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Objectives: To assess human in vivo intrarenal pressure (IRP) and peristaltic activity at baseline and after ureteric stent placement, using a narrow calibre pressure guidewire placed retrogradely in the renal pelvis., Patients and Methods: A prospective, multi-institutional study recruiting consenting patients undergoing ureteroscopy was designed with ethical approval. Prior to ureteroscopy, the urinary bladder was emptied and the COMET™ II pressure guidewire (Boston Scientific) was advanced retrogradely via the ureteric orifice to the renal pelvis. Baseline IRPs were recorded for 1-2 min. At procedure completion, following ureteric stent insertion, IRPs were recorded for another 1-2 min. Statistical analysis of mean baseline IRP, peristaltic waveforms and frequency of peristaltic contractions was performed, thereby analysing the influence of patient variables and ureteric stenting., Results: A total of 100 patients were included. Baseline mean (±SD) IRP was 16.76 (6.4) mmHg in the renal pelvis, with maximum peristaltic IRP peaks reaching a mean (SD) of 25.75 (17.9) mmHg. Peristaltic activity generally occurred in a rhythmic, coordinated fashion, with a mean (SD) interval of 5.63 (3.08) s between peaks. On univariate analysis, higher baseline IRP was observed with male sex, preoperative hydronephrosis, and preoperative ureteric stenting. On linear regression, male sex was no longer statistically significant, whilst the latter two variables remained significant (P = 0.004; P < 0.001). The mean (SD) baseline IRP in the non-hydronephrotic, unstented cohort was 14.19 (4.39) mmHg. Age, α-blockers and calcium channel blockers did not significantly influence IRP, and no measured variables influenced peristaltic activity. Immediately after ureteric stent insertion, IRP decreased (mean [SD] 15.18 [5.28] vs 16.76 [6.4] mmHg, P = 0.004), whilst peristaltic activity was maintained., Conclusions: Human in vivo mean (SD) baseline IRP is 14.19 (4.39) mmHg in normal kidneys and increases with both hydronephrosis and preoperative ureteric stenting. Mean (SD) peristaltic peak IRP values of 25.75 (17.9) mmHg are reached in the renal pelvis every 3-7 s and maintained in the early post-stent period., (© 2024 BJU International.)

The ureteric wall is a complex multi-layered structure. The ureter shows variation in passive mechanical properties, histological morphology and insertion forces along the anatomical length. Ureter mechanical properties also vary depending on the direction of tensile testing and the anatomical region tested. Compliance is greatest in the proximal ureter and lower in the distal ureter, which contributes to the role of the ureter as a high-resistance sphincter. Similar to other human tissues, the ureteric wall remodels with age, resulting in changes to the mechanical properties. The passive mechanical properties of the ureter vary between species, and variation in tissue storage and testing methods limits comparison across some studies. Knowledge of the morphological and mechanical properties of the ureteric wall can aid in understanding urine transport and safety thresholds in surgical techniques. Indeed, various factors alter the forces required to insert access sheaths or scopes into the ureter, including sheath diameter, safety wires and medications. Future studies on human ureteric tissue both in vivo and ex vivo are required to understand the mechanical properties of the ureter and how forces influence these properties. Testing of instrument insertion forces in humans with a focus on defining safe upper limits and techniques to reduce trauma are also needed. Last, evaluation of dilatation limits in the mid and proximal ureter and clarification of tensile strength anisotropy in human specimens are necessary., (© 2023. Springer Nature Limited.)

Objectives: To evaluate the pressure range generated in the human renal collecting system during ureteroscopy (URS), in a large patient sample, and to investigate a relationship between intrarenal pressure (IRP) and outcome., Patients and Methods: A prospective multi-institutional study was conducted, with ethics board approval; February 2022-March 2023. Recruitment was of 120 consecutive consenting adult patients undergoing semi-rigid URS and/or flexible ureterorenoscopy (FURS) for urolithiasis or diagnostic purposes. Retrograde, fluoroscopy-guided insertion of a 0.036-cm (0.014″) pressure guidewire (COMET™ II, Boston Scientific, Marlborough, MA, USA) to the renal pelvis was performed. Baseline and continuous ureteroscopic IRP was recorded, alongside relevant operative variables. A 30-day follow-up was completed. Descriptive statistics were applied to IRP traces, with mean (sd) and maximum values and variance reported. Relationships between IRP and technical variables, and IRP and clinical outcome were interrogated using the chi-square test and independent samples t-test., Results: A total of 430 pressure traces were analysed from 120 patient episodes. The mean (sd) baseline IRP was 16.45 (5.99) mmHg and the intraoperative IRP varied by technique. The mean (sd) IRP during semi-rigid URS with gravity irrigation was 34.93 (11.66) mmHg. FURS resulted in variable IRP values: from a mean (sd) of 26.78 (5.84) mmHg (gravity irrigation; 12/14-F ureteric access sheath [UAS]) to 87.27 (66.85) mmHg (200 mmHg pressurised-bag irrigation; 11/13-F UAS). The highest single pressure peak was 334.2 mmHg, during retrograde pyelography. Six patients (5%) developed postoperative urosepsis; these patients had significantly higher IRPs during FURS (mean [sd] 81.7 [49.52] mmHg) than controls (38.53 [22.6] mmHg; P < 0.001)., Conclusions: A dynamic IRP profile is observed during human in vivo URS, with IRP frequently exceeding expected thresholds. A relationship appears to exist between elevated IRP and postoperative urosepsis., (© 2023 The Authors. BJU International published by John Wiley & Sons Ltd on behalf of BJU International.)

Paediatric urinary catheters are often necessary in critical care settings or to address congenital anomalies affecting the urogenital system. Iatrogenic injuries can occur during the placement of such catheters, highlighting the need for a safety device that can function in paediatric settings. Despite successful efforts to develop devices that improve the safety of adult urinary catheters, no such devices are available for use with paediatric catheters. This study investigates the potential for utilising a pressure-controlled safety mechanism to limit the trauma experienced by paediatric patients during inadvertent inflation of a urinary catheter anchoring balloon in the urethra. Firstly, we establish a paediatric model of the human urethra using porcine tissue by characterising the mechanical and morphological properties of porcine tissue at increasing postnatal timepoints (8, 12, 16 and 30 weeks). We identified that porcine urethras harvested from pigs at postnatal week 8 and 12 exhibit morphological properties (diameter and thickness) that are statistically distinct from adult porcine urethras (postnatal week 30). We therefore utilise urethra tissue from postnatal week 8 and 12 pigs as a model to evaluate a pressure-controlled approach to paediatric urinary catheter balloon inflation intended to limit tissue trauma during inadvertent inflation in the urethra. Our results show that limiting catheter system pressure to 150 kPa avoided trauma in all tissue samples. Conversely, all of the tissue samples that underwent traditional uncontrolled urinary catheter inflation experienced complete rupture. The findings of this study pave the way for the development of a safety device for use with paediatric catheters, thereby alleviating the burden of catastrophic trauma and life changing injuries in children due to a preventable iatrogenic urogenital event., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: John Mulvihill reports financial support was provided by Enterprise Ireland. Eoghan Cunnane, Michael Walsh, Niall Davis, Hugh Flood reports a relationship with Class Medical Ltd that includes: equity or stocks. Eoghan Cunnane, Michael Walsh, Niall Davis, Hugh Flood have patent #EP3057644B1: A transurethral catheter kit, syringe assembly and nozzle assembly suitable for use in correctly inflating a transurethral catheter, licensed to Class Medical Ltd by the University of Limerick., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Purpose: Areas of disturbed shear that arise following arteriovenous fistula (AVF) creation are believed to contribute to the development of intimal hyperplasia (IH). The presence of helical flow can suppress areas of disturbed shear, which may protect the vasculature from IH. Therefore, the aim of this study is to determine if helical flow, specifically spiral laminar flow (SLF), is present in patient-specific AVF models and is associated with a reduction in exposure to disturbed shear., Methods: Four AVF were imaged using MRI within the first two weeks following fistula creation. Patient-specific boundary conditions were obtained using phase-contrast MRI and applied at the inlet and outlets of each model. Computational fluid dynamics was used to analyse the hemodynamics in each model and compare the helical content of the flow to the distribution of disturbed shear., Results: BC-1 and RC-2 are characterised by the presence of SLF, which coincides with the lowest distribution of disturbed shear. Contrastingly, SLF is absent from BC-2 and RC-1 and experience the largest amount of disturbed shear. Interestingly, BC-2 and RC-1 developed an anastomosis stenosis, while BC-1 and RC-2 remained stenosis free., Conclusion: These findings are in agreement with previous clinical studies and further highlight the clinical potential of SLF as a prognostic marker for a healthy AVF, as its presence correlates with an overall reduction in exposure to disturbed shear and a decrease in the incidence of AVF dysfunction, albeit in a small sample size., (© 2022. The Author(s) under exclusive licence to Biomedical Engineering Society.)

Objectives: To perform a multi-institutional investigation of incidence and outcomes of urethral trauma sustained during attempted catheterization., Patients & Methods: A prospective, multi-center study was conducted over a designated 3-4 month period, incorporating seven academic hospitals across the UK and Ireland. Cases of urethral trauma arising from attempted catheterization were recorded. Variables included sites of injury, management strategies and short-term clinical outcomes. The catheterization injury rate was calculated based on the estimated total number of catheterizations occurring in each center per month. Anonymised data were collated, evaluated and described., Results: Sixty-six urethral catheterization injuries were identified (7 centers; mean 3.43 months). The mean injury rate was 6.2 ± 3.8 per 1000 catheterizations (3.18-14.42/1000). All injured patients were male, mean age 76.1 ± 13.1 years. Urethral catheterization injuries occurred in multiple hospital/community settings, most commonly Emergency Departments (36%) and medical/surgical wards (30%). Urological intervention was required in 94.7% (54/57), with suprapubic catheterization required in 12.3% (n = 7). More than half of patients (55.56%) were discharged with an urethral catheter, fully or partially attributable to the urethral catheter injury. At least one further healthcare encounter on account of the injury was required for 90% of patients post-discharge., Conclusions: This is the largest study of its kind and confirms that iatrogenic urethral trauma is a recurring medical error seen universally across institutions, healthcare systems and countries. In addition, urethral catheter injury results in significant patient morbidity with a substantial financial burden to healthcare services. Future innovation to improve the safety of urinary catheterization is warranted.

Cryopreservation is required to preserve the native properties of tissue for prolonged periods of time. In this study, we evaluate the impact that 4 different cryopreservation protocols have on porcine urethral tissue, to identify a protocol that best preserves the native properties of the tissue. The cryopreservation protocols include storage in cryoprotective agents at -20 °C and -80 °C with a slow, gradual, and fast reduction in temperature. To evaluate the effects of cryopreservation, the tissue is mechanically characterised in uniaxial tension and the mechanical properties, failure mechanics, and tissue dimensions are compared fresh and following cryopreservation. The mechanical response of the tissue is altered following cryopreservation, yet the elastic modulus from the high stress, linear region of the Cauchy stress - stretch curves is unaffected by the freezing process. To further investigate the change in mechanical response following cryopreservation, the stretch at different tensile stress values was evaluated, which revealed that storage at -20 °C is the only protocol that does not significantly alter the mechanical properties of the tissue compared to the fresh samples. Conversely, the ultimate tensile strength and the stretch at failure were relatively unaffected by the freezing process, regardless of the cryopreservation protocol. However, there were alterations to the tissue dimensions following cryopreservation that were significantly different from the fresh samples for the tissue stored at -80 °C. Therefore, any study intent on preserving the mechanical, failure, and geometric properties of urethral tissue during cryopreservation should do so by freezing samples at -20 °C, as storage at -80 °C is shown here to significantly alter the tissue properties., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

This study addresses a crucial gap in the literature by characterising the relationship between urethral tissue mechanics, composition and gross structure. We then utilise these data to develop a biomimetic urethral scaffold with physical properties that more accurately mimic the native tissue than existing gold standard scaffolds; small intestinal submucosa (SIS) and urinary bladder matrix (UBM). Nine human urethra samples were mechanically characterised using pressure-diameter and uniaxial extension testing. The composition and gross structure of the tissue was determined using immunohistological staining. A pressure stiffening response is observed during the application of intraluminal pressure. The elastic and viscous tissue responses to extension are free of regional or directional variance. The elastin and collagen content of the tissue correlates significantly with tissue mechanics. Building on these data, a biomimetic urethral scaffold was fabricated from collagen and elastin in a ratio that mimics the composition of the native tissue. The resultant scaffold is comprised of a dense inner layer and a porous outer layer that structurally mimic the submucosa and corpus spongiosum layers of the native tissue, respectively. The porous outer layer facilitated more uniform cell infiltration relative to SIS and UBM when implanted subcutaneously (p < 0.05). The mechanical properties of the biomimetic scaffold better mimic the native tissue compared to SIS and UBM. The tissue characterisation data presented herein paves the way for the development of biomimetic urethral grafts, and the novel scaffold we develop demonstrates positive findings that warrant further in vivo evaluation., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Areas of disturbed shear that develop following arteriovenous fistula (AVF) creation are believed to trigger the onset of intimal hyperplasia (IH), leading to AVF dysfunction. The presence of helical flow can suppress the flow disturbances that lead to disturbed shear in other areas of the vasculature. However, the relationship between helical flow and disturbed shear remains unevaluated in AVF. In this study, computational fluid dynamics (CFD) is used to evaluate the relationship between geometry, helical flow, and disturbed shear in parameterised models of an AVF characterised by four different anastomosis angles. The AVF models with a small anastomosis angle demonstrate the lowest distribution of low/oscillating shear and are characterised by a high helical intensity coupled with a strong balance between helical structures. Contrastingly, the models with a large anastomosis angle experience the least amount of high shear, multidirectional shear, as well as spatial and temporal gradients of shear. Furthermore, the intensity of helical flow correlates strongly with curvature (r = 0.73, P < .001), whereas it is strongly and inversely associated with taper (r = -0.87, P < .001). In summary, a flow field dominated by a high helical intensity coupled with a strong balance between helical structures can suppress exposure to low/oscillating shear but is ineffective when it comes to other types of shear. This highlights the clinical potential of helical flow as a diagnostic marker of exposure to low/oscillating shear, as helical flow can be identified in vivo with the use of ultrasound imaging., (© 2019 John Wiley & Sons, Ltd.)

A vascular access (VA) is used to facilitate hemodialysis in patients that suffer from end-stage renal disease. However, they suffer from high failure rates due to non-maturation and venous stenosis, with intimal hyperplasia (IH) the underlying cause of both conditions. Abnormal hemodynamic profiles, which arise following VA creation, are believed to lead to the development of IH. However, the exact physiological response that initiates this process is unknown. This review evaluates the different hemodynamic parameters that are hypothesised to correlate with the development of IH. Review studies that examine the correlation between hemodynamic parameters and the onset of IH using computational fluid dynamics. These studies are divided into groups depending on the type of analysis conducted; longitudinal studies, patient specific arteriovenous fistula (AVF) studies, arteriovenous graft studies, idealised AVF studies and studies that analyse the bulk flow. Studies that conduct longitudinal analysis identify an overall reduction in wall shear stress (WSS) as the VA matures. This is further associated with outward remodelling and the successful maturation of the VA. The majority of studies that conduct a transversal analysis find that low/oscillating shear is associated with the development of IH. However, a number of studies find a link between high shear and high spatial and temporal WSS gradients and the onset of IH. This review highlights the lack of unanimity between studies and emphasises the fact that the exact physiological response that leads to the development of IH remains unknown. This accentuates the need for a single, precise hypothesis capable of accurately predicting the onset of IH. If computational modelling is to assist in this process, the number of longitudinal studies conducted must increase. This will provide a better understanding of the effect that hemodynamic parameters have on the remodelling process and potentially identify a single/group of parameter/s that can accurately predict the onset of IH.

Objective: To evaluate an alternative catheter labelling approach for 3-way catheters based on the drainage channel and irrigation channel cross-sectional area (CSA), which impacts catheter flow rate characteristics., Materials and Methods: Three-way 22Fr catheters from Bard (Bard Limited), Rusch Simplastic (Teleflex Medical), Dover (COVIDIEN), and Rusch Golden were included in the study. Irrigation channel, drainage channel, and overall CSAs were digitally measured with an image-processing program. Irrigation channel and drainage channel flow rates were measured and correlated with their corresponding catheter CSA values., Results: Catheter CSA and French value did not predict flow-rate characteristics, but irrigation channel CSA and drainage channel CSA were predictive. The 22Fr Rusch Simplastic catheter had the largest irrigation channel CSA (2.87 mm(2)) and drainage channel CSA (12.6 mm(2)), and had the greatest irrigation (5.27 ± 0.02 ml/s) and drainage flow rates (14.42 ± 0.22 ml/s). Twenty-two French gauge Rusch Golden catheters had the smallest irrigation channel CSA (1.34 mm(2)) and drainage channel CSA (7.82 mm(2)) and the lowest irrigation (1.83 ± 0.03 ml/s) and drainage flow rates (1.83 ± 0.03 ml/s)., Conclusion: An alternative catheter labelling system to include overall CSA, irrigation channel CSA, and drainage channel CSA values would provide more accurate and transparent data relevant to anticipated drainage and irrigation flow rates. The proposed labelling method will assist urologists in selecting 3-way catheters for bladder irrigation., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Purpose: We investigated urethral diametric strain and threshold maximum inflation pressure for rupture during inadvertent inflation of a catheter anchoring balloon in the urethra. In addition, we evaluated a novel safety device to prevent trauma based on these parameters., Materials and Methods: Inflation of a urethral catheter anchoring balloon was performed in the bulbar urethra of 21 ex vivo porcine models using 16Fr catheters. Urethral trauma was assessed with retrograde urethrography. Urethral rupture was correlated with internal urethral diametric strain and maximal urethral pressure threshold values in kPa. Urethral catheters were then inflated in the bulbar urethras of 7 fresh male cadavers using a standard syringe and a prototype syringe. The plunger of the standard syringe was depressed until opposing resistance pressure generated by the urethra prevented further inflation of the anchoring balloon. The plunger of the prototype safety syringe was depressed until sterile water in the syringe decanted through an activated safety threshold pressure valve., Results: Retrograde urethrography demonstrated that porcine urethral rupture consistently occurred at an internal urethral diametric strain greater than 40% and a maximum inflation pressure greater than 150 kPa. The mean ± SD maximum human urethral threshold inflation pressure required to activate the safety prototype syringe pressure valve was 153 ± 3 kPa. In comparison, maximum inflation pressure was significantly greater using the standard syringe than the activated prototype syringe (mean 452 ± 188 kPa, p <0.001)., Conclusions: Internal urethral diametric strain and threshold maximum inflation pressures are important parameters for designing a safer urethral catheter system with lower intrinsic threshold inflation pressures., (Copyright © 2015 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.)