Urodynamic systems are used for the study of bladder and urethral functions using pressure and flow measurements. Urine flow testing is an integral part of urodynamic study, however “stand alone” flow meters are used primarily for uroflowmetry.
Urodynamic study includes the following measurements:
- Urine free flow testing
- Cystometry – urine flow and bladder pressure curve
- Urethral pressure measurement
- Ambulatory monitoring studies using portable equipment
Urodynamic studies are performed when the patient has one of the following symptoms: frequent urination, incontinence or difficulties in bladder emptying. Urodynamic equipment includes a flow meter, so that pressure/ flow studies can be performed. For urine free flow study, the patient voids into a machine that measures the rate and pattern of urinary flow. There are two types of urine flow meters: spinning disc and weight transducer. In addition, the perineal electromyography within muscles is sometimes performed during voiding.
During filling cystometry, bladder pressure and abdominal pressure are measured. Abdominal pressure is recorded to allow for any changes which might influence bladder pressure.
When filling and voiding cystometry is performed, the bladder must be actively filled by infusion of saline or radio opaque solution and bladder and abdominal pressures are continuously measured via inserted catheters. When the bladder is filled, voiding cystometry is performed: while the patient urinates, pressures and flow rate are recorded. Sometimes electromyographic signals are simultaneously recorded. Data is analyzed and pressure flow curves are generated.
Sometimes ambulatory monitoring of the bladder is carried out in special urodynamics centers. During ambulatory monitoring, bladder and abdominal pressures are recorded, but the bladder is allowed to fill naturally.
Urethral pressure profile measurement is performed with the aid of a special catheter, which is slowly withdrawn through the urethra while fluid is slowly infused through it. The urethral pressure at the tip of the catheter is continuously recorded. Machines normally use a small, motorized device which withdraws the catheter at a fixed rate.
The urodynamic systems are usually designed for mobile clinic use and can be portable within a department. Some systems are mounted on dedicated cart and include a desktop computer.
Bladder and abdominal pressure can be measured with several types of pressure transducers that can be a water -filled catheter connected to an external pressure sensor. Solid state sensors on the tip of the catheter provide reliable pressure measuring devices.