Michael R. Bailey
David T. Blackstock
Appl. Res. Labs. and Mech. Eng. Dept., Univ. of Texas at Austin, Austin, TX 78713-8029
Diane Dalecki
Carol H. Raeman
Sally Z. Child
Edwin L. Carstensen
Univ. of Rochester, Rochester, NY 14627
Murine lung and Drosophila larvae were used to compare effects of isolated positive and negative pulses on tissue containing gas bodies. The basic pulse, produced by an underwater spark, was positive. It could be isolated by floating absorptive, nonreflecting rubber on the water surface to prevent reflection. When an isolated negative pulse was desired, the rubber was removed and the direct, positive pulse was blocked by inserting a jagged-edge barrier between the spark and the exposure area. The jagged edge rendered the diffracted wave (from the barrier edge) incoherent and therefore negligible in the exposure area. Exposure levels were varied by altering the proximity of the exposure area to the source. For each level, lung damage and larva mortality due to 20-pulse exposures were measured. Positive pulses were found to be at least as damaging, to both tissues, as negative pulses having the same amplitude. If the damage was due to cavitation, this result is contrary to conventional wisdom, which holds negative pressure largely responsible for the violence of inertial cavitation. It is speculated that the expansion and ensuing catastrophic collapse of a bubble are hindered in the presence of tissue. [Work supported by ONR, NIH, and ARL: UT IR&D program.]