A new urodynamic measurement system for urethral retroresistance pressure (URP) has been described. URP is defined as the pressure required to achieve and maintain an open urethral sphincter and is measured by occluding the urethral meatus with a cone-tipped plug placed 5 mm in the urethra.
Sterile fluid is then infused retrograde at a rate of 1 mm/s while the required pressure is measured on a pressure vs time plot, and the plateau of the asymptotic curve represents the URP (10,11).
In a randomized, multicenter trial of 258 symptomatic females, URP, LPP, and MUCP were measured after assessment of incontinence severity by validated questionnaires.
The authors concluded that URP has a consistent relationship to incontinence severity, whereas MUCP and LPP were not reliably decreased in patients with increased degrees of incontinence (10). In a second study, 61 asymptomatic females underwent URP measurement after confirming a negative standing stress test; the goal was to characterize the distribution and reproducibility of URPs in asymptomatic women (11).
The URP measurements in this population exhibited a normal distribution, and in 32 females who underwent retesting 3–7 d later, there was no statistically significant difference between test and retest URP measurements. Furthermore, when comparing the symptomatic and asymptomatic premenopausal patients, the mean URP was significantly different.
This work represents an attempt to define and characterize a novel approach to measuring urethral function with the goal of finding a parameter that is reproducible, accurately identifies stress incontinent patients, and predicts treatment outcome. Although initial investigations of URP are promising, it remains investigational and will require further evaluation before its clinical utility can be determined.
Kelly M. Maxwell, MD, and J. Quentin Clemens, MD, MSCI