The present invention relates to a system for measuring respiratory function of living organisms. More particularly, signals indicative of the change in lung volume, defined as active and passive work, required to breathe and the airflow through the respiratory system of the living organism are obtained and processed as waveforms to provide a signal indicative of the respiratory restriction. The methods of the present invention measure clinical forms of airway obstruction, airway reactivity and lung volume and may be used to continuously or intermittently monitor patients with compromised respiratory function. In a preferred embodiment, a head-out, breath in respiratory plethysmograph system provides the signals indicative of change in lung volume as related to pressure changes in a chamber. Further, flowmetric variables are generated that provide a characterization of airway obstructions.