CHAPTER 3 Urodynamic procedures

INTRODUCTION

Symptomatic evaluation of urinary tract dysfunction is difficult since the bladder often proves to be an ‘unreliable witness’, not only because of subjective bias from both the patient and the clinician; but also because there is considerable overlap between the symptoms from different disorders. Urodynamic techniques are objective investigations developed to clarify these symptoms. The term urodynamics encompasses a variety of complementary techniques of varying complexity (Table 3.1).

Table 3.1 Urodynamic techniques.

Urodynamic techniques
Complexity of technique	Technique
Simple – voiding diary	Micturition/time chart Frequency/volume chart Bladder diary
Simple – investigation	Pad testing Uroflowmetry ± ultrasound residual Ultrasound cystodynamogram Intravenous urodynamogram
Pressure/flow studies (Chapter 4)	Cystometry Leak point measurements Video urodynamics Ambulatory urodynamics
Complex – investigation	Urethral pressure measurement Neuro-physiological investigation Upper tract urodynamics (Whitaker test)

In this chapter the indications and methodology for these various techniques will be discussed along with introducing common clinical findings. The majority of invasive urodynamic investigations are pressure/flow studies and these will be discussed in detail in the next chapter (Chapter 4). More detailed discussion of common lower urinary tract disorders and associated urodynamic findings will occur in later chapters.

INDICATIONS FOR URODYNAMIC ASSESSMENTS

Only a good understanding of the various techniques including methodology, limitations and specific indications will allow the clinician to choose an appropriate test. In many cases a number of investigations may be necessary to answer all the clinical questions or further investigations may be required if the first investigation was unhelpful or presents a new avenue for investigation.

Before embarking on any urodynamic investigation the following should be considered:

• Is there a clear indication for the chosen test?

Will it aid in diagnosis?

Will it aid in making management decisions?

• Is this the most appropriate test?

Would a simpler test answer the clinical questions?

Is a more complex test more likely to answer all the clinical questions?

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• Are there appropriate local facilities and expertise to perform the chosen test?

• Is the most appropriate person, with an understanding of the patient’s individual condition performing the test?

STANDARDIZATION AND QUALITY CONTROL

All urodynamics should be performed in a standardized manner; this not only maintains the quality of the data, but also allows for comparison of the results if a patient has a repeat investigation. In addition a standardized technique and recording of the data using recognized terminology allows the accurate exchange and comparison of information for both clinical and experimental purposes. The official terminology suggested by the International Continence Society (ICS) is used throughout this book. However investigations must still be tailored for individual patients so that the clinical questions are answered thoroughly without undue time spent on obtaining clinically irrelevant data.

Maintaining the quality of any study also requires that all equipment is appropriately set up and regularly calibrated with sufficient working knowledge to ‘troubleshoot’ any problems encountered during an investigation.

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In all cases precise measurement and complete documentation must be coupled with accurate analysis and critical reporting of the results. However, it must be borne in mind that whilst these are objective tests that can be standardized to a high degree, there remains a significant subjective element in the interpretation of the results. Urodynamics is not an exact science!

AIMS OF URODYNAMIC INVESTIGATIONS

The principal aim of any urodynamic assessment is to reproduce the symptoms whilst obtaining physiological measurements, so as to determine the pathophysiology underlying the symptoms.

Both the precise nature of the condition and the severity can be established, thus allowing the clinician to understand the clinical implications and plan further appropriate management.

URODYNAMICS IN PRACTICE

Aims of urodynamic investigations:

• Reproduce the troublesome symptoms.

• Answer specific clinical questions.

• Establish a precise diagnosis.

• Determine the severity of the condition.

• Plan further investigations or therapies.

In most cases the indications for urodynamic investigation are clear and its appropriate application is essential to the modern practice of urology, gynaecology, and any specialties dealing with the management of lower urinary tract dysfunction.

CLINICAL NOTES

Always exclude urinary tract infections prior to an urodynamic investigation

• Urinary tract infections (UTIs) are a common cause of LUTS.

• A UTI may aggravate pre-existing LUTS.

• The presence of a UTI may invalidate the results of a urodynamic investigation, as a UTI may falsely result in:

increased bladder sensation (± pain or discomfort)

detrusor overactivity

poor bladder compliance.

• Prophylactic antibiotics may play a role in patients with recurrent UTIs, allowing the study to be performed with sterile urine.

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VOIDING DIARIES

Voiding diaries are the simplest of all urodynamic assessments, yet their value is often overlooked. They provide an important natural urodynamic record of bladder function.

Indications and aims

Voiding diaries are simple, non-invasive tools that are frequently part of the initial evaluation of patients complaining of LUTS, particularly those who have storage symptoms such as increased urinary frequency and incontinence.

They give an indication of the voiding pattern, the severity of symptoms and they add objectivity to the history. They may also give an indication of the impact on the patient’s life and may highlight ‘coping strategies’ that the patient has adopted to help manage their symptoms. Voiding diaries are also useful in identifying pathophysiology of renal origin such as abnormal production of urine related to the circadian rhythm.

A number of different diaries have been defined by the ICS:

• Micturition time chart – records only the times that voids occur with no volumetric data.

• Frequency/volume chart (FVC) – records the time and volume of each micturition.

• Bladder diary – records the time and volume of each micturition and may also include other data such as incontinence episodes, pad usage, fluid intake and urgency (Table 3.2).

Table 3.2 Bladder diary. Recording volume and time of each void, fluid intake, pad usage and incontinence episodes (W). Patients also record waking/retiring time to allow calculation of nocturia.

Method and standardization

The patient is asked to record as accurately as possible the time of events such as voids and incontinent episodes on the chart and to measure the volume voided using a graduated container (jug). They are also asked to record the time they are awake and asleep. Patients must be instructed to continue their normal activities during the course of the assessment, so as to obtain an accurate representation of their normal lower urinary tract function. The ICS has recommended that voiding diaries are performed for at least 24 hours, although in practice a period of 3–7 days is usually chosen. Most patients find them acceptable for use over short periods.

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Frequent findings

• Normal frequency and voided volumes.

• Increased frequency and normal volumes – therefore an increased 24-hour production of urine, suggesting a high fluid intake. This may be related to diabetes mellitus or diabetes insipidus but is more usually habitual, especially with the increasing popularity of high fluid diets.

• Reduced volumes with minimal variation in the volume voided – suggesting a bladder wall pathology such as bladder pain syndrome/painful bladder syndrome/interstitial cystitis or carcinoma in situ (Note – An anatomical capacity measured under general anaesthesia will confirm the presence of a reduced bladder capacity due to anatomical reasons such as fibrosis or a contracted bladder. A reduced anatomical capacity often implies a low likelihood of response to conservative therapeutic modalities).

• Reduced volumes with variation in the volume voided – suggestive of underlying detrusor overactivity as the bladder contracts at variable degrees of distension before maximum capacity, erroneously informing the patient that it is full; resulting in urinary frequency and low and variable voided volumes.

• Increased nocturnal production – (nocturnal polyuria), suggestive of cardiac failure, dependent fluid shifts in the supine position, hormonal fluid balance abnormality or idiopathic in origin. This is not a urological condition.

Voiding diaries must not be over-interpreted, but should be used in combination with other forms of urodynamic and urological assessment (Table 3.3).

Table 3.3 Urodynamic parameters measured by voiding diaries.

Urodynamic parameters measured by voiding diaries
Daytime frequency	Number of voids recorded in waking hours
Nocturia	Number of voids recorded during sleep hours with each void preceded and followed by sleep
24-hour frequency	Total number of awake and sleep voids during a specified 24-hour period
24-hour production	Total volume of urine voided during a specified 24-hour period
Polyuria	Voiding of more than 2.8 litres in 24 hours
Nocturnal urine volume	Total volume of urine voided during sleep hours, excluding the last void before sleeping but including the first void on waking
Nocturnal polyuria	When an increased proportion of the 24-hour production occurs at night, usually >33% (but age-dependent)
Maximum voided volume (replaces the term ‘functional volume’)	The largest volume voided during a single micturition. Particularly important when deciding how much to fill the bladder during pressure/flow urodynamics, to prevent overfilling
Pad usage	Number of pads used during a specified period
Frequency of incontinence episodes	Number of incontinence episodes during a specified period
Frequency of urgency episodes	Number of urgency episodes during a specified period
Fluid intake	Volume of fluid ingested during a specified period

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CLINICAL NOTES

Example of bladder retraining programme

In order to bring your bladder problem under control you must re-educate your bladder and learn to resist early false sensations of bladder fullness. Retraining (or ‘stretching’) your bladder will help to control leakage and you can do this by trying to hold on for as long as possible before passing water.

• It is important that you do not restrict your fluid intake.

• When you get the feeling that you need to pass urine, suppress the urge until the sensation lessens or subsides.

• At first this will be difficult but as you persevere it will become easier.

• Sitting on a hard seat may help you to hold on to your urine for longer. Helpful distractors include taking deep breaths, counting backwards from 100, etc.

• Contracting the pelvic floor muscles (Kegel manoeuvre) can also help to abort the desire to void.

• If you wake up at night, try to hold on if you can; if possible, turn over and go back to sleep.

• If you have been prescribed tablets to help you pass your urine less frequently take them regularly as directed.

• You should aim to reduce the frequency with which you pass urine to five or six times in 24 hours.

Remember:

You are trying to re-educate your bladder so that it will hold more urine. Although you may find this difficult at first, with practice it will get easier.

Example of bladder drill

Patients are instructed to:

• hold on to their urine for a fixed time, such as an hour

• Use the bladder retraining programme to suppress early urges

• and gradually increase the time interval (for instance, an additional 15 minutes weekly) between voids until an acceptable voiding pattern is achieved.

Bladder retraining

In addition to having diagnostic benefit, voiding diaries have therapeutic value and can provide important information that is helpful in treating bladder dysfunction. It is particularly useful for providing biofeedback during bladder retraining drills commonly used in patients with small volume frequency and urgency incontinence. They also often provide important feedback to the practitioner and patient so that they can objectively evaluate the effectiveness of any therapy.

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Pad testing

Pad testing is a simple, non-invasive and objective method for detecting and quantifying urinary incontinence. It is easy to perform and interpret and provides a great deal of useful information.

Indications and aims

The principal aim is to determine the amount of urine leaked during a specified period, e.g. one hour, thus quantifying the severity of incontinence to both clinician and patient, as frequently the degree of incontinence is unclear from the history. In addition, the test is particularly useful to confirm the presence of incontinence when other tests, e.g. pressure/flow urodynamics, have failed to demonstrate any urinary leakage.

Method and standardization

To obtain a representative result, especially for those who have variable or intermittent urinary incontinence, the test period should be as long as possible in circumstances that approximate to those of everyday life; yet it must be practical. The pad test should be conducted in a standardized fashion and the ICS have provided guidelines on performing a ‘1-hour pad test’.

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URODYNAMICS IN PRACTICE: 1-HOUR PAD TEST

The International Continence Society has suggested the following guidelines:

• The test should occupy a 1-hour period during which a series of standard activities are carried out.

• The test can be extended by further 1-hour periods if the result of the first 1-hour test is not considered to be representative by either the patient or the investigator; alternatively the test can be repeated after filling the bladder to a defined volume.

• The total amount of urine leaked during the test period is determined by weighing a collecting device such as a nappy, absorbent pad, or condom appliance (ensure that the collecting device has adequate capacity).

• A nappy or pad should be worn inside waterproof underpants or should have a waterproof backing.

• Immediately before the test begins the collecting device is weighed to the nearest gram.

Typical test schedule

• Test is started without the patient voiding.

• Pre-weighed collecting device (pad) is put on and first 1-hour test period begins.

• Patient drinks 500 ml sodium-free liquid within a short period (maximum 15 min), then sits or rests.

• Patient walks for 30 min, including stair climbing equivalent to one flight up and down.

• For remaining period the patient performs the following activities: standing up from sitting, 10 times; coughing vigorously, 10 times; running on the spot for 1 min; bending to pick up small object from floor, 5 times; washes hands in running water for 1 min.

• At the end of the 1-hour test the collecting device is removed and weighed. The change of weight of the collecting device is recorded. A change of less than 1 g is within experimental error and the patient should be regarded as essentially dry.

• If the test is regarded as representative the subject voids and the volume is recorded, otherwise the test is repeated preferably without voiding.

• If the collecting device becomes saturated or filled during the test it should be removed and weighed, and replaced by a fresh device.

• The activity programme may be modified according to the patient’s physical ability.

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Practical points

• The total weight of urine lost during the test period is taken to be equal to the gain in weight of the collecting device(s). An increase in weight of the pad of less than 1 g in 1 hour is not considered to be a sign of incontinence, as such as small weight change may be due to weighing errors, sweating, or vaginal discharge.

• The test should not be performed during a menstrual period.

• A negative result should be interpreted with caution; the test may need to be repeated or supplemented with a more prolonged test.

• Any variations from the usual test schedule should be recorded, so that the same schedule can be used on subsequent occasions.

• In principle, patients should not void during the test period. If they experience urgency, they should be persuaded to postpone voiding and to perform as many of the activities listed for the last 15–30 min of the test as possible to detect leakage.

• Before voiding the collection device is removed for weighing. Patients may influence the test result by voiding prior to removing and weighing the pad.

• If voiding cannot be postponed the test is terminated. The voided volume and duration of the test should be recorded. The results for patients who are unable to complete the test may require separate analysis or the test may be repeated after rehydration.

Urodynamic parameters measured by pad testing

Pad testing determines the volume of leakage during a specified period. One gram is equal to one millilitre, therefore an increase in weight of the collection device (pad) by for example 10 g is equal to urinary incontinence of 10 ml.

Normal values

The hourly pad weight increase in continent women varies from 0.0 to 2.1 g/hour, averaging 0.26 g/hour. With the 1-hour International Continence Society pad test, the upper limit (99% confidence limit) has been found to be 1.4 g/hour.

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URODYNAMICS IN PRACTICE: VARIATIONS TO THE PAD TEST

• Colouration of the urine with oral pyridium before pad testing can help differentiate between vaginal discharge and urinary incontinence.

• Additional changes and weighing of the collecting device can give information about the timing of urine loss.

• The collecting device may be an electronic recording pad so that the timing is recorded directly.

• Home pad tests lasting 24–48 hours are superior to 1-hour tests in detecting urinary incontinence. However they are less practical and more cumbersome. The pads must be stored in an airtight container before and after use to prevent evaporation, until they have been weighed. The normal upper limit for a 24-hour test is 8 g.

• Experts who routinely perform pad testing do so for a number of reasons:

severe patients with high volume incontinence may experience lower cure rates with anti-incontinence procedures

pad testing provides an excellent objective outcome measure.

UROFLOWMETRY

This is the simplest and often most useful investigation in the assessment of patients with predominantly voiding symptoms.

Indications and aims

This is a non-invasive and inexpensive test that gives a great deal of information regarding voiding function by measuring the rate of flow of voided urine.

• It can often be used to support the diagnosis of bladder outlet obstruction (BOO) or a poorly functioning detrusor, suspected from the history.

• It is an excellent screening tool for BOO, particularly when combined with measurement of residual urine volume and is frequently the first line screening investigation for most patients with suspected voiding dysfunction.

• It is useful for identifying those patients who require more extensive urodynamic evaluation.

Uroflowmetry is an adequate investigation for uncomplicated BOO in over 60% of patients. More detailed investigations are only indicated in limited situations, such as when the findings are at variance with the symptoms, if there are significant storage symptoms or if initial treatment has been unsuccessful.

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Method and standardization

Uroflowmetry is performed using a flowmeter, a device that measures the quantity of fluid (volume or mass) voided per unit time (Figure 3.1). The measurement is expressed in millilitres per second (ml/s). Patients are instructed to void normally, either sitting or standing, with a comfortably full bladder and should be provided with as much privacy as possible and comfortable surroundings, so as to remove the inhibitory effects of the test environment. Uroflowmetry can be carried out either by itself or in combination with other techniques such as the measurement of post-void residual (PVR) urine. The patient should be asked if the void was representative of their usual voiding. (It is important that the flowmeter is regularly calibrated as per the manufacturer’s instructions to maintain the accuracy of the readings.)

Figure 3.1 Flowmeter. Photograph of a typical flowmeter which is usually placed below a large funnel for the patient to void into. The funnel is normally placed under a commode for females; men can void directly into the funnel whilst standing. Photograph also shows results printersterm.

URODYNAMICS IN PRACTICE: TYPES OF FLOWMETER

• Rotating disk flowmeter: the voided fluid is directed onto a rotating disk and the amount landing on the disk produces a proportionate increase in its inertia; the power required to keep the disk rotating at a constant rate is measured, so allowing calculation of the flow rate of fluid landing on the disk.

• Electronic dipstick flowmeter: a dipstick is mounted in a collecting chamber and as urine accumulates the electrical capacitance of the dipstick changes, allowing calculation of the rate of fluid accumulation and hence the flow rate.

• Gravimetric flowmeter: the weight of collected fluid or the hydrostatic pressure at the base of a collecting cylinder is measured. The change in weight or pressure allows calculation of the flow rate.

Normal values

Males under 40 years of age generally have maximum flow rates over 25 ml/s. Flow rates decrease with age and men over 60 years of age with no bladder outlet obstruction usually have maximum flow rates over 15 ml/s.

Females have higher flow rates than males, usually of the order of 5–10 ml/s more for a given bladder volume. Exaggerated maximum flow rates are typical in women who have stress incontinence, where the outlet resistance is minimal and also in patients who have marked detrusor overactivity – the so-called ‘fast bladder’.

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Interpretation

Uroflowmetry is invaluable in the assessment of voiding function for a wide range of urological conditions. Reliance should be placed on the observed flow pattern as well as any absolute values obtained (Figures 3.2 and 3.3). The results must always be interpreted within the context of the clinical situation, recognizing the limitations of the study.

Figure 3.2 Flow rate recording. Illustrating the International Continence Society nomenclature.

(Reproduced with permission from Neurourology and Urodynamics 1988; 7:403–426.)

Figure 3.3 Intermittent void. Showing the relationship between flow time and voiding time in an intermittent voiding pattern.

The measured flow rate is dependent upon a number of factors including:

• strength of detrusor contraction (detrusor contractility)

• presence of bladder outlet obstruction (BOO)

• adequacy of relaxation of the sphincter mechanisms

• patency of the urethra

• compensatory mechanisms such as abdominal straining.

The flow rate and pattern give important clues as to the underlying dysfunction, however the major limitation of uroflowmetry is that the flow rate is a composite of both the function of the detrusor and the function of the bladder outlet/urethra. It is therefore impossible to determine from a flow rate alone if voiding dysfunction is due to a detrusor pathology or bladder outlet/urethral pathology or from a combination of problems; only pressure/flow urodynamics can differentiate between such conditions. For example, prolonged flow time with an abnormally low Q_max may be due to bladder outlet/urethral obstruction or a poorly contractile detrusor muscle (detrusor underactivity). However, a number of characteristic uroflowmetry patterns have been described, and whilst these may not be specific, in the majority of patients they give an acceptable indication of the most likely pathology and allow empirical therapy to be instigated (Table 3.4).

Table 3.4 Urodynamic parameters measured by uroflowmetry.

Urodynamic parameters measured by uroflowmetry
Parameter	Definition	Notes
Voided volume	Total volume expelled via the urethra
Maximum flow rate (Q_max)	Maximum measured flow rate	The flow curve should be assessed visually and the Q_max must not be taken at the peak of an artefact but at the peak of the line of best fit for the curve
Average flow rate	Voided volume divided by flow time	Calculation of average flow rate is only meaningful if flow is continuous and without terminal dribbling
Flow time	Time over which measurable flow actually occurs (i.e. excluding interruptions)	The flow pattern must be described when flow time and average flow rate are measured
Voiding time	Total duration of micturition (i.e. including interruptions)	When voiding is completed without interruption, voiding time is equal to flow time
Time to maximum flow	Elapsed time from onset of flow to maximum flow rate

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Characteristic flow patterns

Normal

An easily distensible bladder outlet with a normal detrusor contraction results in a smooth bell-shaped curve with a rapid rise to a high amplitude peak (Q_max). The time to Q_max should not exceed one-third of the flow time. Any other patterns (flat, multiple peaks, asymmetric, prolonged) indicate abnormal voiding (Figure 3.4a).

Figure 3.4 Characteristic flow patterns. (a) Normal – there is rapid change before and after the peak flow. (b) ‘Fast bladder’ – an exaggeration of normal associated with high pre-micturition pressure and seen in cases of detrusor overactivity. (c) Prolonged flow – associated with outflow obstruction. (d) Intermittent flow – resulting from abdominal straining to compensate for poor detrusor contractility; a similar picture may be seen with urethral overactivity (detrusor sphincter dyssynergia or dysfunctional voiding). (e) Classical pattern of a urethral stricture with a long plateau.

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‘Fast bladder’

This is an exaggeration of the normal curve and may be due to a raised end fill bladder pressure associated with detrusor overactivity or may be due to a significant decrease in outflow resistance as can occur with stress urinary incontinence (Figure 3.4b).

Prolonged flow

This is a flow with a prolonged time to reach a low maximum amplitude and an extended flow time; often it is an asymmetric curve with a prolonged declining terminal end. This is frequently seen with bladder outlet obstruction (BOO), although a similar pattern may be seen with a poorly contractile detrusor muscle (Figure 3.4c).

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Intermittent flow

This irregular spiking pattern is frequently due to abdominal straining to overcome the poor flow associated with BOO or a poorly contractile detrusor, although more complex outlet conditions such as sporadic sphincter activity may also cause an intermittent pattern (Figure 3.4d).

Flat plateau

A low maximum flow rate which plateaus for a prolonged time in a ‘box-like’ fashion is characteristic of a constrictive obstruction from a urethral stricture. A urethral stricture in the presence of a normally functioning bladder usually does not cause voiding symptoms until the urethral calibre is reduced below 11 F (Figure 3.4e).

To provide more detailed information a simple flow rate can be combined with a measurement of the post-voiding residual (PVR) volume. If there is doubt about the diagnosis after uroflowmetry, more complex urodynamic (usually pressure/flow) studies may be required. For instance, it may be ill-advised to perform a prostatectomy in men with lower urinary tract symptoms (LUTS) who have a normal flow pattern, a ‘fast bladder’, or very intermittent flow and a high PVR, without first performing pressure/flow urodynamics.

Practical points

There are a number of important factors to consider when interpreting flow rates including:

• Volume voided – low voided volumes of <150 ml can lead to erroneous results and should be repeated; whereas high voided volumes of >400–600 ml may lower flow rates by overstretching the bladder, resulting in detrusor overdistension and decompensation (Note – Many patients complain of slower flow rates at night when the bladder is relatively overstretched).

• The nature of the fluid – flowmeters need to be calibrated for the type of fluid being voided, due to differences in specific gravity.

• Age and sex – as these may alter the flow rates.

• Pattern – in particular whether the flow is continuous or intermittent.

• Position of the patient when voiding – should be noted, e.g. sitting, standing, supine.

• Free flow – a ‘free flow’ occurs after natural filling of the bladder, whereas a ‘non free flow’ void occurs when the bladder is filled using a catheter. The ‘free flow’ void is more physiological.

CLINICAL NOTES

Note: normal flow rate does not rule out bladder outlet obstruction (BOO)

Frequently uroflowmetry is performed to detect the presence and severity of BOO. However, particularly in the early stages of obstruction there may be a compensatory increase in the voiding pressure generated by the detrusor muscle, thus overcoming the obstruction. Uroflowmetry may therefore be normal in the presence of BOO. Pressure/flow urodynamics can detect the BOO in such a situation. This high pressure, normal flow voiding (>15 ml/s) occurs in approximately 7–15% of patients with bladder outflow obstruction.

A Q_max of <12 mL/s is generally considered abnormal in men >60 years; data suggest that approximately 90% of men with LUTS and a Q_max <10 mL/s are obstructed on pressure/flow studies.

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Artefacts

The maximum flow rate recorded by the uroflowmetry machine is frequently misleading. Common artefacts are shown in Figure 3.5 and include:

• Straining, causing an artificial rise in the maximum flow rate.

• Irregularities in the measured flow rate due to collecting funnel artefacts and variations in direction of the urinary stream. Such as occurs when a man voiding into a funnel changes the point he is ‘aiming’ at within the funnel.

Figure 3.5 Artefacts. (a) The artefact (a spurious maximum flow rate of 19 ml/s) results from squeezing the prepuce of the penis during voiding. (b) It is eliminated revealing a true maximum flow rate of 7.4 ml/s when the patient stops squeezing the penis. (c and d) Both these flow curves show artefactual spikes, but an experienced urologist has corrected the traces (dotted line) so that the true maximum flow rates are 17.5 and 9.2 ml/s, as shown. Frequently an artefactual spike occurs at the start of the recorded flow due to the initial flow of urine registering on the flowmeter; or during the flow pattern due to abdominal straining.

Due to the kinetics of smooth muscle contraction the detrusor is unable to generate short lived changes in amplitude (spikes). Therefore these artefacts need to be removed by the clinician by examining the pattern and ‘smoothing’ the curve with a line of best fit to determine the actual Q_max. It is incorrect to blindly assume that the electronically reported Q_max is accurate.

It must also be remembered that any alteration in the urinary stream after the urine leaves the meatus may alter the flow and introduce artefacts. The funnel/collecting device will invariably cause such modifications. There is also a lag in the flowmeter registering the flow from when the urine left the meatus; this is unimportant in free flow uroflowmetry but is a consideration when uroflowmetry is combined with pressure/flow urodynamics (see Chapter 4).

The pattern of the flow is also altered by the speed of the recording and the ICS have recommended that:

• 1 millimetre should equal 1 second on the x-axis

• 1 millimetre should equal 10 millilitres on the y-axis.

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POST-VOID RESIDUAL (PVR) DETERMINATION

Frequently uroflowmetry is combined with simple post-void residual (PVR) estimation using a handheld ultrasonic ‘bladder scanner’ to estimate the completeness of bladder emptying. When more information on bladder anatomy and function is needed an ultrasound cystodynamogram can be performed (see next section).

An elevated post-void residual (PVR) may represent obstruction; or more commonly is a surrogate marker for detrusor failure which may be due to a number of causes, including chronic BOO, neurogenic bladder or myogenic failure. An elevated PVR is an indication for pressure/flow urodynamics.

There are a number of clinical implications of an elevated PVR:

• may be an indication for prostatectomy in obstructed male patients

• requires long-term surveillance in those followed conservatively

• may be associated with hydronephrosis

• predisposes patient to recurrent urinary tract infections and bladder calculi

• potential risk factor for retention in patients managed with antimuscarinic agents.

ULTRASOUND CYSTODYNAMOGRAM

The ultrasound cystodynamogram (USCD) combines ultrasound examination of the bladder with uroflowmetry to provide more detailed information on bladder structure and function than uroflowmetry alone.

Indications and aims

Additional information obtained during an USCD includes the structure of the bladder (shape, presence of diverticulia), distal ureteric anatomy (presence of hydroureteronephrosis), completeness of bladder emptying and the prostate size (Figure 3.6).

Figure 3.6 Ultrasound cystodynamogram. The additional ultrasonic data, on the right showing incomplete emptying, thickened bladder wall and bilateral hydronephrosis associated with chronic poor voiding.

An USCD is of particular value for assessing patients who may have a raised PVR (e.g. patients with suspected outflow obstruction, a poorly functioning detrusor or if there is suspected compromised voiding after a repair procedure for stress incontinence).

The addition of ultrasound assessment is easy, requiring little specialized equipment and is non-invasive with no ionizing radiation, yet it provides a more thorough assessment of the lower urinary tract.

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Method and standardization

Ensure that the patient has a subjectively full bladder before carrying out the study to provide a representative result.

URODYNAMICS IN PRACTICE: ULTRASOUND CYSTODYNAMOGRAM

• The full bladder (>200 ml) is scanned using any form of ultrasound probe allowing adequate visualization of the bladder – patients should be scanned when they feel ‘full’, so providing an idea of the ‘functional’ bladder capacity.

• The following are noted:

bladder wall thickness

bladder volume

presence of diverticula

distal ureteric anatomy

prostatic volume

presence of intra-vesical pathology (carcinoma or calculi).

• The patient voids into a flowmeter in private.

• A post-voiding scan is taken as soon after voiding as possible to provide accurate assessment of the true bladder post-void residual volume.

• Interpretation of the flow rate takes account of the artefacts and factors mentioned in the uroflowmetry section of this chapter.

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INTRAVENOUS URODYNAMOGRAM

The intravenous urodynamogram (IVUD) combines a conventional intravenous urogram (IVU) with uroflowmetry thus providing markedly more information than either investigation alone.

Indications and aims

This test is of value in patients who are to undergo imaging of the upper urinary tracts using an IVU. The addition of uroflowmetry also provides a comprehensive assessment of the lower urinary tract including an estimation of the pre-void bladder volume and the post-void residual (PVR). It is of particular value because it can be easily integrated into the routine of the radiology department and involves little additional equipment or staff training.

Method and standardization

Ensure that the patient has a subjectively full bladder before carrying out the study, to provide a representative result.

URODYNAMICS IN PRACTICE: INTRAVENOUS URODYNAMOGRAM

• An intravenous urogram (IVU) is performed to assess the upper tracts.

• When the patient feels that his or her bladder is naturally full (an event that can be hastened by using a suitable diuretic), uroflowmetry is performed.

• The subsequent post-micturition film after natural micturition allows accurate assessment of the patient’s true bladder residual volume.

URETHRAL PRESSURE MEASUREMENT

Originally urethral pressure measurement and in particular urethral pressure profilometry (UPP) enjoyed a disproportionate amount of attention. However the techniques for the investigation of urethral sphincteric function are far from satisfactory and their clinical utility has been questioned; therefore, most experts consider them as research tools and not suitable for widespread clinical usage.

New developments in technology such as air charged technology with true circumferential recording and ease of recording are leading to a resurgence of interest in urethral pressure measurements and may lead to an increasing understanding of the clinical utility of these tests and the clinical significance of the results. However, at present it must be concluded that these techniques remain research tools and the various techniques need to be standardized before urethral pressure measurements can be recommended in routine practice.

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The main concerns with urethral pressure measurements are:

• The results obtained are extremely susceptible to experimental artefacts and the patient’s degree of relaxation.

• The studies can be distressingly uncomfortable for patients, especially males.

• The mere act of measuring urethral pressures alters the intraurethral pressure and introduces artefacts.

• At rest the urethra is closed, therefore the urethral pressure and urethral closure pressure are idealized concepts that represent the ability of the urethra to prevent leakage.

• A number of techniques have been developed which do not always yield consistent values. Not only do the values differ with the method of measurement, but there is often lack of consistency within a single technique.

• The techniques as yet cannot definitively differentiate intrinsic sphincteric deficiency (ISD) from other disorders (see Chapter 5).

• The techniques as yet cannot establish the severity of the condition.

• The techniques as yet cannot provide a reliable indicator of surgical success and return to normal function following successful therapy.

• Total profile length is not generally regarded as a useful parameter in UPP.

• The information gained from urethral pressure measurements in the storage phase is of limited value in the assessment of voiding disorders and the voiding UPP is not yet fully developed as a technique.

A detailed discussion of the various techniques is therefore outside the scope of this book; however a summary of the techniques is provided below.

Methods

Point pressure measurement

The intraluminal pressure within the urethra may be measured at a single point over a period of time:

1. At rest, with the bladder at a certain volume (storage phase).

2. During stress, e.g. coughing/Valsalva.

3. During voiding (voiding phase).

Urethral pressure profilometry

The intraluminal pressure can also be measured along the length of the entire urethra to produce a urethral pressure profile (UPP). This is performed by withdrawing the measuring catheter mechanically at a constant speed (Figure 3.7). The resulting profile indicates the pressures within the urethra from the bladder neck to the meatus. Several techniques have been described including:

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• Resting urethral pressure profile, with the bladder at rest (storage phase). A low maximum urethral closure pressure (MUCP) on this test may be associated with ISD which may in turn be associated with a poor outcome with certain stress incontinence procedures. The test may also be useful in diagnosing sphincter damage and determining if implantation of an artificial urinary sphincter is appropriate. A high MUCP is associated with Fowler’s syndrome in young women with voiding dysfunction, as well as in patients with pelvic pain syndrome.

• Stress urethral pressure profile, with increased abdominal pressure, e.g. coughing/Valsalva. In stress incontinence the abdominal pressure transmission, which is thought to keep the normal urethra closed during stress is inadequate; therefore the urethral closure pressure decreases on increased intra-abdominal pressure.

• Voiding urethral pressure profile (voiding phase). This technique can be used to determine the pressure and site of urethral obstruction. Accurate interpretation depends upon simultaneous measurement of intra-vesical pressure and measurement of pressure at a precisely localized point in the urethra; this localization may be achieved by a radio-opaque marker on the catheter allowing the pressure measurements to be related to a visualized point in the urethra. Pressures measured whilst voiding are the fluid pressures in the urethra and not the urethral pressure.

Figure 3.7 Urethral pressure profilometry, using the perfusion method.

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Fluid bridge test

A related but different test of bladder neck competence has been described. The test can detect the entry of fluid into the proximal urethra because a continuity of fluid (fluid bridge) between the bladder and urethra occurs in such a situation. The pressure transmission is measured down the infusion channel of a standard Brown–Wickham perfusion catheter (see below) but with the perfusion switched off.

URODYNAMICS IN PRACTICE – URETHRAL PRESSURE MEASUREMENT TECHNIQUES

Perfusion method

• The perfusion method first described by Brown and Wickham is most widely used and is the measurement of the pressure needed to perfuse a catheter at a constant rate (Figure 3.7).

• The catheter has a dual lumen; one for pressure measurements opening at the end of the catheter and the other for perfusion via two opposing side holes 5 cm from the tip of the catheter.

• The catheter is constantly perfused at a set rate using a syringe pump (2–10 ml/min) while being withdrawn at a speed of less than 0.7 ml/s.

Catheter-mounted (microtip) transducers

• These eliminate errors associated with the use of fluid (leaks and air bubbles), but introduce artefacts related to the orientation of the catheter-mounted transducers on the catheter. In addition they do not measure the urethral pressure directly but instead measure the stress imparted by the urethral tissue on the surface of the transducer only.

Balloon catheter profilometry

• Uses a small soft balloon mounted on a catheter.

• Pressure is transmitted by a fluid column to the external pressure transducer.

• Measures urethral pressure accurately, but this technique is the most difficult to use and requires frequent recalibration.

Air charged technology (see Chapter 4)

• Uses a small balloon mounted on a catheter.

• Pressure is transmitted by an air column to the external pressure transducer.

• Measures urethral pressure accurately and easily, and is omni-directional.

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Practical points

When measuring the urethral pressures all systems should be zeroed to atmospheric pressure; the reference point should be taken as the superior edge of the symphysis pubis for external transducers or the transducer itself for catheter-mounted transducers. Intra-vesical pressure should be simultaneously measured to exclude a detrusor contraction and subtraction of the intra-vesical pressure from the urethral pressure produces the urethral closure pressure profile.

The following information is essential when reporting and interpreting the results of urethral pressure studies:

• bladder fullness

• position of patient, as posture affects the urethral muscle tone

• measurement technique

• size and type of catheter

• rate of infusion (perfusion method)

• infusion medium (liquid or gas)

• stationary, continuous, or intermittent withdrawal of catheter

• rate of withdrawal

• orientation of the sensor (catheter transducers)

• period of time of recording

• manoeuvres, e.g. cough and Valsalva.

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Urodynamic parameters measured by urethral profilometry

TERMINOLOGY: URETHRAL PRESSURE PROFILES (Figure 3.8)

Urethral pressure: The fluid pressure needed to just open a closed urethra.

The urethral pressure profile: Graph indicating the intraluminal pressure along the length of the urethra.

The urethral closure pressure profile: Derived by the subtraction of intra-vesical pressure from urethral pressure.

Maximum urethral pressure: The maximum pressure of the measured profile.

Maximum urethral closure pressure (MUCP): The maximum difference between the urethral pressure and the intra-vesical pressure.

It is thought that a low MUCP (<20cm H₂O) may be associated with intrinsic sphincter deficiency (ISD), whereas a high MUCP may suggest bladder neck hypermobility. However the literature on this subject is contradictory, reflecting both the variability in techniques used and inconsistency of results.

Functional profile length: The length of the urethra along which the urethral pressure exceeds intra-vesical pressure.

Pressure ‘transmission’ ratio: The increment in urethral pressure on stress as a percentage of the simultaneously recorded increment in intra-vesical pressure (Figure 3.9).

Figure 3.8 Diagram of a female urethral pressure profile in storage phase with the nomenclature recommended by the International Continence Society.

(Reproduced with permission from Neurourology and Urodynamics 1988; 7:403–426.)

Figure 3.9 Pressure ‘transmission’ ratio. (a) Urethral pressure profiles in a normal female at rest (on the left) and while coughing (on the right). During coughing there is transmission of intra-abdominal pressure (represented by the bladder trace) to the urethra in all except the distal portion of the profile. (b) Urethral pressure profiles in a patient who has urodynamic stress incontinence at rest (on the left) and while coughing (on the right). At rest the bladder pressure trace is flattened compared with normal and during coughing there is a lack of the normal transmission of intra-abdominal pressure to the urethra, resulting in negative deflections in the urethral closure pressure trace. This abnormal response results from a prolapse of the urethra within a cystourethrocoele.

(Reproduced from Abrams P, Feneley R, and Torrens M, Urodynamics. Berlin: Springer; 1983.)

NEUROPHYSIOLOGICAL INVESTIGATION

As with urethral pressure measurements, neurophysiological urodynamic investigations have failed to achieve widespread clinical usage. Neurophysiological testing allows the researcher to develop a greater understanding of lower urinary tract function but it is uncertain what added value they provide to a clinician. A particular concern is that these tests tend to only be abnormal in the presence of a clinically detectable neurological condition; therefore there is very little additional new information provided by such testing that cannot be obtained by conventional pressure/flow urodynamics and a thorough neurological assessment.

Methods

A number of different neurophysiological methods have been described including:

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• Electromyography – used to study the electrical potentials generated by the depolarization of muscle (Figure 3.10). The action potentials can be detected by either needle electrodes placed into the muscle mass or by surface electrodes. The results are usually displayed on an oscilloscope screen and this procedure can be done either solitarily or as part of an urodynamic investigation. Potential sampling sites include the intrinsic striated muscle of the urethra, the periurethral striated muscle, bulbocavernosus muscle, external anal sphincter and pubococcygeus muscle. Normal motor units have a characteristic waveform which can be altered by disease. In addition during normal voiding there should be no sphincter activity. Increased sphincter activity during voiding in association with increased detrusor pressures and flow changes is characteristic of detrusor sphincter dyssynergia (DSD – see Chapters 6 and 9). This form of neurophysiological testing may also be of utility in detecting Fowler’s syndrome in young females with voiding dysfunction, who have been found to display peculiar sphincter activity during voiding.

• Nerve conduction latency studies – are used to determine the time taken for a response (latency) to occur in a muscle following stimulation of a peripheral nerve.

• Reflex latencies – are similar to nerve conduction studies but instead assess the latency response of reflex arcs which are composed of both an afferent and efferent limb and a synaptic region within the central nervous system (CNS). This is performed by stimulation of a sensory field and recording the reflex muscle contraction. The reflex latency expresses the nerve conduction velocity in both limbs of the reflex arc and also the integrity of the CNS synapse. A prolonged reflex latency therefore may be due to slowed conduction in any of these components of the reflex arc.

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• Sensory testing – sensory function in the lower urinary tract can also be assessed by semi-objective tests that rely upon the measurement of urethral or vesical sensory thresholds to a standard applied stimulus such as a known electrical current. The vesical/urethral sensory thresholds are the least current that consistently produces a sensation perceived by the subject during stimulation at the site under investigation.

Figure 3.10 Muscle action potential from a urethral sphincter electromyogram.

UPPER URINARY TRACT URODYNAMICS

The upper urinary tract is a highly distensible system that is normally protected from the intermittent high pressure generated by the bladder by the competent vesico-ureteric junctions.

The following occurs in the upper tracts under normal circumstances:

• Urine accumulates in the renal pelvis at a resting pressure of less than 5 cm H₂O.

• The pelvic pressure rises to 10 cm H₂O on distension.

• Urine enters the ureter to be transported as a bolus to the bladder by ureteric peristalsis at intra-bolus pressures of 20–60 cm H₂O. Efficient peristalsis is dependent upon apposition of the ureteric walls. Ureteric dilatation (whether obstructive or not) and disorders of ureteric wall mobility, interfere with this process.

The normal response of the upper urinary tract to obstruction at or above the vesico-ureteric junction is to increase the rate of ureteric and pelvic peristalsis; however if the obstruction remains unresolved, ureteric dilatation may occur.

Ureteric dilatation causes uncoordinated peristalsis and inefficient urine transport. As flow is reduced down the ureter, pressure rises are transmitted:

• first to the renal collecting ducts

• then along the renal tubules to the glomeruli.

If there is no parallel increase in the glomerular hydrostatic pressure, filtration will eventually decrease and renal function will become impaired.

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The Whitaker test

The Whitaker test is an upper tract urodynamic study combined with antegrade pyelography (Figure 3.11). The principal indication for the investigation is to determine if upper urinary tract obstruction exists, as a dilated upper tract neither confirms nor excludes obstruction.

Figure 3.11 Whitaker test. Showing method of performing upper tract urodynamics.

The principle of the test is to perfuse the upper tract with a constant flow of contrast in an antegrade manner whilst simultaneously measuring renal pelvic and intra-vesical pressures. The test will differentiate patients with continuing obstruction from those with upper tract dilation secondary to permanent alterations in the musculature/tissues of the upper tract. It may also be of utility in evaluating patients with questionable uretero-pelvic or vesico-ureteric junction obstruction or those with primary defects of the ureteric musculature (e.g. prune-belly syndrome).

Urodynamics in practice: The Whitaker test

• Performed under local anaesthesia following premedication with diazepam unless the patient has an indwelling nephrostomy catheter.

• Bladder pressure is measured via a urethral catheter connected to a transducer.

• Renal pelvic pressure can be measured through a nephrostomy tube or through a needle placed in the collecting system at antegrade pyelography – the puncture technique must be good because any leak from the collecting system degrades the information provided by pressure studies.

• Dilute contrast is infused through one arm of a ‘Y’ connector at an initial rate of 10 ml/min while the other arm of the ‘Y’ is connected to a pressure transducer recording renal pelvic pressure in response to perfusion (Figure 3.11) – perfusion at 10 ml/min is considerably in excess of physiological rates and should stress the upper urinary tract. However at this high flow rate the normal renal pelvis and ureters will tolerate this flow easily with minimal rise in pressure.

• Bladder pressure is continuously recorded and the subtracted pressure (pelvic pressure – bladder pressure) is automatically calculated – appropriate equipment is available in any department performing lower urinary tract urodynamics.

• Simultaneous fluoroscopy defines the anatomy of the upper tract and spot films can be taken.

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Practical points

Upper urinary tract urodynamics is an invasive procedure because a percutaneous nephrostomy tract is required and so it should be reserved for cases where other investigations such as excretory urography and isotope renography have produced equivocal results. The main value of the Whitaker test is in providing an accurate objective assessment of obstruction to renal drainage. Significant rises in pressure are indicative of obstruction whereas free drainage of contrast at low pressure excludes obstruction.

Using this technique a pressure difference between the upper and lower urinary tract of:

• Less than 15 cm H₂O excludes obstruction.

• More than 22 cm H₂O, confirms obstruction.

• Between 15 and 22 cm H₂O lies in the equivocal range.

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• If bladder and pelvic pressure increase equally together, then vesico-ureteric reflux has occurred.

An additional indication is in patients with urinary diversion (e.g. an ileal loop). Loin pain can occur because of the high pressures generated by bowel peristalsis causing reflux up the re-implanted ureters; the extent of this can be easily assessed by upper urinary tract urodynamics.

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