Pericapillary Gas and Water Distribution Volumes of the Lung Calculated from Multiple Indicator Dilution Curves

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Abstract
Simultaneous indicator dilution curves of albumin I131, tritiated water, and an inert gas are identical when the indicators do not traverse a capillary bed. When the same three indicators traverse the pulmonary capillaries before sampling, the shapes of the tritiated water and inert gas dilution curves are altered by movement of these two indicators into an extravascular water space and gas space respectively. The arithmetical difference between the distribution volumes of albumin I131 and tritiated water measures a functional extravascular water space in the lungs. The difference between tritiated water and inert gas distribution volumes is a measure of a lung gas volume in contact with perfusing capillaries. Pericapillary water distribution volume in normal dogs was found to be 4.2 ± 0.8 ml/kg and the gas distribution volume 24 ± 6 ml/kg. In normal human subjects the respective values were 1.1 ± 0.3 ml/cm height and 1.80 ± 0.28 liters/m2 of body surface area. Changes in both gas and water distribution volumes were observed as a result of experimental pulmonary edema in dogs and in various forms of pulmonary disease in man.