Dynamic simulation and analysis of the influence of urethral morphological changes on urodynamics after benign prostatic hyperplasia surgery: A computational fluid dynamics study.

Background And Objective: Computational fluid dynamics (CFD) technology has been widely used in medicine to simulate and analyse urine flow characteristics in urology. In previous studies, researchers have modelled the analysis with a simple circular urethra, ignoring the effect of the patient's true urethral morphology on the urinary flow rate. Moreover, the studies tended to be steady-state simulations rather than dynamic simulations. Therefore, this study is established a relatively realistic model of the posterior urethra based on MRI data combined with the urodynamic data of patients and analysed the urodynamic characteristics of the posterior urethra model after benign prostatic hyperplasia (BPH) surgery using a CFD dynamic simulation.

Methods: Based on clinical MRI data, a three-dimensional real urethral model was established for two patients with BPH after surgery. The boundary conditions were set according to the patients' real urodynamic data, and a Reynolds averaged Navier‒Stokes model was used for transient simulations. The dynamic simulation depicted the entire urination process, and the urine flow characteristics were studied under real urethral morphology after surgery.

Results: 1. By comparing the three-dimensional trajectory of urine and the vortex identification cloud map based on the Q criterion, we intuitively observed the distribution of the vortex in the model, and a 'gourd-shaped' urethra was more likely to generate a vortex than a 'funnel-shaped' urethra. 2. After surgery for BPH, the changes in the posterior urethral pressure were mainly concentrated in the urethral membrane, and the velocity increased while the pressure decreased. The curve of the posterior urethral pressure changes during urination was simulated and calculated. The posterior urethral pressure gradients of the two patients were 6.6 cmHO and 5.26 cmHO.

Conclusions: The complete urinary discharge process can be dynamically simulated using CFD techniques. By comparing the simulation results, the posterior urethral morphology can have an important impact on the urinary flow characteristics. Determining the location of vortex generation can lay a foundation for personalized surgical plans for patients in the future. Furthermore, numerical simulations can provide a new method for the study of non-invasive posterior urethral pressure gradients.