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Multiple-breath inert gas washout test and early cystic fibrosis lung disease
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  1. P Aurora
  1. Correspondence to Dr Paul Aurora, Portex Respiratory Unit, UCL Institute of Child Health, 30 Guilford Street, London WC1N 1EH, UK; p.aurora{at}ich.ucl.ac.UK

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An ideal lung function test should be easy to obtain, and involve no risk to the subject. In order to be of value, it should be able to help diagnosis, assist prognosis, monitor disease progress or measure the effect of therapeutic interventions.1

Regular spirometry measurement is an accepted component of clinical monitoring of adults and school-age children with cystic fibrosis (CF). Specifically, the forced expired volume in 1 s (FEV1), or its rate of decline, is commonly used to monitor disease progression in individuals, and as an outcome measure in clinical trials. However, as the survival of subjects with CF improves,2 there has been a shift towards closer monitoring and more aggressive treatment of early CF lung disease.3 As a consequence, two major disadvantages to the use of FEV1 in early CF lung disease have become apparent. Many school-age children with CF now have FEV1 within the normal range, even though they probably have lung disease.3 Also, reliable forced expiratory manoeuvres are difficult to obtain in children under the age of 5 years, with testing in infants being largely confined to specialist laboratories,4 and testing in preschool children relatively novel.5

There are good theoretical reasons why spirometry may be insensitive to early CF lung disease. First, airway disease in CF is known to be non-uniformly distributed. As flow measured during forced expiration is the integrated output of all airways,6 then it is possible that minor alterations of airway calibre in some lung regions may be masked by normal function in other regions. Secondly, airway obstruction in CF is partly due to intraluminal mucus, and this may be dislodged by a forced …

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