Computational model of airway narrowing: mature vs. immature rabbit.

Immature rabbits have greater maximal airway narrowing and greater maximal fold increases in airway resistance during bronchoconstriction than mature animals. We have previously demonstrated that excised immature rabbit lungs have more distensible airways, a lower shear modulus, and structural differences in the relative composition and thickness of anatomically similar airways. In the present study, we incorporated anatomic and physiological data for mature and immature rabbits into a computational model of airway narrowing. We then investigated the relative importance of maturational differences in these factors as determinants of the greater airway narrowing that occurs in the immature animal. The immature model demonstrated greater sensitivity to agonist, as well as a greater maximal fold increase in airway resistance. Exchanging values for airway compliance between the mature and immature models resulted in the mature model exhibiting a greater maximal airway response than the immature model. In contrast, exchanging the shear moduli or the composition of the airway wall relative to the airway size produced relatively small changes in airway reactivity. Our results strongly suggest that the mechanical properties of the airway, i.e., greater compliance of the immature airway, can be an important factor contributing to the greater airway narrowing of the immature animal.