Evaluation of a multiple breath nitrogen washout system in children

Abstract

Introduction The multiple breath nitrogen washout (MBW) test offers a sensitive measure of airway function. In this study we aim to (a) assess the validity of the EasyOne Pro LAB (MBW_ndd) in an in vitro lung model, (b) assess the feasibility, repeatability, and reproducibility of MBW_ndd and (c) compare outcomes with the Exhalyzer D (MBW_EM) and body plethysmography. Methods In vitro, functional residual capacity (FRC) measurements were assessed using a lung model under quasi-physiological conditions and compared to measured FRC. In vivo plethysmography and MBW were performed in a prospective study of children at two visits (n = 45 healthy; n = 41 cystic fibrosis [CF]). Bland-Altman plots were used to compare agreement between FRC and lung clearance index (LCI) measurements. Results In vitro FRC_ndd measurements were repeatable but lung volumes were underestimated (mean relative difference −5.4% (limits of agreement [LA] −9.6%; −1.1%), 95% confidence interval (CI) −6.27; −4.45). In vivo, compared to plethysmography, FRC_ndd was consistently lower (−19.3% [−40.5; 1.9], 95% CI [−23.9; −14.7]), and showed a volume dependency. LCI_ndd values were also higher in children with smaller lung volumes. The within-test coefficient of variation of the FRC_ndd and LCI_ndd were 4.9% in health, and 5.6% and 6.9% in CF respectively. LCI_ndd was reproducible between-visits (mean relative difference [LA] −3.7% [−14.8, −7.5; 95% CI −6.6; −0.73] in health [n = 17] and 0.34% [−13.2, 22.8; 95% CI −5.0; 5.69] in CF [n = 23]). When calculated using the same algorithm, LCI_ndd was similar to LCI_EM in health. Conclusions MBW_ndd measurements are feasible, repeatable, and reproducible, however, MBW-derived outcomes are not interchangeable with MBW_EM.