Feasibility and Inter-Test Reproducibility of Lung Clearance Index and Slow Vital Capacity in Children with Neuromuscular Disorders

<bold>Introduction:</bold> Children with neuromuscular disorders (NMD) have progressive respiratory muscle weakness but there are no reliable outcome measures to predict changes in lung health. Changes in lung clearance index (LCI) and slow vital capacity (SVC) could be markers of disease progression but the inter-visit reproducibility is unknown in children with NMD. We aimed to assess the feasibility and inter-visit reproducibility of LCI and SVC in children with and without NMD across two centres. <bold>Methods:</bold> LCI and SVC measurements were attempted by NMD and control groups, aged 6-17 years, on 2 occasions separated by 3-6 months. LCI by Multiple Breath Washout was obtained with the EcoMedics Exhalyzer D system. SVC was performed using Jaeger Master Screen Body according to ATS/ERS guidelines. <bold>Results:</bold> LCI was feasible in children as young as 6 years, with acceptable LCI obtained in 67 (77%) of 87 children (16 NMD, 51 control) (mean(±SD) age, 10.6±3.4 years). Average(±SD) LCI at baseline was not significantly different in NMD and control groups (6.08±0.66 and 6.36±0.64, respectively). Average(±SD) absolute difference in LCI between visits was -0.18±0.39 in NMD, and -0.10±0.62 in control. SVC was feasible in children as young as 6 years, with acceptable SVC obtained in 74 (95%) of 78 children (22 NMD, 52 control) (mean(±SD) age, 10.5±3.0 years). NMD group had lower SVC z-score compared to control (−2.91±2.13 and -0.43±1.49, respectively, p<0.001). Average(±SD) absolute difference in SVC z-score between visits was 0.04±0.49 in NMD and -0.26±1.09 in control. <bold>Conclusion:</bold> LCI and SVC are feasible and reproducible between repeat occasions in children with and without NMD.