The relationship between infant and preschool lung function in cystic fibrosis. A pilot follow-up study.

<bold>Background:</bold> Lung function impairment is present early in infancy in cystic fibrosis (CF) but follow-up data are sparse. <bold>Aims:</bold> To track lung function in CF between infancy and preschool age. <bold>Methods:</bold> Lung clearance index (LCI) from nitrogen multiple breath washout test (N2-MBW) and maximal expiratory flow at functional residual capacity (V´maxFRC) from tidal volume rapid thoracoabdominal compression were measured in sedated Czech infants with CF. N2-MBW and forced spirometry (outcomes: FEV1/FVC and MMEF25-75) were repeated in preschool age. Body mass index was calculated at both timepoints. Outcomes were expressed as z-scores (z-s). Relevant outcomes in infancy and preschool age were compared (paired t-test) and correlated (Pearson coefficient, r). <bold>Results:</bold> Longitudinal data from 19 patients were available. Mean (SD) follow-up time was 3.98 (1.28) years. LCI z-s significantly deteriorated from 0.80 (2.82) in infancy to 2.59 (3.33) in preschool age, p = 0.011. Increased LCI (z-s >1.64) was found in 31.6% infants and 52.6% preschoolers. LCI z-score in infancy correlated with preschool LCI z-s (r=0.61, p=0.006) and MMEF25-75 z-s (r=-0.57, p=0.022). V´maxFRC was decreased (z-s <-1.64) in 21.1% infants and MMEF25-75 z-s in 21.1% preschoolers. V´maxFRC z-s correlated with preschool BMI z-s (r=0.69, p=0.038) and FEV1/FVC z-s (r=-0.70, p=0.036), but not MMEF25-75 z-s. <bold>Conclusion:</bold> Ventilation inhomogeneity significantly deteriorated from infancy to preschool age in CF patients despite standard care (without modulators), while expiratory flows remained stable. Moderate and significant correlation between selected lung function parameters in infancy and in preschool age was found.