A problem in the measurements of pulmonary extravascular water volume by double indicator dilution method, using heat and dye Thermal diffusion into the left ventricular wall.

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Abstract
Pulmonary extravascular water volume was obtained as the lung thermal volume (LTV) in mongrel dogs (n = 31) by double indicator dilution method, using negative heat and indocyanine green. A technique of 1 injection site (right atrium) and 2 sampling sites, i.e., pulmonary artery trunk and aortic root. In 13 dogs, cardiac outputs determined simultaneously from thermodilution curves in pulmonary artery trunk, aortic root and from dye dilution curve in aortic root, were in a good agreement with a coefficient of variation of .+-. 12%. Lung thermal volume measured twice within a period of 5 min in 17 dogs, gave closely similar values with a coefficent of variation of .+-. 9%. Lung thermal volume was 5.7 .+-. 1.1 ml/kg (mean .+-. SD) and corresponding weighed lung water (WLW), which was measured by destructive, direct method, was 5.0 .+-. 1.0 ml/kg, the ratio of LTV to WLW (LTV/WLW) being 1.2 .+-. 0.2 in control state. LTV/WLW ratio was 1.2 .+-. 0.2 in 11 dogs loaded with dextran, and 1.1 .+-. 0.1 in 6 dogs loaded with alloxan. Thus, the lung thermal volume slightly exceeded WLW. To evaluate the extent to which the thermal diffusion into the left ventricular wall would cause LTV to slightly overestimate the pulmonary extravascular water volume, dye dilution curves and thermodilution curves were recorded simultaneously in the left atrium (LA) and aortic root (Ao) in a total of 25 runs in 5 dogs. The ratio of LTV obtained in LA to that in Ao was 0.9 .+-. 0.1 (mean .+-. SD). The pulmonary extravascular water volume was apparently overestimated, by .apprx. 10% due to the thermal diffusion into the left ventricular wall.