Urodynamic Testing

If you have a problem with urine leakage or blocked urine flow, your doctor or nurse can help.

One of the first steps may be urodynamic testing to find

precisely what the problem is.

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. Normal urine flow is one way. If urine

backs up toward the kidneys, infections are more likely.

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 for 2 to 5 hours.

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 tighten, squeezing urine out. Urine can then leave

the bladder 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 your

ureters, bladder, and urethra tend to become weaker with age. You may have more urinary

infections because your bladder muscles have weakened and cannot empty your bladder

completely. Also, weakening in the muscles of the sphincters and the pelvis can cause

incontinence because the sphincter cannot remain tight enough to hold urine in the bladder or

does not have enough support from the pelvic muscles.

Urodynamics is the study of how the body stores and releases 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

Urinary tract

• problems starting a urine stream

• painful urination

• problems emptying your bladder completely

• recurrent urinary tract infections

These tests may involve imaging equipment that films urination or may be as simple as urinating

behind a curtain while a doctor or nurse listens.

Seeing Your Doctor or Nurse

The first step in solving a urinary problem is to talk to your doctor or nurse. He or she should ask

you about your general medical history, including any major illnesses or surgeries. You should

talk about the medicines you take, both prescription and nonprescription, because they might be

part of the problem. You should talk about how much fluid you drink a day and whether you use

alcohol or caffeine. Give as many details as you can about the problem and when it started. The

doctor or nurse may ask you to keep a voiding diary, which is a record of fluid intake and trips to

the bathroom, plus any episodes of leakage.

If leakage is the problem, a pad test is a simple way to measure how much urine seeps 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 and then seal it in a 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, such as

weakening pelvic muscles or prostate enlargement.

Preparing for the Test

If the doctor or nurse recommends bladder testing, usually no special preparations are needed,

but make sure you understand any instructions you do receive. 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.

Taking the 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.

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 (postvoid residual). Urodynamic tests can range from simple

observation to precise measurement using sophisticated instruments.

Uroflowmetry (Measurement of Urine Speed and Volume)

A uroflowmeter automatically measures the amount of

urine and the flow rate (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. The volume of urine is

divided by the time to see what your average flow rate is.

For example, 330 milliliters (mL) of urine in 30 seconds means that your average flow rate is 11

mL per second.

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 remove it with a

catheter, a thin tube that can be gently glided into the urethra. Ultrasound equipment that uses

harmless sound waves to create a picture of the bladder can also be used. 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 with a pressure-measuring tube called a

cystometer will be used to fill your bladder slowly with warm

water. Another catheter may be placed in the rectum to

record pressure there as well. 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 cystometer 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 try to exhale while holding your nose and mouth to apply

Uroflowmeter equipment

Cystometry in a female patient

abdominal pressure to the bladder or cough or shift positions. 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 so that the catheter can measure the

pressures required to urinate. 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. Some 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 damage, you may be

given an electromyography. This test measures the muscle activity in the urethral sphincter

using sensors placed on the skin near the urethra and rectum. Sometimes the sensors are 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 liquid used to fill the bladder may be a contrast medium that will show up

on the x ray. The pictures and videos show the size and shape of the urinary tract and help your

doctor or nurse understand your problem.

After the Test

You may have mild discomfort for a few hours after these tests. Drinking two 8-ounce glasses of

water each hour for 2 hours should help. Ask your doctor whether you can take a warm bath. If

not, you may be able to hold a warm, damp washcloth over the urethral opening to relieve the

discomfort.

Your doctor may give you an antibiotic to take for 1 or 2 days to prevent an infection. If you have

signs of infection—including pain, chills, or fever—call your doctor at once.

Getting the Results

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.