@article {Al-Khathlanp2023, author = {Noor Al-Khathlan and Ruslan Garipov and John Owers-Bradley and Erol Gaillard and Caroline Beardsmore}, title = {Excluding extreme breaths from analysis can change conductive airway ventilatory inhomogeneity by over 25\% in cystic fibrosis}, volume = {38}, number = {Suppl 55}, elocation-id = {p2023}, year = {2011}, publisher = {European Respiratory Society}, abstract = {Gas washout tests assess ventilatory inhomogeneity. Analysis of normalised phase 3 slopes (SnIII) allows differentiation of inhomogeneity of conducting and acinar airways (Scond and Sacin). Standardising data collection and analysis in subjects with a wide range of tidal volumes remains problematic, though multiplying each SnIII by the expired tidal volume (Vt) of the breath has been used as a correction. OurAim was to examine the effect of excluding breaths with extreme Vt on Scond.Methods: We performed multi-breath nitrogen washout in 16 children with CF aged 6 -17 yr. An auditory signal indicated when the child has inspired a pre-set Vt. Measurements were performed in triplicate in all except 2 and analysed with a custom-built programme. SnIII from every breath was plotted against lung turnover (TO), separately for each run and for all runs combined. The slope of SnIII against TO was calculated for all data between 1.5 and 6 TO to determine Scond. Analysis was repeated after excluding breaths that differed from the mean expired Vt by \>10\%. Results were compared with paired t-tests and Bland-Altman plots.Results: The number of breaths between 1.5 and 6 TO ranged from 7-26. 15 children had 1-10 extreme breaths excluded, which had no effect on Scond for the group as a whole (mean, 95\%CI=-0.0015, -0.0076 to 0.0046, p= 0.61). In 5/16 cases Scond altered by \>25\%. Biggest changes were seen in those with lowest values of Scond. Size and direction of the change was unrelated to the number of breaths excluded.Conclusion: Retaining or excluding individual breaths can make a significant difference to Scond, which may be relevant in longitudinal studies.}, issn = {0903-1936}, URL = {https://erj.ersjournals.com/content/38/Suppl_55/p2023}, eprint = {https://erj.ersjournals.com/content}, journal = {European Respiratory Journal} }