Procedure

The bladder is filled with fluid or carbon dioxide. The usual fluids are water or saline. In video-cystometry, radio-opaque contrast material is used. Gas cystometry has the advantage of being easy and clean but does not permit simultaneous measurement of flow rate and may affect bladder behaviour. It is not widely used in the UK.

Bladder function is monitored using:

• a urethral catheter in the bladder to measure total intravesical pressure
• a second urethral catheter connected to a fluid reservoir to fill the bladder; filling volume is measured by means of a strain gauge connected to the reservoir that shows the change in weight as the bladder empties
• a catheter inserted in the rectum or vagina to measure intra-abdominal pressure

Detrusor pressure i.e. pressure produced by the bladder wall, is calculated as total intravesical pressure minus intra-abdominal pressure.

The bladder is filled with fluid at a constant rate, usually, 60-70 ml per min. With the patient upright, various manoeuvres - coughing, straining, changing posture - are performed to provoke abnormal detrusor activity. The patient then voids into the flow meter to empty the bladder and permit recording of flow rate.