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Published April 1, 2000 | public
Journal Article Open

Mechanical haemolysis in shock wave lithotripsy (SWL): II. In vitro cell lysis due to shear


In this work we report injury to isolated red blood cells (RBCs) due to focused shock waves in a cavitation-free environment. The lithotripter-generated shock wave was refocused by a parabolic reflector. This refocused wave field had a tighter focus (smaller beam width and a higher amplitude) than the lithotripter wave field, as characterized by a membrane hydrophone. Cavitation was eliminated by applying overpressure to the fluid. A novel passive cavitation detector (HP-PCD) operating at high overpressure (up to 7 MPa) was used to measure acoustic emission due to bubble activity. The typical 'double-bang' emission measured in the lithotripter free-field was replaced by a continuum of weak signals when the fluid was enclosed in a pressure chamber. No acoustic emissions were measured above an overpressure of 5.5 MPa. Aluminium foils were used to study shock wave damage and had distinct deformation features corresponding to exposure conditions, i.e. pitting and denting accompanied by wrinkling. Pitting was eliminated by high overpressure 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 haemolysis four-fold compared with untreated controls and was twice that of cell lysis with the flat reflector. Recently we analysed deformation and rupture of RBCs when subjected to a flow field set up by a focused shock. The cell lysis results presented here are in qualitative agreement with our theoretical prediction that haemolysis is directly related to the gradient of shock strength and validates shearing as a cell lysis mechanism in SWL.

Additional Information

© Institute of Physics 2001. Received 26 October 2000, in final form 5 January 2001; Print publication: Issue 4 (April 2001) We thank Dr Michael Bailey of Applied Physics Laboratory, University of Washington, for providing the PVDF membrane hydrophone and Dr Robin Cleveland of Boston University for his assistance with the design of HP-PCD. We also thank Dr Lawrence Crum and Dr Tim Colonius for their comments and suggestions. This work was supported by NIH Grant P01 DK43881.


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