Diagnosis and treatment of intrinsic sphincter deficiency.

The urethra resists two expulsive forces, detrusor pressure and abdominal pressure. The high pressure area of the urethra resists detrusor pressure, while the lower pressure maximal urethra resists abdominal pressure. At the moment of flow driven by detrusor pressure, however it is produced, detrusor pressure is directly proportional to urethral resistance (pressure) at that moment. Abdominal pressure has no fixed relationship to urethral pressure. A normal urethral sphincter will not leak at any abdominal pressure, while a poorly closed maximal urethra will leak at very low abdominal pressure, despite normal high pressure zone function and pressure. A study of the abdominal pressure required to induce leakage in males after prostatectomy, and in women with incontinence or general prolapse, showed no relationship between maximum urethral pressure and the abdominal pressure required to cause leakage, or the presence or even absence of leakage. These data indicate that urethral pressure and "continence" are not directly related, that and measurement of the force produces leakage is a more accurate assessment of urethral sphincter function. Injectable agents have been found to be effective in females with involuntary urine leakage related to low or very low abdominal pressure in the absence of urethral hypermobility.