Turning Lung Clearance Index on its head. Reference data for SF6 Multiple Breath Washout Derived Ventilation distribution efficiency (VDE)

Abstract

AbstractIntroductionCystic fibrosis (CF) is characterized by increased ventilation inhomogeneity (VI), as measured by multiple breath washout (MBW), from infancy. Lung clearance index (LCI) is the most reported VI outcome. This study aimed to evaluate historically published reference equations for sulphur hexafluoride (SF6) MBW outcomes, to data collected using updated commercial SF6MBW equipment and to produce device specific equations if necessary.MethodSF6MBW was performed in 327 healthy children aged 0.1-18.4 years (151 [46%] girls), 191 (58.4%) < 3 years. Z-scores were calculated from published reference equations (FRC and LCI) and multivariate linear regression performed to produce device specific reference equations. Due to increasing residual standard deviations with increasing LCI values, investigation of methods for improvement, were investigated, based on the relationship between VI and dead space ventilation (VD/VT; dead space volume/tidal volume) in a cohort of 59 healthy children, 26 children with CF (n=138 test occasions) and 49 adults with lung disease.ResultsHistorical SF6MBW reference equations were unsuitable for Exhalyzer D® data. In contrast to LCI and log10(LCI), 1/LCI (ventilation distribution efficiency; VDE) was linearly related to VD/VT, with z-scores linearly related to its absolute values. Reference equations were reported for VDE and log10(FRC). Significant predictors for VDE and log10(FRC), respectively, were log10(age) and gender, and log10(height), gender and posture.Conclusion1/LCI (e.i., FRC/CEV[%]) reflecting ventilation distribution efficiency (VDE) in the lungs was a superior index of ventilation inhomogeneity compared to LCI and log10(LCI) due to its linear relationship to VD/VT.