Cystometric study measures the amount of fluid in the bladder when you first feel the need to urinate, when you are able to sense fullness, and when your bladder is completely full.

CMG; Cystometrogram

You will be asked to urinate (void). The following will be recorded:

• The time it takes you to begin urinating
• The size, force, and continuity of your urinary stream
• The amount of urine
• How long it took you to empty your bladder
• Any straining, hesitancy, or dribbling that occurred

You lie down, and a thin, flexible tube (catheter) is gently placed in your bladder. The catheter measures any urine left in the bladder. A smaller catheter is then placed in your rectum. Measuring electrodes are placed near the rectum.

Next, heat sensation is measured. Room-temperature salt-water (saline) solution is placed into the bladder. This is followed by warm water. You will tell the health care provider what, if any, sensations you feel. The water is then drained from the bladder.

A tube used to monitor bladder pressure (cystometer) is attached to the catheter. Water or carbon dioxide gas flows into the bladder at a controlled rate. You will be asked to tell the health care provider when you first feel the need to urinate.

You may be asked to cough or push so that the health care provider can check for urine leakage. When your bladder is full, you will be told to urinate. The pressure of your urine flow will be recorded.

Your bladder is again drained of any urine or water, and the catheter is removed.

In some cases, x-rays are taken during the test. This is called videourodynamics.

No special preparations are needed for this test.

For infants and children, preparation depends on the child's age, past experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:

• Preschooler test or procedure preparation (3 to 6 years)
• School age test or procedure preparation (6 to 12 years)
• Adolescent test or procedure preparation (12 to 18 years)

There is some discomfort associated with this test. You may experience:

• Bladder filling
• Flushing
• Nausea
• Pain
• Sweating
• Urgent need to urinate

The test will help determine the cause of bladder voiding dysfunction.

Normal values vary and should be discussed with your health care provider.

Abnormal results may be due to:

• Enlarged prostate
• Multiple sclerosis
• Overactive bladder
• Reduced bladder capacity
• Spinal cord injury
• Stroke
• Urinary tract infection

There is a slight risk of urinary tract infection and blood in the urine.

This test should not be done if you have a known urinary tract infection. Existing infection increases the possibility of false test results. The test itself increases the possibility of spreading the infection.

Nitti V. Urodynamic and videourodynamic evaluation of voiding dysfunction. In: Wein AJ, ed. Campbell-Walsh Urology. 10th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 62.

Lentz GM. Urogynecology: Physiology of micturition, voiding dysfunction, urinary incontinence, urinary tract infections and painful bladder syndrome. In: Lentz GM, Lobo RA, Gershenson DM, Katz VL, eds. Comprehensive Gynecology. 6th ed. Philadelphia, Pa: Mosby Elsevier; 2012:chap 21.