Urethral Pressure Profile

Urethral pressure profile (UPP) is a measure of urethral resistance along the urethral lumen. The measurement can be made at one point in the urethra over a period of time or at several points along the length of the urethra. There are three techniques used to measure UPP: the perfusion method, catheter-mounted transducers, and air-charged balloon catheter profilometry. We employ the most widely used perfusion method. Intravesical pressure should be measured to exclude a simultaneous detrusor contraction and to calculate the closure pressure. The intraluminal pressure can be determined at rest, at any given bladder volume, during cough, or during voiding.

Stress UPP (during cough) measurement evaluates pressure transmission from the abdominal cavity to the urethra. In patients with stress incontinence, this pressure transmission is inadequate and the urethral closure pressure becomes negative with coughing. Voiding urethral pressure is used to determine the pressure and site of ure-thral obstruction. This technique is plagued by artifacts secondary to catheter movement. Relevant measurements relating to resting UPP include maximal urethral pressure (MUP), maximal urethral closure pressure (MUCP), and functional urethral length. The maximum pressure measured is the MUP, and the maximum difference between urethral pressure and intravesical pressure is the MUCP. The functional profile length is the length of the urethra along which the urethral pressure exceeds intravesical pressure in women. Pressure transmission ratio is the increment in urethral pressure with stress, as a percentage of the simultaneously recorded increment in intravesical pressure.1

The drawback of UPP is that no normal values have been defined, and considerable variations have been reported. Although MUCP tends to be lower in women with genuine stress incontinence, there is overlap between SUI patients and normal subjects. Other drawbacks of UPP are its difficulty to standardize and perform. Also, the correlation between SUI severity and low MUCP has limited rele-vance.24 Although UPP has limited applications because of broad inter- and intraindividual variations, it can be used to diagnose ISD, or "low pressure urethra."

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