Evaluation of a multiple breath nitrogen washout system in children.

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 ) in an in vitro lung model, (b) assess the feasibility, repeatability, and reproducibility of MBW and (c) compare outcomes with the Exhalyzer D (MBW ) 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 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 was consistently lower (-19.3% [-40.5; 1.9], 95% CI [-23.9; -14.7]), and showed a volume dependency. LCI values were also higher in children with smaller lung volumes. The within-test coefficient of variation of the FRC and LCI were 4.9% in health, and 5.6% and 6.9% in CF respectively. LCI 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 was similar to LCI in health.

CONCLUSIONS

MBW measurements are feasible, repeatable, and reproducible, however, MBW-derived outcomes are not interchangeable with MBW .