PEDIATRICS Vol. 35 No. 1 January 1965, pp. 185-193
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III. PULMONARY DIFFUSION

George R. DeMuth M.D.1 and William F. Howatt M.D.1

1 Department of Pediatrics, University of Michigan, Ann Arbor

1. Equations describing the normal variation and changes with size of the diffusing capacity (rebreathing technique) for boys and girls have been obtained from 230 observations on 139 children.

2. The use of covariance analysis on the longitudinal data reduces the residual variance by about half, indicating that in children the diffusing capacity for carbon monoxide, Dco, grows along growth lines. This aids in finding significant deviations from the predicted in children who are followed with repeated examinations.

3. The Dco increases with growth in a manner very similar to that of the lung volumes, not only in respect to height, but also in respect to age, weight, and surface area. The ratio Dco/TLC expresses a relationship which does not vary with body size, age, or sex in these healthy individuals. Although boys and girls have the same mean values, the correlation between each individual's values from the two series is significant for boys but not for girls.

4. The constancy of the Dco/TLC during growth supports the hypothesis that the lung grows between the ages of 5 and 18 years by the addition of new air spaces rather than by enlarging the pre-existing ones.