The influence of gaseous diffusion on the alveolar plateau at different lung volumes

Abstract

The effect of gaseous diffusion upon the alveolar plateau has been investigated using an aerosol which behaves as a gas with very low diffusivity (10 −6), a poorly diffusible gas, Sulphur Hexafluoride (0.37), and a readily diffusible gas, Neon (1.0). The mathematical solution of the diffusion equation in a model representing lung anatomy suggested that the expired curves after inspiring these gases should differ. Experiments confirmed that the expired curves, within the same expirate, were different and that the manner of difference was such that it could be explained only on the basis of diffusion. Since the difference between the curves rapidly diminished with breath holding this again suggested a diffusion mechanism. Experiments at different lung volumes showed that different slopes of alveolar plateaux were produced. It is concluded that whilst regional inhomogeneity is undoubtedly present in the lung it is difficult to obtain information about it from a study of the alveolar plateau produced in the manner described, and that this plateau results in the main from stratified inhomogeneity.