Moment analysis of multibreath nitrogen washout in young children

The purpose of this study was to determine whether on-line computerized moment analysis of multibreath N2 washout (MBNW) could be used as a method of estimating lung function in children too young to cooperate with routine pulmonary function testing. The limits of normal variability were determined from results obtained from duplicate studies performed on 36 healthy children ages 3-6 yr. Five healthy adults were studied for comparison. Test sensitivity was estimated by comparing the results in the healthy group to those of 10 age-matched children with cystic fibrosis (CF). Outcome variables of interest included functional residual capacity, the first-to-zeroth moment ratio (M1/M0), the second-to-zeroth moment ratio (M2/M0), and the lung clearance index. Test precision in the healthy group was high with the intrasubject coefficient of variation for all variables being less than 10%. There was no difference in mean within- or among-subject variability between the healthy children and the older, theoretically more cooperative, healthy adults. Mean M1/M0 and M2/M0 were both higher in CF than in the healthy group, 2.69 vs. 2.32 and 13.04 vs. 9.31, respectively (P less than 0.001). Moment ratios in CF showed good negative correlations with Shwachman scores; thus those CF patients with the most advanced lung disease had the highest moment ratios and vice versa. Moment analysis of MBNW has promise as a means of quantifying lung function in young children, since the method is noninvasive, low in inherent variability, requires only quiet breathing, and has the sensitivity required to detect rather mild ventilation inhomogeneity.