Ureteral peristalsis can be considered as a series of waves on the ureteral wall, which transfers the urine along the ureter toward the bladder. The stones that form in the kidney and migrate to the ureter can create a substantial health problem due to the pain caused by interaction of the ureteral walls and stones during the peristaltic motion. Three-dimensional (3D) computational fluid dynamics (CFD) simulations were carried out using the commercial code ansys fluent to solve for the peristaltic movement of the ureter, with and without stones. The effect of stone size was considered through the investigation of varying obstructions of 5%, 15%, and 35% for fixed spherical stone shape. Also, an understanding of the effect of stone shape was obtained through separate CFD calculations of the peristaltic ureter with three different types of stones, a sphere, a cube, and a star, all at a fixed obstruction percentage of 15%. Velocity vectors, mass flow rates, pressure gradients, and wall shear stresses were analyzed along one bolus of urine during peristalsis of the ureteral wall to study the various effects. It was found that the increase in obstruction increased the backflow, pressure gradients, and wall shear stresses proximal to the stone. On the other hand, with regard to the stone shape study, while the cube-shaped stones resulted in the largest backflow, the star-shaped stone showed highest pressure gradient magnitudes. Interestingly, the change in stone shape did not have a significant effect on the wall shear stress at the obstruction level studied here.
The flow of urine from the kidneys to the bladder is accomplished via peristaltic contractions in the ureters. The peristalsis of urine through the ureter can sometimes be accompanied, more specifically, obstructed to a certain degree, by entities such as kidney stones. In this paper, 2D axisymmetric computational fluid dynamics simulations are carried out using the commercial code ANSYS FLUENT[Formula: see text], to model the peristaltic movement of the ureter with and without stone. The peristaltic movement was assumed to be a sinusoidal wave on the boundary of the ureter with a specific physiological velocity. While the first part of the study considers flow in the ureter with prescribed peristaltic contractions in absence of any obstruction, the second part compares the effect of varying obstructions (0, 5, 15, and 35%) in terms of spherical stones of different sizes. Pressure contours, velocity vectors, and profiles of pressure gradient magnitudes and wall shear stresses are presented along one bolus of the ureter, during contraction and expansion of the ureteral wall, in order to understand backflow, trapping and reflux phenomena, as well as monitor the health of the ureteral wall in the presence of any obstruction. The 35% ureteral obstruction case resulted in a significant backflow at the inlet in comparison to the other cases, and also a wall shear stress that was up to 20x larger than the case without any obstruction.
The findings can be used to design a "smart device" that can provide visual force feedback to clinicians while they are operating, leading to improved patient outcome.
to receive treatment with low power/high frequency settings of 0.2 J-0.4 J and 50 Hz [LP/HF group] or with conventional laser settings of 0.5 J-1.0 J and 5-10 Hz [conventional group]. Patient demographics and perioperative parameters were assessed.RESULTS: Of 103 patients, 52 patients were in the LP/HP group and 51 were in the conventional group. The mean age was 60 years (26-85) [LP/HF] and 57 years (25-91) [conventional]. The mean aggregate stone diameter/burden was 1.6 cm (0.5-4.5 cm) [LP/HF] and 1.0 cm (0.4-3.5 cm) [conventional]. All stones were treated with a 200 micron holmium laser fiber. In 13 cases (25%) using LP/HF settings, the energy level was increased from 0.2 J to 0.3 J-0.4 J. In 2 additional cases (3.8%), conventional settings (0.5 J-1.0 J, rate 5-10 Hz) were used due to harder stone compositions. Stone compositions included: calcium oxalate/mixed composition (54%), calcium oxalate monohydrate (26%), uric acid (10%), struvite (8%), and cystine (2%). The mean operative time was 64.4 min [LP/ HF] and 57.4 min [conventional] (P ¼ 0.37), and the total energy usage was 5.42 W [LP/HF] and 1.96 W [conventional] (P < 0.01).No trimming of the laser fiber tip was required in the LP/HF group as compared to 24% of cases that required trimming in the conventional group. Complete stone fragmentation into fine dust was achieved in 7 cases (13.4%) [LP/HF] obviating the need for stone basketing. No bleeding complications or gross ureteral perforations were encountered during any procedures. Subjectively, there was decreased visibility due to bleeding during 5 cases (9.8%) using conventional settings.CONCLUSIONS: Selecting energy settings of 0.2 J-0.4 J and 50 Hz results in effective stone fragmentation into fine dust, thus reducing the use of stone baskets to achieve stone-free status. These settings can be adjusted to work well for all stone compositions. Additionally, these settings serve to reduce laser fiber tip degradation and minimize stone retropulsion without increasing operative time.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.