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 patientunfriendly 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. This way, the contributions of the breathing and the excitation signal can be separated. This paper discusses the implementation, testing and the actual measurement results in a clinical setting using this method.

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. The presence of the patient's breathing generally results in patient-unfriendly measurement protocols. These are needed to extract the important low frequency information about the patients' respiratory system.This work presents a novel technique to apply the low frequency FOT during spontaneous breathing. This is accomplished by adding an external visual stimulus to encourage the patient to approximately synchronize his/her breathing in combination with an excitation signal that is adapted to the patient's natural breathing frequency. The breathing and FOT contributions can therefore be separated. This paper contains a proof of concept of this method and proposes measurements on healthy subjects.