Zhou Yufeng, Cocks Franklin H, Preminger Glenn M, Zhong Pei
Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708-0300, USA.
J Urol. 2004 Jul;172(1):349-54. doi: 10.1097/01.ju.0000132356.97888.8b.
The comminution of kidney stones in shock wave lithotripsy (SWL) is a dose dependent process caused primarily by the combination of 2 fundamental mechanisms, namely stress waves and cavitation. The effect of treatment strategy with emphasis on enhancing the effect of stress waves or cavitation on stone comminution in SWL was investigated. Because vascular injury in SWL is also dose dependent, optimization of the treatment strategy may produce improved stone comminution with decreased tissue injury in SWL.
Using an in vitro experiment system that mimics stone fragmentation in the renal pelvis spherical BegoStone (Bego USA, Smithfield, Rhode Island) phantoms (diameter 10 mm) were exposed to 1,500 shocks at a pulse repetition rate of 1 Hz in an unmodified HM-3 lithotripter (Dornier Medical Systems, Kennesaw, Georgia). The 3 treatment strategies used were increasing output voltage from 18 to 20 and then to 22 kV every 500 shocks with emphasis on enhancing the effect of cavitation on medium fragments (2 to 4 mm) at the final treatment stage, decreasing output voltage from 22 to 20 and then to 18 kV every 500 shocks with emphasis on enhancing the effect of stress waves on large fragments (greater than 4 mm) at the initial treatment stage and maintaining a constant output voltage at 20 kV, as typically used in SWL procedures. Following shock wave exposure the size distribution of fragments was determined by the sequential sieving method. In addition, pressure waveforms at lithotripter focus (F2) produced at different output settings were measured using a fiber optic probe hydrophone.
The rate of stone comminution in SWL varied significantly in a dose dependent manner depending on the treatment strategies used. Specifically the comminution efficiencies produced by the 3 strategies after the initial 500 shocks were 30.7%, 59% and 41.9%, respectively. After 1,000 shocks the corresponding comminution efficiencies became similar (60.2%, 68.1% and 66.4%, respectively) with no statistically significant differences (p = 0.08). After 1,500 shocks the final comminution efficiency produced by the first strategy was 88.7%, which was better than the corresponding values of 81.2% and 83.5%, respectively, for the other 2 strategies. The difference between the final comminution efficiency of the first and second strategies was statistically significant (p = 0.005).
Progressive increase in lithotripter output voltage can produce the best overall stone comminution in vitro.
冲击波碎石术（SWL）中肾结石的粉碎是一个剂量依赖性过程，主要由应力波和空化这两种基本机制共同作用引起。本研究探讨了着重增强应力波或空化对SWL中结石粉碎效果的治疗策略的影响。由于SWL中的血管损伤也是剂量依赖性的，优化治疗策略可能在提高结石粉碎效果的同时减少SWL中的组织损伤。
使用一种模拟肾盂结石破碎的体外实验系统，将球形BegoStone（美国Bego公司，罗德岛州史密斯菲尔德）模型（直径10毫米）在未改装的HM - 3碎石机（多尼尔医疗系统公司，佐治亚州肯尼索）中以1赫兹的脉冲重复频率接受1500次冲击。所采用的3种治疗策略分别为：每500次冲击将输出电压从18 kV提高到20 kV，再提高到22 kV，在最终治疗阶段着重增强空化对中等大小碎片（2至4毫米）的作用；每500次冲击将输出电压从22 kV降低到20 kV，再降低到18 kV，在初始治疗阶段着重增强应力波对大碎片（大于4毫米）的作用；以及保持输出电压恒定在20 kV，这是SWL手术中通常使用的设置。冲击波暴露后，通过顺序筛分法确定碎片的尺寸分布。此外，使用光纤探头水听器测量不同输出设置下碎石机焦点（F2）处的压力波形。
根据所采用的治疗策略，SWL中结石的粉碎速率在剂量依赖性方面有显著差异。具体而言，在最初的500次冲击后，这3种策略产生的粉碎效率分别为30.7%、59%和41.9%。在1000次冲击后，相应的粉碎效率变得相似（分别为60.2%、68.1%和66.4%），无统计学显著差异（p = 0.08）。在1500次冲击后，第一种策略产生的最终粉碎效率为88.7%，优于其他两种策略分别对应的81.2%和83.5%。第一种和第二种策略的最终粉碎效率之间的差异具有统计学显著性（p = 0.005）。
逐步提高碎石机输出电压可在体外产生最佳的总体结石粉碎效果。
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