Air trapping on chest CT is associated with worse ventilation distribution in infants with cystic fibrosis diagnosed following newborn screening

Abstract

Background: In school-aged children with cystic fibrosis (CF) structural lung damage assessed using chest CT is associated with abnormal ventilation distribution. The primary objective of this analysis was to determine the relationships between ventilation distribution outcomes and the presence and extent of structural damage as assessed by chest CT in infants and young children with CF.

Methods: Data of infants and young children with CF diagnosed following newborn screening consecutively reviewed between August 2005 and December 2009 were analysed. Ventilation distribution (lung clearance index and the first and second moment ratios [LCI, M(1)/M(0) and M(2)/M(0), respectively]), chest CT and airway pathology from bronchoalveolar lavage were determined at diagnosis and then annually. The chest CT scans were evaluated for the presence or absence of bronchiectasis and air trapping.

Results: Matched lung function, chest CT and pathology outcomes were available in 49 infants (31 male) with bronchiectasis and air trapping present in 13 (27%) and 24 (49%) infants, respectively. The presence of bronchiectasis or air trapping was associated with increased M(2)/M(0) but not LCI or M(1)/M(0). There was a weak, but statistically significant association between the extent of air trapping and all ventilation distribution outcomes.

Conclusion: These findings suggest that in early CF lung disease there are weak associations between ventilation distribution and lung damage from chest CT. These finding are in contrast to those reported in older children. These findings suggest that assessments of LCI could not be used to replace a chest CT scan for the assessment of structural lung disease in the first two years of life. Further research in which both MBW and chest CT outcomes are obtained is required to assess the role of ventilation distribution in tracking the progression of lung damage in infants with CF.

Figure 1. Lung clearance index (LCI) plotted against age (weeks) in infants diagnosed with cystic fibrosis following newborn screening.

Infants with air trapping are shown in closed circles.

Figure 2. Lung clearance index (LCI; upper panel) and the second moment ratio (M₂/M₀; lower panel) difference with the presence and absence of bronchiectasis (n = 13 with and n = 36 without bronchiectasis) and air trapping (n = 24 with and n = 25 without air trapping) in infants with cystic fibrosis.

Data are presented as box and whisker plots representing the 25^th and 75^th centiles and 10^th and 90^th centiles respectively. There were no differences in LCI between those infant with (grey box) and without (white box) lung damage while M₂/M₀ was significantly increased (p = 0.049) in those infants and young children with air trapping present on chest CT.

Figure 3. Changes in the lung clearance index (LCI; panel A) and the first (M₁/M₀; panel B) and second moment ratios (M₂/M₀; panel C) with the increasing extent of air trapping.

Increasing extent of air trapping was associated with an increased LCI (r = 0.31 p = 0.03) and M₂/M₀ (r = 0.40; p<0.005) but not M₁/M₀ (r = 0.28; p = 0.051).