Oscillometry: theoretical bases

This chapter focuses on the theoretical basis of oscillometry, specifically the methodology for data acquisition, data processing, and the modelling used to interpret the results. First, we explain the difficulty of noninvasively measuring respiratory mechanics during spontaneous breathing and describe the principles of oscillometry, which solves this problem by applying small amplitude, high-frequency oscillations through a mouthpiece. Secondly, technical issues related to implementing these principles in oscillometry devices are discussed: specifically, the generation of oscillations, the device requirements for minimally disturbing the patient’s breathing, and the data processing to compute respiratory impedance. Next, the theoretical aspects and limitations of the mathematical models used to interpret oscillometry data are discussed. Among them are the ability of models to selectively capture pathophysiological mechanisms, the sensitivity of model parameters, and the potential effect of the extrathoracic upper airway wall compliance in routine oscillometry. Finally, a simple interpretation of oscillometry data based on both theoretical and experimental evidence is proposed for clinical application.