Assessment of alveolar-capillary membrane permeability of dogs by aerosolization.

We developed a method for measuring an index of alveolar-capillary membrane permeability (PI) by aerosolizing a mixture of 99mTc-diethylenetriaminepentaacetic acid (Tc-DTPA) and 125I-antipyrine (I-AP) and injecting 111In-DTPA (In-DTPA). The I-AP was used to compute the quantity of Tc-DTPA delivered and the In-DTPA the quantity of Tc-DTPA in the body. The PI was the ratio of the uptake of Tc-DTPA per minute to the amount deposited at the end of aerosolization. In 14 anesthetized dogs we measured the volume of distribution of I-AP (0.54 +/- 0.034 l/kg body wt) and/or showed that the volumes of distribution of Tc-DTPA and In-DTPA were similar. We measured PI in four groups of dogs: control (n = 5), oleic acid (n = 5), hydrochloric acid (n = 6), and high left atrial pressure (n = 5). The PI increased significantly in both groups with acid-induced increased permeability compared with the control and high left atrial pressure groups, which did not differ from each other. We conclude that the aerosolization method is suitable for differentiating increased from normal permeability.