A non-systematic signal-correction error in a commercial multiple-breath washout device significantly impacts outcomes in children and adults

BackgroundMultiple-breath nitrogen washout is an established and sensitive technique to assess functional residual capacity and ventilation inhomogeneity in the lung. Indirect calculation of nitrogen concentration requires precise calibration and accurate measurement of gas concentrations. AimWe investigated the accuracy of the carbon dioxide gas concentration used for the indirect calculation of nitrogen concentration in a commercial multiple-breath washout (MBW) device (EasyOne Pro LAB, ndd Medizintechnik AG, Zurich, Switzerland) and its impact on outcomes. MethodsA high-precision calibration gas mixture was used to evaluate sensor output and calculated carbon dioxide concentration. We assessed the impact of a corrected CO2 signal on MBW outcomes in a dataset of healthy children and adults and children with lung disease. ResultsThe EasyOne device uses a respiratory quotient-based adjustment to correct the measured carbon dioxide signal for potential long-term changes in sensor output. In the majority of measurements (89%), this resulted in an overestimation of expired nitrogen concentrations (range -0.7 to 1.7%), and consequently MBW outcomes. Correction of the CO2 signal reduced the mean (range) cumulative expired volume by 27.1% (-58.1%; 1.0%), functional residual capacity by 11.1% (-21.6%; 1.2%), and lung clearance index by 18.3% (-44.0%; -0.3%). Additionally, within-visit variability was substantially reduced with the corrected signals. ConclusionInadequate signal-correction of the measured CO2 concentration in the EasyOne Pro LAB device leads to a non-systematic error in expired nitrogen concentrations and overestimation of test outcomes. Two-point calibration of the CO2 sensor may maintain accurate measurement of gas concentrations and overcome this error.