This paper describes a novel extension of the Forced Oscillation Technique (FOT), namely the volume-dependent Forced Oscillation Technique (v-FOT). This extension is based on the measurement of the respiratory impedance over the whole lung volume. A new measurement protocol was introduced: subjects breathe slowly from residual volume to total lung capacity, while oscillations are applied simultaneously. The respiratory impedance is computed by means of the windowed cosine fitting method. The respiratory impedance becomes frequency- and volume-dependent Z(jω,V). The novel impedance-volume (ZV) diagram was introduced for diagnostic purposes. Least-squares parameter estimation was performed for the extended-RIC and the constant phase models. However, both models failed in presenting the volume-dependency of Z. We proposed two new models: the volume-dependent extended RIC and the volume-dependent Mead model for a better fit of the data. The volume-dependent Mead model yields the smallest estimation error.
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