Lung clearance index is a sensitive, repeatable and practical measure of airways disease in adults with cystic fibrosis

Alex Robert Horsley ^1*, Per Magnus Gustafsson ², Kenneth Macleod ³, Clare J Saunders ⁴, Andrew P Greening ¹, David Porteous ⁵, Jane Davies ⁴, Steve Cunningham ³, Eric Alton ⁴ and J Alastair Innes ¹

¹ Western General Hospital, Edinburgh, United Kingdom
² Queen Silvia Children's Hospital, Sweden
³ Royal Hospital for Sick Children, Edinburgh, United Kingdom
⁴ Imperial College, London, United Kingdom
⁵ Molecular Medicine Centre, Edinburgh University, United Kingdom

^* To whom correspondence should be addressed. E-mail: alex.horsley{at}ed.ac.uk.

Accepted 19 July 2007

Abstract

Background: Lung clearance index (LCI) is a sensitive marker of early lung disease in children, but has not been assessed in adults. Measurement is hindered by the complexity of the equipment required. The aims of this study were to assess performance of a novel gas analyser (Innocor^TM), and to use it as a clinical tool for the measurement of LCI in cystic fibrosis (CF).

Methods: LCI was measured in 48 healthy adults, 12 healthy school-age children, and 33 adults with CF, by performing an inert gas washout from 0.2% sulphur hexafluoride (SF₆). SF₆ signal:noise ratio and 10-90% rise time of Innocor were compared to a mass spectrometer used in similar studies in children.

Results: Compared to the mass spectrometer, Innocor has a superior signal:noise ratio, but a slower rise time (150 ms v 60 ms) which may limit its use in very young children. Mean (SD) LCI in healthy adults was significantly different from that in CF patients: 6.7 (0.4) v 13.1 (3.8), p<0.0001. Ten of the CF patients had FEV₁80% predicted but only one had a normal LCI. LCI repeats were reproducible in all three groups of subjects (mean intra-visit coefficient of variation ranged from 3.6 to 5.4%).

Conclusions: Innocor can be adapted to measure LCI and affords a simpler alternative to a mass spectrometer. LCI is raised in CF adults with normal spirometry, and may prove to be a more sensitive marker of effects of therapy in this group.

Keywords: Cystic fibrosis, Innocor, Multiple breath washout, Respiratory physiology

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