Urodynamics is a group of diagnostic test procedures to assess how the bladder and urethra are functioning with respect to storing and releasing urine. Generally speaking, urodynamic testing provides precise measurements using sophisticated instruments to assess the bladder’s ability to eliminate urine steadily and completely. The tests help physicians determine if:
- a patient is experiencing difficulty in starting a urine stream
- the amount of effort put forth to maintain it
- the stream is interrupted
- there is residual urine left in the bladder after voiding.
This test uses an uroflowmeter to measure the amount of urine and how quickly it is removed from the bladder. It provides a chart identifying changes in urine flow that shows the peak flow rate and the amount of time needed to achieve it. Abnormal test results occur if the bladder muscle is weakened or if there is an obstruction in urine flow.
When urinating is completed, there may a small amount of urine left in the bladder. To find out how much is remaining (called a post-void residue) and to measure it, a catheter can be inserted into your bladder. A post-void residual of more than 200 ml (about half a pint) usually indicates a problem. If 100 ml (about half a cup) remains, additional testing may be indicated.
This test measures the amount of urine a bladder can hold, the amount of pressure that builds up as it stores urine, and how full it is when a patient feels an urge to urinate. It involves inserting a catheter into the patient’s bladder to fully drain it. A specialized catheter containing a pressure sensitive tube (cystometer) is then inserted to slowly fill the bladder with a saline solution and to measure pressure. An additional catheter is then inserted into the rectum to measure and record the pressure there as well. The procedure is also used to identify involuntary bladder contractions.
Leak Point Pressure Measurement.
As a patient’s bladder is being filled during the Cystometry test, it can suddenly contract and force water out without warning. The cystometer records the pressure at the time the leak occurs. The cystometer’s reading indicates the type of bladder problem that a patient has. The procedure is also used to evaluate the sphincter muscles.
Pressure Flow Study.
Following the cystometry test, the patient will be asked to empty his or her bladder so that the catheter can measure the pressures required to urinate. This study helps identify obstructions in the bladder outlet that is typical in men with prostate problems. While a bladder outlet obstruction is less common in women, it can occur with a condition such as a fallen bladder or infrequently after surgery for urinary incontinence.
Electromyography is used to measure nerve impulses and muscle activity in the urethral sphincter with sensors placed on the skin near the urethra and rectum. Occasionally, the sensors are on the urethral or rectal catheter. The recorded patterns of these impulses shows whether the messages sent to the bladder and urethra are coordinated correctly.
Urodynamic tests can be performed with imaging equipment such as x-ray or ultrasound to provide images of the bladder during filling and emptying. When x-rays are used, the bladder will be filled with a contrast medium instead of water to better visualize the bladder. The resulting images can help the physician better diagnose the patient’s problem.