Bladder Function

Bladder Function Impacting Continence Across Lifespan

Infancy

During infancy, micturition occurs by means of a classic reflex mechanism. The bladder fills until proprioceptive stretch receptors stimulate the brain center or spinal reflex mechanisms to provoke a detrusor contraction.

For the majority of infants (about two-thirds), this triggers coordinated voiding under the influence of the pontine micturition center. However, about 33% of full-term neonates demonstrate an interrupted voiding pattern and vesicosphincter dyssynergia (uncoordinated contraction of urethral and pelvic floor muscle), leading to interrupted voiding and functional obstruction.

Fortunately, this pattern of vesicosphincter dyssynergia usually resolves within the first year of life, resulting in more efficient bladder emptying and fewer voids during a 24-hour period. The developmental processes that account for this resolution are not known, but maturation of the pontine micturition center remains a strong possibility.

During the first 6 months of life, the bladder capacity is small in relation to hourly urine production, and voiding occurs about 20 times daily. At about 6 months of age, the frequency of voiding begins to diminish. This change in the pattern of urine elimination may occur as a result of increased ability to inhibit micturition unconsciously as the brain matures or because of changes in the functional capacity of the bladder in relation to the volume of urine produced by the kidneys.

Mastering Continence

Between 1 and 2 years of age, the neurologically normal child develops a conscious awareness of bladder filling. This event probably marks the first major milestone toward the mastery of continence. Initially, this perception of urinary urgency occurs immediately before voiding.

The child is also learning to identify, contract, and relax the pelvic muscles, including the periurethral striated muscles. Mastery of these skills allows the child to temporarily postpone micturition and to briefly interrupt the urinary stream during micturition, and this ability marks the second milestone toward continence. Nonetheless, a third developmental milestone must be reached before the child can be described as “ready” for toilet training. Direct control over the detrusor is thought to occur when modulatory centers in the frontal cortex, thalamus, hypothalamus, and basal ganglia establish inhibitory control over the micturition centers in the pons and spinal cord. The processes by which these milestones are reached are unknown.

The neurologically normal child reaches a stage of readiness for toilet training between 1 and 4 years of age. Although it is not currently possible to determine the precise point at which the developing child gains control over detrusor contractions, several signs indicate a readiness to achieve urinary continence.

Nighttime bowel control is typically mastered first, followed by diurnal fecal continence. However, unlike fecal incontinence Opens in new window, daytime urinary continence typically precedes nocturnal control over micturition.

Successful toilet training is feasible when a child has gained fecal continence, is able to verbalize the perception of urinary urgency, is able to postpone urination briefly, and is able to interrupt the urinary stream voluntarily. Attempts to toilet train a child before mastery of these skills are likely to fail or to produce a child who experiences urinary frequency and frequent episodes of urinary leakage when s/he is unable to reach the toilet after the onset of an unstable detrusor contraction.

Although most children master an adult voiding pattern by 4 years of age, as many as 10% to 15% experience persistent voiding problems. The most common voiding problem is so-called nocturnal enuresis Opens in new window, a condition characterized by episodes of urinary leakage during sleep. A smaller percentage of children will experience episodes of urge urinary incontinence Opens in new window associated with unstable detetrusor contractions that occur during waking hours. Further growth and maturation typically resolve these conditions, although a few of these individuals experience urinary frequency or occasional episodes of enuresis Opens in new window that persist into adulthood.

Aging and Continence

Although it is known that aging by itself does not cause urinary incontinence Opens in new window, there are many age-related changes in the central nervous system, urinary bladder, and adjacent organs that increase the risk of incontinence Opens in new window in the elderly.

Specifically, elderly individuals tend to urinate smaller volumes more frequently during waking hours and are more likely to experience nocturia. In addition, elderly persons are more prone to urinary incontinence Opens in new window and urinary retention Opens in new window when compared with younger adults.

Unfortunately, although a great deal of research has focused on voiding dysfunction in the elderly, less work has been done on physiologic changes of the lower urinary tract directly associated with aging. Nonetheless, valuable research has been completed in this area, and some age-associated changes in the lower urinary tract have been described.

1. Changes in Microscopic Anatomy

Changes in the microscopic architecture of the bladder wall can be observed with aging. Susset and colleagues reported an increase in the collagen content of the bladder wall in women older than 50 years of age, although these changes have not been observed by others.

However, further studies have demonstrated that collagen fibers in the aging bladder cross-link and stiffen, even if there is no increase in volume. In addition, a growing body of evidence suggests that the number of cholinergic receptors tends to diminish with aging, whereas the number of purinergic and adrenergic receptors increases.

The implications of these observations are not totally clear; however, they may provide partial explanations for detrusor hyperactivity with insufficient contractility, a voiding disorder characterized by both urge incontinence Opens in new window and incomplete bladder emptying.

This change in receptor distribution also may account for the often disappointing clinical response of elders to antimuscarinic medications. In addition, because circulating catecholamines reach a peak during the morning, an enhanced adrenergic response may account for the relatively common complaint among men of a poor urinary stream during the morning hours, followed by improved voiding efficiency as the day progresses.

Elbadawi and colleagues correlated histologic changes in the detrusor (as evidenced by biopsy studies), urodynamic findings, and clinical signs and symptoms related to bladder function for a group of elderly patients. They were able to identify three distinctive types of histologic characteristics that correlated with the following three “clinical urodynamic” categories among elderly individuals:

1. those with normal voiding function,
2. those with detrusor instability, and
3. those with a combination of detrusor instability and impaired contractility.

It is not known whether these changes represent primary causes of voiding dysfunction in the elderly or a secondary effect f changes originating in the nervous system.

2. Changes in the Central Nervous System

Alterations in central nervous system function also affect continence in the elderly person. CVAs affect approximately 1% of the population, and epidemiologic studies have demonstrated that age is the most powerful predictor of the risk for stroke; the risk is estimated at 5% among Americans 55 to 59 years of age, but it increases to 25% among persons 80 to 84 years of age.

The occurrence of a stroke places the elderly person at risk for urinary incontinence Opens in new window for several reasons. First, the neurologic damage caused by the infarction itself and by the edema and ischemia in surrounding tissues may damage the detrusor motor center or other modulatory areas essential to detrusor muscle control, resulting in detrusor instability and urge incontinence Opens in new window. In addition, a significant stroke acutely impairs the functional status of the elderly person.

Alterations in mobility, cognition Opens in new window, speech, and dexterity limit the individual’s ability to recognize the cues of bladder filling and to act on these cues by moving to the toilet or by alerting caregivers of the need to toilet. The influence of functional impairment on continence Opens in new window is demonstrated by studies regarding the prevalence of urinary incontinence after a stroke.

In one study, 47% of a group of 935 patients admitted to the hospital for acute CVA experienced urinary incontinence. However, the prevalence of urinary incontinence fell to 19% 6 months after the stroke, at which point functional status had improved as a result of recovery and rehabilitation.

Parkinsonism, also called Parkinson’s disease, is a progressive neurodegenerative disease that affects the neurons of the basal ganglia. Although parkinsonism is clearly not a normal part of aging, age is the primary risk factor for development of this disorder; the prevalence of parkinsonism is approximately 0.2% in the general population but rises to approximately 3% among persons 79 years of age and older. Because the basal ganglia are known to contribute to detrusor control, parkinsonism is associated with detrusor hyperreflexia and urge urinary incontinence. However, the likelihood of urinary incontinence associated with parkinsonism is influenced by the individual’s functional status and by the urodynamic characteristics of the lower urinary tract. In advanced cases, the bradykinesia, resting tremors, and postural reflex disorders associated with parkinsonism impair balance, mobility, and dexterity, and the ability to toilet.

Parkinsonism is sometimes confused with a condition called multiple system atrophy (MSA), or the Shy-Drager syndrome. MSA is an autonomic disorder affecting the intracerebral and spinal cord tracts; as a result of these mixed effects, detrusor instability typically coexists with intrinsic sphincter deficiency. This disease affects approximately twice as many men as women, and aging is a risk factor.

Differentiation between MSA and parkinsonism is particularly important among men when prostatic resection is being considered. Although men with parkinsonism may benefit from prostatectomy, those with MSA are likely to develop significant stress urinary incontinence when the prostate is removed.

Dementia or senile dementia is defined as the diffuse deterioration of mental function, causing changes in memory, behavior, and emotional stability. Alzheimer’s disease is the primary cause of dementia, accounting for more than 50% of all cases of senile dementia in the elderly. Alzheimer’s disease is a neurohistopathologic diagnosis based on identification of senile plaques and neurofibrillary tangles in the brain. However, in the clinical setting, the diagnosis of Alzheimer’s disease is typically based on its clinical features and on the exclusion of related disorders causing senile dementia (such as hydrocephalus, cerebrovascular disorders, intracranial tumors, metabolic disorders, or Pick’s disease).

Alzheimer’s disease affects approximately 3 to 4 millon Americans, and its incidence rises steadily with aging. However, unlike the pattern with CVA or parkinsonism, urinary incontinence does not commonly occur during the early stages of the disease. Instead, urinary incontinence typically occurs during the advanced stages of the disease, and the functional decline associated with Alzheimer’s probably plays an important role in the loss of bladder control.

Although Alzheimer’s disease is not known to cause unstable detrusor contractions, Griffiths and colleagues identified evidence of a cerebral component in the development of urge incontinence in many older persons. They correlated single-photon emission computerized tomography scans, clinical signs and symptoms, and urodynamic findings and suggested that impaired perfusion of specific areas in the frontal lobes of the cerebral cortex may cause detrusor instability in many elderly persons.

This detrusor instability was distinctive from that seen among younger persons because it was associated with impaired sensation of bladder filling. Unlike the younger person with urge incontinence, who experiences urinary urgency at low volumes, their elderly subjects experienced no sense of urinary urgency before the onset of an unstable detrusor contraction resulting in urinary leakage. In addition, this form of urge incontinence was associated with impaired cognitive function, especially with orientation to time.

3. Sphincter Mechanism Function

The function of the urethral sphincter mechanism is affected by alterations in nervous system function and also by changes in the urethra itself. The maximum urethral closing pressure is lower in elderly women than in younger women. Multiple factors may contribute to this alteration in sphincter function, and estrogens clearly play a central role.

Estrogens are known to increase smooth muscle sensitivity to alpha-adrenergic stimulation, and this increase may partly account for the lower maximum urethral closure pressure noted in older, postmenopausal women. However, estrogen treatment of postmenopausal women with atrophic vaginal changes and stress urinary incontinence rarely resolves the stress-related urine loss. Rather, exogenous estrogens are more effective for the treatment of irritative voiding symptoms and urge incontinence than for the treatment of stress incontinence.

In addition, the proportion of elderly women who experience stress urinary incontinence is relatively stable, particularly when compared with the increasing prevalence of urge incontinence within this group, a finding that reflects the increasing significance of detrusor instability as a cause of urinary leakage in the elderly.

Clearly, the greatest change in sphincter mechanism function in the male occurs as a result of prostatic enlargement. BPH is the gradual enlargement of the glandular elements of the prostate gland. Aging, in combination with functioning testes, is the primary risk factor for BPH, and its prevalence rises steadily with age.

Although as many as 10% of men demonstrate some evidence of glandular hyperplasia as early as 30 years of age, clinical symptoms of BPH seldom occur before the fifth decade of life. Among men more than 60 years of age, the prevalence of BPH rises to approximately 50%, and it reaches 90% among men 85 years of age.

BPH Opens in new window is rarely a direct cause of mortality; rather, it typically is a quality-of-life disorder because of the associated voiding symptoms. The enlarging prostate produces bladder outlet obstruction by encroaching on the lumen of the prostatic urethra and by increasing the smooth muscle tone in the bladder neck and prostatic urethra.

In some cases, the bladder outlet obstruction remains mild, and the detrusor muscle is able to compensate for the increased outlet resistance by increasing the power of its contraction. In other cases, more significant obstruction causes decompensation of the detrusor muscle and bothersome voiding symptoms including diminished urinary stream, intermittency of the stream, frequent urination, and incomplete bladder emptying. In particularly severe cases, episodes of acute urinary retention occur.

The effects of bladder outlet obstruction involve more than just the sphincter mechanism. Studies of animals and humans have demonstrated that bladder outlet obstruction also produces unstable detrusor contractions, which contribute to or cause the irritative voiding symptoms frequently associated with BPH. Although this instability is associated the morphologic changes in the bladder wall, it has also been shown that obstruction causes changes in spinal pathways in the rat; a positive response to iced saline cystometry in humans further supports involvement of the central nervous system.

These relationships are particularly significant when one is considering treatment for the elderly male with BPH and symptoms of urgency. Although the obstructive prostate may cause detrusor instability, it also provides a “protective” mechanism, and the presence of prostate enlargement has been associated with preservation of continence, whereas prostate surgery that removes this protective mechanism has been associated with the presence of urinary incontinence.

4. Changes in Renal and Metabolic Function

Changes in renal and metabolic functions may also affect voiding function in the elderly. Unlike younger persons, who produce the bulk of their urine during waking hours, older adults produce roughly equal volumes of urine during the day and night. As a result, more than half of adults older than 70 years of age experience two episodes of nocturia on a regular basis.

Kikuchi studied human atrial natriuretic peptide and vasopressin, also called the antidiuretic hormone, in a group of “younger” versus “older” elderly men. They found that the “older” subjects experienced changes in the circadian rhythm of these hormones as well as higher urinary output at night as compared with the “younger” subjects enrolled in the study.

Specific diseases associated with aging also predispose the elderly person to nocturia. Chronic venous insufficiency, edema of the lower extremities, congestive heart failure, and diabetes predispose to increased urine production during nighttime hours.

Although the elderly person who is relatively mobile and alert can manage this increase in nighttime urine production by getting up to void during the night, the person with immobility or altered cognition may be unable to recognize the urge to urinate or to move to the toilet; immobility and altered cognition are common among elderly individuals who are acutely ill or hospitalized or who have been given sleeping aids.

5. Functional Aspects of Continence

In addition to factors that directly affect lower urinary tract function, any discussion of the physiology of the aging bladder must involve consideration of the functional aspects of aging and its effect on continence. Although most elderly persons remain alert and mobile, many disorders associated with aging reduce mobility, dexterity, and the ability to maintain continence.

Elderly persons are at risk for arthritis, osteoporosis, hip fractures, peripheral vascular disease, and other disorders that affect balance, mobility, and dexterity. In some cases, these disorders may cause urinary incontinence Opens in new window in a person with an otherwise healthy lower urinary tract Opens in new window. In other cases, these conditions push an elderly person from a condition of mild voiding dysfunction to clinically significant urinary leakage.

Drugs also affect the functional status of the elderly individual. Sedative hypnotic medications and narcotic analgesics impair alertness and mobility and may lead to urinary incontinence. Diuretics cause polyuria and may lead to urinary incontinence, particularly in the individual with preexisting detrusor instability. Antidepressants, anticholinergic or antispasmodic agents, decongestants, antiparkinsonian drugs, or calcium-channel blockers can predispose elderly individuals to urinary retention, particularly those who have preexisting impairment of detrusor contractility or bladder outlet obstruction.

Despite all the previously the previously mentioned challenges to urinary continence associated with aging, it is important to remember that most elderly persons living in the community and nearly half of those confined to their homes or a long-term care facility retain continence.