Differential lung blood flows in experimental unilateral emphysema: nonvalidity of perfusion scans

As part of an evaluation of the effects of left lung transplantation in dogs with papain emphysema of the right lung, differential lung blood flows were estimated by in vivo scintiscan of 99Mc-macroaggregated albumin (99mTc-MAA) and, after sacrifice, by direct counting of isotopically labeled carbonized microspheres. In six dogs, percentage flow to the right lung was calculated at the following four times: before and after induction of papain emphysema and 2 and 6 weeks after left lung autotransplantation. After the induction of right lung emphysema, the right lung in four of six animals continued to receive more than 50 percent of the total pulmonary blood flow. No correlation could be established between right lung blood flow determined by carbonized microsphere distribution (true right lung blood flow) and the flow determined by anterior and posterior scintiscans (apparent right lung blood flow). This discrepancy was caused by gross distortion of the right, emphysematous lungs, which had herniated into the left hemithoraces. This herniation was demonstrated by coronal slices taken through the thoraces of two additional dogs with right lung emphysema that were given radiolabeled carbonized microspheres and 99Tc-MAA and frozen after sacrifice. These results indicate that external scintiscans for which the particulate distribution technique are used are invalid in circumstances of altered lung geometry.