The influence of catheter design on Urodynamics and their potential role on biofilm formation

The most commonly used indwelling urinary catheter design is the one proposed by Foley in 1930s. This is a closed system, consisting of a tube inserted through the urethra held in place by an inflatable balloon. The catheter is connected to a drainage system which allows drainage of urine from the bladder. These devices were originally designed for short-term use, but they are currently used for long-term treatments. The design has been changed little so far and it is considered obsolete by the scientific community. These catheters are vulnerable to encrustation and consequent blockage due to biofilm crystal deposition. The aim of this study is to characterise the effect of catheter design on urinary flow and to explore the potential role of urodynamics on biofilm development and encrustation. This study focused firstly on the correlations between catheter design, urodynamics and the phenomenon of encrustation using an idealized geometry to validate the CFD model with experimental data; subsequently it was used on a real geometry to study the role of the catheter design on the flow properties. The research hypothesis is that catheter design may affect internal urodynamics, and, as a consequence, the process of biofilm formation. A computer model, mimicking the physics of flow through a catheter, was used to predict and investigate flow near its tip. Model geometries were created based on measurements obtained from μCT scans of a Foley catheter. The fluid solver used was ANSYS-CFX, and the physical problem was simplified by using water as a fluid which has similar properties of urine during the first stage. During the second part of the study the fluid solver used was a fluid modelling the rheological behaviour of human urine. Predicted values of volumetric flow rate were validated with data previously obtained experimentally. The results showed flow discontinuities in the proximity of the areas were encrustation is believed to start occluding the catheter. Low velocity values were found in proximity of the tip and near the lower edge of the eyelets. Wall shear stress value were also lower where encrustation commonly develops. These results are in good agreement with experimental data in the literature, indicating a possible correlation between urodynamics and encrustation. A parametrized study was also performed to understand the correlations between catheter design and flow behaviour. All the results obtained were then exhaustively analysed and discussed. To conclude this study provides a methodology which could be used to analyse the influence of catheter design and their potential role on the biofilm formation.