EFFECT OF PULMONARY VOLUME LOSS ON THE SIZE AND APPEARANCE OF EXPERIMENTALLY PRODUCED SCINTIGRAPHIC PERFUSION DEFECTS

Rationale and Objectives. Atelectasis is a frequent concomitant of pul monary embolism (PE) and other conditions that mimic PE. Accordingly, we developed an animal model to study the effect of regional loss of p ulmonary volume on the size and configuration of experimentally induce d perfusion defects that simulated PE. Methods. After baseline anterop osterior and lateral chest radiographs were taken, 11 pulmonary vascul ar occlusions were created in 10 anesthetized, intubated mongrel dogs, Three were created by balloon occlusions of segmental pulmonary arter ies, and eight were created by release of autologous PE. The size and shape of the affected lung zones were determined by perfusion scintigr aphy (technetium-99m-macroaggregrated albumin [Tc-99m-MAA]) and the re sults recorded. A balloon-tip Fogarty catheter then was passed through the trachea and inflated at preselected endobronchial sites to produc e bronchial occlusion and volume loss, which were documented radiograp hically, Because one animal had two such occlusions sequentially, a to tal of 12 volume reduction experiments were performed. After inducing volume loss? perfusion imaging was repeated without reinjection of Tc- 99-MAA to allow any changes in the perfusion defects to be recorded, m easured, and compared with the degree of volume loss visualized radiog raphically. Results. Volume loss did not alter the shape of ipsilatera l scintigraphic perfusion defects, but it did result in the expansion of eight of the 12 perfusion defects (range = 18-137% increase in area , Mdn = 33%) and a 28% decrease in the size of one defect located with in a lobe that lost volume. Despite these quantitative changes, only t hree of the perfusion defects appeared substantially larger. When inde pendently interpreted radiographs demonstrated large volume losses, qu antitative changes in perfusion defects were no greater on average tha n when radiographic volume loss was modest. Conclusion. Loss of pulmon ary volume is occasionally associated with considerable ipsilateral al terations in the size of scintigraphic perfusion defects. It is probab ly advisable to consider the effects of anatomic distortions such as v olume loss when interpreting the significance of scintigraphic perfusi on defects in patients suspected of having PE.