Urodynamic Study

What is a urodynamic study?
Your health care provider has ordered a urodynamic study, which is a group of tests that show how your lower urinary tract is working. Your lower urinary tract includes the bladder, which stores urine, and the urethra, which is the tube that carries urine from your bladder out of your body.

How does the urinary tract work?
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. The bladder stores urine until you are ready to empty it. It swells into a round shape when it is full and gets smaller as it empties. A healthy bladder can hold up to 16 ounces (2 cups) of urine comfortably. How frequently it fills depends on how much excess water your body is trying to get rid of.

The bladder opens into the urethra, the tube that allows urine to pass outside 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 tell you when it is time to empty your bladder. When the bladder begins to fill with urine, you may notice a feeling that you need to urinate. The sensation becomes stronger as the bladder continues to fill and reaches its limit. At that point, nerves in the bladder send a message to the brain, and your urge to urinate intensifies.

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, thus allowing urine to flow through the urethra. When these signals occur in the correct order, normal urination occurs.

Why do I need a urodynamic study?
Problems in the urinary system can be caused by aging, illness, or injury. The muscles in and around your bladder and urethra tend to become weaker with age. Weak bladder muscles may result in your not being able to empty your bladder completely, leaving you at a higher risk for urinary tract infections. Weak muscles of the sphincter 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.

A urodynamic study assesses how the bladder and urethra are performing their job of storing and releasing urine. Urodynamic tests help your doctor or nurse see how well your bladder and sphincter muscles work and can help explain symptoms such as

• Incontinence
• Frequent urination
• Sudden, strong urges to urinate
• Problems starting a urine stream
• Painful urination
• Problems emptying your bladder completely
• Recurrent urinary tract infections

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. Urodynamic tests can range from simple observation to precise measurement using sophisticated instruments.

Amount of urine and rate of flow. 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.

Your doctor or nurse can also get some idea of your bladder function by using a stopwatch to time you as you urinate into a graduated container.

How much urine the bladder can hold. 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. Filling your bladder should not hurt.

Bladder pressure measurement. 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.

X-rays and video. 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.

When will I get results from my tests?
Results for simple tests can be discussed with your doctor or nurse 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

This material is for educational purposes only and should in no way be taken to be the practice or provision of medical, nursing, or professional healthcare advice or services. The information should not be used in place of a visit, call, consultation, or advice of your physician, nurse, or other health care provider. The information obtained herein is not exhaustive and does not cover all aspects of the specific disease, ailment, physical condition, or their treatments. Should you have any health care related questions, please call or see your physician, nurse or other health care provider promptly.

Source: National Kidney and Urologic Diseases Information Clearinghouse, a service of the National Institutes of Health

7/2008