Multiple-Breath Inert Gas Washout And Spirometry Vs. Structural Lung Disease In Cystic Fibrosis

¹ Queen Silvia Children's Hospital, Göteborg, Sweden
² Erasmus Medical Center-Sophia Children's Hospital, Rotterdam, Netherlands
³ Queen Silvia Children's Hospital, Göteborg, Sudan

^* To whom correspondence should be addressed. E-mail: per.gustafsson{at}vgregion.se.

Accepted 19 July 2007

	Abstract

A sensitive and valid non-invasive marker of early cystic fibrosis (CF) lung disease is sought. The lung clearance index (LCI) from multiple-breath washout (MBW) is known to detect abnormal lung function more readily than spirometry in children and teenagers with CF, but its relationship to structural lung abnormalities is unknown.

OBJECTIVES: To determine the agreements between LCI and spirometry, respectively, with structural lung disease as measured by high-resolution computed tomography (HRCT) in children and teenagers with CF.

METHODS: This is a retrospective study of 44 consecutive CF patients aged 5-19 yrs (mean 12 yrs). At an annual check-up inspiratory and expiratory HRCT scans, LCI and spirometry (FEV1 and FEF75) were recorded. Abnormal structure was defined as a composite HRCT score >5 per cent, the presence of bronchiectasis, or air trapping >30 per cent. Abnormal lung function was defined as LCI above the predicted mean +1.96 residual standard deviations (RSD), or FEV1 or FEF75 below the predicted mean -1.96 RSD. Sensitivity /specificity assessments and correlation analyses were done.

RESULTS: The sensitivity to detect abnormal lung structure ranged from 85-94% for LCI, 19-26% for FEV1, and 62-75% for FEF75. Specificity ranged from 43-65% for LCI, 89 100% for FEV1, and 75-88% for FEF75. LCI correlated better with HRCT scores (Rs +0.85) than FEV1 (-0.62) or FEF75 (-0.66).

CONCLUSIONS: LCI is a more sensitive indicator than FEV1 or FEF75 for detecting structural lung disease in CF, and a normal LCI almost excludes HRCT abnormalities. The findings of abnormal LCI in some patients with normal HRCT scans suggest that LCI may be even more sensitive than HRCT to lung involvement in CF.

Keywords: Cystic Fibrosis, High-Resolution CT, Lung Clearance Index, Spirometry, Ventilation inhomogeneity

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