Morphometric analysis of oleic acid-induced permeability pulmonary edema: correlation with gravimetric lung water

The technique used most commonly to quantitate pulmonary edema in in vivo animal models is postmortem gravimetric analysis (wet:dry) ratio. To determine whether lung water can be quantitated morphometrically, as accurately as by the commonly used gravimetric analysis, perivascular edema (cuff) area to vessel area ratio was correlated to wet:dry ratio. Anesthetized pigs were given either oleic acid (20 mg/kg/h, intravenously) or physiologic saline. At 4 h, lungs were excised and cuff:vessel and wet:dry ratio analysis was performed. The intermediate lobe was clamped across its main stem bronchus to maintain peak inspiratory inflation, excised, frozen in liquid nitrogen, and stored at -70 degrees C until cryostat sectioning and quantification of perivascular interstitial edema (cuff) area. Gravimetric analysis (wet:dry ratio) was performed on the remaining lung. Mean cuff:vessel and wet:dry analyzes showed that lung water increased significantly (p < .01) in the oleic-acid treated group (4.9 +/- .22 and 6.78 +/- .47, respectively), compared with the saline group (.03 +/- .02 and 2.55 +/- .27, respectively). The correlation coefficient between mean cuff:vessel and wet:dry ratios was .86 (p = .0016). This study demonstrates that cuff:vessel ratio analysis can be used to identify the distribution of edema fluid versus vessel diameter, and seems to be as effective a technique as gravimetric analysis to quantitate lung water changes in acute lung injury models. Moreover cuff:vessel ratio analysis can differentiate modest changes in pulmonary edema by direct quantitation, an important end-point not provided by wet:dry analysis. Therefore, it may be a more sensitive technique when investigating therapeutic interventions in in vivo models of acute lung injury.