Nitrogen multiple-breath washout outcomes and variability.

Triplicate nitrogen multiple-breath washout (N2MBW) tests applied to measure functional residual capacity (FRC) in vitro in the small* (n = 7) and the large† lung model (n = 41), and in 30 healthy adults‡. LCI = lung clearance index. Sacin = phase III slope index of acinar ventilation inhomogeneity. Scond = phase III slope index of conductive ventilation inhomogeneity. CV = intra-test coefficient of variation (SD/mean*100). Mean difference§ (95% confidence interval) from paired t-tests comparing measured and actual model FRC [in vitro] or N2MBW outcomes between two test occasions [in vivo]. CR = coefficient of repeatability (1.96*SD of differences between measured and actual model FRC or differences of N2MBW outcomes between tests). CR is given in respective units or as percentage of the mean. n.a. = not applicable.