To assess the effect of diffusion limitation on gas exchange in injured lungs with non-cardiogenic
pulmonary edema, an experimental model of
acute lung injury with alveolar flooding was produced in six mongrel dogs by intravenously injecting
oleic acid at 0.06 ml/kg. The effect of diffusion limitation was quantitatively examined by measuring the excretion (E) of three
indicator gases (
acetylene,
ethylene and
freon-22) with differing solubility (lambda) and tissue diffusivity (d). The
indicator gases were dissolved in
normal saline and infused at a constant rate through a peripheral vein. Since
acetylene and
ethylene have nearly identical of d but differing lambda, the difference in E values of these two
gases may solely reflect the effect of uneven distribution of ventilation-perfusion ratios (VA/Q) in the lung. Thus, measured E values of
acetylene and
ethylene allowed us to approximately predict the E of freon-22, the value corresponding to the condition where d of freon-22 was taken to be equal to that of
acetylene or
ethylene. The difference between predicted and measured E values of freon-22 is indicative of the limitation of diffusion in the lung periphery. In all the lungs studied, measured E values of freon-22 were consistently smaller than those predicted from
acetylene and
ethylene, leading to the conclusion that gas exchange in injured lungs with widespread
pulmonary edema was partly impaired by diffusion in aqueous media.