Forced oscillations in applied respiratory physiology Theoretical Principles

This is a literature review of the theoretical principles which frame the two widely used techniques of forced oscillations applied to the respiratory system, forced oscillation technique (FOT) and impulse oscillometry (IOS). The effect of forced oscillations on the respiratory system is investigated as a phenomenon of motion expressed as changes of pressure, volume, flow and acceleration in the classical mathematical approach to a linear system which, under the pressure of a stimulating force, is impelled into forced oscillation. The physiology of respiratory input impedance is presented as a parameter which describes the correlations between pressure, volume, flow, elastance, resistance and inertia of the respiratory system. The principles of basic practice for test completion are described, and the epidemiological factors which form the framework for the evaluation of the measurements, derived from research in healthy adults, are reviewed.