Urodynamics is a study that assesses how well the bladder and urethra are storing and releasing urine. If you have a problem with urine leakage or blocked urine flow, one of the tools your doctor may use to evaluate the cause of your symptoms is urodynamic testing.
Urodynamic tests help your doctor to see how well your bladder and sphincter muscles work. Urodynamic tests can range from simple observation to precise measurement using sophisticated instruments.
- Uroflowmetry: An uroflowmeter automatically measures the amount of urine and the flow rate. 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 your doctor 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.
- Postvoid Residual Measurement: After you have finished urinating, you may still have some urine, usually only an ounce or two, remaining in your bladder. To measure this postvoid residual, the doctor may use a catheter, a thin tube that can be gently glided into the urethra. Your doctor 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.
- Cystometric Test: 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. During the test a catheter is used to empty your bladder completely and 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 to see if the bladder pressure changes. With this test involuntary bladder contractions can also be identified.
- Leak Point Pressure Measurement: 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 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: If your doctor feels 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.
- 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. The pictures and videos show the size and shape of the urinary tract and help your doctor understand your problem.
Following urodynamics a small number of patients may experience minor problems such as passing urine more often, traces of blood in the urine, and mild discomfort when you urinate. All these symptoms are temporary and should go away quickly. Your doctor may prescribe an antibiotic to take for a few days to prevent an infection depending on the type of urodynamic testing you had.
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