Effect of increased ambient pressure on lithotripsy-induced cavitation in bulk fluid and at solid surfaces

Abstract

By reducing cell damage but maintaining stone comminution, overpressure (OP)—increased hydrostatic pressure—offers the promise of safer more effective shock wave lithotripsy (SWL) [Delius, UMB 23, 611–617]. A current hypothesis is that stones offer cavitation sites—sites of violent bubble activity—when the cavitation nuclei in a free field have been dissolved into the fluid by overpressure. Cavitation around solid bodies and in a free field with and without overpressure is investigated. High-speed photography and dual passive cavitation detection (PCD) were used to measure the temporal and spatial extent of cavitation in a 10-cm3 plastic chamber that minimally altered the shock wave. In a free field at OP=0 atm, cavitation bubbles formed and collapsed in 280±20 μs. The time of collapse tc was halved at OP=1 atm, and cavitation activity was not detectable at OP=3 atm. With a stone present, a bubble ∼10 times larger than free-field bubbles grew on the surface of the stone and collapsed after 440±50 μs. With overpressure tc shortened cavitation was still measurable (tc=80±12 μs at OP=3 atm). Results were similar with human kidney stones, artificial cement stones, and an aluminum plate, and support the caviation hypothesis. [Work supported by NIH DK43881, FIRCA, and CRDF.]