Age dependence of ultrasonically induced lung hemorrhage in mice.

Thresholds for ultrasonically induced lung hemorrhage were determined in neonatal mice (24-36 h old), juvenile mice (14 d old) and adult mice (8-10 weeks old) to assess whether or not the threshold for lung hemorrhage is dependent upon age. Ultrasonic exposures were at 1.15 MHz with a pulse length of 10 microseconds, pulse repetition frequency of 100 Hz and a total exposure duration of 3 min. The threshold for lung hemorrhage occurred at a peak positive acoustic pressure of approximately 1 MPa for mice in all three age groups. Although the thresholds were similar for neonatal, juvenile and adult mice, the sizes of the suprathreshold hemorrhages were significantly larger in adult mice than in neonatal or juvenile mice.