RESUMO
BACKGROUND: At present a syringe is being used for calibration of lung function devices, but biological controls are used to detect prospectively the variability and reproducibility of lung volumes measured by spirometers. Laboratory personnel is often used as biological control and therefore the cost for these measurements is substantial and may be reduced by replacement of a syringe procedure to increase the capacity of the laboratory to measure more patients. OBJECTIVES: To develop a mechanical syringe procedure for identification of instrument problems. METHODS: A commercial 3-liter precision syringe is used to simulate breathing maneuvers (inspiratory vital capacity, functional residual capacity, residual volume and total lung capacity) on a spirometer. Three healthy males representing biological controls performed spirometry, maximum expiratory flow volume and helium dilution forced residual capacity at bimonthly intervals for 3 years. Confidence intervals and interval widths are calculated for each parameter. Levene's test for equality of variances was used to test for significance between standard deviations. RESULTS: The interval width of inspiratory vital capacity, functional residual capacity, total lung capacity and residual volume of repeated measurements obtained from the syringe was significantly narrower than those of biological controls. In addition, almost all standard deviations from lung volumes obtained from the syringe were smaller and significantly different from those of the biological control. CONCLUSION: Our syringe procedure may replace biological controls for detection of variability of lung volumes. This will result in cost reduction and improve quality assessment of lung function devices.