The interaction between breathing flow and breathing organs causes a phase shifting between pressure and volume rate of change. Therefore, impedance, power and work of breathing may be decomposed into a dissipative and a reactive component. These are determined by integration over one cycle of breathing. If breathing is varied, so called ‘locus diagrams’ representing the load behaviour of breathing organs are plotted from these components. According to linear laws of flow, impedance would depend upon frequency only. An additional dependence upon amplitude will point to nonlinearit