Cell lysis due to shear in shock wave lithotripsy

Abstract

Injury to isolated red blood cells (RBCs) and deformation of aluminum foils due to focused shock waves in a cavitation-free environment were investigated. The lithotripter-generated shock wave was refocused by a parabolic reflector. This refocused wave field had a tighter focus (smaller beamwidth and a higher amplitude) than the lithotripter wave field, as characterized by a membrane hydrophone. Cavitation was eliminated by applying overpressure to the fluid. Aluminum foils were used to study shock wave damage and had distinct deformation features corresponding to exposure conditions, i.e., pitting and denting accompanied with wrinkling. Pitting was eliminated by high overpressure (∼12 MPa) and so was due to cavitation bubble collapse, whereas denting and wrinkling were caused by the reflected shock wave refocused by the parabolic reflector. RBCs suspended in phosphate-buffered saline (PBS) were exposed to the reflected wave field from a parabolic reflector and also from a flat reflector. Exposure to the wave field from the parabolic reflector increased hemolysis fourfold compared to untreated controls and was twice that of cell lysis with the flat reflector. Thus, hemolysis was shown to be directly related to the shock-strength gradient and validates shearing as a cell lysis mechanism in SWL. [Work supported by NIH Grant No. P01 DK43881.]