Age-dependent threshold and superthreshold behavior of ultrasound-induced lung hemorrhage in pigs

Age-dependent threshold and superthreshold behavior of ultrasound-induced lung hemorrhage was investigated with 116 4.9±1.6-day-old neonate crossbred pigs, 103 39±5-day-old crossbred pigs, and 104 58±5-day-old crossbred pigs. Exposure conditions were: 3.1 MHz, 10-s exposure duration, 1-kHz PRF, and 1.4-μs pulse duration. The in situ (at the pleural surface) peak rarefactional pressure ranged between 2.2 and 10.4 MPa with either 8 or 9 acoustic pressure groups for each of the three pig ages (12 pigs/exposure group) plus sham exposed pigs; there were no lesions in the shams. Pigs were exposed bilaterally with the order of exposure (left and right lung) and acoustic pressure both randomized. Logistic regression analysis was used to examine the dependence of the lesion incidence rates on in situ peak rarefactional pressure, left versus right lung, order of exposure (first versus second) and age in three categories. Likewise, lesion depth and root surface area were analyzed using Gaussian to bit regression analysis. A significant threshold effect on lesion occurrence was observed as a function of age; younger pigs were less susceptible to lung damage given equivalent in situ exposure