Lung function testing for disease monitoring: extending Forced Oscillation Technique (FOT) to low frequencies

A new medical device for the monitoring of lung diseases is proposed. This device is based on the forced oscillation technique (FOT) which is a noninvasive method that does not require any effort of the patient. An estimate of the respiratory impedance is made by applying a small amplitude pressure oscilation at the mouth of the patient. By measuring the resulting air flow generated by the patient, the respiratory impedance can by obtained as the ratio of the pressure ossilation and the generated air flow. The pressure oscillation is mostly a broadband signal that excites a frequency band of 4 to about 50 Hz. The main difference of our proposed device is that the frequency band of the pressure oscilaation is lowered to the frequency range of spontaneous breathing (0.1-1Hz). In this way, the respiratory impedance can be obtained at a lower frequency range which leads to a new approach for lung disease monitoring. The main difficulty is that the breathing of the patient disturbs both the input (pressure oscillation) as the output (generated air flow) signal. Therefore, advanced control and signal processing techniques are required to make a high quality estimate of the respiratory impedance obtainable.