Incompetent urethral closure mechanism in females. Experimental and clinical studies with special reference to...

A urethral/bladder model was placed in a reservoir simulating the abdominal cavity. Increased "intraabdominal' pressure was transmitted to the urethra-like part of the model only when this was situated inside the "abdominal cavity'. The use of H2O and CO2 as filling medium was indifferent as only the relation between rise in urethral pressure and in bladder pressure is of practical importance. However, the increase in transmitted pressure was 25% lower than CO2 was used. Incompetent urethral closure mechanism is found in three categories of female patients: (1) patients with sensory urge who have an unstable urethra, (2) patients with genuine stress incontinence, and (3) patients who have a sphincteric insufficiency due to a low maximal urethral closure pressure and atrophy of the urethral mucosa. These categories can be separated urodynamically using simultaneous urethracystometry combined with transmission studies. Out of 20 patients with sensory urge 16 were found to have an unstable urethra. Transmission studies in 51 women with symptoms of stress incontinence revealed positive transmission, i.e. the increase in urethral pressure exceeded the rise in bladder pressure, in 23 patients. They were all elderly women and had a low maximal urethral closure pressure and their leakage of urine was due to an endourethral weakness. The remaining 28 patients had negative transmission and thus genuine stress incontinence.

To classify the three different types of incompetent urethral closure mechanism it is necessary to perform a simultaneous urethracystometry, in which transmission studies are mandatory, as this is the most appropriate way to distinguish between patients who will benefit from operation and patients who will not.