P188 Normative values of Lung Clearance Index in children and adults using SF6 as washout gas

Background: Multiple breath washout (MBW) is increasingly used to detect and follow disease progression in cystic fibrosis.Washout of an exogenous tracer gas (SF6) avoids some of the challenges of using N2, and can be performed rapidly using a closed circuit washin using a portable system.Objectives: 1) To establish normal Lung Clearance Index (LCI) in children and adults with no known respiratory impairment.2) Assess impact of age on LCI. 3) Assess feasibility of a portable LCI system.Method: LCI was measured in triplicate in healthy subjects aged >5 years, recruited from local schools (and performed on-site), and two specialist hospitals in the UK.Closed circuit washin was used to equilibrate tracer gas (0.2% SF6).Spirometry was only collected from volunteers attending hospital assessments.Results: 172 subjects were recruited, and 160 successful LCI measurements performed (8 excluded due to poor repeatability/patient unable, 4 for technical factors).37 repeats (7.7%) were excluded due to insufficient quality control or repeatability.Mean(SD) age was 17.2 (11.0) yrs, range 5-59 years.Mean (SD) LCI for the entire cohort was 6.1 (0.5), median (IQR) coefficient of variation of repeat LCI values was 3.4 (1.8-5.2).LCI was not significantly different between adults (age 18-59 years) and children (5-18 years) (mean difference = 0.006, 95% CI 0.15 to -0.16).There was no significant correlation between age and LCI (R 2 0.008, p = 0.3).Median (IQR) test time was 18.7 (16.0-22.5)mins.Conclusions: LCI can be assessed in a naive volunteer population rapidly and reproducibly using a portable system that allows measurements to be performed in community and hospital settings.Normal LCI does not to change significantly over the age group described.Work is ongoing to explore the impact of environmental factors on LCI.