The male urethral pressure profile (UPP) shows the pressure change from the bladder neck (BN) through the sphincter (Sph) to the penile urethra, and also shows the length of the urethra, which functions to maintain continence. As the length from the BN to the Sph measured in the UPP trace is related to the longitudinal length obtained from the transrectral ultrasound (TRUS) median image, we assumed that the length from the BN to the Sph in the UPP trace can represent the prostate volume. In addition, we investigated whether the pattern of pressure change from the BN to the Sph in the UPP trace is related to bladder outlet obstruction (BOO).

From January 2021 to May 2022, we retrospectively analyzed the pressure flow and UPP trace of 85 patients with TRUS results among 135 male patients who were referred for urodynamics due to lower urinary tract symptoms. Among them, 78 UPP trace and TRUS were analyzed except for 6 patients who underwent urodynamics after prostate surgery and 1 patient who underwent urodynamics after maximal androgen blockade for prostate cancer. In TRUS image, the prostate volume of 25-45 cc were defined as moderate benign prostatic hyperplasia (BPH), and exceeding 45 cc were defined as severe BPH. In the urodynamic diagnosis, BOO was defined as bladder outlet obstruction index (BOOI) is more than 40, and UPP trace was classified into saddle, ladder, and slope shaped.

In the analysis for the relationship between the length of the UPP trace from the BN to the Sph and the prostate volume, data from 75 patients were analyzed except for 3 patients whose TRUS measurement value was unclear. Among 75 patients, 24 patients had moderate BPH with a prostate volume of 25-45 cc and 32 patients had severe BPH with a prostate volume exceeding 45 cc. The length of the urethra from the BN to the Sph was 3.86 ± 0.74 cm in 24 patients with moderate BPH, and 32 patients with severe BPH were 5.0 ± 1.8 cm. For the relationship between the UPP trace and pressure flow plot, data from 73 patients were analyzed excluding 5 patients who failed to urinate in pressure flow study. Among 73 patients, obstructed, equivocal, and unobstructed voiding were 18, 20, and 35, respectively. The UPP trace pattern of 18 obstructed patients was saddle-shaped, ladder-shaped, and slope-shaped 8, 8, and 2, respectively. Equivocal 20 patients were 6, 10, and 4, respectively. Nonobstructed 35 patients were 14, 9, and 12 respectively. The average length from bladder neck to sphincter in 18 obstructed patients was 5.2 ± 1.8cm, equivocal 18 patients was 4.3 ± 1.5cm, and unobstructed 35 patients was 3.8 ± 1.2cm.

The length of the urethra from the bladder neck to the sphincter showed an average difference of 3.86 cm in patients with moderate prostatic hyperplasia (prostate volume of 25-45 cc) and 5.0 cm in patients with severe prostatic hyperplasia (prostate volume exceeding 45 cc). In other words, it has been shown that the length of the urethra from the bladder neck to the sphincter can be a predictor of prostate size. In addition, obstructed voiding patients with a BOOI of 40 or higher had an average length of 5.2 cm from the bladder neck to the sphincter, which was longer than 4.3 cm of equivocal voiding or 3.8 cm of unobstructed voiding patients. The length from the bladder neck to the sphincter showed the possibility of predicting the pattern of urination in male patients with lower urinary tract symptoms.

The length from the BN to the Sph in the UPP trace is an index predicting prostate volume in patients with BPH. Patients diagnosed BOO on urodynamic evaluation had a longer length from the BN to the sph than patients with equivocal, unobstruced voiding, and mainly showed saddle or ladder-shaped in the UPP trace.