The bladder, a hollow muscular organ shaped like a sac located in the human pelvis near the uterus (female) or the prostate (male). 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.

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 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 help your doctor or nurse see how well your bladder and sphincter muscles work and can help explain symptoms such as

These tests may be as simple as urinating behind a curtain while a doctor or nurse listens or more complicated, involving imaging equipment that films urination and pressure monitors that record the pressures of the bladder and urethra.

The first step in evaluating a urination problem is to tell your doctor exactly what your symptoms are. The doctor will find out important information such as when your symptoms started, if they are constant, what causes them, when they occur, if you have leakage etc.

If leakage is the problem, the doctor or nurse may ask you to do a pad test. This 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.

A physical exam will also be performed to rule out other causes of urinary problems. This exam usually includes an assessment of the nerves in the lower part of your 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 is given to assess the prostate. Your doctor will also want to check your urine for evidence of infection or blood.

If the doctor or nurse recommends bladder testing, usually no special preparations are needed, but make sure you understand the instructions you are given. It is not necessary to fast prior to the test.You will be asked to come with a full bladder in order perform a flow rate (uroflownetry). You may continue to take all your medications, unless asked otherwise.

Be as calm and cooperative as you can. The specific technique used may depend on your problem. Most urodynamic testing focuses on the bladder’s ability to store fluid at steady and low pressureand empty completely whithout excessive bladder pressure. 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. Urodynamic tests can range from simple observation to precise measurement using sophisticated instruments.

A uroflowmeter automatically measures the amount of urine and the flow rate—that is, how fast the urine comes out of the baldder. 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 blocked.

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, may indicate a problem. Even 3 ounces, about half a cup, requires further evaluation. However, the amount of postvoid residual can be different each time you urinate.

A cystometrogram (CMG) measures how much fluidyour bladder can hold, how much pressure builds up inside your bladder as thefluid idis being infused. We will use a tiny catheter to empty your bladder completely prior to the beginning of the study. Then a special small (spaghetti size) catheter with multiple lumenwill be placed in the bladder. This catheter has a pressure-measuring device called a manometer. Another catheter willbe placed in the rectum to record rectal pressure.. Your bladder will be filled slowly with warm saline. During this time you will be asked how your bladder feels and when you feel the need to urinate. The volume offluid and the bladder pressure will be recorded by a computerized system. You may be asked to cough or strain during this procedure. Involuntary bladder contractions may be noted by the computerized tracings. If you are unable to urinate with the catheter in the urethra, youmay be asked to void without the catheter or in the restroom. This does not mean thatyou “failed” the test.

After the test you may resume your normal activity. It is normal to feel some burning during voiding after the test or experience some mild urethral bleeding or bloody urine. Call your doctor if you experience fever, inability to urinate, or very grossly bloody urine. Your doctor will give you an appointment to discuss the resultsafter the examination with you. The results of the test are often very useful in the long-term management of your urination problem.