Since the bladder is a low-pressure reservoir, intravesical bladder pressure typically rises very little despite increasing amounts of urine and distention of the smooth muscle or detrusor muscle of the bladder. Pressure ranges from 2 to 6 cm of water in an empty state and rarely exceeds 10 cm of water at maximum capacity.
At maximum capacity, a woman should be able to get to the toilet easily, initiate voluntary bladder contraction with complete relaxation of her pelvic floor, and void to completion.
Urge incontinence is more detrimental to quality of life
Of women who complain of urinary incontinence, more than 90% have either loss of detrusor muscle control (urge incontinence) or urethral sphincteric incompetence (stress incontinence).4 In addition, 30% to 50% of women with stress incontinence have coexistent urge incontinence. 1
Urge incontinence has a much more dramatic impact on a woman’s quality of life than stress incontinence, because stress incontinence is predictable and controllable. The patient understands she will leak urine only with increases in intraabdominal pressure associated with exercise, coughing, etc. These leakages tend to occur in small spurts that are easily absorbed by protective wear. In contrast, urge incontinence manifests as an unpredictable, involuntary void in which urine is released in a gushing stream, often in quantities large enough to soak through heavy absorbent pads.
Although one might assume that subjective complaints would readily distinguish the 2 conditions, the bladder is a very poor “witness.” What the patient perceives often fails to correlate with the true mechanism of incontinence. Since therapies for these 2 conditions are completely different, the evaluation of incontinence is very important.
In aging women, the prevalence of frequency, urgency, and urge incontinence is much higher than that of stress incontinence. Among women 60 to 80 years of age—growth-wise, the largest segment of our population—as many as 50% experience frequency, urgency, and urge incontinence.
High economic cost. The tremendous expense of urinary incontinence is increasingly recognized. In 1995, for example, the economic cost in the United States was $26.3 billion, or $3,565 per person 65 years or older with the condition.5,6 Of these resources, 48%, or $12.53 billion, were drawn directly from the economy to diagnose, treat, care for, and rehabilitate patients with incontinence.
Contributing factors and causes of overactive bladder
Overactive bladder is thought to be multifactorial. Symptoms often occur in the absence of any obvious pathology, which makes it difficult to pinpoint a cause. Coexisting conditions may also contribute to symptoms or may even be the sole cause.
Examples include infection or inflammation of the lower urinary tract, such as a simple case of cystitis, or a foreign body in the bladder.
Injury or diseases of the nervous system can disrupt voluntary control of voiding in adults, triggering the reemergence of reflex voiding, which leads to bladder hyperactivity and urge incontinence. At a local level, urge incontinence can develop secondary to intrinsic detrusor myogenic abnormalities.
Outlet obstruction can result in urge incontinence such as the well recognized symptoms of urethral obstruction in men with benign prostatic hyperplasia.
Detrusor sphincter dysnergia, most commonly secondary to spinal cord injury or multiple sclerosis, may affect younger men and women.
A deficient urethral sphincter in women with stress incontinence may induce urge incontinence, as urine leaking into the urethra secondary to the stress incontinence stimulates urethral afferents that induce involuntary voiding reflexes.7
Women with stress incontinence may unwittingly contribute to overactive bladder by voiding more and more often, hoping to prevent any involuntary urine loss. As a result of the frequent voiding, they develop frequency and urgency symptoms. That is, over time, this frequent, voluntary voiding leads to decreased bladder compliance. Thus begins a vicious cycle that ultimately leads to more frequency and urgency.
Urogenital atrophy. Irritative symptoms of the lower urinary tract in the form of frequency, urgency, and dysuria can result from lack of estrogen, leading to urogenital atrophy.
Pelvic organ prolapse is another common coexisting condition. Although the correlation between anatomic descent of pelvic organs and lower urinary tract symptoms is poorly understood, frequency and urgency—with or without urge incontinence—coexist with symptomatic pelvic organ prolapse in approximately 30% to 50% of cases.
An enlarged uterus or adnexal mass may cause external compression of the bladder and lead to lower urinary tract symptoms.
Previous surgery of the anterior vaginal wall or bladder neck may sometimes trigger de novo symptoms of frequency, urgency, and urge incontinence. In women who have undergone a previous antiincontinence procedure, these symptoms may be related to some form of outlet obstruction. In some cases these patients have no increase in the postvoid residual, and only subtle urodynamic testing elicits evidence of obstruction.