Accuracy of an electronic spirometer--a field trial.

Biological calibration of the Hewlett-Packard electronic spirometer against a Stead-Wells 13.5-litre spirometer shows a good concordance for forced vital capacity (FVC; systematic error 0% in women, 1% in men, probable error 4% in both sexes). However, the electronic device underestimates both 1-second forced expiratory volume (FEV1.0) and maximum mid-expiratory flow rate (MMEF) by 8-10%. This bias is unlikely to reflect technical problems of calibration, voltage drift, condensation of moisture or an inappropriate BTPS calibration; possible causes are a non-linearity in the pneumotachograph response characteristics, a lower resistance to expiration in the electronic device, and greater feedback to the subject and observer with the traditional spirometer. Given reports that similar discrepancies arise with other electronic spirometers, care should be taken in overinterpreting data obtained by such devices.