Reproducibility of multibreath nitrogen washout measurements

The reproducibility of data obtained from the analysis of the pulmonary nitrogen clearance during oxygen breathing was studied in a group of normal subjects and in patients with chronic obstructive pulmonary disease. As shown by statistical analysis, the reproducibility of some relatively simple measures of gas distribution inequality and ventilatory efficiency (lung clearance index and mixing ratio) was found to be satisfactory; the intrasubject variation of data obtained from the graphic analysis of the nitrogen washout curve according to a multicompartment lung model was found to be greater than that of the lung clearance index and mixing ratio, but tolerable for most of these data. The results indicated that the intrasubject variability of the nitrogen washout measurements analyzed in the present study, although acceptable, is not negligible and should be taken into account when assessing the significance of experimental nitrogen clearance changes.