Two methods for the measurement of pulmonary edema are compared. The first method, which permits serial measurements in vivo, depends on the difference in mean transit time of a water label and an intravascular label. The second method is a postmortem one in which total lung water is measured and allocated to the pulmonary blood or to pulmonary extravascular water. Three groups of six dogs each were studied: controls, a group with pulmonary edema produced by elevating pulmonary venous pressure, and a group with pulmonary edema produced by alloxan. The isotopic as compared with the postmortem method accounted for 71% of the pulmonary extravascular water found in the controls, 94% in high pressure edema and 57% in alloxan edema. Shunting, as measured by a large fall in PaO 2 despite 100% oxygen breathing, became marked in a second group of five alloxan dogs and only 31% of the postmortem pulmonary extravascular water was measured by the isotope method. It is concluded that the isotope transit time method is a useful one for the serial measurement of pulmonary edema in vivo. The edema water is determined more accurately when pulmonary edema is due to elevated pulmonary venous pressure than when due to increased vascular permeability.

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