Comparison of functional residual capacity (FRC) measured by plethysmography (FRCpleth) and multiple breath washout (FRCmbw) in schoolchildren with cystic fibrosis (CF).

Rationale: Nitrogen multiple-breath washout is an established technique to assess functional residual capacity and ventilation inhomogeneity in the lung. Accurate measurement of gas concentrations is essential for the appropriate calculation of clinical outcomes. Objectives: We investigated the accuracy of oxygen and carbon dioxide gas sensor measurements used for the indirect calculation of nitrogen concentration in a commercial multiple-breath washout device (Exhalyzer D, Eco Medics AG, Duernten, Switzerland) and its impact on functional residual capacity and lung clearance index. Methods: High precision calibration gas mixtures and mass spectrometry were used to evaluate sensor output. We assessed the impact of corrected signal processing on multiple-breath washout outcomes in a dataset of healthy children and children with cystic fibrosis using custom analysis software. Results: We found inadequate correction for the cross sensitivity of the oxygen and carbon dioxide sensors in the Exhalyzer D device. This results in an overestimation of expired nitrogen concentration, and consequently multiple-breath washout outcomes. Breath-by-breath correction of this error reduced the mean (SD) cumulative expired volume by 19.6 (5.0)%, functional residual capacity by 8.9 (2.2)%, and lung clearance index by 11.9 (4.0)%. It also substantially reduced the level of the tissue nitrogen signal at the end of measurements. Conclusions: Inadequate correction for cross sensitivity in the oxygen and carbon dioxide gas sensors of the Exhalyzer D device leads to an overestimation of functional residual capacity and lung clearance index. Correction of this error is possible and could be applied by re-analyzing the measurements in an updated software version.

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Estimation of lung functional residual capacity by the multiple-breath washout test versus bodyplethysmography in healthy subjects

10.1183/13993003.congress-2020.3194 ◽

2020 ◽

Author(s):

Galina Nekludova ◽

Alexander Cherniak

Keyword(s):

Functional Residual Capacity ◽

Healthy Subjects ◽

Multiple Breath Washout ◽

Residual Capacity

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Leaks during multiple-breath washout: characterisation and influence on outcomes

ERJ Open Research ◽

10.1183/23120541.00012-2017 ◽

2018 ◽

Vol 4 (1) ◽

pp. 00012-2017 ◽

Cited By ~ 5

Author(s):

Nina Lenherr ◽

Kathryn A. Ramsey ◽

Kerstin Jost ◽

Linn Hornwall ◽

Florian Singer ◽

...

Keyword(s):

Functional Residual Capacity ◽

Cycle Duration ◽

European Respiratory Society ◽

Physiological Noise ◽

Lung Clearance ◽

Air Leaks ◽

Heterogeneous Effects ◽

Lung Clearance Index ◽

Multiple Breath Washout ◽

Residual Capacity

Nitrogen multiple-breath washout (N2MBW) is increasingly used in patients with cystic fibrosis. The current European Respiratory Society/American Thoracic Society consensus statement for MBW recommends the rejection of measurements with leaks. However, it is unclear whether this is necessary for all types of leaks. Here, our aim was to 1) model and 2) apply air leaks, and 3) to assess their influence on the primary MBW outcomes of lung clearance index and functional residual capacity.We investigated the influence of air leaks at various locations (pre-, intra- and post-capillary), sizes, durations and stages of the washout. Modelled leaks were applied to existing N2MBW data from 10 children by modifying breath tables. In addition, leaks were applied to the equipment during N2MBW measurements performed by one healthy adolescent.All modelled and applied leaks resulted in statistically significant but heterogeneous effects on lung clearance index and functional residual capacity. In all types of continuous inspiratory leaks exceeding a certain size, the end of the washout was not reached. For practical application, we illustrated six different “red flags”, i.e. signs that enable easy identification of leaks during measurements.Air leaks during measurement significantly influence N2MBW outcomes. The influence of leaks on MBW outcomes is dependent on the location, relation to breath cycle, duration, stage of washout and size of the leak. We identified a range of signs to help distinguish leaks from physiological noise.

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