Urodynamic studies assess the function of the bladder and urethra and are often useful in the assessment and diagnosis of patients presenting with lower urinary tract symptoms (LUTS).¹ Urodynamic tests such as cystometry, uroflowmetry, pressure flow studies, electromyography and video-urodynamics tests provide objective information regarding the normal and abnormal function of the urinary tract and pelvic floor, and therefore a better understanding of the cause of LUTS.² Urodynamic studies are particularly recommended if LUTS are persistent and suggest detrusor overactivity or sphincter incompetence.³

Initial assessment¹

Frequency volume charts (voiding diaries, bladder diaries and charts)

Information from a voiding diary can provide valuable additional information but should not be used in isolation.⁴

• Voiding diaries are often part of the initial evaluation of patients complaining of lower urinary tract symptoms (LUTS), especially those who have storage symptoms such as increased urinary frequency and urinary incontinence.
• Diaries provide an indication of the voiding pattern and the severity of symptoms.

Diaries that have been defined by the International Continence Society (ICS) include:⁵

• Micturition time chart: records only the times that voids occur with no data on volume.
• Frequency/volume chart: 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.

The ICS has recommended that voiding diaries be performed for at least 24 hours, although in practice a period of 3-7 days is usually chosen.⁶ Findings may include:

• Increased frequency and normal volumes - 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 often habitual (psychogenic polydipsia).
• Reduced volumes with minimal variation in the volume voided suggests bladder wall pathology such as carcinoma in situ or interstitial cystitis.
• Reduced volumes with variation in the volume voided suggests underlying detrusor overactivity.
• Increased nocturnal production (see also separate article Nocturia).

Pad tests

• A non-invasive objective method for detecting urinary incontinence. It may be useful to confirm the presence of incontinence when other tests have failed to demonstrate any urinary leakage.
• The principal aim of the test is to determine the amount of urine lost during a specified period (e.g. one hour), as the degree of incontinence is often unclear from the history.
• However, the usefulness of pad tests as part of the assessment of urinary incontinence remains unclear.⁴

Urinary flow rate¹

The need for an initial assessment of flow rate is disputed in primary care and the presence of a reduced flow rate can usually be gained by a thorough clinical history.⁴

• Uroflowmetry is useful in the assessment of voiding function for a wide range of urological conditions. Uroflowmetry is a non-invasive test that measures the rate of flow of voided urine.
• It can often be used to suggest the presence of bladder outlet obstruction or a poorly functioning detrusor muscle.
• Uroflowmetry is performed using a flow meter to measure the quantity of fluid voided per unit of time (expressed in millilitres per second (ml/s)).
• Patients are instructed to void normally, either sitting or standing, with a comfortably full bladder.
• A flow rate based on a voided volume of under 150 ml is insufficient for reliable interpretation.
• Men aged under 40 years generally have maximum flow rates over 25 ml/s. Flow rates decrease with age and men aged over 60 years, with no urinary obstruction, usually have maximum flow rates over 15 ml/s.

Post-void residual measurement¹

Post-void residual (PVR) volume is an important part of the assessment of patients with symptoms of voiding dysfunction or recurrent urinary tract infections, which may be due to incomplete bladder emptying.⁴

• Portable ultrasound devices can be used to scan and calculate the volume of urine in the bladder (whether in urinary retention or after micturition).
• These devices are easy to use but are less accurate than bladder volume measurements made by a trained person using diagnostic-quality ultrasound equipment.
• More accurate assessment of PVRs can be obtained by catheterisation, but this is invasive and patients generally dislike this means of assessing residual urine.

Multichannel cystometry¹

• Simultaneous measurement of bladder pressure and flow rate allows the best assessment of the presence or absence of bladder outlet obstruction.
• Simultaneous imaging using transrectal ultrasonography (videourodynamics) can accurately localise the site of bladder outlet obstruction to the bladder neck, prostate or the urethra.⁷
• Cystometry provides information regarding the function of the lower urinary tract during both the storage and voiding phases of the bladder cycle and often supports a definitive diagnosis for LUTS.
• Cystometry can help inform decisions about future management, including possible surgery for bladder outlet obstruction or detrusor overactivity, and neurological lower urinary tract dysfunction.
• Multichannel cystometry may also help to characterise bladder compliance, sensation and capacity.

Leak point pressure

• While the bladder is being filled during cystometry, it may suddenly contract and squeeze some water out without warning. The manometer records the pressure at the point when the leakage occurred.
• The patient may also be asked to apply abdominal pressure to the bladder by coughing, shifting position, or trying a Valsalva manoeuvre. These actions help to evaluate the sphincter muscles.

Urethral pressure profilometry is also used to assess urethral function.⁶ However, it is not clear whether leak point pressure measurement or urethral pressure profilometry can accurately predict which patients will achieve the best outcome of surgical treatment for urinary stress incontinence.⁸

Pressure flow study

• After cystometry, the patient is asked to empty the bladder. The catheter can measure the bladder pressures required to urinate and the flow rate that a given pressure generates.
• This pressure flow study helps to identify bladder outlet obstruction that men may experience with prostate enlargement.
• Bladder outlet obstruction is less common in women but may occur as a result of genital prolapse or after a surgical procedure for urinary incontinence.

Ambulatory urodynamics

Ambulatory urodynamics can provide objective evidence of clinically important bladder overactivity in women with symptoms suggestive of bladder overactivity.⁹

• Urine is initially passed into a special toilet which records the volume of urine passed and the urine flow rate.
• An ultrasound scan can then check whether the bladder has been emptied.
• Two fine tubes are then passed, one into the bladder to measure pressures within the bladder, and one into the rectum to measure abdominal pressure.
• An electronic continence pad is worn to record any leaks of urine.
• The patient is then asked to get dressed, walk around and eat, drink and go to the toilet normally.
• The test should be continued until the patient has passed urine on at least two occasions and the patient is asked to record when they passed urine and when they experienced any symptoms such as urgency (and what they were doing at the time).

Electromyography

• This measures the muscle activity in and around the urethral sphincter by using sensors which are placed on the skin near the urethra and rectum or placed on a urethral or rectal catheter.
• Muscle activity is recorded and the patterns of the impulses demonstrate whether the muscles of the bladder neck are functioning properly.
• However, problems with isolating the real signal from artefacts and the doubtful existence of electromyographic activity during cholinergic muscle contraction have limited the use of lower urinary tract electromyography.¹⁰

Document references

1. Lower urinary tract symptoms, NICE Clinical Guideline (May 2010); The management of lower urinary tract symptoms in men
2. Bradley CS, Smith KE, Kreder KJ; Urodynamic evaluation of the bladder and pelvic floor. Gastroenterol Clin North Am. 2008 Sep;37(3):539-52, vii. [abstract]
3. Guidelines on Urinary Incontinence, European Association of Urology (2010)
4. Management of urinary incontinence in primary care, Scottish Intercollegiate Guidelines Network - SIGN (2005)
5. International Continence Society; Dynamic Testing.
6. Urinary incontinence: the management of urinary incontinence in women, NICE (2006)
7. Tosaka A, Murota-Kawano A, Ando M; Video urodynamics using transrectal ultrasonography for lower urinary tract Neurourol Urodyn. 2003;22(1):33-9. [abstract]
8. Lemack GE; Urodynamic assessment of patients with stress incontinence: how effective are Curr Opin Urol. 2004 Nov;14(6):307-11. [abstract]
9. Radley SC, Rosario DJ, Chapple CR, et al; Conventional and ambulatory urodynamic findings in women with symptoms suggestive J Urol. 2001 Dec;166(6):2253-8. [abstract]
10. Ballaro A; The elusive electromyogram in the overactive bladder: a spark of understanding. Ann R Coll Surg Engl. 2008 Jul;90(5):362-7. [abstract]