Reappraisal of extravascular lung thermal volume as a measure of pulmonary edema

Previous papers have evaluated extravascular thermal volume of the lung (ETVL) as a measure of lung water by using median transit time (tmed) rather than the correct mean transit time (tmean). Calculation of ETVL using tmean (ETVLmean) and tmed (ETVLmed) gave an excellent relationship, ETVLmean = 1.48 ETVLmed - 0.74 (r = 0.99). This allowed us to calculate a new ratio of ETVLmean to PETW = 1.55 +/- 0.17, WHERE PETW is the postmortem value of pulmonary extravascular tissue weight. Thermistors were placed in dogs to determine the contribution of chest wall, pleural and pericardial fluid, left heart, bronchi, and lung gas to the ETVL measurement. We found ETVLmean greater than PETW because of thermal distributioninto left heart (18 +/- 2% of ETVL), bronchi (estimate 7% of ETVL), pulmonary arteries and veins (estimate 7% of ETVL), and perhaps a small portion of chest wall. We could not detect any portion of lung gas or pleural or pericardial effusions as a part of the ETVL measurement. When the distribution into left heart, bronchi, pulmonary arteries, and veins is removed ETVLmean/PETW = 1.07.