Urethral Profilometry

(1)

Functional Urology Unit, Casa Madre Fortunata Toniolo, Bologna, Italy

The urethral pressure profile (UPP) is a graph indicating the intraluminal pressure along the length of the urethra from the bladder neck to the external meatus in females and from the bladder neck to bulbous urethra in males.

The urethral pressure profile is performed at rest as well as during stress maneuvers. At rest, the UPP is measured with a bladder filling at least one third of the capacity (approximately 200 ml). Under stress, the UPP is performed while the patient performs repetitively (at least three times) the Valsalva maneuver or coughing. In this way it evaluates the coefficient of transmission of abdominal pressure to the proximal urethra.

9.1 Terminology (Fig. 9.1)

Figure 9.1

Urethral profilometry measurements according to ICS

The urethral closure pressure profile is given by the subtraction of intravesical pressure from urethral pressure.
Maximum urethral pressure is the maximum pressure of measured profile.
Maximum urethral closure pressure (MUCP) is the maximum difference between the urethral pressure and the intravesical pressure.
Functional profile length is the length of the urethra along which the urethral pressure exceeds intravesical pressure.
Pressure “transmission” ration (% PTR) is the increment in urethral pressure on stress as a percentage of the simultaneously recorded increment in intravesical pressure.

9.2 Method of Measurement

There are currently three methods of measuring urethral pressure profile:

Fluid perfusion technique or Brown-Wickham technique
Microtip/fiberoptic catheters
Air-charged balloon catheters

Water-perfused catheters measure the fluid pressure needed to just open a closed urethra.

Microtip catheters measure a true hydrostatic pressure and are very sensitive to rapid changes in pressure. The catheters are fragile and expensive and the measurement depends upon transducer orientation.

Air-filled balloon catheters measure the average variation of hydrostatic pressure over the length of the balloon. The ability of air-filled catheters to measure pressure circumferentially is widely considered a main advantage over microtip catheters.

Fiberoptic catheters have been utilized during invasive cardiac monitoring but only recently applied to the study of the function of lower urinary tract in women. A proposed advantage of fiberoptic catheters is the relatively low cost compared with microtip catheters, a better resistance with everyday usage, and a circumferential measurement of the pressure.

Table 9.1 indicates advantages and disadvantages of each method.

Table 9.1

Advantages and disadvantages of different methods of measuring urethral pressure profile

	Advantages	Disadvantages
Fluid perfusion technique	Cheap	Slow response to pressure variations
Fluid perfusion technique	Less susceptible to movement artifacts	Slow response to pressure variations
Microtip/fiberoptic transducers	Responsive to rapid pressure changes	Expensive and fragile. Stiffness of the catheter may alter the record. Record influenced by catheter orientation
Balloon catheters	No orientation dependance	Expensive. Dilating effect on the urethra

9.3 Technique

Water profilometry (also known as Brown-Wickham method) is still the most widely used method for urethral pressure measurement. The pressure recorded is not the real hydrostatic pressure, but the pressure of fluid necessary to open a closed urethra.

A triple-lumen catheter is the most convenient for simultaneous measurement of bladder pressure (Pves) and urethral pressure (Pura) as well as fluid infusion.

Pves channel is usually close to tip of the catheter, while Pura channel is 5–6 cm distal to the tip. Separate orifice for infusion can be located both close to the tip near Pves channel and 5–6 cm below near Pura channel.

UPP is most commonly performed in sitting position: however, it can virtually be performed in any position depending on individual clinical requirements.

The initial setup is the same as in cystometry: the whole circuit is made air-free and zeroing is performed in standard fashion.

Footnote

With microtip or air-charged catheters, zeroing is performed outside the patient.

The puller system is placed facing the introitus or the penis, and the catheter is attached to it.

Bladder filling is initiated through the infusion channel at a rate of 50 mL/min.

After a filling between 50 and 150 ml depending upon the presence or absence of detrusor overactivity or poor compliance, resting urethral pressure profile is recorded.

The infusion pump is slowed down to 2–6 ml/s and the puller is started to pull at 2 mm/s

If puller is not available, the catheter can be pulled manually each time by 5–10 mm, and each pull is market on the screen.