Air features in spirometric transducers

The report presents a metrological analysis of the influence of the expiratory air physical features on the preciseness of the expiratory parameters defined during lung ventilation. Two kinds of spirometric transducers were taken into consideration. It is theoretically analysed and experimentally confirmed that, when a volumetric transducer (a bell) is used, the air temperature inside it changes and a special correction is necessary. Moreover, its value depends on time. When a flowmeter is used (being placed near the mouth) the expired air is measured before its temperature becomes substantially lower. For this reason a correction factor should not be the same as for a volumetric transducer. Such different kinds of transducers require the usage of different temperature correction. In the opposite case the misapplicated correction made for the flowmeter can be a source of error.