Temporal and spatial evaluation of lesion reparative responses following superthreshold exposure of rat lung to pulsed ultrasound

This study characterized the reparative responses in rat lung. Forty-five a dult female rats were exposed at two sites over the left lung to 3.1-MHz su perthreshold pulsed ultrasound. The repair of lung lesions was evaluated fr om 0 through 44 days postexposure. Macroscopic lesions at 0 days postexposu re were large bright red ellipses of hemorrhage. By 1 and 3 days postexposu re, lesions were the same size and dark red to red-black, but, by 3 days po stexposure, lesions had a raised surface appearance. From 5 to 10 days post exposure, lesions grew smaller in size, progressed from red-gray to yellow- brown, and retained a raised surface appearance, From 13 through 44 days po stexposure, lesions gradually decreased in size, had a faint yellow-brown d iscoloration, and gradually lost the raised surface appearance. By 37 and 4 4 days postexposure, lung returned to near normal morphology, but had small areas of light yellow-brown discoloration in the areas where lung was expo sed. Microscopic lesions at 0 and 1 days postexposure were areas of acute a lveolar hemorrhage. By 3 days postexposure, lesions had loss of alveolar er ythrocytes and the formation of hemoglobin crystals. From 3 through 44 days postexposure, iron in degraded erythrocytes was processed to hemosiderin a nd was negligible in quantity at 44 days postexposure, The proliferation of resident cells (likely alveolar epithelial cells, fibroblasts and endothel ial cells) and the infiltration of inflammatory cells in lesions declined i n intensity as the lesions aged and was minimal by 44 days postexposure, Un der the superthreshold exposure conditions described, lesions induced by ul trasound do not seem to have long-term residual effects in lung. (C) 2001 W orld Federation for Ultrasound in Medicine & Biology.