By: 1 December 2008
Up to 30% of women experience, lower urinary tract symptoms (LUTS) and 15% of them have troublesome incontinence. The bladder has been described as ‘unreliable witnesses’. Although urinary symptoms provide a framework for diagnosis, they do not on their own allow an accurate impression to be formed of the underlying pathology. This may lead to inappropriate treatment being given and is especially important if surgical management is being considered, as the effects of surgery are irreversible.Urodynamics aim at providing a pathophysiological explanation by correlating the patient’s symptoms with the urodynamics findings. The success of urodynamics studies depends on the ability to reproduce the patient’s symptoms. This can be achieved if a full history is taken before commencing the tests and by trying to make the tests as interactive as possible.

Urodynamic tests are indicated in women with LUTS especially when empirical conservative treatment such as antimascarinics have failed or when surgical treatment for any form of incontinence has been considered. Urodynamic tests are also indicated in patients with voiding difficulty, mixed symptoms and previous unsuccessful incontinence surgery.

Urodynamic Techniques
There are two principal methods of urodynamic investigation;

  • Conventional urodynamic studies normally take place in urodynamic laboratory and involves artificial bladder filling with specified liquid at a specific rate.
  • Ambulatory urodynamic studies involve natural filling of the bladder by the production of urine.

In this article, we will discuss conventional urodynamic studies.

Components of Urodynamics studies

  • History and examination.
  • Frequency volume chart.
  • Uroflowmetry.
  • Substracting cystometry (filling and voiding)

History and Examination
History should be focused on analysing the patient main symptoms and reviewing other symptoms of lower urinary tract. These symptoms are best classified into three groups as shown in Table 1.

Table 1: Classification of LUTS

Abnormal storage Abnormal emptying Abnormal sensation
Stress incontinence Hesitancy Urgency
Urge incontinence Incomplete emptying Dysuria
Frequency Poor stream Painful bladder
Nocturia Postmicturition dribble Absent sensation
Nocturnal enuresis Straining to void

Examination should focus on any pelviabdominal masses, the presence of prolapse and signs of vaginal atrophy or perineal skin excoriation. Simple neurological examination aiming at assessing sensation, reflexes and muscle function in the legs. In particular, special attention should be given to the sensory sacral dermatomes, the motor divisions of which supply the bladder (S2, S3, and S4).

Frequency Volume Chart
The patit, before attending at the urodynamics laboratory, should complete a frequency volume chart. The patient is asked to record the volume of urine passed and the time of micturition for 3 – 4 consecutive days. She is also asked to record any episodes of incontinence. The volume and nature of consumed fluid should be also recorded for each day (Figure 1)

Figure 1: Normal urinary flow trace

An accurely completed frequency volume chart provides invaluable information about the patient’s voiding functions and functional bladder capacity. This prevents over distending the bladder during the filling phase of the cystometry. The chart can highlight any excessive fluid intake. In addition, it can form a useful tool in objectively evaluating the effectiveness of any therapy.

Uroflowmry is a simple and non-invasive test. It consists of measuring urinary flow over time. When combined with the measurement of residual urine volume by ultrasound or catheterization, it provides useful information on the efficiency in emptying the bladder.

Uroflowmetry should be considered as first line investigation in patients with LUTS before surgical or medical treatment as both treatments have the potential of affecting micturition efficiency and residual volume. Some of these women may have occult voiding dysfunction such as straining to void or slow stream. Dificulty in voiding may increase after surgery and sometimes lead to incomplete or complete urinary incontinence.

There are several different physical principles that can be utilised to provide an accurate assessment of the flow. The three methods, which are in common use, are:

  • The gravimetric method: The rate of change of the weight of the voided urine in the collecting jug is converted into a flow rate.
  • The rotating disc method: A known amount of power is required to keep a rotating disc spinning at a constant rate. Voided fluid is directed onto the disc increasing its inertia. The flow rate is proportional to the amount of extra power that is required to keep the disc spinning at a constant rate.
  • The capacitance dipstick: A metal capacitor strip is attached to the side of the flowmeter. As urine accumulates in the container, the electrical capacitance from the dipstick changes and from this the rate, flow can be calculated.

The test should be performed in a private and comfortable environment with the patient has a normal desire to void. It is recognisable that results in patient who voided less then 150 mls are difficult to interpret.

Flow rate (Q) is defined as the volume of fluid expelled via the urethra per unite time. It is expressed in ml/s.

Maximum flow rate (Qmax) is the maximum measured value of the flow rate. It should be 15ml/s or more in women. Pelvic organ prolapse (POP) especially cystocoele can lead to reduction in Q max.

Average flow rate (Qavg) is voided volume divided by flow time.

Voiding time (seconds) is the total duration of micturition includes interruptions

Flow time (TQ) (seconds) is the time over which measurable flow actually occurs.

Voided volume (ml) is the total volume expelled via urethra.

A normal flow curve is bell; shaped and characterized by a rapid rise to maximal flow.

Altered detrusor function influences flow rate by determining the contractile force with which urine expelled. In addition, bladder neck and urethral anatomy influence urine flow by affecting outflow resistance. To distinguish between these two causes of voiding dysfunction, simultaneous pressure/flow measurements are undertaken as in voiding cystometry.

Table 1: Classification of LUTS

Time Day 1 Day 2 Day 3
Volume Volume Volume
6 am
7 am
8 am
9 am
10 am
11 am
12 noon
1 pm
2 pm
3 pm
4 pm
5 pm
6 pm
7 pm
8 pm
9 pm
10 pm
11 pm
12 midnight
1 am
2 am
3 am
4 am
5 am

Fluid intake mls, Coffee mugs, Tea Cups

Cystometry (filling and voiding)
Filling cystometry is the method used to measure the pressure /volume relationship of the bladder. This achieved by measuring the detrusor pressure during controlled bladder filling.

Voiding cystometry coupled with urine flow rate measurements studies the relationship between detrusor pressure during voiding and urine flow rate.


  • Voiding difficulty.
  • If invasive or surgical treatment are being considered:
    To exclude overactive bladder
    To confirm the diagnosis of urodynamic stress incontinence which is leakage occurring during increase of intra-abdominal pressure in absence of detrusor activity.
    To exclude detrusor under activity or obstruction which are the main risk factors for complete or incomplete retention following surgery.
  • Failed surgical or non-surgical therapy.
  • When history and examination do not lead to definite diagnosis.

Cystometry should be performed in a comfortable and private atmosphere. The patient should be informed about the test and what to expect. There should be no interruptions by intruders during the test.

Figure 2: filling cystometry trace showing stable bladder

Figure 3: Substracting cystometry trace showing detrusor overactivity

The test should be performed interactively with the women, who must be informed about various sensations occurring during the filling stage and the need to report them. This could involve the desire to void, urgency or pain.

Urinary tract infection should always be excluded before urodynamic investigation.

Normal parameters

  • Residual volume of less then 5omls
  • Bladder capacity at SDV greater then 400 mls
  • Negligible rise in detrusor pressure during filling (less then 15 cmH2O for a filling volume of 500 mls
  • No provoked detrusor contractions
  • No leakage in association to increased intra-abdominal pressure
  • Maximum voiding detrusor pressure of less then 50 cmH2O
  • Maximum flow rate greater then 15ml/s

After physical examination is performed, a rectal or vaginal pressure-recording catheter is introduced to measure the abdominal pressure (pabd).

Under complete aseptic technique, bladder is catheterised using a thin catheter for artificial filling and a thin pressure-measuring catheter to measure the intravesical pressure (pves). The bladder is then emptied and the residual volume is measured.

The bladder is filled artificially with sterile water or normal saline at room temperature. The filling rate is usually 50 ml/min.

The pressure inside the bladder my rise due to increased abdominal pressure occurring during activities such as laughing, coughing or straining or secondary to a detrusor contraction. The proportion of intravesical pressure that is due to detrusor activity alone (detrusor pressure or pdet) is obtained by subtracting abdominal pressure (pabd) from intravesical pressure (pves)

Quality control is an essential part of the test. The system should be flushed with water to get rid of any air bubbles. The system should be zeroed to atmospheric pressure. The patients should be asked to cough form time-to-time to check adequate subtraction by the system. An equal pressure rise should be observed in both the intra-abdominal and intravesical pressure traces, which should cancel out to leave the detrusor pressure unchanged.

Pathological findings

  • Detrusor overactivity: Urodynamic observation characterised, during filling phase, by involuntary detrusor contractions, which may be spontaneous or provoked, in which the detrusor pressure raises and then falls possibly accompanied by a sensation of urgency.
  • Detrusor overactivity incontinence due to involuntary detrusor contraction.
  • Urodynamic stress incontinence: Leakage associated with increase in abdominal pressure causing increase in intravesical pressure that exceeds the intrauretheral pressure in the absence of detrusor contraction.
  • Detrusor underactivity: Low detrusor pressure and low flow rate during voiding phase.
  • Bladder outlet obstruction: High detrusor pressure and low flow rate.

During filling phase the patient is asked to indicate her first desire to void (FDV) and when she experience a strong desire to void (SDV).At this stage filling should stop. The filling catheter is removed, and the patient is asked to stand up.

At the end of the filling phase, different manoeuvres could be done to provoke detrusor activity such as asking the patient to listen to running water or washing her hands. Any increase of detrusor pressure should be noticed. The patient is also asked to cough several times or to perform more strenuous activity to check for any urinary leakage. Any associated increase in detrusor pressure should be noticed.

Finally, the woman is transferred back onto the uroflowmetre with the pressure catheters still in situ. She is asked to void and the detrusor pressure as well as the urine flow rate are measured simultaneously to provide a pressure-flow study.

Failed previous incontinence surgery.
If symptoms suggest an anatomical lesion such as urethral diverticulum.
Neurological lower urinary tract dysfunction where vesicoureteric reflux is suspected.

In videourodynamic studies, the test is performed in a room set up for radiological X-ray screening. Radio-opaque contrast is used to fill the bladder. Screening takes place if the woman complains of leaking. This allow the assessment of bladder neck opening, the severity of leakage and the extend of bladder-base descent. The presence of any vesicoureteric reflux, bladder diverticulae and trabeculation are noted. The woman then commences voiding and, once flow is established, she is asked to interrupt it. This should result in cessation of flow and urine being milked back from the urethra. Finally, the postvoid residual can be determined.

Urethral pressure profile
This test is useful when previous surgery for incontinence has failed.

Normally the urethral pressure exceeds the vesical pressure at all time except during voiding. Urethral Pressure profile assesses the ability of the urethra to exert a positive closure pressure in order to prevent leakage. This is done by simultaneously measuring the intravesical and intrauretheral pressure with a catheter with two pressure transducers 6 cm apart.

A low maximum urethral closure pressure correlates with a poor outcome for incontinence surgery.

Urodynamic investigations provide clinician with reliable diagnosis in patients suffering from LUTS. Urodynamic investigations should reproduce the patient’s symptoms and correlate them to the urodynamic findings. Hence, it need to interactive. Quality assurance is a key factor that determines the successfulness of any urodynamic test.


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