Department of Urology, Kaplan Medical Center, Rehovot, Israel.
Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israel.
J Endourol. 2020 Jan;34(1):68-73. doi: 10.1089/end.2019.0465. Epub 2019 Aug 28.
Extrinsic ureteral obstruction is caused frequently by pelvic malignancies or metastatic lymphadenopathy, necessitating renal drainage with ureteral stents to prevent renal failure and kidney damage. Understanding the nature of stent behavior under deformation and realistic external pressures may assist in evaluation of stent performance. Few published studies have investigated the flow and mechanical properties of stents within ureters, and none has considered the effects of deformation and compression on flow in realistic, , ureter-stent systems. The purpose of this work was to determine whether or not stent failure is due only to stent compression and deformation in the presence of extrinsic obstruction. We developed an ureter-stent experimental setup, using latex tubing to simulate a flexible ureter connecting a renal unit and a bladder side. We examined flow behavior in three stents (4.8F, 6F, 7F). The ureter-stent configuration was varied, simulating four levels of deformation (0°, 20°, 40°, 60°) and then simulating different external compressive forces on a stented ureter with 40° deformation. A constant, realistic fluid flow was applied through the ureter-stent configurations, and pressure fluctuations in the renal unit were monitored. Deformation alone on four different levels (0°, 20°, 40°, 60°) has essentially no influence on fluid flow and renal pressure variation. Under increasing external compressive forces of 500, 1000, 2000, and up to 5000 g at 40° deformation, no effect on fluid flow and pressure within the renal unit was noted for the 6F and 7F stents. The only exception was for the 4.8F stent, which demonstrated complete failure at compressive forces near 4000 g. Neither realistic extrinsic ureteral compression forces nor ureteral deformation explain the high frequency of stent failure in extrinsic ureteral obstruction. Other factors such as urine composition may be a major contributor to stent failure.
外在输尿管梗阻常由盆腔恶性肿瘤或转移性淋巴结病引起，需要通过输尿管支架进行肾脏引流，以防止肾衰竭和肾脏损伤。了解支架在变形和实际外部压力下的行为特性可能有助于评估支架性能。很少有发表的研究调查过输尿管内支架的流动和力学特性，也没有研究考虑变形和压缩对真实的、带有输尿管-支架系统中的流动的影响。这项工作的目的是确定支架失效是否仅仅是由于外在梗阻存在时支架的压缩和变形。
我们开发了一个输尿管-支架实验装置，使用乳胶管模拟连接肾脏单元和膀胱侧的柔性输尿管。我们检查了三个支架（4.8F、6F、7F）的流动行为。输尿管-支架的配置有所变化，模拟了四个变形水平（0°、20°、40°、60°），然后模拟了带有 40°变形的支架输尿管上不同的外部压缩力。通过输尿管-支架配置施加恒定的、现实的流体流动，并监测肾脏单元中的压力波动。
在四个不同的水平（0°、20°、40°、60°）上单独的变形对流体流动和肾脏压力变化基本没有影响。在 40°变形下，外部压缩力逐渐增加至 500、1000、2000 直至 5000g 时，6F 和 7F 支架对肾脏单元内的流体流动和压力没有影响。唯一的例外是 4.8F 支架，在接近 4000g 的压缩力下完全失效。
外在输尿管的现实压缩力和输尿管变形都不能解释外在输尿管梗阻中支架失效的高频率。其他因素，如尿液成分，可能是支架失效的主要原因。
