Use of Multiple Indicator Dilution (MID) for detection of lung tissue composition changes

Differences in lung tissue composition were-detected using MID in perfused rabbit lungs treated to mimic permeability edema (PE), hydrostatic edema (HE) and granulomatous inflammation (GI). Treatments resulted in perfused lungs of similar wet wt. Boluses containing FITC dextran, 14C-diazepam (D), 3HOH, or 14C-phenylethylamine were injected via the pulmonary artery with sampling from the left atrium, and used as vascular reference, tissue binding, extravascular water (Ew) and endothelial surface indicators, respectively. Kinetic modeling of the data identified the parameters α and H, capacities of rapidly and slowly equilibrating D-lung tissue interactions respectively, ψ (sec), avg. interaction time of H, Kseq (ml/sec), rate of D sequestration and PS, a measure of perfused surface. Treatment Wet wt. g Ew ml H ψ Kseq PE 44.5±.8 33.1±.4 6.3±.3 1.1±.3 0.8±.1 HE 45.1±.8 32.8±.9 1.2±.4 4.3±3 0.3±.2 GI 47.1±3.8 22.8±1.1 9.5±.6 6.5±.3 3.0±.6 The vascular vol., PS and α were similar for all treatments. However differences in Ew, H, ψ and Kseq indicate that the similar increases in lung mass for each lung injury treatment results from differences in lung tissue composition that are distinguishable by the MID method.