The error of method in spirometry

The author shows, in metrological analysis, that during forced expiration the resistance of the spirometric flow transducer cooperates with the patients respiratory resistance. For this reason the values of almost all expiratory parameters can be changed, depending on the relation which exists between both resistances, and the patient (his respiratory system defect) may be diagnosed incorrectly. Such error is classified as an error of method. The transducer flow resistance makes errors in all the respiratory parameters definition, with error of some percent, making its value comparable with the other transducer errors (its accuracy, linearity, stability etc.). The differences are biggest particularly at the beginning part of the forced expiration, when air flow velocity is maximal. Therefore the flow transducer should be chosen according to the maximal flows appearing during such expiration.