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P184 Calculation of conductive inhomogeneity in children with severe cf lung disease: which method works?
  1. N Verger1,
  2. M Arigliani2,
  3. E Raywood3,
  4. JA Duncan3,
  5. A Bush4,
  6. P Aurora5
  1. 1Master Biologie intégrative et physiologie, Université Pierre et Marie Curie Paris 6, Paris, France
  2. 2Department of Clinical and Experimental Medical Sciences, Unit of Paediatrics, University Hospital of Udine, Udine, Italy
  3. 3Respiratory, Critical Care and Anaesthesia Section, UCL Great Ormond Street Institute of Child Health, London, UK
  4. 4The National Heart and Lung Institute, Imperial College, London, UK
  5. 5Department of Respiratory Medicine, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK


Introduction Convection Dependent Inhomogeneity (CDI, a measure of ventilation inequality among larger lung units) quantified by Scond cannot be assessed in subjects with severe ventilation inhomogeneity (VI) as assumptions underlying the calculation are invalid; an alternate index that has been suggested is Scond.1

Aim To compare these two methods of CDI assessment in CF children

Methods Children with cystic fibrosis (CF; 67) and healthy controls (61) performed multiple breath washout with sulphur hexaflouride measured using mass spectrometry. Scond was calculated from 1.5 to 6 turnovers and Scond* from breath 2 to 3 turnovers.

Results All measures of VI were significantly higher for CF vs control, mean difference: LCI 4.0, Scond 0.054, Scond* 0.081.

In CF, LCI correlated better with Scond* than Scond (See figure: correlation coefficient LCI vs. Scond* 0.75; LCI vs. Scond 0.42). If children with moderate-severe VI (LCI > 11) were excluded there was an improved correlation for both relationships (correlation coefficient LCI vs. Scond 0.83; LCI vs. Scond* 0.86).

An asymptote for the Scond vs LCI relationship was at Scond 0.07 and Scond* 0.13.

Conclusion Scond* quantifies the mechanism of VI in moderate to severe lung disease, but it may reach asymptote in very severe VI.


  1. Verbanck. Respiratory Physiology & Neurobiology, 2013.

Abstract P184 Figure 1

CF triangles, Control circles. A. Scond vs LCI b, Scond* vs LCI c. Scond* vs Scond with line of equivalence

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