The effect of low-frequency ultrasound on immersed pig lungs

Acoustic models suggest that high-intensity, low-frequency ultrasound (US) at 21-31 kHz, could cause damage to divers' lungs. The purpose of the study was to investigate lung tissue changes secondary to water-borne low-frequency US produced by commonly used underwater acoustic beacons (pingers). Explanted pig lungs were immersed and exposed to four different modes of low-frequency US pinger transmission. In each trial, 5 pairs of lungs were exposed to sound and 5 pairs served as controls. One central and one peripheral section were taken from each lung and evaluated microscopically for location and extent of damage. When present, microhaemorrhages were primarily found in a patchy alveolar distribution, as well as in the septal and subpleural regions. Only rare focal microhaemorrhages could be found in the Control Group. The results demonstrate a potential hazard to the immersed lungs of large mammals on exposure to prolonged transmission by commercially available underwater pingers. The relevance of these findings to human exposure should be further evaluated.