combination with an excitation signal that is adapted to the subject’s natural breathing frequency. In this way, the contributions of the breathing and the excitation signal can be separated. This article discusses the implementation, testing, and actual measurement results in a clinical setting using this method.