Zhong P, Preminger G M
Department of Surgery, University of Texas Southwestern Medical Center, Dallas.
J Endourol. 1994 Aug;8(4):263-8. doi: 10.1089/end.1994.8.263.
Clinical experience with extracorporeal shockwave lithotripsy (SWL) has demonstrated significant variations in stone fragility. To understand the physical mechanisms of the differences, we quantitatively determined shockwave-stone interaction under clinically relevant SWL conditions for six stone compositions: calcium oxalate monohydrate (COM), struvite (MAPH), calcium apatite (CA), uric acid (UA), brushite, and cystine. We also characterized the acoustic and mechanical properties of the stones using ultrasound and microindentation techniques. Our results show that renal calculi have distinctly different acoustic and mechanical properties. Higher wave speed, Young's modulus, and fracture toughness were measured from COM and cystine stones, whereas lower values of the corresponding properties were found in CA and MAPH, and the values for brushite and UA stones were in between. Computer modeling of shockwave propagation revealed that under the same shockwave intensity, larger deformation was induced in CA and MAPH stones than in COM and cystine stones. In addition, multiple reflected tensile waves were predicted for stones with concentric layer structure, indicating their susceptibility to shockwave fragmentation. These findings elucidate the mechanisms of the differences in stone fragility observed clinically. Their implications to SWL are discussed.
体外冲击波碎石术（SWL）的临床经验表明结石易碎性存在显著差异。为了解这些差异的物理机制，我们在临床相关的SWL条件下，对六种结石成分：一水草酸钙（COM）、磷酸镁铵（MAPH）、磷酸钙（CA）、尿酸（UA）、透钙磷石和胱氨酸，定量测定了冲击波与结石的相互作用。我们还使用超声和微压痕技术对结石的声学和力学性能进行了表征。我们的结果表明，肾结石具有明显不同的声学和力学性能。从COM和胱氨酸结石中测得较高的波速、杨氏模量和断裂韧性，而在CA和MAPH中发现相应性能的值较低，透钙磷石和UA结石的值介于两者之间。冲击波传播的计算机模拟显示，在相同的冲击波强度下，CA和MAPH结石比COM和胱氨酸结石产生更大的变形。此外，预测具有同心层结构的结石会出现多次反射拉伸波，表明它们易受冲击波破碎的影响。这些发现阐明了临床上观察到的结石易碎性差异的机制。并讨论了它们对SWL的影响。
