Intra-luminal urethral pressure may be measured:

i.At rest( the storage phase), with the bladder at any given volume – Resting urethral pressure profile (UPP).

ii.During coughing or straining – Stress urethral pressure profile.

Ambulatory Urodynamics: This form of cystometry overcomes some of the problems associated with conventional urodynamics. The equipment is portable, allowing the subject to move freely and void in private. In addition the patient fills her bladder spontaneously after drinking a fluid load. As the technique is not adequately standardized with no internationally accepted diagnostic criteria it is best regarded as a research tool at present, particularly since some studies have reported involuntary detrusor contractions in up to 70% of apparently normal subjects.

Urethral Pressure Profilometry: Although UPP has the potential to be highly informative, the test has multiple problems, the most significant being the large overlap in values obtained from normal and symptomatic patients. UPP does not discriminate SUI from other urinary disorders, provide a measurement of the severity of the condition or predict a return to normal following successful intervention.

Abdominal Leak Point Pressures: Abdominal leak point pressure (ALPP) is defined as the vesical pressure at leakage during abdominal stress in the absence of detrusor contraction.The abdominal stress may be induced by a cough (CLPP) or a Valsalva maneuver (VLPP), with the two stressors differing physiologically in particular with regard to the rate and nature of pressure rise which is seen. Whilst higher abdominal pressures can be achieved with CLPP, the VLPP is better controlled and less variable.20 Generally, CLPP is used for patients who do not leak during VLPP measurement. The pressure at which the urine is expelled can be measured visually, fluoroscopically, by flowmetry or by electrical conductance.

Although the concept of ALPP as a method of investigating incontinence is empirically sound, its value is limited by a lack of standardized methodology. Variations occur in the type of catheter (transurethral, rectal, vagina), catheter caliber, bladder volume, and patient position. The exact baseline used during the test also

varies (e.g. zero level or the level at which the pressure just starts to rise), which can make a dramatic difference to the ALPP value. For ALPP to be a valid test, it is assumed that: the transurethral catheter used does not obstruct the urethra or alter coaptation; straining or coughing does not distort the urethra; and no pelvic relaxation or contraction occurs. However, it is difficult to know whether these are actually occurring during the test, which is a major drawback.

Few data are available on the magnitude of the change in ALPP post-SUI treatment, and how this correlates with cure, improvement, or failure. One general finding is that VLPP does not change significantly if the treatment fails. For example, following suburethral sling operations in 30 women,VLPP increased significantly after a successful operation (mean change: 61.1 cm H2O; p < 0.001) but not after failure (mean change: 9.7 cm H2O, p = 0.226).21

Neurophysiological Evaluation

The electrical activity of action potentials of depolarizing striated muscle fibers in the urethra can be studied with electromyography using surface or needle electrodes. Results must be interpreted in the light of symptoms and other investigations. This remains a research tool but has provided valuable insight into the pathophysiology and the effect of treatment on various conditions.

Neurophysiological investigations, like urethral pressure profilometry have not entered widespread usage. Four different neurophysiological methods have been described:

•Electromyography – Needle electrodes are placed in to a muscle mass or surface electrodes are used to record electrical action potentials generated by depolarization of muscle. Potential sampling sites include; the intrinsic striated muscle of the urethra, the periurethral striated muscle, bulbocavernosus muscle,external anal sphincter, and pubococcygeus muscle. These have a characteristic waveform and in disease this may be altered or the impulse may be recorded at an inappropriate time, such as in detrusor sphincter dyssynergia, where the urethral striated muscle contracts during voiding.