Evaluation of renovated double J stents using ureter models with and without stenosis.

PURPOSE: Commercial double J stents (DJS) have a uniform shape regardless of the specific nature of various ureteral diseases. We tested renovated DJS and compared them with conventional DJS using ureter models. METHODS: One straight ureter model included stenosis at the distal ureter near the ureterovesical junction and the other did not. We used conventional DJS and renovated 5- and 6-Fr soft DJS for ureter stones and 6-, 7-, and 8.5-Fr hard DJS for tumors. The DJS comprised holes in the upper, middle, or lower one-third of the shaft (length, 24 cm; 2-cm-diameter coils at both ends). More holes were created along the shaft based on the ureteral disease location. Conventional DJS had holes spaced 1 cm apart along the shaft. Renovated DJS had holes spaced 1 cm apart along the shaft with 0.5-cm intervals on the upper, middle, or lower one-third of the shaft. Urine flow was evaluated. RESULTS: As the DJS diameter increased, the flow rate decreased. The flow rates of DJS with holes in the lower shaft were relatively lower than those of conventional DJS and DJS with holes in the upper and middle shafts. In the ureter model without stenosis, 6-, 7-, and 8.5-Fr renovated stents exhibited significantly higher flow rates than conventional stents. In the ureter model with stenosis, 5-, 6-, 7-, and 8.5-Fr renovated stents did not exhibit significantly higher flow rates than conventional stents. CONCLUSION: Renovated stents and conventional stents did not exhibit significant differences in urine flow with stenosis.

Optimal thrombin injection method for the treatment of femoral artery pseudoaneurysm.

BACKGROUND: Iatrogenic femoral artery pseudoaneurysm (IFP) incidence is increasing with increase in diagnostic and therapeutic angiography, and so, the less invasive percutaneous thrombin injection (PTI) is the most widely used treatment. Moreover, studies that minimize PTI complications and highlight therapeutic effects are lacking. OBJECTIVES: This study performed in vitro thrombosis modeling of pseudoaneurysms and analyzed thrombosis within and thromboembolism outside the sac during thrombin injection. METHODS: We evaluated PTI in terms of thrombin injection location (at the junction of the IFP sac and neck, the center, and the dome, located farthest from the neck of the sac), thrombin injection time (5 and 8 seconds), and blood flow rate (ranging from 210 mL/min to 300 mL/min). Porcine blood was used as the working fluid in this study. RESULTS: Thrombin injection at the junction of the IFP sac and the pseudoaneurysm neck led to less thrombosis within the sac but substantial thrombi consistently outside the sac, whereas thrombin injected at the sac center mostly led to complete thrombosis within the sac, preventing further blood flow into the sac and reducing likelihood of thrombi outside the sac. A longer thrombin injection time enhanced the therapeutic effect and decreased the possibility of thromboembolism. Thromboembolism occurred more frequently at flow rates of >240 mL/min. CONCLUSION: The thrombin injection site in a pseudoaneurysm significantly influences thrombogenesis within and thromboembolism outside the sac. Thus, slow and deliberate injection of thrombin into the center of the sac could potentially reduce complications and enhance treatment efficacy.

Effects of size and shape of the side holes of a double J stent on the ureter fluid flow after stenosis.

The effect of side holes morphology changes in double J stent (DJS) on encrustation was analyzed using computational fluid dynamics (CFD). We analyzed DJS side holes with inner diameter of 1 mm and outer diameters of 1 (type A), 1.2 (type B) and 1.4 (type C) mm, respectively. Concentric stenosis with three intraureteral degree (0%, 12%, and 88%) was analyzed. The flow rate, shear stress and wall shear stress (WSS) distribution were investigated. Urine flow through SH1 before the ureteropelvic junction (UPJ) differed based on the ureteral stenosis degree. The sum of flow rates through the SHs increased with diameter. In the stented ureter with 12% stenosis, the flow rate through SH1 approximately doubled than that without ureteral stenosis, and the flow rate through SH1 was maximal for the type 'C' stent in both 12% and 88% ureteral stenosis. The mean shear stress in the SHs increased with the degree of stenosis. The WSS around the SHs was higher for type 'C' than types A and B. From the flow rates and shear stresses in and around the SHs, the larger SH diameter of the DJS from the UPJ to mid-ureter is expected to induce encrustation reduction, especially in patients with urinary lithiasis.

CFD study on vesicoureteral reflux in the urinary tract with double J stent.

OBJECTIVE: This study investigates the effects of vesicoureteral reflux (VUR) in the upper and lower urinary tracts with and without ureteral stenosis and with a double J stent (DJS). METHODS: The entire length of the urinary tract with an implanted DJS was modeled. To assess the possibility of VUR, the measured values were used as boundary conditions for the baseline, the maximum cystometric bladder capacity (MCBC) during the filling phase, and maximum vesical pressure during the voiding phase were computed. The flow rates, flow patterns, wall shear stress (WSS) distribution, impact force induced by reflux urination, and helicity of the bladder were investigated for the urinary system. RESULTS: The flow from the bladder to the renal pelvis was detected at maximum vesical pressure (75 cmH2O) during the voiding phase, and a small amount (1.09 mL/s) of VUR was noted at the MCBC during the filling phase. The WSS increased when the reflux was large. Helicity within the bladder varied with the stenosis as well as opening and closing of the urethra. The reflux within the stent was reduced by 40% by inserting a ball into the stent. CONCLUSION: The main VUR factor was the opening and closing of the vesicoureteric junction by the detrusor muscle. The largest urine reflux (11.7 mL/s) to the kidney occurred when the detrusor muscle was relaxed. SIGNIFICANCE: Ureteral stenosis affected the VUR and reduced urine reflux. Ball insertion in the stent reduced urine reflux through the stent lumen.

Percutaneous Thrombin Injection Based on Computational Fluid Dynamics of Femoral Artery Pseudoaneurysms.

OBJECTIVE: To analyze the computational fluid dynamics (CFD) of femoral artery pseudoaneurysm (FAP), identify a suitable location and timing for percutaneous thrombin injection (PTI) based on this analysis, and report our clinical experience with the procedure. MATERIALS AND METHODS: CFD can be used to analyze the hemodynamics of the human body. An analysis using CFD recommended that the suitable location of the needle tip for PTI is at the center of the aneurysm sac and the optimal timing for starting PTI is during the early inflow phase of blood into the sac. Since 2011, seven patients (three male and four female; median age, 60 years [range, 43-75 years]) with FAP were treated with PTI based on the devised suitable location and time. Prior to the procedure, color Doppler ultrasonography was performed to determine the location and timing of the thrombin injection. RESULTS: The technical success rate of the PTI was 100%. The amount of thrombin used for the procedure ranged from 200 IU to 1000 IU (median, 500 IU). None of the patients experienced any symptoms or signs of embolic complications during the procedure. Follow-up CT images did not reveal any embolism in the lower extremities and showed complete thrombosis of the pseudoaneurysm. CONCLUSION: Based on our study of CFD, PTI administered centrally in the FAP during early inflow, as seen on color Doppler, can be an effective technique.

Clogged water bridges for fog harvesting.

Capillary water bridges clogged in the holes of mesh-type fog harvesters have previously been considered only as a drawback because they decrease fog-harvesting yield by hindering airflow in front of the clogged mesh in the usual wind conditions. In this study, we show that the role of a clogged water bridge may not be entirely negative and can contribute to increased fog harvesting by increasing the effective shade coefficient in a special condition with high fog inertia. As the fog speed close to the mesh or the plate increases, clogged mesh as well as the impermeable solid plate are found to produce high fog-harvesting efficiency owing to the high inertia of fog particles that impact the blocked wall. For fast fog speeds (∼4 m s-1) near the mesh, our results show that the fog-harvesting efficiency is proportional to the effective shade coefficient because fog flow circumventing the mesh is limited owing to high fog inertia. We analyzed the clogging effect on fog-harvesting performance by distinguishing between self-clogging and non-self-clogging patterns based on the water bridge stability clogged in mesh holes.