1 Department of Biomedical Engineering, University of Michigan , Ann Arbor, Michigan.
J Endourol. 2014 Jan;28(1):90-5. doi: 10.1089/end.2013.0313. Epub 2013 Oct 4.
Rate-dependent efficacy has been extensively documented in shock wave lithotripsy (SWL) stone comminution, with shock waves (SWs) delivered at a low rate producing more efficient fragmentation in comparison to those delivered at high rates. Cavitation is postulated to be the primary source underlying this rate phenomenon. Residual bubble nuclei that persist along the axis of SW propagation can drastically attenuate the waveform's negative phase, decreasing the energy which is ultimately delivered to the stone and compromising comminution. The effect is more pronounced at high rates, as residual nuclei have less time to passively dissolve between successive shocks. In this study, we investigate a means of actively removing such nuclei from the field using a low-amplitude acoustic pulse designed to stimulate their aggregation and subsequent coalescence. To test the efficacy of this bubble removal scheme, model kidney stones were treated in vitro using a research electrohydraulic lithotripter. SWL was applied at rates of 120, 60, or 30 SW/min with or without the incorporation of bubble removal pulses. Optical images displaying the extent of cavitation in the vicinity of the stone were also collected for each treatment. Results show that bubble removal pulses drastically enhance the efficacy of stone comminution at the higher rates tested (120 and 60 SW/min), while optical images show a corresponding reduction in bubble excitation along the SW axis when bubble removal pulses are incorporated. At the lower rate of 30 SW/min, no difference in stone comminution or bubble excitation was detected with the addition of bubble removal pulses, suggesting that remnant nuclei had sufficient time for more complete dissolution. These results corroborate previous work regarding the role of cavitation in rate-dependent SWL efficacy, and suggest that the effect can be mitigated via appropriate control of the cavitation environment surrounding the stone.
在体外使用研究型液电碎石机对模型肾结石进行了处理。以 120、60 或 30 SW/min 的速率施加 SWL，或在施加 SWL 的同时施加气泡去除脉冲。还收集了显示结石附近空化程度的光学图像。结果表明，气泡去除脉冲在较高的测试速率（120 和 60 SW/min）下极大地提高了结石粉碎的效果，而光学图像显示，当加入气泡去除脉冲时，SW 轴上的气泡激发相应减少。在较低的速率 30 SW/min 下，加入气泡去除脉冲对结石粉碎或气泡激发没有差异，这表明残余核有足够的时间进行更完全的溶解。这些结果与关于空化在 SWL 功效的速率依赖性中的作用的先前工作一致，并表明可以通过适当控制结石周围的空化环境来减轻这种影响。
