[Impact of bladder-neck angle on urination: An application study based on fluid-structure interaction]

Objective： To assess the deformation of the bladder-neck opening and the impact of the bladder-neck angle (BNA) on urination in male patients by fluid-structure interaction (FSI) analysis.

We established geometric models of the bladder, prostate and urethra were established, incorporating both normal and enlarged BNAs, and assessed the effects of BNA alteration on urinary flow by FSI simulation of the flow rate and pressure of the urine within the bladder, bladder neck and urethra, and that of prostate displacement as well. We retrospectively analyzed the clinical data on 145 male patients from the Second Hospital of Hebei Medical University between June 2020 and June 2023, 39 with acute urine retention (the AUR group) and 106 without (the non-AUR group), and evaluate the impact of BNA on urination based on the urinary flow rate and prostate volume.

Comparative simulation analysis showed significant differences in the total urethral pressure and flow rate between the normal and enlarged BNA models (P < 0.05). The maximum prostate displacement was found at the bladder neck, with moderate displacement and unchanged urethral diameter in the normal BNA model, but significant displacement and a reduced urethral opening diameter in the enlarged BNA model. FSI analysis confirmed an evident impact of enlarged BNA on urination, more significant in the AUR than in the non-AUR patients (P < 0.05). The BNAs in the patients with the maximum urinary flow rate (Qmax) of <10, 10－15 or >15 ml/s were 83.7° ± 2.5°, 67.5° ± 1.8° and 65.1° ± 4.8° respectively, with statistically significant difference between the former one and the latter two groups (P < 0.05). The BNAs in the patients with normal prostate volume or BPH of grade I, II, III or IV were 65.0° ± 3.7°, 67.2° ± 3.1°, 71.5° ± 2.0°, 82.8° ± 3.5° and 105.8° ± 6.0°, respectively (P< 0.05), with statistically significant difference between BPH grades III and IV (P< 0.05) as well as between these two and the other three groups (P < 0.05), but not among the normal prostate volume, BPH grade I and BPH grade II groups (P > 0.05). Spearman correlation analysis indicated that BNA was strongly correlated with total prostate volume (TPV), transition zone volume (TZV), intravesical prostatic protrusion (IPP), prostatic urethral angle (PUA), IPSS, and Qmax (P < 0.05).

Changes in BNA affect urination and are closely associated with the severity of prostate hyperplasia. The BNA may be an important anatomical factor for assessing the severity of lower urinary tract symptoms in BPH patients.