Urodynamic Studies for Urinary Incontinence 

Urodynamics are a means of evaluating the pressure-flow relationship between the bladder and the urethra for the purpose of defining the functional status of the lower urinary tract. The ultimate goal of urodynamics is to aid in the correct diagnosis of urinary incontinence based on pathophysiology.

Urodynamic studies should assess both the filling-storage phase and the voiding phase of bladder and urethral function. In addition, provocative tests can be added to try to recreate symptoms and to assess pertinent characteristics of urinary leakage.

Simple urodynamic tests involve performing a noninvasive uroflow study, obtaining a postvoid residual (PVR) urine measurement, and performing single-channel cystometrography (CMG). A single-channel CMG (ie, simple CMG) is used to assess the first sensation of filling, fullness, and urge. Bladder compliance and the presence of uninhibited detrusor contractions (eg, phasic contractions) can be noted during this filling CMG. A simple CMG may be performed using water or gas (carbon dioxide). Water is the most common filling medium.

Multichannel urodynamic studies are more complex than simple urodynamics and can be used to obtain additional information, including a noninvasive uroflow, PVR urine, filling CMG, abdominal leak-point pressure (ALPP), voiding CMG (pressure-flow), and electromyography (EMG). Water is the fluid medium used for multichannel urodynamics.

The most sophisticated study is videourodynamics, the criterion standard in the evaluation of a patient with incontinence. In this study, the following are obtained:

• Noninvasive uroflow
• PVR urine
• Filling CMG
• ALPP
• Voiding CMG (pressure-flow)
• EMG
• Static cystography
• Voiding cystourethrogram (VCUG)

The fluid medium used for videourodynamics is radiographic contrast.

Selection of patients for complex urodynamic testing can be difficult. Universally agreed-upon criteria for complex testing do not exist. The criteria that do exist are rooted more in expert opinion than in evidence-based scientific findings.

Urodynamic testing is expensive and requires specialized equipment and expertise. The availability of testing facilities is not universal.

The potential importance of urodynamic testing lies in the fact that the outcome of therapy is tied to understanding the pathophysiology in any given case and to making the correct and complete diagnosis. Surgery for incontinence carries with it substantial failure and complication rates. Many poor outcomes may be attributed to diagnostic failures.

Urodynamic studies are, by their nature, unphysiologic. Studies have shown that the reference range in such tests as uroflowmetry and cystometry is wide. Urodynamic findings of significance must be associated with reproduction of the patient's symptoms. Studies that do not reproduce the patient's symptoms are inconclusive. Likewise, studies that result in abnormalities with no associated symptoms, or symptoms differing from the patient's complaints, are not conclusive. Nevertheless, these are the best tests available for examination of lower urinary tract function.

For more information, see Urinary Incontinence, as well as Urinary Incontinence Relevant Anatomy and Cystoscopy and Urethroscopy in the Assessment of Urinary Incontinence.

The history and physical examination alone may not provide sufficient and accurate information on which to base surgical therapy, but such basic data may provide the foundation from which to select patients for more invasive and complex testing.

The following historical factors suggest the need for complex testing.

• Unclear or complicated history
• Significant urge component
• Irritative voiding symptoms
• History of urinary retention
• Previous failed incontinence surgery
• Continuous incontinence or leakage with minimal activity
• Elderly patient (ie, >65 y)
• Male patient
• Blacks with stress incontinence history
• Advanced pelvic organ prolapse
• Advanced diabetes (bladder neuropathy)
• Nocturnal enuresis
• Nulliparous woman with stress incontinence
• Known or suspected neurologic disease as a cause or contributor to incontinence

Physical examination findings that may prompt consideration of complex urodynamic evaluation include the following:

• Evidence of severe pelvic organ prolapse
• Abnormal CNS, lower extremity, or pelvic floor neurologic findings
• High PVR
• Stress incontinence with minimal increases in intra-abdominal pressure, with an empty bladder, and positive results on supine stress test
• Abnormal simple cystometry

The individual components of urodynamic testing are numerous. It is uncertain which of these components are essential, which ones may be important in specific and unusual circumstances, and which ones serve primarily as research tools. The following components are most essential to planning surgical therapy:

• Stress testing
• Cystometry
• Uroflowmetry
• PVR urine determination
• ALPP (also known as Valsalva leak point pressure)
• Urethral pressure profile

Within the scope of some of these tests, differing levels of complexity also exist. For example, the urethral pressure profile can consist of a simple determination of resting closure pressure, or it may also involve cough profiles, pressure transmission ratios, and measurements of functional urethral length. In general, the more sophisticated the procedure, the more narrow the scope of current clinical usefulness. However, these procedures ultimately may increase the understanding of urinary incontinence and, thus, improve clinical practice.

For urodynamic testing, the urine should be free from bacteria or evidence of inflammation. Many practitioners administer a single dose or short course of prophylactic antibiotics if invasive testing is scheduled. The literature suggests that this prophylaxis probably is not necessary if proper technique is used.^[1]

In female patients, some evidence shows that urodynamic findings do not change significantly in individuals when testing is performed at different times in the menstrual cycle.^[2] In another small retrospective study, cystometry was less likely to reveal an abnormality during the luteal phase, especially in patients who reported that their symptoms were influenced by the menstrual cycle.^[3] These researchers suggested avoiding urodynamic studies during the luteal phase if possible.

Instruct the patient to arrive at the urodynamic laboratory with a full bladder. Perform a noninvasive uroflow and post-void residual (PVR) urine test. Place the patient in the dorsolithotomy position. Prepare her genitalia, and drape using sterile technique.

Perform flexible cystoscopy. Survey the entire bladder urothelium, and then retroflex the cystoscope to examine the bladder neck. Fill the bladder with 250 mL of water. Commence bladder filling using room temperature water. Cold water may evoke false-positive detrusor contractions (phasic contractions). Fill the bladder at a medium rate (eg, 60 mL/min).

Next, perform the cough stress test and cotton swab test. Perform a detailed speculum examination with one half of the gynecology speculum pointing at the anterior, posterior, and vaginal apex for a view of pelvic organ prolapse. During the pelvic examination, assess the functional integrity of the pelvic floor muscles by examining the perineal body and checking the rectal tone. The presence of levator ani muscle dysfunction or tenderness may be elicited by gentle palpation of the levator ani musculature in the paravaginal fornices.

Perform a standing cough stress test and/or pelvic examination as needed.

Drain the bladder. Place a urodynamic urethral catheter (ie, 7F Cook dual-lumen pigtailed catheter), rectal tube, and electromyography (EMG) electrodes.

Rotate the patient to a sitting position, and equalize transducers. Commence bladder filling using room-temperature contrast (Conray). Cold water may evoke false-positive detrusor contractions (ie, phasic contractions). Fill the bladder at a medium rate (eg, 60 mL/min). Assess the first sensation of filling fullness, and assess urge. Note bladder compliance, and mark the presence of uninhibited detrusor contractions.

When the bladder fills to 250 mL, measure the abdominal leak-point pressure (ALPP). Instruct the patient to perform the Valsalva in gradients (ie, mild, moderate, severe) followed by cough (ie, mild, moderate, severe). Observe the urine leakage fluoroscopically and by direct inspection. At this point, note the activity of the bladder neck, urethral mobility, and the presence of cystocele using fluoroscopy (static cystography).

Upon completion of ALPP, finish the filling cystometrogram (CMG) to completion. When the patient has a strong desire to void, perform a voiding CMG (pressure-flow). At this point, note urodynamic parameters, such as maximal flow rate (Qmax) and detrusor pressure at maximal flow rate (PdetQmax).

During the voiding CMG, note the activity of the EMG electrodes and voiding cystogram for possible detrusor sphincter dyssynergia (DSD). The presence of DSD is confirmed by increases in EMG activity during detrusor contraction or closure of the external sphincter on voiding cystourethrography (VCUG).

After the patient voids to completion, the videourodynamic study is complete. The patient is informed about the findings and is sent home with an oral antibiotic.

Fluoroscopic video urodynamics has become the investigative technique of choice for incontinence in many referral and research centers. This technique involves the simultaneous display of real-time images of the bladder neck and urethra and cystometric summaries of bladder, intra-abdominal, and, in some cases, urethral pressures. (See the images below.)

The precise placement of pressure transducers and a constant understanding of their exact anatomic location is one of the advantages of this technique. Another advantage is the ability to fluoroscopically observe the bladder neck area throughout bladder filling and during stress maneuvers.

Contrast material can be observed entering the proximal urethra just before leakage; thus, leak-point pressure findings can be more precise. Cough profiles and pressure transmission ratios can be determined.

The physical location of the transducer tip can be observed during urethral pressure profilometry (UPP) and correlated with the pressure findings. Although probably not necessary for the evaluation of straightforward stress incontinence, video urodynamics can be a valuable diagnostic tool in complex or confusing cases.

Video urodynamic studies are the criterion standard for the evaluation of an incontinent patient. Video urodynamic studies combine the radiographic findings of a VCUG and multichannel urodynamics. A videourodynamic study is the most sophisticated diagnostic test for an incontinent patient.

In the absence of videourodynamics, the clinician may obtain adequate information from the following:

• Noninvasive uroflow and PVR
• Simple cystometry in combination with cystoscopy
• Detailed speculum examination
• Cough stress test and Q-tip test
• Dynamic retrograde urethroscopy

Static cystography is typically performed during videourodynamics under fluoroscopy. When the bladder is halfway full (ie, 200-250 mL), anteroposterior and lateral images of the bladder and bladder neck are obtained with the patient at rest and during Valsalva and coughing maneuvers.

A static cystogram helps confirm the presence of stress incontinence, degree of urethral motion, and presence of cystocele. Intrinsic sphincter deficiency is evident by the presence of an open bladder neck. Vesicovaginal fistula may also be documented in this fashion. (See the image below.)

Antegrade or retrograde cystourethrography is a useful adjunct to incontinence workups in situations where urinary tract fistulas are suspected. A voiding cystourethrogram (VCUG) is used to assess bladder neck and urethral function (internal and external sphincter) during filling and voiding. A VCUG can reveal a urethral diverticulum, urethral obstruction, and vesicoureteral reflux.

Cystometry is a technique of assessing the filling phase of bladder function. Much information can be gained during cystometry, including the diagnosis of bladder instability, bladder oversensitivity, sensory neuropathy, loss of compliance, and determination of bladder capacities. Abnormal cystometric findings should be consistent with the patient’s clinical complaint.

In addition, leak point pressures and cough stress tests can be performed during cystometry, and pressure-flow studies can be performed if the cystometry catheters are left in place during uroflow studies.

The simplest forms of cystometry can be performed with a catheter and syringe or manometer held 15 cm above the pubic bone. This inexpensive and readily available method may be adequate for screening in uncomplicated cases but may miss subtle findings.

Single-channel cystometry consists of recording isolated intravesical pressures during filling with a single catheter. With this method, increases in intra-abdominal pressure cannot always be differentiated from increases in true detrusor pressure.

Multichannel cystometry is performed with a bladder catheter and a second catheter to approximate intra-abdominal pressure. The second catheter can be placed in the rectum or vagina. In cases of severe pelvic organ prolapse, a rectal catheter may perform more reliably.

The summary consists of a vesicle pressure channel, an abdominal pressure channel, and true detrusor pressure channel. The true detrusor pressure channel, also called the subtracted channel, is the bladder pressure minus the abdominal pressure. Depending on the individual set up, additional channels may accommodate simultaneous urethral pressure readings and continuous electromyography readings.

Basic technical points include the choice of medium, the fill rates, and the types of catheters. Carbon dioxide gas is a convenient infuser; it is quick and clean. However, it is unphysiologic and may irritate the bladder and result in false-positive findings. A liquid medium, usually saline, is preferred. Most testing is performed with room temperature solutions. Cold solutions can be used as a provocative maneuver to promote bladder contractions.

The filling rate can vary but usually ranges from 10-100 mL per minute. Slower, more physiologic rates can be used if a suspected false-positive result is obtained at faster rates. Likewise, faster rates can be used to provoke subtle instability or can be used in patients with significant urgency who do not allow sufficient volumes to be infused at slower rates and longer infusion times.

Catheters generally should be 10F or less in caliber to avoid urethral irritation and obstruction of flow. Microtip transducers are used most commonly in clinical practice. Fiberoptic and piezoelectric catheters also are available.

Patient position during testing varies in the literature, but most commonly, the patient is sitting, semi-erect, or standing. The catheters generally are calibrated so that zero corresponds to atmospheric pressure. A complete cystometric evaluation monitors the filling-storage segment and emptying segment of bladder function.

For clinical purposes, the emphasis often is on the filling-storage segment. During filling, normally, detrusor pressure does not rise. This finding reflects the compliance of the bladder. With rapid filling rates, a small-to-moderate increase in pressure may be noted. The 4 recognized cystometric phases of bladder function are described below. The first 3 of these phases make up the filling-storage segment of bladder function. The last phase represents the emptying segment. The 4 phases are as follows:

1. Initial small increase in intravesical pressure at the beginning of filling
2. Stable pressure that comprises the majority of the filling phase
3. Terminal rise in pressure at bladder capacity representing the limit of viscoelastic expansion; in a clinical setting, this phase often is not reached due to patient discomfort
4. Voiding phase with an inconsistently observed small increase in intravesical pressure

Bladder sensation and capacity can be measured during filling cystometry. The first sensation is described as the volume at which the patient first is aware of fluid in the bladder (reference range of 50-150 mL). The second sensation (full) has been described as the volume at which the individual normally would consider voiding due to an urge sensation (reference range of 200-400 mL). Maximum capacity is when the patient is experiencing pain and does not allow continued filling (reference range of 400-600⁺ mL).

Low bladder capacities can be observed in patients with urinary tract infections, sensory-urgency syndrome, interstitial cystitis, detrusor overactivity, and stress incontinence. In the urodynamics laboratory, some patients prematurely terminate filling to avoid the possibility of having an episode of incontinence. Considerable reassurance and clear instructions on the part of the practitioner usually help to avoid this type of false-negative study.

Increased capacity can be observed with a neurogenic bladder. Either increased or decreased bladder capacities can represent long-term abnormal voiding habits. These habits can develop in the presence or absence of identifiable pathology.

Low-compliance bladders are demonstrated through cytometry by a slowly rising bladder pressure through all or most of the filling segment. Compliance problems can be due to chronic infection, fibrosis, cancer, radiation effect, and inflammation from long-term indwelling catheters. As previously mentioned, supraphysiologic fill rates can result in nonpathologic loss of compliance.

Any bladder contraction during filling is considered abnormal, but the clinical significance of bladder contractions that are asymptomatic or not identified by the patient as representing their symptomatology are uncertain. The International Continence Society has identified a minimal contraction amplitude of 15 cm H₂ O over baseline to be considered significant. Many experts believe that some contractions of lesser amplitude may be clinically relevant.

Demonstration of urgency coincident with increased true detrusor pressure and urinary leakage in the neurologically intact patient defines the diagnosis of detrusor overactivity, as depicted in the image below.

Many urodynamics centers use provocative maneuvers consisting of common triggers for bladder contractions in an attempt to induce detrusor overactivity. Provocative maneuvers include the sound and sight of running water, hand washing, coughing, and heel bouncing. These maneuvers may be important in patients with high clinical suspicion for detrusor overactivity but without instability findings on filling.

Bethanechol supersensitivity test

If conventional cystometry does not reveal detrusor overactivity in a patient strongly suspected of having this disorder, 2.5 mg of bethanechol can be administered subcutaneously, and the cystometrogram can be repeated 30 minutes later. The validity of this pharmacologic intervention in cystometric testing has not been determined.

High post-void residual (PVR) urine volumes in males often indicate prostate-related bladder outlet obstruction or impaired bladder contractility due to detrusor problems. Uroflowmetry and pressure-flow studies can help clarify the diagnosis.

High PVR volumes are uncommon in females. Only 5% of females who are asymptomatic and 13% of females who are symptomatic have PVR volumes greater than 30 mL.

Abnormal residual volumes have been defined in several ways. No particular definition is clinically superior. Some authorities consider volumes greater than 50-100 mL to be abnormal. Others use a value greater than 20% of the voided volume to indicate a high residual.

Abnormal findings should be confirmed by a second study. If the premeasurement void takes place in a public restroom and a high residual is obtained, the female patient should be asked if she was relaxed and if she sat on the toilet seat during voiding. Voiding in a crouched but not fully seated position has been associated with PVR volumes in the 50-100 mL range.

Ultrasonographic post-void testing

Ultrasound can be used as a noninvasive means of obtaining PVR volume determinations, especially if a precise measurement is not required.^[4] Scanning is performed transabdominally in the transverse and sagittal planes, and the height, width, and depth are determined. These 3 diameters are multiplied by a correction coefficient of 0.7, which accounts for the nonspherical shape of the bladder when it is less than completely full. This formula probably is the simplest US formula for PVR volume determination.

The error using this formula, compared with the criterion standard of postvoid catheterization, is approximately 21%. The formula is not accurate at volumes less than 50 mL, but in clinical applications, precise determination of PVR values of less than 50 mL usually are not needed.

Other methods and formulas have been described. Some speculate that transvaginal scanning may be more accurate at low bladder volumes.

Portable ultrasound scanners for measurement of bladder volume have been developed (eg, BladderScan, Bardscan). These devices avoid the disadvantages of catheterization, and recent studies have found them to be accurate.^[5]

Uroflow is the volume of urine voided per unit of time. The simplest uroflowmetry method uses a stopwatch and a commode that is equipped to measure urine volume. More complicated devices use the increasing weight of the urine over time to determine flow rates.

A useful screening test, uroflow is used mainly to evaluate bladder outlet obstruction. Consistently low flow rates generally indicate a bladder outlet obstruction but may also indicate decreased detrusor contractility. Uroflowmetry alone cannot distinguish between those two conditions. To properly diagnose bladder outlet obstruction, perform pressure-flow studies.

Urine flow rates are a product of detrusor contraction strength; urethral resistance; and, in some instances, the contribution of abdominal straining. Normal flow curves are bell shaped and display a rapid rise to peak flow, a short duration of peak flow, and a rapid fall.

In males, the resistance factor is greater because of the longer urethra and the presence of the prostate. To compensate for these factors, the detrusor contribution to voiding must be greater.

In males, maximum flow rates are affected greatly by age, ranging from 35 mL/s in males aged 14 years to approximately 5 mL/s in males aged 80 years. Low flow curves often are predictive of the need for surgery to protect the upper tract, but they do not provide specific information about the etiology. Decreased detrusor contractility, outlet obstruction, or a combination of both may be responsible for low flows.

In women, aging by itself results in little or no drop in flow rates. Factors such as pelvic organ prolapse, stress incontinence, prior hysterectomy, increased parity, and, perhaps, hypoestrogenism are far more predictive of decreased flow rates than age alone. Note that flow rates are dependent on voided volume. Uroflow studies should be performed with a minimum of 150-200 mL in the bladder.

Flow patterns generally do not point to a specific urodynamic diagnosis, although some associations have been noted. Detrusor overactivity is often associated with high flow rates, although the opposite can be true. In patients with aging bladders or in the early stages of neuropathy, detrusor overactivity may coexist with detrusor underactivity. Stress urinary incontinence is sometimes associated with low flow rates.

In some instances, such as in cases with a strong component of intrinsic sphincter deficiency, super flow patterns may be observed. Bladder oversensitivity may be associated with low flow rates, especially if the bladder is contracted. Noncontinuous patterns can indicate Valsalva voiding or detrusor sphincter dyssynergia.

A prostatic uroflow curve has been described. This consists of an unbroken pattern with asymmetry and an elongated flattened area from Qmax to the end of voiding, as depicted in the image below. Abnormal findings, especially low flow rates, should be confirmed by repeat studies. Nervousness or embarrassment can result in nonrepresentative dysfunctional voiding patterns.

In females, the role of uroflowmetry is controversial. Voiding dysfunction is uncommon, except in the patient who recently had incontinence surgery. Females can complete successful voiding in a number of ways. Valsalva voiding or Valsalva augmentation of voiding is not uncommon. Some females void by urethral relaxation alone.

Reference range values for uroflow parameters are not well established for females. Maximum flow rates of 15-20 mL/s or higher generally are considered normal. Flow rates of less than 10 mL/s are considered low, but if the PVR volume is minimal, this finding is of dubious clinical significance. A normal voiding time is considered 15-20 seconds. Most often in females, low flow rates indicate a functional rather than an obstructive problem.

Uroflow studies may be useful in predicting the risk for voiding dysfunction and high residual volumes after incontinence surgery. Patients with low flow rates may be at risk for prolonged catheterization. In one study, 38% of the patients with abnormal uroflow study results before surgery required postoperative catheter drainage for more than 1 week. Only 10% of those with normal study results required prolonged drainage.

This prognostic information is important for both the physician and the patient. Teaching patients with low flow rates about intermittent self-catheterization preoperatively may be prudent. Patients who are long-term Valsalva voiders also may be at increased risk for breakdown of surgical repairs.

Voiding cystometry or pressure-flow studies can be a valuable adjunct to standard uroflowmetry. To perform these studies, cystometry catheters are left in place during uroflowmetry. In males, these studies can be vital in differentiating outlet obstruction from functional detrusor problems. Low-flow, low-pressure findings would be consistent with the latter. High pressures and low-flow rates suggest outlet obstruction. Maximum detrusor pressures of less than 20 cm H₂ 0 generally are considered abnormal.

Normal parameters for pressure-flow studies have not been established for females. Many females void with very low detrusor pressures because of the short, relatively low-resistance urethra. Detrusor contraction during voluntary voiding may serve the purpose of bladder accommodation to decreasing volumes rather than the generation of significant expulsive forces. Successful voiding with urethral relaxation alone is not uncommon. Valsalva voiding and Valsalva augmentation of detrusor voiding also are observed. If residual volumes are low, then no specific treatment is required.

Valsalva Leak-Point Pressure

The Valsalva leak-point pressure, or abdominal leak-point pressure (ALPP), is a test of the resistance of the urethral sphincter to increases in intra-abdominal pressure. The overall assumption is that the lower the leak point pressure, the weaker the urethral sphincter and the more severe the stress incontinence.

Leak-point pressure testing is an important component of multichannel videourodynamics. It is used to determine whether stress urinary incontinence in a woman results from urethral hypermobility, intrinsic sphincter deficiency, or both in combination. Results are used to inform clinical decisions such as whether to perform a sling procedure versus a retropubic urethropexy.

Interestingly, no consensus exists as to how to perform the test. In addition, many assumptions have been made as to the validity and clinical utility of the tests. Results of the other major objective test of urethral sphincter function, urethral closure pressure measurement, do not always agree with leak point pressure findings. Some studies have shown a weak correlation between these tests, and other studies have found no correlation. Comparing these studies is difficult because of differences in technique.

For the basic ALPP test, intravesical and intravaginal or intrarectal catheters are placed and the bladder is filled with 150-250 mL of fluid. The patient, who is in either the sitting or standing position, is asked to perform a Valsalva maneuver of slowly building intensity. The lowest pressure at which leakage from the urethral meatus is observed is recorded as the leak point pressure. (See the image below.)

The test should be repeated several times to ensure consistency. If properly performed, the test has excellent test and retest reproducibility.

Many variables may affect the results, including the caliber of the catheter, patient position, bladder volume, and the presence of pelvic organ prolapse. Experts generally believe that if pelvic organ prolapse is severe, some form of prolapse reduction should be accomplished during the test. The best method of prolapse reduction for this purpose is uncertain.

If no leakage is produced or the patient is unable to perform the Valsalva maneuver properly, a cough leak-point pressure can be attempted. A cough leak-point pressure is less accurate than an ALPP and more difficult to measure because pinpointing the precise pressure at which leakage occurs is difficult due to the fast-spiked increase in pressure associated with coughing. The cough leak-point pressure overestimates the actual ALPP in many instances.

To prevent overestimation, the patient can be asked to cough until leakage occurs and then to perform less intense coughs until leakage disappears. The lowest value producing leakage is taken as the leak-point pressure. Unfortunately, this technique is more easily described than performed.

Another alternative, if no leakage occurs with the initial testing, is to repeat the Valsalva maneuver after progressive bladder filling in 50- to 100-mL increments (eg, 250 mL, 300 mL, 350 mL) or to perform the test with the bladder catheter removed.

Bladder volume has been shown to be related inversely to leak-point pressure, even at volumes between 100 and 300 mL. Most protocols call for a bladder volume of 150-200 mL, although this has not been standardized.

The presence of a transurethral bladder catheter may affect leak-point pressure significantly, compared with measurements obtained with a vaginal catheter only. Leak-point pressures are as much as 20 cm H₂ O lower without a transurethral catheter. Some think that transurethral catheters may cause some degree of obstruction and that the degree of obstruction may increase with the size of the catheter. The obstruction may elevate the leak-point pressure artificially. Patient position also may affect leak point pressure, but this has not been studied.

Interpretation of the results also has generated some disagreement and controversy. Many authorities use leak-point pressures below 60 cm H₂ O to define intrinsic sphincter deficiency. Others have cited 80 or 90 cm H₂ O as the threshold.

One study used a value of 50 cm H₂ O or less in conjunction with urethral closure pressure and urethral angle parameters.^[6] This study defined leak-point pressure as the increase in vesical pressure minus resting vesical pressure. Other studies have defined the leak-point pressure as the actual vesical pressure at which leakage occurred.

It is important to note that a normal leak-point pressure should approach infinity. In other words, patients with a normal continence mechanism can generate intra-abdominal pressures high enough to cause fainting without provoking stress incontinence.

Classification of stress incontinence

In the past, ALPP measurement comprised part of a classification system of stress incontinence. Currently, no accepted classification of stress urinary incontinence is used in clinical practice because stress urinary incontinence is caused by a continuum of intrinsic sphincter deficiency severity with or without significant urethral hypermobility. For historical purposes, the most widely accepted classification, by Blaivas and others, divides stress incontinence into 3 types.

Type I stress urinary incontinence is defined as urine loss occurring in the absence of urethral hypermobility. This is the mildest form of stress urinary incontinence. Patients with type I stress urinary incontinence have a Valsalva cotton-swab angle less than 30° and an ALPP of greater than 120 cm water.

Type II stress urinary incontinence is defined as stress incontinence due to urethral hypermobility. Patients with urethral hypermobility have a Valsalva cotton-swab angle greater than 30° and an ALPP of more than 90 cm water.

Type III stress urinary incontinence is defined as stress incontinence due to intrinsic sphincter deficiency. Patients with intrinsic sphincter deficiency have a Valsalva cotton-swab angle less than 30° and an ALPP of less than 60 cm water.

Current evidence suggests that all patients with stress urinary incontinence have some component of intrinsic sphincter deficiency. The distinctions between types I, II, and III are now less important than they once were.

In 40% of patients, stress and urge incontinence coexist. In many instances, stress incontinence may lead to the development of urge incontinence. Filling cystometrography (CMG) may be useful in such cases. CMG assesses bladder capacity, bladder compliance, and the presence of phasic contractions. This test may be performed using either gas or liquid to fill the bladder, with different interpretive criteria applying to each.

A catheter connected to a special computer is inserted into the bladder for single-channel cystometry. Information recorded by the computer is interpreted.

Eyeball cystometry does not require special computers. Perform bedside cystometry by inserting a catheter into the bladder, hanging the irrigant bag at a predetermined height (eg, 100 cm water), and observing the fluctuation of the meniscus within the water chamber during uninhibited detrusor contractions.

Eyeball cystometry using a flexible cystoscope is the same as eyeball cystometry except that the flexible cystoscope acts as the connection tubing. This allows simultaneous cystoscopy.

Multichannel cystometry is a more sophisticated method of measuring filling CMG. With this technique, intravesical pressure (Pves), intra-abdominal pressure (Pabd), detrusor pressure (Pdet), and maximum flow rate (Qmax) are recorded simultaneously. (See the images below.)

Usually, the patient feels the first sensation as the bladder begins to fill with 100-200 mL of water. As the bladder nears capacity, 300-400 mL, the patient may begin to feel uncomfortable. True urge to void occurs when the bladder has been filled to capacity. An average adult bladder holds approximately 450-500 mL. During the test, provocative maneuvers (eg, coughing, hand washing, sitting on the commode for 1 full minute, heel jouncing) may help to unveil bladder instability.

Voiding cystometrography (pressure-flow study)

A pressure-flow study simultaneously records the voiding detrusor pressure and the rate of urinary flow, as shown in the image below. Voiding cystometrography is the only test able to provide information about bladder contractility and the extent of a bladder outlet obstruction. For complicated cases of incontinence, pressure-flow studies can be combined with a voiding cystogram and videourodynamic studies.

Electromyography (EMG) enables documentation of voiding and is used to distinguish coordinated voiding (ie, detrusor sphincter synergia) from uncoordinated voiding (ie, detrusor sphincter dyssynergia) resulting from failure of urethral relaxation during bladder contraction. EMG is most useful in patients with a suspected neurologic disorder.

Electromyography (EMG) is a type of neurophysiologic testing. The test can be performed with surface electrodes, monopolar needle electrodes, or concentric needle electrodes. Each modality has distinct advantages and disadvantages. A detailed discussion of the technical aspects of EMG is beyond the scope of this article.

EMG studies can be used to test the neuromuscular integrity of the urethral and anal external striated sphincters, puborectalis, and pubococcygeus muscles. Digital palpation and manometric measurements are 2 other methods to assess the strength of voluntary pelvic muscle contractions. These methods correlate well with surface EMG findings, but only surface EMG measurements are predictive of pelvic floor pathology.

A study by Glazer and colleagues demonstrated that poor pelvic floor muscle function, based on surface EMG measurements, was predictive of symptoms of general incontinence, stress incontinence, urge incontinence, and parity.^[7] In addition, statistically significant lower microvoltage pelvic floor contractions were found in postmenopausal women not on estrogen replacement therapy.

EMG studies also can be combined with studies of bladder filling (eg, cystometry) and emptying (eg, uroflowmetry). Slowly increasing external urethral sphincter tone with filling and relaxation with emptying is a normal finding. When evaluating patients with neurological disorders and discoordination of the bladder and urethral sphincter, detrusor-sphincter dyssynergia can be revealed. EMG recordings also can be used as biofeedback in pelvic floor exercise therapy.

EMG studies are most useful in the research setting. Experience with recording and interpretation in the clinical setting by gynecologists and urologists is limited.

Another type of neurophysiologic assessment is the pudendal nerve terminal motor latencies (PNTML) study, which is performed with bipolar electrodes. The stimulating electrode is placed at the ischial spine, close to the pudendal nerve. The recording electrode is placed in the area of interest such as the anal or urethral sphincter.

The St Marks electrode, which is worn on a gloved finger, is the most well known of these devices. With this technology, the association of pelvic floor denervation injury with urinary incontinence was uncovered.

In addition, age-related increases in pudendal nerve latencies have been described. Although PNTML studies have increased the understanding of the neuromuscular dysfunction component of pelvic support and incontinence disorders, their role in day-to-day clinical practice is unclear.

Urethral pressure profilometry (UPP) is a technique of recording pressures along the length of the urethra with the bladder at rest. The maximal urethral closure pressure (MUCP) is the maximum urethral pressure minus intravesical pressure, as depicted in the image below. The functional urethral length is the distance along the urethra in which urethral pressure exceeds bladder pressure.

Static UPP studies can be performed in a number of ways. Generally, a microtip pressure catheter is pulled through the urethra either manually or via a mechanical arm at a rate of 1-2 mm/s. The catheter can have a single transducer or 2 transducers, 1 in the bladder and 1 in the urethra, approximately 6 cm apart. The transducers are directed to the 3-o'clock or 9-o'clock lateral positions. Fiberoptic transducers also are available but tend to record significantly lower urethral pressures.

The test commonly is performed with the patient in the supine position, but the sitting and erect positions have been described. An increase in pressure of approximately 23% from the supine to the standing position can be expected, although the increase may be less in individuals with poor urethral support and greater in patients who are neuropathic.

The test most commonly is performed after cystometry; therefore, the bladder is full. Some investigators have recommended performing the test 2 or more times and averaging the results to increase accuracy.

Fluid perfusion profilometry via the Brown and Wickham technique is used in some centers. With this technique, a slow steady perfusion rate of 2-10 mL/min is maintained during withdrawal of the catheter.

In addition to resting or static UPP, cough or stress profiles can be performed. The procedure basically is the same, except that the patient coughs repeatedly throughout these profiles. The patient is asked to produce coughs of a consistent intensity every 2-3 seconds. Any urinary leakage is recorded.

The pressure transmission ratio, expressed in percentage form, can be calculated at any point along the urethra. The change in urethral pressure from rest to the top of the cough spike is divided by the change in bladder pressure recorded at the same time. The result is multiplied by 100 to produce the pressure transmission ratio.

UPP has many clinical applications. MUCPs of less than 20 cm H₂ 0 have been associated with higher failure rates when these patients are treated with a Burch colposuspension. Closure pressures below 20 cm H₂ 0 suggest intrinsic sphincter deficiency as an indication for a suburethral sling.

Attempts have been made to explain and diagnose genuine stress incontinence with the use of pressure transmission ratios. No threshold value has been determined that is consistently associated with stress-induced leakage. At this time, cough profiles have limited clinical utility.

Urethral instability is a rare and controversial cause of incontinence. The diagnosis can be made with UPP if a decrease in urethral pressure is observed along with a stable bladder and urinary leakage.

Urethral diverticula can be suggested by a biphasic UPP curve. This type of curve also has been observed in cases of genuine stress incontinence. The presence of a diverticulum, if suspected, should be confirmed by imaging studies. If a diverticulum is confirmed, the location of the observed sudden fall in pressure on UPP can help in localizing the diverticular opening in relation to the striated sphincter. This information may aid in the planning of surgical therapy.

Urethral pressure profiles augmented by pelvic floor contraction are being investigated. Researchers hope that this variation of UPP may help in the clinical assessment of urethral competency. In addition, this technique may prove useful in selecting patients for pelvic floor physiotherapy. Some have observed that MUCP increases and functional urethral length decreases during pelvic floor contraction. The latter finding may be indicative of the presence and importance of longitudinal urethral musculature.

The positive pressure urethrogram probably is the most useful single test in the workup of a known or suspected urethral diverticulum. Dye is injected under pressure into the urethra through a specially designed catheter, which isolates the urethral lumen between 2 occluding balloons. One balloon occludes the urethra at the meatus/vaginal introitus. The other balloon rests snugly at the urethrovesical junction. Radiographs are taken after the dye is injected.

This study helps define the anatomy of the diverticulum in terms of size, number, and location of loculations and the location of the orifice(s) along the length of the urethra. This information is essential in planning surgical therapy.

An intravenous pyelogram (IVP) may be useful in defining the course and caliber of the ureter preoperatively in cases of stress incontinence and coexisting severe apical or anterior vaginal wall prolapse. An IVP also can help differentiate between ureterovaginal and vesicovaginal fistulas. Finally, if ureteral obstruction is suspected following incontinence surgery, an IVP is indicated.

Ambulatory urodynamic monitoring was developed to address some of the many shortcomings of laboratory urodynamics. Ambulatory urodynamic monitoring is an attempt to record bladder function in a more physiologic setting through many natural fill-void cycles.^[8]

Microtip catheters are worn in the bladder (generally transurethrally) and in the rectum or vagina. A portable, battery-operated recording device is worn with a shoulder strap. Often, a fluid-sensing undergarment liner is used to record episodes of leakage objectively.

A universal finding in ambulatory monitoring is increased detrusor activity compared with conventional cystometry. Rates of detrusor activity of approximately 20% have been recorded in individuals who are asymptomatic. Other work has shown rates of detrusor contractions in 38-69% of volunteers who are asymptomatic.

Several possible explanations exist for this phenomenon. Normal and physiologic, but previously unrecognized, phasic detrusor contractions may be occurring. Alternatively, contractions may be related to irritation of the urethra and trigone by the catheter. Finally, the findings may represent a subclinical defect in bladder control.

Bladder capacities also tend to be less with ambulatory monitoring. This finding has been demonstrated even when patients are provided the same reporting instructions that are provided in the urodynamic laboratory setting.

Artifacts resulting in a false-positive diagnosis of detrusor overactivity have been problematic and limit the usefulness of ambulatory cystometry. In an attempt to decrease monitoring artifacts, a group conducted monitoring with a double transducer catheter in the bladder. The group also stressed the importance of using a symptom diary.

For a rise in detrusor pressure to be classified as abnormal, the increase had to be reflected in the urinary diary and observed in both transducer channels. The results demonstrated that a 58% reduction in detrusor pressure increases that were classified as abnormal was attributable to the symptom diary and that an additional 19% decrease was due to the second transducer.

Clinically, the role of ambulatory urodynamic monitoring in the evaluation of incontinence has not been studied adequately. Some investigations demonstrate high rates (60-91%) of the results of ambulatory monitoring influencing clinical management. No studies to date show any improvement in treatment outcomes as a result of ambulatory urodynamics.

Possible clinical roles for this technology may include the workup of patients with suspected detrusor overactivity but negative findings on conventional studies. In addition, useful information in patients undergoing treatment for detrusor overactivity or in patients with incontinence after surgical procedures may be gained. Ambulatory monitoring is expensive, requires specialized equipment, and is time consuming. Currently, this type of urodynamic evaluation serves mainly as a research tool.