The female continence mechanism measured by high resolution manometry: Urethral bulking versus midurethral sling

Traditional technology to characterize urethral pressure changes during dynamic conditions is limited by slow response times or artifact-inducing withdrawal maneuvers. The 8F high-resolution manometry (HRM) catheter (ManoScan™ ESO, Covidien) has advantages of fast response times and the ability to measure urethral pressures along the urethral length without withdrawal. Our objective was to determine static and dynamic maximum urethral closure pressures (MUCPs) and resting functional urethral length (FUL) in women using HRM before and after transurethral bulking and compare results to other women who underwent midurethral sling (MUS).

We recorded rest, cough, and strain MUCPs and FUL in 24 women before and after transurethral bulking with polydimethylsiloxane (Macroplastique®) using the HRM catheter and compared these changes to HRM values from 26 women who had the same measures before and after MUS.

At rest, MUCPs increased minimally after both urethral bulking and MUS (3 vs 0.4 cm H₂ O respectively, P = 0.4). Under dynamic conditions there were statistically insignificant small increases in MUCP and these increases were markedly less than after MUS (cough: 1.5 vs 63.8 cm H₂ O, P < 0.001 and strain: 11.5 vs 57.7 cm H₂ O, P < 0.001). FUL increased by 0.5 cm after transurethral bulking (P = 0.003), and decreased by 0.25 cm after MUS placement (P = 0.012).

The mechanism of continence after urethral bulking differs from MUS. While MUS increases dynamic MUCP, bulking may rely on increasing the length of the continence zone.