Hemorrhage in rat fetuses from exposure to pulsed ultrasound

Abstract

Morphological effects of diagnostic pulsed Doppler ultrasound on fetal tissues, particularly lung, in rat fetuses from 16 to 22 days gestation were investigated in this study. A clinical ultrasound machine with two types of focused transducers (3.5, 5 MHz) was used with an adjustment for a small experimental animal. Three levels of exposures were represented by a mechanical index (MI) of 0.5, 0.6 and 1.0. Subpleural uni‐ or multifocal hemorrhage was found in exposed fetal lung. Fetal lungs were microscopically investigated by sectioning through the whole fetal body, which facilitated the discovery of hemorrhage at other sites. The percentage of exposed fetuses with hemorrhage is significant. A threshold for fetal hemorrhage could not be determined, because a significant variation due to age within each exposure group affected the results. Fetuses with lung in the canalicular stage of development (18–19 days) showed the greatest degree of lung hemorrhage. Following laparotomy of the dam to achieve a precise and uniform exposure, a small number of fetuses within each exposure group were exposed directly. There was no higher degree of hemorrhage in these fetuses, than in others indirectly exposed through the dam's abdominal wall.