Center for Industrial and Medical Ultrasound, University of Washington, Seattle, Washington, USA.
Department of Urology, University of Washington School of Medicine, Seattle, Washington, USA.
J Endourol. 2022 Jul;36(7):996-1003. doi: 10.1089/end.2021.0714. Epub 2022 Jun 22.
In clinical trial NCT03873259, a 2.6-mm lower pole stone was treated transcutaneously and with 390-kHz burst wave lithotripsy (BWL) for 40 minutes and failed to break. The stone was subsequently fragmented with 650-kHz BWL after a 4-minute exposure. This study investigated how to fragment small stones and why varying the BWL frequency may more effectively fragment stones to dust. A linear elastic theoretical model was used to calculate the stress created inside stones from shock wave lithotripsy (SWL) and different BWL frequencies mimicking the stone's size, shape, lamellar structure, and composition. To test model predictions about the impact of BWL frequency, matched pairs of stones (1-5 mm) were treated at (1) 390 kHz, (2) 830 kHz, and (3) 390 kHz followed by 830 kHz. The mass of fragments >1 and 2 mm was measured over 10 minutes of exposure. The linear elastic model predicts that the maximum principal stress inside a stone increases to more than 5.5 times the pressure applied by the ultrasound wave as frequency is increased, regardless of the composition tested. The threshold frequency for stress amplification is proportionate to the wave speed divided by the stone diameter. Thus, smaller stones may be likely to fragment at a higher frequency, but not at a lower frequency below a limit. Unlike with SWL, this amplification in BWL occurs consistently with spherical and irregularly shaped stones. In water tank experiments, stones smaller than the threshold size broke fastest at high frequency ( = 0.0003), whereas larger stones broke equally well to submillimeter dust at high, low, or mixed frequencies. For small stones and fragments, increasing frequency of BWL may produce amplified stress in the stone causing the stone to break. Using the strategies outlined here, stones of all sizes may be turned to dust efficiently with BWL.
在临床试验 NCT03873259 中，使用 390kHz 冲击式碎石术（BWL）对 2.6mm 的下极结石进行了 40 分钟的治疗，但未能将结石破碎。随后，将结石暴露在 650kHz 的 BWL 下 4 分钟，将其粉碎。本研究旨在探讨如何将小结石粉碎，以及为什么改变 BWL 频率可能更有效地将结石粉碎成粉尘。本研究使用线性弹性理论模型来计算冲击波碎石术（SWL）和不同 BWL 频率产生的结石内部的应力，这些频率模拟了结石的大小、形状、层状结构和成分。为了测试 BWL 频率对模型预测的影响，对匹配的结石（1-5mm）进行了以下三种处理：（1）390kHz；（2）830kHz；（3）390kHz 后接 830kHz。在 10 分钟的暴露时间内，测量大于 1 和 2mm 的碎片质量。线性弹性模型预测，无论测试的成分如何，随着频率的增加，结石内部的最大主应力增加到超过施加在超声波上的压力的 5.5 倍以上。应力放大的阈值频率与波速除以结石直径成正比。因此，较小的结石可能更容易在较高频率下破碎，但在低于一定频率的情况下不会破碎。与 SWL 不同的是，这种在 BWL 中的放大作用与球形和不规则形状的结石一致。在水箱实验中，小于阈值尺寸的结石在高频下（ = 0.0003）破碎最快，而较大的结石在高频、低频或混合频率下都能同样破碎到亚毫米级的粉尘。对于小结石和碎片，增加 BWL 的频率可能会在结石中产生放大的应力，导致结石破裂。使用这里概述的策略，所有大小的结石都可以通过 BWL 有效地转化为粉尘。
