Infant lung function testing: Firstin vivoreport of a novel inert gas washout method to measure LCI

Abstract

Introduction: The value of lung clearance index (LCI) is well recognised. It is a sensitive measure of lung disease in infants, particularly with cystic fibrosis(CF). Measuring LCI in infants is technically challenging due to the need to accurately combine flow and gas measurements at rapid respiratory rates. There is no simple method of assessing lung function outside research laboratories in this population. We have previously described a novel method of performing inert gas washout, in which expired gas is collected and analysed to derive functional residual capacity (FRC) and LCI without directly measuring flow. This has been demonstrated to be highly accurate in vitro (Ped Pulmonol, 2015). Aims: We aim to assess the practical applicability and accuracy of the novel method in vivo . Method: Infants with CF and healthy controls will undergo FRC and LCI measurement using the novel method.The number of successful LCI measurement and within-subject repeatability will be used to assess practical applicability of the system. Comparison will be made with LCI measurements obtained using a respiratory mass spectrometer, currently considered the gold standard for infant LCI measurement. Results: To date, 3 patients (all healthy, mean age 55 weeks) have successfully undergone the washout process using the novel method. Mean LCI was 6.47 (range 6.14-7.0, CV 8%) Conclusions: Preliminary data suggest this is a feasible and precise method of performing LCI in infants, with results in healthy children falling within the normal range predicted from the mass spectrometer (Lum, ERJ). Once validation is complete, this could provide a more accessible alternative to previously described systems.