Ultrasonically induced lung hemorrhage in young swine

Ten-day old swine were used in the final step of a study of the age dependence of the threshold for lung hemorrhage resulting from exposure to diagnostically relevant levels of pulsed ultrasound. A 2.3-MHz focused transducer (pulse length of 10 μs, 100-Hz pulse repetition frequency) was incremented vertically at several sites for a distance of 2 or 2.5 cm over the chest of the subject for a total exposure period of 16 or 20 min. The procedure was repeated at a total of four sites per animal. Animals were euthanized and lungs were scored by visual inspection for numbers and areas of gross hemorrhages. The threshold level for hemorrhage was approximately 1.3-MPa peak positive pressure in water at the surface of the animal or, at the surface of the lung, 0.8-MPa peak positive pressure, 0.8-MPa fundamental pressure, 0.7. MPa maximum negative pressure and 20 Wcm⁺² pulse average intensity. These values are essentially the same as those reported previously for neonatal swine, and neonatal, juvenile and adult mice.