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Computational Fluid Dynamics to Assess Urine Flow After Surgery for Benign Prostatic Hyperplasia

Key findings

  • During transurethral surgery for benign prostatic hyperplasia (BPH), relieving obstruction in the prostatic urethra may depend not just on expanding the lumen but also on restoring the luminal shape to be consistent with urodynamic requirements
  • This study made use of a computational fluid dynamics (CFD) model to explore the effects of different diameter ratios of the prostatic urethra on the mechanical behavior of mid-voiding urine flow after transurethral surgery
  • In 182 of 210 iterations, vortices—which are known to occur in urine flow in the prostatic urethra after transurethral surgery and cause fluid energy loss—appeared on both sides of the simulated prostatic urethra
  • CFD modeling is a viable research tool for evaluating urine flow behavior within the prostatic urethra after transurethral surgery for BPH

Most transurethral surgical procedures for benign prostatic hyperplasia (BPH) aim to remove proliferative tissue from the prostatic urethra (PU). However, urine flow does not always improve: Recent studies have demonstrated that a vortex, which causes fluid energy loss, can form in urine not just preoperatively but also postoperatively.

Chin-Lee Wu, MD, PhD, associate pathologist and director of Genitourinary Pathology Services at Massachusetts General Hospital and the Mass General Cancer Center, and colleagues believe relieving obstruction of the PU depends not just on expanding the lumen but also on restoring the luminal shape to be consistent with urodynamic requirements.

The team wanted to study urine flow in the hollowed-out PU after transurethral surgery, but the problem was finding the technology to do it. Imaging, such as ultrasound and MRI, can't provide information about the dynamic state of urine flow. Even traditional urodynamics research tools don't do well at directly evaluating hydrodynamic effects in vivo.

Therefore, the researchers turned to the field of computational fluid dynamics (CFD). In Scientific Reports, they describe how they determined CFD is useful for assessing the relationship between urine flow and luminal hollowing in the PU after BPH surgery.

Study Methods

To focus their study on the impact of different diameters of the PU, the team simplified the lower urinary tract in men into three regions: the lower half of the bladder, the PU and the rest of the urethra. Using data from a postsurgical patient, they created a two-dimensional CFD model of mid-voiding urine flow after transurethral surgery and used flow dynamics simulation to monitor its pressure and velocity.

The PU is shaped differently after different transurethral surgeries, so the researchers created 209 more examples of the model. Ultimately:

  • Three different measurements of the longitudinal diameter of the PU (LD-PU) were evaluated
  • Each LD-PU group contained five subgroups with different measurements of the transverse diameter of the bladder neck (TD-BN)
  • Each TD-BN subgroup contained 14 variations in the transverse diameter of the PU

Key Results

According to the distribution of pressure and velocity, different characteristics were observed:

  • Pressure decreased rapidly between the PU and the rest of the urethra, compared with the pressure between the bladder and the PU
  • The direction of velocity was not always toward the urethral outlet—vortices were present on both sides of the PU in 182 of the 210 examples
  • Laminar flow and vortex flow coexisted in most examples
  • Within each subgroup, examples with a vortex presented significantly lower midpoint velocity at the external urethral orifice than examples without a vortex

The researchers consider CFD a viable research tool for evaluating urethral vortex flow and believe it has the potential for high clinical impact.

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