Overactive bladder: why it occurs

Women suffering from overactive bladders frequently need to pass urine urgently, and may suffer from urinary incontinence. Bladders from women with this condition show characteristic changes, including loss of some of the motor nerves and an increased sensitivity of the smooth muscles to stimuli. In most cases it is not clear what causes these changes, although predisposing factors are increasing age, childbirth and pregnancy, menopause, hysterectomy and obesity. The condition is, however, more common in patients with neurological disorders, and can sometimes occur as a result of operations for stress incontinence. Results from research using animal models have shown that reduced blood flow to the bladder can result in death of neurones in the bladder wall and the development of overactivity. In many of the predisposing factors and conditions in humans, enhanced pressure rises in the bladder during voiding may occur, which result in periodic reduction in blood flow, or else reduced blood flow may occur due to pressure on the vessels supplying the bladder. It is thus possible that bladder overactivity in humans also results from damage to the nerves innervating the bladder, and that this damage, which may be caused by reduced blood flow to the bladder wall, changes the muscle properties predisposing to overactivity.