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Urology Care Foundation The Official Foundation of the American Urological Association


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Get the facts. And the help you need.


Urodynamics is a group of tests that allow your health care provider to look at how your lower urinary tract works. Your lower urinary tract includes the bladder (which stores urine) and the urethra (which is the tube that carries urine from your bladder to the outside). This is the only form of testing we have to look at the function of the lower urinary tract.

How does the lower urinary tract work?

The bladder's responsibility is to store and empty your urine. The bladder is made up of muscle that should work to store and empty urine in a way that keeps urine from backing up into the kidneys. As the kidneys fill the bladder, the urine is stored there. The bladder muscle (called the detrusor muscle) should stretch easily to allow the bladder to fill. The sphincter muscles at the bottom of the bladder should be tight and not let the urine leak out. Urine can leak out for several reasons. Sometimes it is because the sphincter muscles are weak or because the bladder muscle is overactive.

When the bladder is full, a message is sent to the brain that it is time for you to empty your bladder. Your bladder muscle then squeezes while the sphincter muscles and pelvic floor muscles relax and let the urine out. Sometimes a blockage in the urethra can cause the urine flow to be weak. Different things, such as an enlarged prostate or a bladder that has dropped in women, can cause this.

After your bladder empties, your sphincter muscles tighten up again so that the urine stays in the bladder.

Why would I need urodynamics?

After your health care provider has spent some time going over your symptoms and complaints, performed a physical exam and possibly done some simple urine tests, he or she may feel the puzzle isn’t complete and may order urodynamics. Urodynamics helps identify specific problems related to:

  • Controlling your urine
  • Not emptying your bladder completely
  • Feeling of frequent and/or urgent need to urinate
  • Weak or intermittent (stopping and starting) urine flow
  • Frequent urinary tract infections

What is urodynamics?

There are several pieces that make up urodynamics. Patients should come for the test with a full bladder (if possible). You will be asked to urinate into a special commode chair or funnel. This will measure how much urine comes out and how fast it comes out. The test is called a uroflow.

Next, a catheter (a small soft tube) will be placed into your bladder to drain out all the leftover urine. This will show how well your bladder emptied. Through a catheter, your bladder will be filled and the pressure of your bladder muscle and its response to being filled will be measured. At the same time, an estimate of the pressures outside the bladder will be measured by inserting another small soft tube, or catheter, into the rectum or the vagina. This tube is about the size of a spaghetti noodle and doesn’t do anything except measure pressure. The measurement of these pressures during filling is called a Cystometrogram (or CMG).

As the bladder fills, the different pressure measurements will be recorded and you will be asked questions about the way your bladder feels as it is filling. Your bladder will be filled with either a sterile water type fluid or a fluid that can be seen on x-ray. Filling your bladder should not hurt. You may also be asked to cough and push or bear down to check for any leakage.

Small sticky patches are often placed on either side of the bottom to measure the electrical activity of certain muscles. This is called an Electromyogram (or EMG).

When you feel your bladder is full, you will be asked to empty your bladder into the special commode again. This time you will urinate with the tubes in place. The tubes are specially designed to let the fluid come out around them. This lets us look at the function of your bladder as it empties. This is called a Voiding Pressure Study or a Pressure Flow Study.

Other things that might happen during urodynamics include:

  • X-ray pictures may be taken with any or all parts of these tests.
  • The catheter might be moved back and forth in the urethra or urine channel to get more information about the outlet. This is called a Urethral Pressure Profile (or UPP)
  • Before and/or after your test you may receive an antibiotic as a precaution to prevent infection.

In closing

After your urodynamics are completed, your health care provider will review all the information and discuss the results with you. Then you and your health care provider will decide on the best plan of treatment for you.

Reviewed: January 2011

Last updated: June 2014

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Urodynamics Glossary
  • antibiotic: Drug that kills bacteria or prevents them from multiplying.

  • bladder: The bladder is a thick muscular balloon-shaped pouch in which urine is stored before being discharged through the urethra.

  • catheter: A thin tube that is inserted through the urethra into the bladder to allow urine to drain or for performance of a procedure or test, such as insertion of a substance during a bladder X-ray.

  • CMG: Also known as a cystometrogram. This is a test used to evaluate the bladder's ability to store and release urine. It uses a device to pump water into the bladder. The device then measures the amount of fluid that goes into the bladder when you first feel the desire to void, when you are able to sense fullness, and when your bladder is completely full.

  • detrusor muscle: Contracting muscle in the bladder that helps to expel urine.

  • infection: A condition resulting from the presence of bacteria or other microorganisms.

  • ions: Electrically charged atoms.

  • kidney: One of two bean-shaped organs that filter wastes from the blood and discharge these waste products in urine. The kidneys are located on either side at the level of the 12th ribs toward the back. The kidneys send urine to the bladder through tubes called ureters.

  • kidneys: One of two bean-shaped organs that filter wastes from the blood and discharge these waste products in urine. The kidneys are located on either side at the level of the 12th ribs toward the back. The kidneys send urine to the bladder through tubes called ureters.

  • pelvic: Relating to, involving or located in or near the pelvis.

  • pelvic floor muscles: The hammock or sling of muscles in the pelvic floor that normally assists in maintaining continence by supporting the pelvic organs (bladder, uterus and rectum).

  • prostate: A walnut-shaped gland in men that surrounds the urethra at the neck of the bladder. The prostate supplies fluid that goes into semen.

  • pus: The yellowish or greenish fluid that forms at sites of infection.

  • rectum: The lower part of the large intestine, ending in the anal opening.

  • sphincter: A round muscle that opens and closes to let fluid or other matter pass into or out of an organ. Sphincter muscles keep the bladder closed until it is time to urinate.

  • sphincter muscle: Circular muscle that helps keep urine from leaking by closing tightly like a rubber band around the opening of the bladder.

  • sterile: Incapable of becoming pregnant or inducing pregnancy.Can also mean free from living germs or microorganisms.

  • urethra: A tube that carries urine from the bladder to the outside of the body. In males, the urethra serves as the channel through which semen is ejaculated and it extends from the bladder to the tip of the penis. In females, the urethra is much shorter than in males.

  • urge: Strong desire to urinate.

  • urinary: Relating to urine.

  • urinary tract: The system that takes wastes from the blood and carries them out of the body in the form of urine. Passageway from the kidneys to the ureters, bladder and urethra.

  • urinary tract infection: Also referred to as UTI. An illness caused by harmful bacteria, viruses or yeast growing in the urinary tract.

  • urinate: To release urine from the bladder to the outside. Also referred to as void.

  • urine: Liquid waste product filtered from the blood by the kidneys, stored in the bladder and expelled from the body through the urethra by the act of urinating (voiding). About 96 percent of which is water and the rest waste products.

  • vagina: The tube in a woman's body that runs beside the urethra and connects the uterus (womb)to the outside of the body. Sometimes called the birth canal. Sexual intercourse, the outflow of blood during menstruation and the birth of a baby all take place through the vagina.

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