Vorticity in lower urinary tract can be assessed and associates with urinary tract morphology in men

Objectives The aim of this study is to develop a method to evaluate the fluid dynamics of urine flow in the lower urinary tract (LUT), especially that of vorticity. Materials and Methods This investigation included three sub-studies to demonstrate urine flow in the entire LUT. First, we attempted to observe vorticity generation in the urinary bladder during spontaneous voiding using transabdominal color Doppler ultrasonography (CDUS). Second, we performed transrectal CDUS to evaluate the vorticity of urine flow in the prostatic urethra. Patients with prostate cancer were enrolled before robotic surgery and divided into the vorticity and non-vorticity groups based on CDUS findings for comparisons of longitudinal urethral diameter and prostatic urethral angle. Third, the vorticity of the voided urine stream was observed using a high-speed video-camera. Micturition was done in a standing position while synchronously monitored for urine flow using uroflowmetry. Results Vorticity formation could be dynamically demonstrated in the urinary bladder and prostatic urethra using CDUS. The prostatic urethral angle of the vorticity group was more than that of the non-vorticity group. High-speed video recording could clearly capture vorticity and spiral shape generation in voided urine. The distance from the external urethral orifice to the first twist changed in accordance with urine flow rate. Conclusions In a series of sub-studies, this investigation proved vorticity generation in the LUT and voided urine. Vorticity was detectable in the LUT and in voided urine using CDUS and a high-speed video-camera. Vorticity generation might be associated with urethral morphology.