Pulmonary Single Circulation Dilution Curves of T-1824, Sodium, and Tritiated Water in Intact Piglets

Abstract

Summary: In order to assess pulmonary endothelial permeability to sodium in the immature lung, 15 multiple indicator dilution curves were done in eight intact piglets. An indicator bolus consisting of T-1824, ²²Na, and tritiated water (THO) was delivered into the right atrium and blood was sampled from the aorta. The concentration of sodium, expressed as a fraction of the quantity injected and of the corresponding fractional concentration of T-1824, was averaged for the samples prior to recirculation. The permeability-surface area product calculated from these data is 2.0 ± 10^-5 cm sec^-1, and is virtually identical with the value reported elsewhere for adult dogs. Extravascular lung water obtained from the tritiated water and T-1824 curves averaged 64%, whereas that obtained from the ²²Na and T-1824 curves averaged 23% of blood-free lung water.

Speculation: Several lines of evidence indicate that the endothelium of the immature lung may permit edema formation more readily than that of the adult lung. However, no differences have been found with regard to transendothelial passage of protein molecules or of the sodium ion. We still have no satisfactory explanation for hyaline membrane formation in the respiratory distress syndrome of prematurity. Such information may be provided by the application in prematurely delivered fetuses of techniques available for the assessment of pulmonary capillary permeability.