Assessment of urethral resistance at external sphincter zone during voiding by static withdrawal urethrometrogram.

We investigated the intraurethral pressure changes at the external sphincter zone during voiding act and during an attempt to contract the anal sphincter on 26 neurologically intact subjects (normal group) and 12 cases after intrapelvic surgery (6 after amputatio recti and 6 after radical hysterectomy) (disturbed group). During voiding the pressure was decreased in 25 of 26 cases of the normal group, but was increased in 11 of 12 cases of the disturbed group. In contracting the anal sphincter, urethral pressure rose in all cases of both normal and disturbed groups. A significant positive correlation (p less than 0.01) was found in the urethral pressure changes between voiding and during the attempt to contract the anal sphincter in the disturbed group, but not in the normal group. It is supposed that the pressure decreased during voiding is an indication of not only normally functioning external urethral sphincter but also non-underactive detrusor, and that the pressure increase means either underactive detrusor or spastic external urethral sphincter due to detrusor-sphincter dyssynergia. To measure the urethral pressure changes at the external sphincter zone during voiding is thought to be useful for assessment of the urethral resistance at that zone.