Urethral opening pressure: its clinical significance in prostatic obstruction

Abstract

In the evaluation of prostatic obstruction by using the pressure-flow study (PFS), we defined intravesical pressure at initiation of voiding as urethral opening pressure. This simple parameter could reflect the degree of compressive prostatic obstruction to some extent. The aim of this study is to analyze if a correlation exsists between clinical signs and urethral opening pressure, and if they bear any prognostic value in postoperative outcome of the patients. We analyzed 46 patients with clinical benign prostatic hypertrophy who underwent urodynamic evaluations including PFS. They were divided into 2 groups according to their urethral opening pressure. The high opening pressure was defined as greater than 70 cm water, which was noted in 24 patients (group A). Twenty-two patients had lower opening pressure (group B). Comparison of the clinical findings in these patients were reviewed. Medium-filling cystometry and PFS were performed transurethrally, by using a microtip transducer and rectal balloon. Cystoscopy was performed when possible, wherein we could examined the presence or absence of detrusor trabeculation. Transurethral prostatectomy was indicated in a total of 26 patients (16 in group A and 10 in group B), in whom postoperative clinical findings were analyzed with regard to the difference in preoperative urethral opening pressure. The patients who void with straining or who void following uninhibited detrusor contraction were excluded from this study. International Prostatic Symptoms Score (I-PSS) revealed no significant difference in both groups, however, patients in group A were often suffering from urge incontinence preoperatively. Significant correlation was found among the incidence of detrusor instability, detrusor trabeculation and increased opening pressure. In PFS the patients with high opening pressure tended to have higher detrusor pressure at maximum flow and greater contractile power of the detrusor in voiding. There were no difference in Qmax and residual volume both groups. Postoperatively, symptomatic improvement was significant in both groups. There was no statistical difference in postoperative I-PSS between group A and B. Although 6 patients in group A demonstrated poor urinary control at 1 month, only two patients remained incontinent at 6 months postoperatively. As to urodynamic findings, the difference in PFS were markedly reduced between both groups. No difference was noted in postoperative Qmax as well. Significant difference was found in preoperative objective findings except the flow rate between the patients with and without high urethral opening pressure, while no symptomatic difference was noted except urege incontinence in both groups. No prognostic value was demonstrated in urethral opening pressure, however, poor postoperative urinary control was often associated with initial high opening pressure in the short term. It was suggested that 1) compensatory detrusor hyperactivity improved voiding efficacy in the patients with prostatic obstruction, which was gradually normalized after the relief of obstruction, 2) symptomatic improvement was highly related to the relative improvement of the obstructive findings on PFS.