Volume calibration alone may be misleading

Abstract

The use of spirometry is becoming more and more widespread in non-laboratory situations such as general practice or occupational medicine. In these non-laboratory situations, volume calibration with a 3000 ml syringe is often the only feasible method to ensure that the spirometer produces valid and reproducible data. Sophisticated equipment to calibrate forced manoeuvres with standard waveforms are not present. In this study, we assessed whether volumetric calibration is a guarantee for valid and comparable spirometric results. Two portable spirometers were tested. On 8 consecutive test days, both spirometers were calibrated with a 3000 ml syringe in accordance with the American Thoracic Society (ATS) guidelines. The comparability of the spirometric results (forced expiratory volume in 1 S, FEV1) was tested in two ways. Firstly, the spirometers were compared to each other using the results from 43 volunteers on the same 8 test days. The spirometers were presented in a randomized order and volunteers were asked to perform a series of reproducible manoeuvres in both spirometers. Paired observations were analysed, using Bland and Altman plots. Secondly, the spirometers were compared to a 'gold standard', a computer-driven syringe (CDS). Calibration with the 3000 ml syringe showed that both spirometers complied with the ATS criteria for volume calibration for diagnostic spirometry. However, paired FEV1 data obtained in subjects showed a systematic, volume-dependent difference between the two spirometers (mean difference: 289 ml, P < 0.001, systematic difference: 8.6%, P < 0.0001). This systematic difference was confirmed by the comparisons with the CDS. Volume calibration may be misleading. The results from volume calibration may meet the ATS criteria, but this is no guarantee that data from forced manoeuvres are accurate. If CDS equipment to simulate standard wave forms is not available, it is recommended that biological calibration is performed regularly and, if possible, that paired data from two (or more) different spirometers are compared.

Accuracy of Office Spirometry Performed by Trained Primary-Care Physicians Using the MIR Spirobank Hand-Held Spirometer

“…Moreover, the observed differences increase with the increase in the value of the pulmonary function parameters [4,7,9]. van den Boom et al [5 ]also reported on this nonlinearity of modern, compact spirometers.…”

“…Volume calibration alone is insufficient. The validity of the measurements should be examined by organizing a series of parallel measurements compared with a reference standard [4,5]. Third, the reliability of the measurements can also be tested from a broader perspective with regard to the kind of changes that need to be measured or the kind of decisions that can be taken based on the measurement.…”

Accuracy and Precision of Desktop Spirometers in General Practices

“…Clearly, regular use of a calibration syringe would be desirable, even while this does not guarantee that the spirometer readings from patients’ forced maneuvers are indeed accurate [15,33]. Regular biological calibration (by a healthy test operator in the practice) [34,35] is probably the most feasible option.…”

The value of spirometry for primary care: Asthma and COPD

“…Calibration with a syringe provides information on volume accuracy, and does not guarantee accurate volume or flow readings during forced breathing manoeuvres. 25 Frequent 'biological calibration' by a healthy test subject may be a valid alternative for primary care, 26 but more studies on this matter are needed.…”