Comparison of different analysis algorithms to calculate multiple-breath washout outcomes

Abstract

Lung clearance index (LCI) is the main outcome of the multiple-breath washout (MBW) test. Current recommendations for LCI acquisition are based on low-grade evidence. The aim of this study was to challenge those recommendations using alternative methods for LCI analysis.Nitrogen MBW measurements from school-aged children, 20 healthy controls, 20 with cystic fibrosis (CF) and 17 with primary ciliary dyskinesia (PCD), were analysed using 1) current algorithms (standard), 2) three alternative algorithms to detect with higher precision the end of MBW testing and 3) two alternative algorithms to determine exhaled tracer gas concentrations. LCI values, intra-test repeatability, and ability to discriminate between health and lung disease were compared between these methods.The analysis methods strongly influenced LCI (mean±sd overall differences (%) between standard and alternative analysis methods: −4.9±5.7%; range: −66–19%), but did not improve intra-test variability. Discrimination between health and disease was comparable as areas under the receiver operator curves were not greater than that from standard analysis.This study supports current recommendations for LCI calculation in children. Alternative methods influence LCI estimates and hamper comparability between MBW setups. Alternative algorithms, whenever used, should be carefully reported.

Shedding light into the black box of infant multiple‐breath washout

“…The lack of transparency into the signal processing and algorithms used, lack of standardized protocol, and ease in which results can be manipulated by changing settings have made it difficult to standardize and interpret MBW outcomes from WBreath software. 7,23,24 We found that WBreath 3.28.0 underestimates the volume of re-inspired tracer gas and does not calculate FRC and LCI in accordance with MBW consensus guidelines. The revised WBreath version 3.52.3 corrects these discrepancies and facilitates reanalysis of raw infant MBW data in accordance with current consensus guidelines.…”

“…However, indirect measurement of SF 6 concentration, delayed tracer gas clearance from the side chambers, and fact that the main‐stream molar mass signal is highly susceptible to fluctuations in humidity and temperature means that many corrections have to be applied to the raw signal to produce a standard washout curve. The lack of transparency into the signal processing and algorithms used, lack of standardized protocol, and ease in which results can be manipulated by changing settings have made it difficult to standardize and interpret MBW outcomes from WBreath software 7,23,24 . We found that WBreath 3.28.0 underestimates the volume of re‐inspired tracer gas and does not calculate FRC and LCI in accordance with MBW consensus guidelines.…”

Multiple breath washout test in infants–still in search for technical ideal

“…9,10 Similarly, differences between data processing algorithms and software versions have also been reported. [11][12][13][14][15] In this issue of Pediatric Pulmonology, Oestreich et al present a very comprehensive analysis of the SF 6 -MBW algorithm used in the WBreath 3.28.0 (ndd AG) software, which was historically combined with the Exhalyzer D device (Eco Medics AG). In this setup, molar mass and flow are measured and the concentration of SF 6 is indirectly estimated.…”

“…9,10 Similarly, differences between data processing algorithms and software versions have also been reported. [11][12][13][14][15] In this issue of Pediatric Pulmonology, Oestreich et al Firstly, different setups are not interchangeable. Secondly, in all commercial devices, technical issues of different origin bias the outcome (functional residual capacity, LCI and other measures of gas mixing efficacy).…”

“…Discrepancies between mass spectrometry based and indirect measuring systems have been reported 9,10 . Similarly, differences between data processing algorithms and software versions have also been reported 11–15 …”