Urology - Oncology, Laparoscopy, General Urology Mischel Neill - BHB MBCHB FRACS - Urology - Oncology, Laparoscopy, General Urology Urology - Oncology, Laparoscopy, General Urology
Patient Info


Cystoscopy :: Digital Rectal Examn ::  Pathology PSA
Radiology :: Urodynamics :: TRUS


Urodynamic testing may be indicated for a problem with urine leakage, blocked urine flow or other urinary difficulties. It differs from a simple urine flow rate and is usually reserved for the investigation of complex urinary problems and in some circumstances prior to surgery.

Several muscles, organs, and nerves are involved in collecting, storing, and releasing urine. The kidneys form urine by filtering wastes and extra water from the bloodstream. The ureters are tubes that carry urine from the kidneys to the bladder. Normally urine flows in one direction. If urine backs up toward the kidneys, infections and kidney damage can occur.

The bladder, a hollow muscular organ shaped like a balloon, sits in the pelvis and is held in place by ligaments attached to other organs and to the pelvic bones. A healthy bladder can hold 400-500mL of urine comfortably. How frequently it fills depends on how much excess water the kidneys are trying to get rid of.
The bladder opens into the urethra, the tube that drains urine out of the body. Circular muscles called sphincters close tightly to keep urine from leaking. The involuntary leakage of urine is called incontinence.

Nerves in the bladder sense when the bladder is filling and send messages to the brain that are translated into a need to urinate. The sensation becomes stronger as the bladder continues to fill and reaches its limit.

When a person is ready to urinate, their brain signals the sphincter muscles to relax. At the same time, the brain signals the bladder muscles to squeeze, allowing urine to flow through the urethra. When these signals happen in the correct order, normal urination occurs.

Problems of the urinary system can be caused by aging, drugs, illness, or injury. The muscles in and around the bladder and urethra tend to become weaker with age. Weak bladder muscles may result in being unable to empty the bladder completely. Weak muscles of the sphincters and pelvis can lead to urinary incontinence because the sphincter muscles cannot remain tight enough to hold urine in the bladder, or the bladder does not have enough support from the pelvic muscles to stay in its proper position.

Urodynamics is a study that assesses how the bladder and urethra are performing their job of storing and releasing urine. Urodynamic tests assess bladder and sphincter muscle function and can help explain symptoms such as

  • Incontinence
  • Frequent urination
  • Sudden, strong urges to urinate
  • Problems starting a urine stream
  • Painful urination
  • Problems emptying the bladder

Part of the assessment requires you to keep a voiding diary, which is a record of fluid intake (how much fluid you drink a day and whether you use alcohol or caffeine) and trips to the bathroom, plus any episodes of leakage.

A physical exam will also be performed to rule out other causes of urinary problems. This exam may include an assessment of the nerves in the lower part of the body. It will also include a pelvic exam in women to assess the pelvic muscles and the other pelvic organs. In men, a rectal exam may be undertaken to assess the prostate.

Preparing for the Test

Usually no special preparations are needed, however you should come with a comfortably full bladder. Some medications should be discontinued beforehand but this will be discussed in the outpatient clinic when deciding whether to undertake the test.

Taking the Test

Urodynamic testing assesses the bladder’s ability to fill without unwanted contractions and to empty steadily and completely. It can also show whether the bladder is having abnormal contractions that cause leakage.

Uroflowmetry (Measurement of Urine Speed and Volume)

A uroflowmeter automatically measures the amount of urine and the flow rate—that is, how fast the urine comes out. You may be asked to urinate privately into a toilet that contains a collection device and scale. This equipment creates a graph that shows changes in flow rate from second to second, the peak flow rate and how many seconds it took to get there. Results of this test will be abnormal if the bladder muscle is weak or urine flow is obstructed.

Measurement of Post Void Residual

After you have finished, you may still have some urine remaining in your bladder, known as the post void residual (PVR). This can be measured by passing a catheter, a thin tube inserted through the urethra, or with ultrasound equipment that uses sound waves to create a picture of the bladder. A post void residual of more than 200 mL, about half a pint, may indicate a problem. However, the amount of post void residual can be different each time you urinate.

Cystometry (Measurement of Bladder Pressure)

A cystometrogram (CMG) measures how much your bladder can hold, how much pressure builds up inside your bladder as it stores urine, and how full it is when you feel the urge to urinate.

A catheter is passed to empty the bladder completely, along with a smaller catheter to measure pressure inside the bladder. Another catheter may be placed in the rectum to record pressure there as well. The bladder will be filled slowly with warm water. The volume of water and the bladder pressure will be recorded. You may be asked to cough or strain during this procedure. Unwanted bladder contractions can be identified.

Measurement of Leak Point Pressure

While your bladder is being filled for the CMG, it may suddenly contract and squeeze some water out without warning, the pressure at the point when the leakage occurs is noted. This reading may provide information about the kind of bladder problem you have. You may also be asked to apply abdominal pressure to the bladder by coughing, shifting position, or trying to exhale while holding your nose and mouth.

Pressure Flow Study

After the CMG, you will be asked to empty your bladder. The catheter can measure the bladder pressures required to urinate and the flow rate a given pressure generates. This pressure flow study helps to identify bladder outlet obstruction that, for example, men may experience with prostate enlargement. Bladder outlet obstruction is less common in women but can occur with a prolapse or rarely after a surgical procedure for urinary incontinence. Most catheters can be used for both CMG and pressure flow studies and don’t need to be changed in between stages of the urodynamic test.

Video Urodynamics

Urodynamic tests may be performed with or without equipment to take pictures of the bladder during filling and emptying. The imaging equipment may use x rays or sound waves. If x-ray equipment is used, the bladder will be filled with a contrast medium that will show up on the x ray instead of the warm water, to show the size and shape of the urinary tract.

After the Test

You may have mild discomfort for a few hours after these tests when you urinate. Drinking a glass of water each half-hour for 2 hours should help. Ural or citravescent sachets are available over the counter at the chemist, to be mixed into a drink. They work by removing the acid from the urine to help make passing it more comfortable.

A single dose of an antibiotic is given routinely to prevent an infection. Some pre-existing medical problems may require more antibiotic treatment. If you develop signs of infection—including pain, chills, or fever—further antibiotics may be necessary.

Getting the Results

Results for simple tests will be discussed immediately after the test. Results of other tests may take a few days. You will have the chance to ask questions about the results and possible treatments for your problem.

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Urology - Oncology, Laparoscopy, General Urology Mischel Neill - BHB MBCHB FRACS Royal Australasian College of Surgeons Urological Society of Australia and New Zealand