STANDARDIZATION OF MULTIPLE SPIROMETERS AT WIDELY SEPARATED TIMES ANDPLACES

We designed a system for a multiyear longitudinal study of lung functi on in 12 widely separated communities, intending to minimize variation in instrument-related data. We used multiple rolling-seal spirometer/ personal computer systems. Calibrations were checked before, during, a nd after each day's field testing, using multiple calibration syringes with electronic readouts. The syringes were rotated to obtain data fo r each syringe-spirometer combination. Before and after each annual fi eld testing season, a laboratory reference spirometer system was calib rated against a water-displacement device and an electronic frequency counter, and then compared against each field spirometer and syringe. Field equipment consistently met American Thoracic Society (ATS) speci fications. Variance among spirometers exceeded variance among syringes . A spirometer occasionally changed its volume readout by approximate to 1 to 2%. More rarely, a syringe changed its delivered volume by app roximate to 1%. Syringes' electronic readouts tracked changes in deliv ered volume. Syringe readouts were the most stable component of the sy stem, and were more reproducible than the laboratory water-displacemen t calibration. We conclude that variation in spirometers may limit the reliability of epidemiologic findings, even when these spirometers me et ATS specifications. Frequent calibration checks traceable to an ind ependent standard, and adjustment of individual test results, can redu ce measurement error.