Optical and radioisotope indicator dilution measurements in pulmonary edema

The objective of this study was a validation of an optical multiple indicator dilution technique for measuring microvascular exchange parameters in edematous lungs by comparison to conventional radioisotope multiple indicator dilution methods. Six anaesthetized dogs were studied at baseline and after alloxan infusion to increase capillary permeability. In addition, 11 isolated, perfused dog lungs were studied at baseline and after edema was created by increasing venous pressure or by infusing alloxan to increase vascular permeability. Increased capillary permeability from alloxan infusion led to increases in most but not all capillary exchange parameters as analyzed by mathematical models and measured by both optical and radioisotope methods. Increased vascular pressure led to increased edema but no significant increases in capillary exchange parameters. Two-way analysis of variance (ANOVA; variations in baseline versus pressure or alloxan and variation in optical versus radioisotope for each transport parameter derived from the mathematical models) indicated few significant differences in capillary exchange parameters between optical and radioisotope measures. Newman-Keuls multiple comparison tests did uncover some variations between a few of the group-mean values derived from optical and radioisotope methods. However, optical and radioisotope parameter measurements were highly correlated for all studies regardless of the mathematical model used for analysis. (C) 1998 Biomedical Engineering Society.