Longitudinal LCI in infants with CF using a portable multiple breath washout (LIMBuS study)

Abstract

<b>Introduction:</b> Lung clearance index (LCI) is an important measure of lung function, especially in those with mild cystic fibrosis (CF). It is however challenging to deliver in infants, with current devices requiring 100% O2 washout or use of 4% SF6. We have previously described a novel portable method using 0.1% SF6 as the tracer gas. In this study we report longitudinal measurement of LCI using this method. <b>Method:</b> LCI measurements were undertaken using 0.1% SF6 and washout on air. All measurements were performed under light sedation, up to age 3.5 years. CF children, clinically stable at time of assessment, had LCI measured at initial visit, 2-4m later and 12-24m later. Healthy controls were measured once. The study took place in one US and two UK centres. <b>Results:</b> 32 CF infants had successful LCI at visit 1, six at visit 2 and five at visit 3 with data analysis still ongoing. Data are also available on 36 healthy infants.&nbsp;There was no difference in overall mean LCI in CF (mean 7.0, SD 0.7) vs controls (mean 7.0, SD 0.6), p=0.9.&nbsp;Median coefficient of variation of LCI repeats was 5.1%. Five of eight measurements in CF infants &lt;52wks old and 15 of 35 measurements in infants &gt;52wks of age showed LCI &gt;7.0. Bland-Altman analysis of visits 1 vs 2 in six children showed a mean change of 0.25, and limits of agreement of -0.66 to 1.16 LCI units, similar to that described in older children. <b>Conclusion:</b> Infant LCI is feasible with light sedation and showed good short term repeatability. Although there was no overall difference in mean LCI, a large proportion of CF patients showed an elevated LCI in infancy.