EVALUATION OF FOCUSED AND UNFOCUSED SHOCK WAVE PROPAGATION IN POLYACRYLAMIDE GEL AND PORCINE TISSUE.

Abstract

Background Extracorporeal shock wave therapy (ESWT) has been shown to increase perfusion in ischemic cardiac tissue and increase autograft healing in both animal models and clinical studies. To help clarify the mechanisms by which ESWT induces tissue healing, we studied the propagation of focused and unfocused shock wave sources in animal tissue by comparing the cavitation pattern in polyacrylamide gel and porcine tissue. Study Design and Method Fifteen percent polyacrylamide blocks, marble-embedded polyacrylamide, and porcine thigh were treated with a focused shock wave source with an OssatronTM machine and unfocused shock wave source with a StorzTM device. Cavitation patterns were visualized using a MicroMaxxTM ultrasound machine immediately after a treatment. Results Focused shock wave treatment of polyacrylamide gel with the OssatronTM produced a focal ellipsoidal cavitation field with a 2 cm depth. An increase in treatment energy or intensity resulted in a more intense cavitation field with a larger diameter. Focused treatment of the marble-embedded gel produced a disturbance of the marble-gel interface with increased cavitation intensity at increased treatment energy. Unfocused shockwave treatment of the polyacrylamide gel produced a focal cavitation field superficially at the site of treatment. However, the cavitation field displayed a radiating pattern with deeper propagation into the gel. Increasing the treatment intensity led to a corresponding increase in the intensity of the cavitation field. Unfocused shock wave treatment of marble-embedded gel showed no observable change in the marble-gel interface. Treatment of porcine thigh with both focused and unfocused shock wave at low and high energy and intensity did not produce any observable changes. Conclusion The result of ESWT in polyacrylamide gel indicates that deep tissue stimulation with an unfocused shock wave source may not yield any benefits because high tissue impedance may reduce shock wave propagation. However, focused shock wave may be more favorable for deep tissue stimulation.