Moment analysis of multibreath nitrogen washout in healthy female goats and calves.

Moment analysis of multibreath nitrogen washout curves was performed for healthy female goats and calves. Curves were plotted, using dimensionless coordinates that minimized effects of alveolar ventilation changes. Results were expressed as the ratio of the first to the zeroth moments, mu 1/mu 0. Variability using this method was compared with that of a graphic analysis technique from which an uncorrected slope of a portion of the washout curve (B1/2) and a slope index corrected for lung and tidal volume (the nitrogen dilution constant) can be derived. Mean moment ratios on the basis of pooled data for 4 goats and 3 calves were 2.04 +/- 0.29 and 2.38 +/- 0.17, respectively. These values represent the weighted average number of times the resting lung volume was diluted with 100% O2; the lower the value, the relatively more uniform the distribution of intrapulmonary gas. The coefficient of variation within and between subjects was smallest using moment analysis and was greatest for the B1/2. Variability expressed as SD was similar between the moment ratio and nitrogen dilution constant and was greatest for the B1/2.