Effect of variable parenchymal expansion on gas mixing.

Using implanted radiopaque markers, Hubmayr et al. (J. Appl. Physiol. 54: 1048-1056, 1983) and Olson et al. (J. Appl. Physiol. 57: 1710-1714, 1984) detected a variability in the volume changes of regions defined by the markers in intact and excised dog lungs, respectively. In dogs lying prone and in excised lobes, there is virtually no large-scale spatial organization of the variability. We interpret these data as evidence of an intrinsic heterogeneity of parenchymal expansion. The effect of variability of parenchymal expansion on gas mixing is calculated. From a statistical model, we infer that the variability of volume changes observed by Olson et al. is a result of an underlying variability with a larger magnitude at a smaller scale and that the variability at the smaller scale is large enough to explain the inefficiency of mixing observed in single-breath oxygen tests on excised dog lobes.