One-dimensional modelling of pulse wave propagation in human airway bifurcations in space-time variables

Airflow in the respiratory system is complicated as it goes through various regions with different geometries and mechanical properties. Three-dimensional (3-D) simulations are typically limited to local areas of the system because of their high computational cost. On the other hand, the one-dimensional (1-D) equations of flow in compliant tubes offer a good compromise between accuracy and computational cost when a global assessment of airflow in the system is required. The aim of the current study is to apply the 1-D formulation in space and time variables to study the propagation of a pulse wave in human airways; first in a simple system composed of just one bifurcation, trachea-main bronchi, according to the symmetrical Weibel model. Then extending the system to include a further generation, the bronchi branches. Pulse waveforms carry information about the functionality and morphology of the respiratory system and the 1-D modelling, in terms of space and time variables, represents an innovative approach for respiratory response interpretation. 1-D modelling in space-time variables has been extensively applied to simulate blood pressure and flow in the cardiovascular system. This work represents the first attempt to apply this formulation to study pulse waveforms in the human bronchial tree

Fluid mechanical modeling of the upper urinary tract

The upper urinary tract (UUT) consists of kidneys and ureters, and is an integral part of the human urogenital system. Yet malfunctioning and complications of the UUT can happen at all stages of life, attributed to reasons such as congenital anomalies, urinary tract infections, urolithiasis and urothelial cancers, all of which require urological interventions and significantly compromise patients' quality of life. Therefore, many models have been developed to address the relevant scientific and clinical challenges of the UUT. Of all approaches, fluid mechanical modeling serves a pivotal role and various methods have been employed to develop physiologically meaningful models. In this article, we provide an overview on the historical evolution of fluid mechanical models of UUT that utilize theoretical, computational, and experimental approaches. Descriptions of the physiological functionality of each component are also given and the mechanical characterizations associated with the UUT are provided. As such, it is our aim to offer a brief summary of the current knowledge of the subject, and provide a comprehensive introduction for engineers, scientists, and clinicians who are interested in the field of fluid mechanical modeling of UUT

Investigating the flow dynamics in the obstructed and stented ureter by means of a biomimetic artificial model

Double-J stenting is the most common clinical method employed to restore the upper urinary tract drainage, in the presence of a ureteric obstruction. After implant, stents provide an immediate pain relief by decreasing the pressure in the renal pelvis (P). However, their long-term usage can cause infections and encrustations, due to bacterial colonization and crystal deposition on the stent surface, respectively. The performance of double-J stents - and in general of all ureteric stents - is thought to depend significantly on urine flow field within the stented ureter. However very little fundamental research about the role played by fluid dynamic parameters on stent functionality has been conducted so far. These parameters are often difficult to assess in-vivo, requiring the implementation of laborious and expensive experimental protocols. The aim of the present work was therefore to develop an artificial model of the ureter (i.e. ureter model, UM) to mimic the fluid dynamic environment in a stented ureter. The UM was designed to reflect the geometry of pig ureters, and to investigate the values of fluid dynamic viscosity (μ), volumetric flow rate (Q ) and severity of ureteric obstruction (OB%) which may cause critical pressures in the renal pelvis. The distributed obstruction derived by the sole stent insertion was also quantified. In addition, flow visualisation experiments and computational simulations were performed in order to further characterise the flow field in the UM. Unique characteristics of the flow dynamics in the obstructed and stented ureter have been revealed with using the developed UM

Simulation of a detoxifying organ function: Focus on hemodynamics modeling and convection‐reaction numerical simulation in microcirculatory networks

International audienceWhen modeling a detoxifying organ function, an important component is the impact of flow on the metabolism of a compound of interest carried by the blood. We here study the effects of red blood cells (such as the Fahraeus-Lindqvist effect and plasma skimming) on blood flow in typical microcirculatory components such as tubes, bifurcations and entire networks, with particular emphasis on the liver as important representative of detoxifying organs. In one of the plasma skimming models, under certain conditions, oscillations between states are found and analyzed in a methodical study to identify their causes and influencing parameters. The flow solution obtained is then used to define the velocity at which a compound would be transported. A convection-reaction equation is studied to simulate the transport of a compound in blood and its uptake by the surrounding cells. Different types of signal sharpness have to be handled depending on the application to address different temporal compound concentration profiles. To permit executing the studied models numerically stable and accurate, we here extend existing transport schemes to handle converging bifurcations, and more generally multi-furcations. We study the accuracy of different numerical schemes as well as the effect of reactions and of the network itself on the bolus shape. Even though this study is guided by applications in liver micro-architecture, the proposed methodology is general and can readily be applied to other capillary network geometries, hence to other organs or to bioengineered network designs

Urine-Contactless Device to Empty Bladders: an Ex-Vivo Proof-of-Concept Study in Porcine Bladders

Current treatments for underactive bladder (UAB) have negative side effects, such as urinary tract infections, mainly because devices used for bladder emptying are in direct contact with urine (e.g. permanent or intermittent catheterisation). Moreover, most of the current solutions are invasive [1]. In the present study, we are evaluating the feasibility of a new approach to help empty the bladder, consisting of a non-invasive, urine-contactless device. If this proves to be successful, it could improve the quality of life in patients suffering from UAB. This system is based on the impedance pump principle. An impedance pump is a valve-less pump which is able to drive flow by means of an impedance mismatch: travelling waves are generated by compressing an elastic tube at a specific frequency and location. Reflections of the waves at the points of impedance mismatch create a complex pattern of nonlinear wave interference. The result of these wave-interactions can be a directed flow [2]. This study tests the hypotheses that an impedance pump externally compressing a porcine urethra is able to: i) increase the urinary flow and ii) lead to complete bladder emptying

Fluid mechanical modeling of the upper urinary tract

The upper urinary tract (UUT) consists of kidneys and ureters, and is an integral part of the human urogenital system. Yet malfunctioning and complications of the UUT can happen at all stages of life, attributed to reasons such as congenital anomalies, urinary tract infections, urolithiasis and urothelial cancers, all of which require urological interventions and significantly compromise patients' quality of life. Therefore, many models have been developed to address the relevant scientific and clinical challenges of the UUT. Of all approaches, fluid mechanical modeling serves a pivotal role and various methods have been employed to develop physiologically meaningful models. In this article, we provide an overview on the historical evolution of fluid mechanical models of UUT that utilize theoretical, computational, and experimental approaches. Descriptions of the physiological functionality of each component are also given and the mechanical characterizations associated with the UUT are provided. As such, it is our aim to offer a brief summary of the current knowledge of the subject, and provide a comprehensive introduction for engineers, scientists, and clinicians who are interested in the field of fluid mechanical modeling of UUT

Development of a biologically inspired in-vitro platform for long-term assessment of commercial and innovative ureteral stents

Ureteral stents are small flexible tubes which are clinically used to restore the urine drainage in presence of obstructions of the ureteral lumen such as tumours, kidney/ureteral stones. The lifetime risk of developing urinary stones is about 20% in men and 10% in women. Despite the wide clinical usage of ureteral stents, several side effects and complications are associated to their use; encrustation and biofilm formation can compromise the urine drainage through the stent even within few weeks after implantation and are widely recognised as the main cause of stent’s failure. Although fluid dynamics of urine in stented ureter is known to affect the initiation and the subsequent growth of encrusting deposits and biofilm, experimental and computational fluid dynamic investigations are still scarce. From previous experiments using a transparent ureter model (with a stent inside), we could identify typical local fluid dynamic patterns (i.e. presence of laminar vortices) which can trigger particle adhesion on the stent surface. We are currently expanding this model to include bladder and urethra, aiming at replicating the physiological properties of the whole urinary system in terms of relevant architecture, flow, volume, pressure and other typical features such as bladder contraction and corresponding filling-emptying cycle. This model will represent an in-vitro biologically inspired platform which will help: i) improve insights of encrustation and biofilm formation processes in available stents, ii) correlate these processes with the local fluid dynamics, and iii) test new stents and other relevant urological devices (e.g. device for incontinence and urinary retention)

Potential strategies to prevent encrustations on urinary stents and catheters – thinking outside the box:a European network of multidisciplinary research to improve urinary stents (ENIUS) initiative

Abstract Introduction: Urinary stents have been around for the last 4 decades, urinary catheters even longer. They are associated with infections, encrustation, migration, and patient discomfort. Research efforts to improve them have shifted onto molecular and cellular levels. ENIUS brought together translational scientists to improve urinary implants and reduce morbidity. Methods & materials: A working group within the ENIUS network was tasked with assessing future research lines for the improvement of urinary implants. Topics were researched systematically using Embase and PubMed databases. Clinicaltrials.gov was consulted for ongoing trials. Areas covered: Relevant topics were coatings with antibodies, enzymes, biomimetics, bioactive nano-coats, antisense molecules, and engineered tissue. Further, pH sensors, biodegradable metals, bactericidal bacteriophages, nonpathogenic uropathogens, enhanced ureteric peristalsis, electrical charges, and ultrasound to prevent stent encrustations were addressed. Expert opinion: All research lines addressed in this paper seem viable and promising. Some of them have been around for decades but are yet to proceed to clinical application (i.e. tissue engineering). Others are very recent and, at least in urology, still only conceptual (i.e. antisense molecules). Perhaps the most important learning point resulting from this pan-European multidisciplinary effort is that collaboration between all stakeholders is not only fruitful but also truly essential