Pathophysiology
The voluntary control of urine storage and elimination, or micturation, is a complex physiologic process involving voluntary and involuntary control. Although some of the basic mechanisms have been clarified, the reason for loss of conscious control in a neurologically intact woman remains a mystery. By contrast, UI that results from anatomic defects is fairly well understood.
Major changes occur in the lower urinary tract as a consequence of aging, and many of them cause symptoms. Estrogen levels declined markedly during the time around menopause with an associated loss of connective tissue throughout the body. This may cause a decrease in bladder compliance (ability to distend) and contractility (ability to empty) and in urethral resistance (ability of the urethra to squeeze and hold urine in the bladder). These factors can promote urinary retention and lower urethral closure pressure, thereby predisposing to stress incontinence. Estrogen deprivation may also lead to painful intercourse, painful urination, urgency and urinary frequency.
A decline in urethral resistances is common in persons older than 65 and is often accompanied by a substantial decrease in maximum bladder capacity. These changes can predispose to frequency, urge incontinences, or an overactive bladder, and urinary tract infections (UTI). These age-related changes in conjunction with factors such as multiparity (having several children), genetic factors, prior hysterectomy or other gynecologic surgery, contribute to anatomic causes of stress incontinence. Some physicians tend to overlook the influence of factors that increase intra-abdominal pressure, including chronic pulmonary disease (especially in smokers), constipation and other gastrointestinal disorders, and obesity.
There are four main categories of urinary incontinence: stress, urge, overflow, and functional. Intrinsic sphincter deficiency (ISD) (low-pressure or weaken urethra) is a subtype of stress incontinence in which the urethra fails to exert sufficient outlet resistance to contain urine bladder under minimal stress or at rest. Measuring urethral outflow resistance during urodynamic testing can establish the diagnosis of ISD. These patients typically describe your loss without any sensation that it is occurring. Some common neurologic disorders, including Parkinson’s disease, cerebral vascular problems and multiple sclerosis may lead to urge incontinence or overactive bladder.
No discussion of urinary incontinence pathophysiology in aging women is complete without mentioning pelvic organ prolapse. Structure and function of the female urinary tract are intrinsically related. The bulge and discomfort of organ prolapse may prompt patients to seek medical attention, which should alert physicians to elicit signs and symptoms of urinary incontinence. Prolapse may present with incontinence, but the incontinence may disappear if the defects leads to kinking of the urethra, which then prevents urine loss. These patients are at risk for developing urinary incontinence when a symptomatic bulge is repaired, or when a pessary is used, both of which may ‘unkink’ the ‘potential incontinence’.