Abstract: A device is provided which measures at least one mechanical property of the Respiratory System (RS) using an input perturbation which linearises the RS and measures the resulting output waveform. In its' full embodiment this device provides for a complete characterization of the RS′ mechanical state. One preferred embodiment utilizes appropriate transducers and associated processing to produce a plot that is able to locate lower inflection point (LIP), maximal slope (MS), over distension (O), upper inflection point (UIP), and closing volume (CV) in a lung with far greater sensitivity and accuracy than the ‘gold standard’ pressure volume curve. Supporting electronics and software provide for, at least, a display of trends, a xy display, and a display of spectral content. An integral alarm alerts the clinician to low signal conditions that may indicate, for example, a loss of respiratory effort. All devices in this family rely on one easily satisfied assumption.