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

Abstract

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 aparabolic reflector. This refocused wave field had a tighterfocus (smaller beam width and a higher amplitude) than thelithotripter 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 athigh overpressure (up to 7 MPa)was used to measure acoustic emission due tobubble activity. The typical `double-bang'emission measured in the lithotripter free-fieldwas replaced by a continuum of weak signals when thefluid was enclosed in a pressure chamber. No acousticemissions were measured above an overpressure of 5.5 MPa.Aluminium foils were used tostudy shock wave damage and had distinctdeformation features corresponding to exposure conditions,i.e. pitting and denting accompanied by wrinkling. Pittingwas eliminated by high overpressure and so was due to cavitationbubble collapse, whereas denting and wrinkling were caused by thereflected shock wave refocused by the parabolic reflector.RBCs suspended in phosphate-buffered saline (PBS) were exposedto the reflected wave field from a parabolic reflectorand also from a flat reflector.Exposure to the wave field from the parabolic reflectorincreased haemolysis four-fold compared with untreated controlsand was twice that of cell lysis with the flat reflector.Recently we analysed deformation andrupture of RBCs when subjected toa flow field set up by a focused shock.The cell lysis results presented here are in qualitativeagreement with our theoretical prediction that haemolysisis directly related to the gradient of shock strength andvalidates shearing as a cell lysis mechanism in SWL.