Flow-pressure study

 This is usually performed immediately after filling cystometry.
The urethral catheter is narrow enough that voiding can occur around it. The important measurement from the study is the detrusor pressure at maximum flow.
By this method, obstruction to passage of urine (high pressure, low flow) can be distinguished from a lack of tone in the detrusor muscle (low pressure, low flow).
Many women void simply by relaxing the urethral sphincter with no associated rise in detrusor muscle pressure, which can make the study difficult to interpret. Following voiding, it's usual to measure the amount of any urine left in the bladder.

Videocystourethography

In situations of particular complexity, flow-pressure studies are combined with the use of X-ray screening in order to gain additional information about the anatomy of the bladder and urethra. (Ultrasound scanning can also be used to demonstrate an abnormally low bladder neck.)