Detrusor instability and low compliance may represent different levels of disturbance in peripheral feedback control of the micturition reflex

Abstract

Background Detrusor instability is a major cause of urinary incontinence in females. Its cause is unknown. Diagnosis is made with cystometry. A phasic pressure rise during cystometry diagnoses the unstable detrusor, and a non-phasic pressure rise the stable “low-compliance” detrusor. The aim was to test the hypothesis that such cystometric findings may represent different levels of disturbance in peripheral feedback control of a prematurely activated, but otherwise normal micturition reflex. Of 169 neurologically normal female incontinent patients (mean age, 50; mean parity, 3) urodynamically tested, 40 had detrusor instability and 16 had low compliance. Digital support of bladder base tested the peripheral control mechanism, and hand-washing the central control mechanism. The data were applied to a non-linear feedback equation with one variable, XNEXT = cX(1 − X), where c = central inhibition and X = fraction of possible nerve impulses in the micturition circuit. Results During filling, all 16 low-compliance patients had a bladder in the activated but stable closed state. Fourteen of the detrusor instability group could not suppress the micturition reflex and lost urine. During hand-washing, unexpectedly greater urine loss was noted in the low-compliance group (13 of 16) than in the detrusor instability group (24 of 40), χ2 (P < 0.005). With digital stretching, urge symptoms disappeared within a few seconds in 18/20 patients, and detrusor instability was suppressed in six patients. Interpretation The bladder has two stable states: open and closed. Closure is regulated by central and peripheral components. In the female, the peripheral component is controlled by the pelvic floor stretching the vagina to support the urine column. This prevents inappropriate activation of the micturition stretch receptors. In patients with low compliance, this peripheral control mechanism was sufficient to maintain the micturition reflex in an activated but stable closed state. In patients with detrusor instability, the micturition reflex could not be suppressed, swinging between the open and closed states. Conclusions Demonstration of a peripheral musculoelastic control mechanism unlocks a new direction for management of female patients with non-neurological bladder instability. It is possible, using simple clinical methods based on digital vaginal stretching, to predict cure of instability by surgical tightening of the vagina and its supporting ligaments. Neurourol. Urodynam. 18:81–91, 1999. © 1999 Wiley-Liss, Inc.