Functional urology

How does micturition normally work?

Normal lower urinary tract function depends on coordination among the bladder, the urethra, the urinary sphincters and the nervous system.

Most of the time, the bladder is storing urine. When it reaches a sufficient volume, the urge to void appears progressively. In a healthy person, voiding begins when the bladder has reached a physiologic capacity and the time and place are socially appropriate.

Therefore, we can divide the voiding cycle into two main phases:

Storage phase

During bladder filling:

• the bladder must remain relaxed;
• the pressure inside the bladder must stay low;
• the urethra and sphincter mechanisms must remain closed;
• the patient must progressively perceive the filling;
• there must be the ability to voluntarily inhibit voiding.

Continence depends on proper coordination between the bladder and urethra during this phase.

Voiding phase

When the patient decides to urinate:

• the sphincter mechanisms relax;
• urethral resistance decreases;
• the detrusor muscle contracts;
• urine is expelled.

Normal voiding therefore requires adequate coordination between bladder contraction and relaxation of the urinary outlet.

Neurological control

Micturition is regulated by a complex interaction among:

• peripheral receptors and afferent pathways;
• spinal centers;
• peripheral efferent pathways;
• higher centers;
• different neurotransmitters.

As the bladder fills, its receptors send information to the nervous system about the degree of distension. This information reaches the spinal cord and the brain, where it is integrated with voluntary control and social behavior.

Sensations during filling

Under normal conditions, the first desire to void usually appears at approximately 150 to 250 mL. A sensation of imminent voiding may appear as the volume approaches 350–550 mL, although there is individual variability.

During filling, intravesical pressure remains relatively low thanks to the bladder's compliance properties.

What is it?

Urinary incontinence is the involuntary loss of urine.

It is not a single disease. It is a symptom that can result from different abnormalities of the bladder, urethra, sphincters, pelvic floor or nervous system.

Main types

Stress urinary incontinence

Leakage occurs when abdominal pressure rises:

• coughing;
• sneezing;
• laughing;
• exercise;
• lifting.

It occurs when the urethral closure mechanism fails to maintain continence against increased abdominal pressure.

It is especially common in women, although it can also occur in men, particularly after prostate surgery.

Urgency urinary incontinence

Urine leakage is associated with a sudden urge to void that is difficult to postpone.

It is usually part of the overactive bladder syndrome.

Mixed incontinence

Symptoms of both coexist:

• stress incontinence;
• urgency incontinence.

Overflow incontinence

It can occur when the bladder fails to empty adequately and a high residual urine volume remains.

It should make you think of conditions such as:

• lower urinary tract obstruction;
• impaired bladder contractility;
• certain neurological diseases.

Why is it important?

Besides the urinary problem, it can significantly affect:

• quality of life;
• physical activity;
• sleep;
• work activity;
• social relationships;
• sexuality.

What is it?

Overactive bladder is a clinical syndrome characterized mainly by urinary urgency, usually accompanied by increased frequency and nocturia, with or without urgency urinary incontinence.

Key symptom: urgency

Urgency is a sudden, intense need to urinate that is difficult to postpone.

It can present:

Without incontinence:

the patient has urgency but manages to reach the bathroom.

With urgency incontinence:

urgency is accompanied by involuntary urine leakage.

Evaluation

It is important to investigate:

• voiding frequency;
• urgency;
• episodes of incontinence;
• nocturia;
• fluid intake;
• medications;
• symptoms of infection;
• voiding symptoms;
• neurological diseases;
• urologic history.

The bladder diary can be especially useful because it records times, voided volumes, urgency and leakage.

Treatment

Management usually begins with conservative measures:

• education;
• habit modification;
• fluid regulation;
• bladder training;
• pelvic floor rehabilitation when appropriate.

When these measures are insufficient, pharmacologic treatments aimed at reducing storage symptoms can be used.

In selected, refractory patients there are second-line treatments, including intravesical botulinum toxin and different neuromodulation techniques.

What does it mean?

Neurogenic bladder encompasses disorders of bladder and/or sphincter function secondary to diseases or injuries of the nervous system.

The presentation will depend mainly on:

• location of the lesion;
• extent;
• course;
• involvement of sensory and motor pathways.

The presentation can vary depending on whether the lesions are cerebral, suprasacral spinal, sacral or of the peripheral nerves.

What can happen?

The neurological disorder can affect the ability to:

• sense bladder filling;
• store urine;
• inhibit bladder contractions;
• contract the detrusor adequately;
• relax the sphincter during voiding;
• empty the bladder completely.

That is why some patients present predominantly with incontinence, while others develop difficulty emptying the bladder or urinary retention.

Treatment goals

In these patients the goal is not only to prevent urine leakage.

The main goals are:

• preserve renal function;
• achieve continence when possible;
• reduce urinary tract infections;
• maintain low-pressure bladder storage;
• prevent upper urinary tract damage;
• promote the greatest possible patient autonomy.

Facilitating storage

When the predominant problem is a bladder that stores poorly or at high pressures, treatment aims to improve capacity and lower bladder pressure.

Depending on the case, pharmacologic treatments, botulinum toxin and, in selected situations, surgical treatments can be used.

Facilitating emptying

When the problem is inadequate emptying, a key tool is intermittent catheterization.

The strategy should be individualized according to the neurological disorder and the functional behavior of the urinary tract.

Evaluation starts with a good medical history.

History taking

We need to determine:

• when it started;
• frequency of leakage;
• approximate amount;
• relationship to exertion;
• presence of urgency;
• voiding frequency;
• nocturia;
• difficulty starting urination;
• sensation of incomplete emptying;
• urinary tract infections;
• neurological history;
• previous surgeries;
• medications.

A simple question can be very informative

"When do you leak urine?"

If the answer is:

"When I cough, laugh or exercise" → think mainly of stress incontinence.

"When I get a very strong urge and can't make it to the bathroom" → think of urgency incontinence.

"Both things happen to me" → think of mixed incontinence.

Physical examination

It should be tailored to sex, age and history. It may include:

• abdomen;
• genitalia;
• pelvic floor assessment;
• digital rectal exam in men when indicated;
• basic neurological assessment when suspected.

Initial tests

Depending on the patient, the following can be used:

• urinalysis;
• bladder diary;
• post-void residual measurement;
• uroflowmetry;
• ultrasound.

Not all patients need invasive tests.

Warning signs

A more in-depth evaluation may be needed in the setting of:

• hematuria;
• recurrent infections;
• pain;
• significant difficulty emptying;
• elevated residual volume;
• suspected neurological disease;
• history of surgery or radiotherapy;
• deterioration of renal function.

What is it?

Urodynamics studies the function of the lower urinary tract.

Unlike ultrasound or CT, which mainly show anatomy, urodynamics tries to answer how the bladder and urethra function during filling and voiding.

What questions does it try to answer?

Among others:

• does the bladder store at low pressure?
• do involuntary contractions appear during filling?
• is bladder sensation normal?
• does the patient generate an adequate contraction to void?
• is there increased resistance during voiding?
• do the bladder and sphincter work in coordination?

Uroflowmetry

It is one of the simplest functional tests.

The patient urinates into a device that records:

• voided volume;
• maximum flow rate;
• average flow rate;
• duration;
• curve shape.

A low flow indicates a voiding disorder, but by itself it does not determine its cause.

Low flow can occur due to:

• obstruction;
• decreased bladder contractility;
• insufficient voided volume.

Cystometry

It studies the behavior of the bladder during filling. It allows analysis of:

• sensation;
• capacity;
• pressure;
• compliance;
• occurrence of involuntary contractions.

Pressure-flow study

It simultaneously analyzes the pressure generated by the bladder and the urinary flow during voiding.

This helps clarify whether impaired emptying is mainly due to:

• increased resistance;
• decreased contractility;
• a combination of both mechanisms.

Do all patients need urodynamics?

No.

Urodynamics is used when knowing the functional mechanism can change a diagnostic or therapeutic decision.

It is especially important in certain patients with:

• neurological disorders;
• complex symptoms;
• discordant results;
• failed previous treatments;
• certain situations before invasive treatments.