Cystometry is a test of bladder function in which pressure and volume of fluid in the bladder is measured during filling, storage, and voiding.
A cystometry study is performed to diagnose problems with urination, including incontinence, urinary retention, and recurrent urinary tract infections. The urinary bladder stores urine produced by the kidneys. The main muscle of the bladder wall, the detrusor, relaxes to allow expansion of the bladder during filling. The urethra, the tube through which urine exits, is held closed by a ring of muscle known as the urethral sphincter. As volume increases, stretching of the detrusor and pressure on the sphincter sends signals to the brain, indicating the need for urination, or voiding. Voluntary relaxation of the sphincter and automatic contractions of the detrusor allow successful and virtually complete voiding.
Urinary difficulties may occur because of weak or hyperactive sphincter or detrusor, or non-coordination of their two activities. Infection of the bladder or urethra may cause incontinence, as can obstruction of the urethra from scar tissue, prostate enlargement, or other benign or cancerous growths. Loss of sensation due to nerve damage can lead to chronic overfilling.
The mild irritation of the urinary tract necessary for insertion of the catheter may occasionally cause flushing, sweating, and nausea. Cystometry is contraindicated in patients with urinary tract infection because of the potential for false results and the possibility of exacerbating the infection.
The patient begins by emptying the bladder as much as possible. A thin plastic catheter is then gently inserted into the urethra until it reaches the bladder. Measurements are taken of the residual urine volume and bladder pressure. Pressure measurements may require a rectal probe to account for the contribution of the abdominal muscles to the pressure recording.
The bladder is then gradually filled with either warm water, room temperature water, saline solution, carbon dioxide gas, or a contrast solution for x-ray analysis, depending on the type of study being done. The patient is asked to describe sensations during filling, including temperature sensations and when the first feeling of bladder fullness occurs. Once the bladder has completely filled, the patient is asked to begin voiding, and pressure and volume measurements are again taken, as well as flow rate. It is important to instruct the patient not to strain while voiding during the test. Straining can alter the test results.
There are no special food or fluid restrictions needed to prepare for this test. The patient may be asked to stop taking certain medications in advance of the test, including sedatives, cholinergics, and anticholinergics.
Cystometry may be somewhat uncomfortable. Urinary frequency or urgency and some hematuria (reddish urine), may last for a day. Increasing fluid intake helps to flush out the bladder. Caffeinated, carbonated, or alcoholic beverages are discouraged, because they may irritate the bladder lining. A warm bath or sitz bath may be recommended to soothe the patient.
There is a risk of upper or lower urinary infection due to tearing of the urethral lining. Although extremely rare, in some male patients, infection of the epididymis (tubules at the back of the testis) can occur and lead to infertility. Damage to the urethra or bladder sometimes occurs but usually heals without treatment. Rarely an allergic reaction may occur due to the contrast dye or medications.
Patients should notify their health care provider if they develop any of these symptoms:
- blood in the urine beyond several voidings
- fever or chills
- lower back pain
The normal bladder should not begin contractions during filling and should initially expand without resistance. A feeling of fullness occurs with a volume of 100-200 ml. Adult bladder capacity varies dependent on gender. Normal adult female bladder capacity ranges between 250 to 550 ml, and normal adult male capacity ranges from 350 to 750 ml. The sphincter should relax and open when the patient wills it, accompanied by detrusor contractions. During voiding, detrusor contraction should be smooth and lead to a steady urine stream.
Inability of the bladder to relax during filling, or low bladder volume, may indicate interstitial cystitis, prostate enlargement, or bladder cancer. Contraction of the bladder during filling may be due to irritation from infection or cysts, obstruction of the bladder outlet, or neurological disease such as stroke, multiple sclerosis, or spinal cord injury. Diminished sensation may occur with nerve lesions, peripheral neuropathy, or chronic overfilling.
Health care team roles
A cystometry may be performed in the hospital, doctor's office, or outpatient facility by a physician or nurse.
Anticholinergics— Drugs that prevent the action of acetylcholine, a compound released by nerve endings.
Cholinergics— Drugs that mimic the action of acetylcholine, a compound released by nerve endings.
Detrusor— Muscle of the bladder wall.
Residual urine volume— Amount of urine remaining after voiding.
Sphincter— Ring of muscle between the bladder and the urethra that functions to close off the urethra.
Urethra— Tube which empties urine from the bladder to the exterior of the body.
Lamm, D. L., A. S. Paola, and F. A. Paola. Campbell's Urology: Review and Assessment. Philadelphia: W.B. Saunders, 1995.
American Nephrology Nurses Association. ANNA National Office, East Holly Avenue, Box 56, Pitman, NJ 08071-0056. (888) 600-2662. 〈http://anna.inurse.com〉.
Society of Urologic Nurses and Associates. National Headquarters, East Holly Avenue, Box 56, Pitman, NJ 08071-0056. (888) TAP-SUNA. 〈http://www.suna.org/〉.
Kidney Information Clearing House. 〈http://www.renalnet.org/〉.