Urodynamics (UDS) is the dynamic study of the storage and voiding function of the urinary tract. The goal of the UDS study is to identify the cause of a patient’s voiding symptoms, assess prognosis or the results of prior therapy, or direct management by collecting quantitative measurements while reproducing the patient’s voiding symptoms where appropriate and possible. Several parts of the UDS study are customized for each individual to maximize the utility of the test. This article summarizes the key points to performing a quality UDS study that can evaluate and diagnose disorders of the lower urinary tract.
Key points
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The clinician should identify the clinical questions that the urodynamics (UDS) study is intended to answer, properly design the study to answer those questions, and be able to adapt the study as necessary.
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The UDS study should be performed interactively and with continuous communication with the patient to confirm that their symptoms have been reproduced.
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Careful observation of signals is important to assess their qualitative and quantitative plausibility, such that artifacts can be recognized and corrected during the study.
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The quality and results of the UDS study are operator-dependent and are only as good as the clinician who performs and interprets the study.
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A well-done UDS study may be invaluable in the diagnosis of lower urinary tract conditions, or assessing prognosis and response to therapy, or directing management; however, a poorly done study may be misleading and potentially harmful.
Introduction
Urodynamics (UDS) is a collection of measurements of bladder, urethral, and pelvic floor muscle function with or without fluoroscopy (videourodynamics or VUDS) in an attempt to evaluate and diagnose functional, and sometimes anatomic, disorders of the lower urinary tract. The goal of performing UDS studies in many cases is to reproduce a patient’s lower urinary tract symptoms while making precise measurements to identify the underlying causes for their symptoms. In other cases, UDS are performed to assess prognosis or the results of prior therapy or to direct optimal therapy. UDS studies are invasive, uncomfortable, and potentially morbid. It is therefore imperative to optimize the quality of the study to maximize the useful information that can be obtained. When possible, UDS should be performed interactively with the patient, which includes confirmation with the patient throughout the study that their symptoms or conditions have been reproduced during the test.
Introduction
Urodynamics (UDS) is a collection of measurements of bladder, urethral, and pelvic floor muscle function with or without fluoroscopy (videourodynamics or VUDS) in an attempt to evaluate and diagnose functional, and sometimes anatomic, disorders of the lower urinary tract. The goal of performing UDS studies in many cases is to reproduce a patient’s lower urinary tract symptoms while making precise measurements to identify the underlying causes for their symptoms. In other cases, UDS are performed to assess prognosis or the results of prior therapy or to direct optimal therapy. UDS studies are invasive, uncomfortable, and potentially morbid. It is therefore imperative to optimize the quality of the study to maximize the useful information that can be obtained. When possible, UDS should be performed interactively with the patient, which includes confirmation with the patient throughout the study that their symptoms or conditions have been reproduced during the test.
Components of UDS
UDS comprises different components that can be used individually or collectively to gain information about urine storage and evacuation. In performing a quality study, a working knowledge of each component and their role is important to understand.
Postvoid Residual
Postvoid residual (PVR) is an assessment of bladder emptying and can be performed by ultrasound/bladder scan or catheterization. An elevated PVR can be an indication of a bladder-emptying problem, but cannot distinguish the cause of the problem, such as bladder outlet obstruction (BOO) or detrusor underactivity or a combination of both. PVR can be assessed using ultrasound, either in real-time or by portable bladder scan, or via catheterization. In obese patients or those with ascites, or prior lower abdominal surgery, bladder scan is inaccurate and real-time ultrasound or catheterization is preferred.
Uroflowmetry
Uroflowmetry is a noninvasive measurement of the rate of urine flow over time. It can also be used to assess bladder emptying but cannot be used alone to diagnose the cause of an abnormality. For example, a low maximum flow and plateaued pattern on uroflowmetry cannot distinguish between BOO and impaired detrusor contractility. Other patterns are easily recognized but are also not completely diagnostic: a superflow pattern implies decreased urethral closure forces but may be due to volitional abdominal straining, whereas a saw-toothed pattern suggests Valsalva voiding but may be due to intermittent voluntary or involuntary contraction of the external sphincter or pelvic floor ( Fig. 1 ). It is imperative in all circumstances to query the patient as to whether their usual voiding pattern or behavior was accurately reflected on the noninvasive uroflowmetry study.
The most commonly used uroflowmeters are mass flow meters, such as those that use a gravimetric method or a rotating disc method. Uroflowmeters that use a gravimetric meter operate by measuring the accumulated weight of the collected fluid or by measuring the hydrostatic pressure at the bottom of a collection cylinder. Rotating disc instruments use the voided fluid directly on a rotating disc to increase the inertia of the disc. The power required to keep the disc rotating at a constant rate is measured and is proportional to the mass flow rate of the fluid.
Filling Cystometry
Filling cystometry is a measurement of the pressure/volume relationship during bladder filling. It is performed using measurements of intravesical pressure (Pves) and intra-abdominal pressure (Pabd) to calculate the detrusor pressure (Pdet = Pves – Pabd). The key features of bladder storage function obtainable with filling cystometry include sensation, cystometric bladder capacity, compliance, and presence of involuntary detrusor contractions or detrusor overactivity (DO). Leak point pressures, an assessment of urethral function, are also assessed during filling cystometry. These features will be discussed in greater detail later.
Pressure-Flow Study
The relationship between bladder pressure and urine flow rate is measured during bladder emptying. The pressure-flow study is currently the only method of diagnosing BOO and/or impaired detrusor contractility (or detrusor underactivity). There are 3 fundamental voiding states that can be diagnosed by the pressure-flow study, which include obstruction, impaired detrusor contractility, and normal. During the pressure-flow urodynamic study (PFUD), several parameters are assessed: detrusor contractility, coordination of the detrusor and outlet, bladder emptying, and the presence or absence of UDS obstruction.
Electromyography
Electromyography (EMG) is the measurement of the electrical signals produced by the depolarization of muscle membranes. EMG studies can be performed using either surface electrodes or needle EMG, which is more invasive, to measure electrical activity from the pelvic floor muscles. EMG is measured throughout the UDS study during both the filling and the emptying phases. The EMG tracing is used to assess the coordination or discoordination of the external urethral sphincter and the detrusor contraction.
Fluoroscopy
When the UDS study is combined with an imaging modality, the anatomy and physiology of the lower urinary tract can be simultaneously assessed, which is referred to as VUDS. The use of fluoroscopy provides anatomic information about the bladder, bladder neck, and urethra during filling and voiding that could not otherwise be obtained during the study without fluoroscopy. This portion of the study is useful for assessing for vesicoureteral reflux (VUR) as well.
Fluoroscopic images may be obtained at various points throughout the study. Before starting the study, a scout film is obtained to identify any surgical hardware or bladder stones before the contrast-filled bladder obscures them. Images can be captured during early bladder filling to assess the contour of the bladder and identify any possible filling defects. Next, a sequence of images taken at rest and then during abdominal strain/Valsalva maneuvers is used to assess mobility of the bladder base, bladder neck, and urethra as well as the competence of the bladder outlet and urethra. Multiple fluoroscopic images taken during voiding can evaluate the bladder neck and urethra as well as document the presence or absence of VUR. Images of the bladder and the upper tracts (kidneys, ureter, bladder, flat plate x-ray [KUB]) can be obtained to assess VUR, bladder or urethral diverticula, and other potential pathologic abnormalities. Because most VUDS studies are done in the seated position using a C-arm apparatus for imaging, anterior-posterior imaging is most commonly used. However, there are instances where oblique or lateral images are superior, such as when assessing for bladder diverticula, cystocele, and urethral stricture.
Pretest considerations
To perform a quality UDS study, the clinician must identify the clinical questions that the UDS study is intended to answer before any testing is performed. To do so, the clinician needs a working knowledge of the patient’s history, physical examination findings, frequency/volume charts, and any other information to identify clinical relevant findings during the UDS study. A bladder diary performed before the UDS study that records voided volumes can be used to correlate the patient’s bladder diary capacity to the cystometric capacity obtained during the study. These capacities should be plausibly similar to appropriately reproduce the patient’s symptoms. Pad testing can be used to quantify the amount of urine lost during incontinence episodes, which can provide valuable information before the UDS study. Small amounts of leakage can suggest stress urinary incontinence, whereas large amounts of leakage can be suggestive of urge urinary incontinence. For the incontinent patient, either of these conditions may be demonstrated; however, it is paramount to relate the condition seen on UDS study to the patient’s primary complaint to ensure that the symptoms, or condition, are reproduced by the finding on the UDS study.
The clinician should design the UDS study to answer the clinical questions and customize the study as needed. For example, in a patient who complains of symptoms of mixed urinary incontinence, the test may be conducted to assess for the predominant type of incontinence. Reproduction of the patient’s incontinence is critically important, especially to the extent that it reproduces the patient’s symptoms. In such a patient, stress maneuvers, change in positioning, or provocative maneuvers (hand washing and so on) may be necessary to induce the symptoms. In contrast, for the patient with neurogenic voiding dysfunction in which potential compliance issues are most important, such maneuvers are unnecessary and even counterproductive. In the patient with vaginal prolapse, a repeat study with a pessary may be needed (see later discussion). In the patient with possible BOO, every effort should be made to produce a detrusor contraction because the voiding phase of the UDS study is likely the most relevant. BOO cannot be definitively diagnosed without a detrusor contraction. Sometimes, in those individuals with difficulty initiating a void, a detrusor contraction might be induced by a change in position or a rapid filling rate.
In deciding when to perform a VUDS over a UDS study, the clinician should consider whether obtaining simultaneous fluoroscopic images would improve the ability to detect and understand the underlying pathologic abnormalities, such as specific sites of obstruction, presence and grade of VUR, and anatomic abnormalities of the bladder. The American Urological Association (AUA) Guidelines for Adult Urodynamics recommends that VUDS be performed in patients with relevant neurologic disease who are at risk for neurogenic bladder, or in patients with other neurologic disease and elevated PVR or urinary symptoms. The AUA Update Series on Urodynamics Best Practices recommends that VUDS be performed in those patients at high risk for voiding dysfunction, such as those with known or suspected neurogenic bladder, prior radical pelvic surgery, urinary diversion, renal transplant, or prior pelvic radiation. Further discussion about indications and techniques for performing VUDS is covered elsewhere in this issue.
For the safety of the patient, it should be confirmed that the patient is not experiencing a urinary tract infection (UTI) before the UDS study. For those patients who perform intermittent catheterization or have indwelling catheters, it may not be possible to sterilize the urine before the UDS study, but it is important to ensure that the patient is asymptomatic to differentiate between bacterial colonization and active infection. If the patient is experiencing a UTI, then the UDS study should be postponed until the patient is free of infection.
Finally, before the UDS study, patients should be well informed about why the test is being done and what to expect during the actual UDS test. Providing reassurances to the patient before the start of the study can reduce anxiety felt by the patient.
Performing the study
Positioning of the patient for the UDS study should account for the patient’s functional status, the symptoms that the clinician would like to reproduce, and the patient’s normal voiding habits. If the patient only experiences urinary incontinence while in the standing position, then the filling portion of the study should be performed with the patient standing. If a patient only voids while sitting, then the voiding portion of the study should be performed with the patient in the seated position. To obtain the best study results, the goal is to make the testing experience as close to the patient’s normal voiding experience as possible.
UDS pressure measurements are obtained via a transducer catheter, which converts pressure into an electrical signal that is displayed as a tracing. There are many different types of transducers, which include air-charged, fluid-filled, microtransducers, and fiberoptic systems. The International Continence Society (ICS) recommends fluid-filled transducers to be used for Pves and Pabd recordings. For simultaneous measurement of intravesical pressure and for bladder filling, the ICS recommends a transurethral double-lumen catheter. For the measurement of abdominal pressures, the ICS recommends the use of a rectal balloon catheter with the balloon only filled to 10% to 20% of its unstretched capacity. In female patients, placement of the rectal catheter in the posterior vaginal vault is an acceptable alternative that provides comparable results.
UDS catheters should be zeroed to atmospheric pressure before insertion, and the ICS recommends strict adherence to its standardization of zero pressure and standard height. Zero pressure is defined as the value recorded when a transducer that is disconnected from any tubes or catheters is open to the environment, or when the open end of a fluid-filled tube is at the same level as the transducer. The ICS defines the reference height as the upper edge of the symphysis pubis.
UDS catheters are inherently uncomfortable during placement except in patients who are insensate or who are on regular intermittent catheterization. Such discomfort with catheter placement can result in artifacts during the study, especially abnormal sensation of filling, as well as suppression of normal micturition. In some individuals, placement of intraurethral topical lidocaine jelly may reduce discomfort associated with catheterization and thereby alleviate some anxiety about the procedure as well as facilitate voiding by reducing the catheter-associated dysuria. Whether such administration of topical anesthetic changes bladder sensation with filling and thus alters the qualitative or quantitative results and findings of the study is unclear.
Filling and Storage
The patient should be instructed to void before the start of the UDS study in a private bathroom. On entry into the UDS room, and under sterile conditions, the patient is catheterized per urethra and the bladder is emptied before the start of the study, providing an accurate assessment of PVR. The catheters are placed and the filling phase then commences.
Throughout the study, the clinician should maintain continuous communication with the patient to confirm that their symptoms have been reproduced. In addition, the clinician should be carefully observing the signals to assess their qualitative and quantitative plausibility. When the quantitative result of a UDS study appears very abnormal or does not represent a plausible result in that particular clinical setting, alternative considerations should be considered. The study should also be adjusted or repeated if the clinician cannot at first answer the questions that were posed at the start of the study. It may be necessary to perform provocative maneuvers, which the ICS has defined as techniques used during UDS in an effort to provoke DO, such as rapid filling, use of cooled or acid medium, postural changes, and hand washing.
Fill Rate and Capacity
When choosing a fill rate, the clinician needs to be aware that a standard fill rate cannot be applied to every patient. A fill rate that is too rapid can induce involuntary detrusor contractions, the appearance of impaired compliance, or an artifactually low cystometric bladder capacity. For children, patients with neurogenic bladder or urinary diversion, anuric patients, or patients with known small capacity bladders, a slower fill rate is preferred. Generally, a starting fill rate of 50 to 70 mL/min is acceptable for the adult patient because it minimizes artifact yet allows the study to be completed in a reasonable amount of time.
Appropriate filling volumes should be attained to facilitate micturition and should be representative of the patient’s normal circumstances. Therefore, it is helpful to have a frequency volume chart (or the more comprehensive voiding diary) before the UDS study to have an estimate of functional bladder capacity.
Sensation
Bladder sensation is judged by 3 defined points during the filling cystometry and is evaluated in relation to the bladder volume at that moment and in relation to the patient’s symptomatic complaints. The 3 sensory landmarks associated with performing a filling cystometry are first sensation of bladder filling, first desire to void, and strong desire to void. The ICS defines first sensation of bladder filling as the feeling when the patient first becomes aware of bladder filling. First desire to void is defined as the need to pass urine at the next convenient moment, but voiding can be delayed if necessary. Strong desire to void is defined as the persistent desire to void without the fear of leakage. The patient should be instructed on each of these 3 sensory landmarks and reminded to report each sensation at regular intervals throughout the filling study.
Leak Point Pressure Testing
Abdominal leak point pressure (ALPP), also known as the Valsalva leak point pressure, is defined as the lowest intravesical pressure at which urine leakage occurs because of increased abdominal pressure in the absence of a detrusor contraction. The ALPP can be used as an assessment of urethral competence and documentation of leak point pressures establishes the diagnosis of UDS stress urinary incontinence. ALPP should be distinguished from a detrusor leak point pressure (DLPP), which is defined as the lowest detrusor pressure at which urine leakage occurs in the absence of either a detrusor contraction or increased abdominal pressure. DLPP is not used to directly measure continence or sphincter function, but is a useful parameter for assessing risk to the upper urinary tract as a result of elevated storage pressures.
ALPP Testing
Although universal guidelines do not exist for the performance of ALPP across UDS laboratories, such testing should be standardized in each individual center so as to obtain reproducible and internally usable quantitative assessments of urethral function. Such testing should be done with a standard size and type of urethral catheter (usually dual lumen 7–8 Fr), in a standard position (sitting, standing, and so on), at a standard volume (150 cc, 200 cc, capacity, and so on), with a standard set of maneuvers (cough, Valsalva, graded or not, and so on). The ALPP measurement should never be performed at the time of an involuntary detrusor contraction, resulting in an artifactually low assessment of urethral function.
In patients with vaginal prolapse, reduction of the prolapse may be necessary to accurately assess the ALPP, as well as completely assess related voiding phase dysfunction later in the study. In such individuals, it can be instructive to perform the entire UDS study with and without the vaginal prolapse appropriately reduced with a pessary or vaginal packing.
In some patients, an ALPP may not be apparent during the study despite multiple attempts to produce it. In such cases, it may be helpful to remove the vesical catheter from the urethra, leaving the abdominal catheter in situ, and repeat testing using the abdominal catheter for the pressure measurement.
DLPP Testing
DLPP was initially described as a method to predict risk for upper urinary tract deterioration as a result of increased lower urinary tract storage pressures in myelodysplastic children. For those patients with decreased bladder compliance and urinary incontinence as a result of neurogenic bladder dysfunction, DLPP testing can be a useful tool to assess risk to the upper urinary tract. A DLPP greater than 40 cm H 2 O is considered hazardous to the upper tracts, whereas patients with a DLPP less than 40 cm H 2 O commonly do not experience upper urinary tract deterioration in the absence of other complicating factors such as infection or VUR. However, some individuals may experience upper tract deterioration at DLPP at somewhat less than 40 cm H 2 O and thus monitoring of such patients should be strongly considered.
Compliance
Compliance describes the relationship between change in bladder volume and change in detrusor pressure and is calculated by dividing the volume change by the change in detrusor pressure during that change in bladder volume. The ICS recommends that the 2 standard points used to calculate compliance should be at the start of bladder filling and then at cystometric capacity or immediately before the start of any detrusor contraction that causes significant leakage. Normal compliance should be greater than 12.5 mL/cm H 2 O.
In patients at risk for upper urinary tract deterioration as a result of increased lower urinary tract storage pressure, compliance should be assessed carefully. Rapid bladder filling, infection, or long-standing indwelling catheter may be associated with an artifactually impaired compliance. A prolonged involuntary bladder contraction can also be misinterpreted as impaired compliance. In those patients with apparent impaired compliance on UDS testing, bladder filling should be stopped and the intravesical pressure examined to distinguish between impaired compliance (Pdet will remain elevated) and a prolonged involuntary detrusor contraction (Pdet will eventually return to near baseline). Finally, high-volume VUR or decompression into a large bladder diverticulum will result in artifactually low filling pressures and an overestimate of bladder compliance in patients who are at risk.
Involuntary Detrusor Contractions (DO)
DO is a UDS observation characterized by involuntary detrusor contractions during the filling phase, which may be spontaneous or provoked. Phasic detrusor overactivity is a pattern of DO defined by a characteristic waveform and may or may not lead to urinary incontinence. Per the ICS standardization documents, there is no lower limit to the amplitude that defines DO, but confident interpretation of low-pressure waves of less than 5 cm H 2 O depends on “high-quality” UDS technique. DO may occur during the filling portion of the study, which may or may not be suppressible. In fact, the ICS has updated the definition of DO so that it no longer includes the statement “involuntary detrusor contraction which the patient cannot completely suppress.” A single involuntary detrusor contraction that occurs at cystometric capacity, which cannot be suppressed and results in incontinence and bladder emptying, is termed terminal detrusor overactivity. An “after contraction” is a phasic increase in Pdet of significant amplitude, which occurs at the end of micturition with an empty bladder. The significance of such a contraction is unclear and may represent artifact from catheter malpositioning or true lower urinary tract pathologic abnormality.
Overall, the finding of DO may be clinically relevant or not. In patients without complaints of frequency, urgency, or urgency urinary incontinence, the finding of DO may be artifactual and irrelevant if it does not reproduce any of the patient’s clinical symptoms. In such individuals, DO may be found in 14% to 18%. In contrast, up to 50% of women with complaints of overactive bladder, symptoms with urgency incontinence will not demonstrate DO on UDS studies. Provocative maneuvers, such as hand washing, and changes in position may induce DO in those individuals in whom it is suspected but not demonstrated.
Emptying
Micturition is typically a private activity for most patients, so reproducing normal voiding habits in a clinical UDS laboratory can be challenging. It is essential to create an environment that promotes privacy and maximal comfort for the patient in this highly unusual setting. In order for the UDS study to adequately answer the clinical questions, the patient should be instructed to void as they normally void at home, despite the artificial clinical setting. Patients should be questioned on whether the void during the UDS study reproduces their usual voiding pattern at home. For example, if the patient states that they push or strain during urination, then the UDS clinician should ensure that the voiding portion of the UDS study reflects that pattern. Alternatively, a straining pattern on the voiding portion of the UDS study that does not reproduce the patient’s usual voiding habit is of minimal diagnostic value. A prestudy noninvasive uroflowmetry can be used to compare with the pressure-flow study of the UDS to ensure that they approximate each other. If not, the UDS clinician must decide which best represents the patient’s voiding pattern and which is artifactual.
Many patients find that initiating a void during the UDS study extraordinarily difficult. Some of these factors may be environmental, such as attempting to void in front of others, with a catheter in the urethra, under fluoroscopy (in the setting of VUDS), and so on. Some patients have pain with urination and the anticipation of the pain, especially with a urethral catheter in place, may inhibit patients from voiding during the study. Other patients may have a long-standing history of “bashful bladder” or psychogenic inhibition, which is a condition characterized by the inability to initiate or maintain micturition in situations where there is a perception of scrutiny by others. Reducing the number of personnel in the UDS laboratory during the study, the use of privacy screens, and the use of a “white noise” generator or playing relaxing music are maneuvers that can help reduce the “clinical” environment of the UDS laboratory and consequently help the patient feel more relaxed. Hearing running water from the sink faucet or bathing the patient’s hands in warm water can help a patient initiate micturition. There are times when it may be necessary to have all the personnel leave the UDS laboratory and monitor the study remotely, or returning only after the patient has begun voiding. Despite all of these maneuvers, there will be some patients who will still be unable to void. In this scenario, the intravesical catheter can be removed and the patient asked to void again in case the urethral catheter was preventing the patient from voiding (whether it be from an anatomic obstruction or from psychogenic inhibition). Data from Pves would be lost, but uroflowmetry combined with the Pabd tracing and fluoroscopic images if performing VUDS can be informative. If this fails, then all transducers and EMG patches/needles should be removed and the patient should be asked to void for a noninvasive uroflowmetry. If the patient is still unable to void for a noninvasive uroflowmetry, then a PVR measurement should be performed.
Obstruction
BOO is the generic term for obstruction diagnosed on a pressure-flow study during voiding and is characterized by a high detrusor pressure and a low flow rate. The ICS recognizes that BOO has been defined for men but as of yet has not been adequately defined for women and children. Also, the diagnosis of BOO can only be made during UDS in the setting of a detrusor contraction. Thus, BOO cannot be diagnosed in the setting of a Valsalva void. However, other clinical entities can mimic BOO during a pressure-flow study, such as dysfunctional voiding, unrecognized pelvic organ prolapse, or pelvic floor/external sphincter spasm secondary to pain from catheterization. It is therefore important to recognize these clinical scenarios during a UDS study to prevent a misdiagnosis of BOO.
Coordination
Normal micturition begins with a relaxation of the bladder outlet and external sphincter followed by a detrusor contraction of adequate magnitude and duration to empty the bladder. The outlet should remain open until satisfactory bladder emptying is completed. Failure of the sphincter to relax or stay completely relaxed during micturition is considered abnormal. Causes of incomplete coordination of the external sphincter and the detrusor muscle include detrusor sphincter dyssynergia (DSD), dysfunctional voiding, and pain from the catheterization during the UDS study. DSD is defined as a detrusor contraction concurrent with an involuntary contraction of the urethral and/or periurethral striated muscle. It is caused by a neurologic lesion in the suprasacral spinal cord and true DSD can only occur when there is a known neurologic lesion above the sacral micturition center. If there is no neurologic lesion, then the lack of coordination is considered to be a learned behavior known as dysfunctional voiding. It is characterized by an intermittent and/or fluctuating flow rate caused by involuntary intermittent contractions of the pelvic floor striated muscles during voiding in neurologically normal individuals. The disorder is well described in children, but can be seen in adult men and women complaining of lower urinary tract symptoms. When diagnosing dysfunctional voiding on UDS studies, a noninvasive uroflowmetry should be performed for comparison to rule-out a test-induced phenomenon such as pain from the urethral catheter.
Contractility
Bladder contractility depends on several factors, including pharmacologic, neurologic, smooth muscle, and others. Appropriate filling volumes should be attained to facilitate micturition. Underfilling or overfilling during UDS will result in an underestimation of detrusor contractility. Therefore, it is helpful to have a voiding diary before the UDS study to have an estimate of functional bladder capacity.
Normal detrusor function during voiding is defined as a voluntarily initiated continuous detrusor contraction that leads to complete bladder emptying within a normal time span, and in the absence of obstruction. Abnormal detrusor activity can be subdivided into detrusor underactivity and acontractile detrusor. Detrusor underactivity is defined as a contraction of reduced strength and/or duration, resulting in prolonged bladder emptying and/or a failure to achieve complete bladder emptying within a normal time span. If bladder contractility cannot be demonstrated during the UDS study, then it is considered an acontractile detrusor. Such a diagnosis of detrusor acontractility should not be applied unless the patient’s voiding pattern during the UDS study is representative of the patient’s usual voiding pattern and is confirmed not to be caused by the environmental circumstances of the study. These 2 states of abnormal bladder contractility can occur for various reasons including neurologic conditions and diabetes. However, pain from catheterization or psychogenic inhibition (bashful bladder) may result in temporary suppression of the micturition reflex and an apparent diminished contractility. A diagnosis of abnormal detrusor activity should not be applied unless the patient’s voiding pattern, as reflected by detrusor acontractility, is representative of their usual voiding pattern at home and is confirmed not to be caused by the environmental circumstances of the study.
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