Validation of fluorescent-labeled microspheres for measurement of relativeblood flow in severely injured lungs

The aim of the study was to validate a nonradioactive method for relative b lood flow measurements in severely injured lungs that avoids labor-intensiv e tissue processing. The use of fluorescent-labeled microspheres was compar ed with the standard radiolabeled-microsphere method. In seven sheep, lung injury was established by using oleic acid. Five pairs of radio- and fluore scent-labeled microspheres were injected before and after established lung injury. Across all animals, 175 pieces were selected randomly. The radioact ivity of each piece was determined by using a scintillation counter. The fl uorescent dye was extracted from each piece with a solvent without digestio n or filtering. The fluorescence was determined with an automated fluoresce nt spectrophotometer Perfusion was calculated for each piece from both the radioactivity and fluorescence and volume normalized. Correlations between flow determined by the two methods were in the range from 0.987 +/- 0.007 ( SD) to 0.991 +/- 0.002 (SD) after 9 days of soaking. Thus the fluorescent m icrosphere technique is a valuable tool for investigating regional perfusio n in severely injured lungs and can replace radioactivity.