Urodynamic testing is used to evaluate problems with urine leakage (incontinence) or blocked urine flow. Urodynamics assess how the bladder and urethra are performing their job of storing and releasing urine. The results can help determine the possible cause and treatment options.
Urinary problems can result from an underlying medical disorder or injury. However, urinary blockage or incontinence often occurs as a result of normal aging. The muscles in and around the bladder and urethra tend to become weaker with age. Weak bladder muscles result in incomplete emptying of the bladder. This leaves residual urine in the bladder so that it fills up again more quickly. Weak muscles of the sphincters and pelvis can lead to urinary incontinence because the sphincter muscles cannot remain tight enough to hold in the urine. Sometimes problems results from weakening of the pelvic muscle and a shift in the position of the bladder.
The Normal Functioning Urinary System
The urinary system involves the coordinated effort of several organs, muscles and nerves to collect, store and release 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, urinary infections (UTIs) and kidney damage can occur.
The bladder is like a balloon lined with muscle designed to store urine until you are ready to urinate. It is held in place by ligaments.A healthy bladder can hold up to 16 ounces (2 cups) of urine comfortably. How frequently it fills up during the day depends on how much excess water your body needs to eliminate.
The urethra is a tube that allows urine to pass from the bladder to the outside. Circular muscles called sphincters normally keep urine from leaking. The involuntary leakage of urine is called incontinence.
Nerves in the bladder inform the body when it is time to urinate. The sense of fullness and desire to urinate increase as the bladder fills up and the messages from the nerves grows stronger. When you are ready to urinate, the brain signals the sphincter muscles to relax. At the same time, the brain signals the bladder muscles to squeeze. Normal urination occurs when the opening of the sphincter muscles is coordinated with the squeezing of the bladder.
Urodynamic tests help your doctor or nurse see how well your bladder and sphincter muscles work and can help explain symptoms such as:
- frequent urination
- sudden, strong urges to urinate
- problems starting a urine stream
- painful urination
- problems emptying your bladder completely
- recurrent urinary tract infections
Medical History and Physical Exam
Your health care provider will ask you about your fluid intake, diet and urinary habits, including how much fluid you drink a day and whether you use alcohol or caffeine. You may also be asked about medications you take that might be helping or worsening symptoms.
A physical exam will evaluate the nerves in the lower part of your body. A pelvic exam of women may be performed to assess the pelvic muscles and the other pelvic organs. A rectal exam of men may be performed to assess the prostate.
Urinalysis may be performed to check for signs of infection or blood.
You may be asked to keep a voiding diary, which is a record of fluid intake and trips to the bathroom, plus any episodes of leakage.
You may be asked you to do a pad test. The pad test is a simple way to measure how much urine leaks out. You will be given a number of absorbent pads and plastic bags of a standard weight. You will be told to wear the pad for 1 or 2 hours while in the clinic or to wear a series of pads at home during a specific period of time. The pads are collected and sealed in a plastic bag. Your health care team will then weigh the bags to see how much urine has been caught in the pad. A simpler but less precise method is to change pads as often as you need to and keep track of how many pads you use in a day.
Preparing for a Urodynamic Test
Any procedure designed to provide information about a bladder problem can be called a urodynamic test. The type of test you take depends on your problem.
These tests may be as simple as urinating behind a curtain while a doctor or nurse listens. More complex tests involve imaging equipment that films urination and pressure monitors that record the pressures of the bladder and urethra.
Depending on the test, you may be asked to come with a full bladder or an empty one. Also, ask whether you should change your diet or skip your regular medicines and for how long.
Most urodynamic testing focuses on the bladder’s ability to empty steadily and completely. It can also show whether the bladder is having abnormal contractions that cause leakage. Your doctor will want to know whether you have difficulty starting a urine stream, how hard you have to strain to maintain it, whether the stream is interrupted, and whether any urine is left in your bladder when you are done. The remaining urine is called the postvoid residual.
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 so the doctor or nurse can see 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 postvoid residual
After you have finished, you may still have some urine, usually only an ounce or two, remaining in your bladder. To measure this postvoid residual, the doctor or nurse may use a catheter, a thin tube that can be gently glided into the urethra. He or she can also measure the postvoid residual with ultrasound equipment that uses harmless sound waves to create a picture of the bladder.
A postvoid residual of more than 200 mL, about half a pint, is a clear sign of a problem. Even 100 mL, about half a cup, requires further evaluation. However, the amount of postvoid 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. The doctor or nurse will use a catheter to empty your bladder completely. Then a special, smaller catheter will be placed in the bladder. This catheter has a pressure-measuring device called a manometer. Another catheter may be placed in the rectum to record pressure there as well. Your bladder will be filled slowly with warm water. During this time you will be asked how your bladder feels and when you feel the need to urinate. The volume of water and the bladder pressure will be recorded. You may be asked to cough or strain during this procedure. Involuntary 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 manometer will record the pressure at the point when the leakage occurred. 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. These actions help the doctor or nurse evaluate your sphincter muscles.
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 men may experience with prostate enlargement. Bladder outlet obstruction is less common in women but can occur with a fallen bladder or rarely after a surgical procedure for urinary incontinence. Most catheters can be used for both CMG and pressure flow studies.
Electromyography (measurement of nerve impulses)
If your doctor or nurse thinks that your urinary problem is related to nerve or muscle damage, you may be given an electromyography. This test measures the muscle activity in and around the urethral sphincter by using special sensors. The sensors are placed on the skin near the urethra and rectum or they are located on the urethral or rectal catheter. Muscle activity is recorded on a machine. The patterns of the impulses will show whether the messages sent to the bladder and urethra are coordinated correctly.
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. The pictures and videos show the size and shape of the urinary tract and help your doctor or nurse understand your problem.