SURFACE AREA-INDEPENDENT ASSESSMENT OF LUNG MICROVASCULAR PERMEABILITY WITH AN AMPHIPATHIC TRACER

A combination of an amphipathic indicatordilution (ID) diffusing tracer 1,4[C-14]butanediol (B) and a hydrophilic tracer ([C-14]urea) (U) was hypothesized to provide a capillary surface area- (S) independent assessment of lung microvascular permeability (P). We performed ID studies on isolated perfused dog lungs and administered randomly two interventions, increasing P by alloxan infusion and reduction in S by lobar ligation. The ratio of PS product of U (PS(U)) to that for butanediol (PS(B)) was sensitive to changes in P yet insensitive to changes in S. We performed ID studies in which the dependence of PS(U) and PS(B) on flow, hematocrit, and plasma protein binding were examined. Measurements of PS(U) and PS(B) after flow and hematocrit were changed suggested that these factors have no significant independent effects. From ID and in vitro studies we also found that no significant binding of B to plasma proteins (albumin) occurred. We concluded that ID techniques using B and U provide a consistent measure of P, despite changes in S, hematocrit, plasma protein concentration, and recruitment.