A method for determining a pulmonary volume change includes: receiving a respiration event from a subject in an airflow chamber interrupting the respiration event by an occlusion of the airflow chamber initiated at a first time instant and terminated at a second time instant subsequent to the first time instant taking a plurality of measurements of airflow rate through the airflow chamber between the second time instant and a third time instant subsequent to the second time instant and determining a pulmonary volume change substantially equal to a reduction of a pulmonary air volume by a pulmonary response air volume and a normal air volume, wherein the pulmonary volume change is related to a change in density of air in the airflow chamber.
