Background:
Methods to measure abdominal leak point pressure vary with respect to mode of provocation, method used to detect leakage, and amount of bladder filling. Altering one or more of these factors might influence the sensitivity of the test as well as its ability to differentiate between patients and healthy subjects. Aim: The aims were 1) to investigate whether bladder volume affects the detection rate of incontinence (sensitivity) or the level of leak point pressure when the Cough Induced Leak Point Pressure measurement method (CILPP)-based on coughs for provocation and urethral electrical conductivity to detect leakage-is used; 2) to study if the method has the ability to differentiate between patients with a history of stress incontinence and controls without such a history and 3) to compare these findings regarding CILPP with the corresponding findings for Valsalva Leak Point Pressure (VLPP).

Material and Methods:
The study was an open, randomized, controlled clinical trial of cough induced and Valsalva leak point pressure measurements at different bladder volumes where 40 female patients with a history of stress incontinence and 11 women without current complaints of stress incontinence were included. Leak point pressure measurements were performed at two different bladder volumes: first at 200 ml and then at 90% of the largest single voided volume as determined from the frequency/volume chart, or at 90% of maximum cystometric capacity, whichever was reached first. Mean volume at 90% of capacity was 451 ml (range 225-810 ml). The order of testing, i.e. whether the testing started with cough provocation or Valsalva maneuver, was randomized. For the individual subject, the order of testing was the same at both volumes. Urinary leakage was detected by measuring distal urethral electrical conductance (DUEC) with a 7F Silastic probe placed in the urethra (UEC-meter). The increase in abdominal pressure above the baseline value during provocation was recorded using a microtip catheter placed in the fornix of the vagina (Figure 1). To determine CILPP, subjects were asked to cough with gradually increasing exertion until leakage was detected. To determine the Valsalva leak point pressure, subjects were asked to bear down-as if trying to push something out of the vagina-until leakage was detected by the UEC-meter.

The practical set-up to determine CILPP and VLPP with the microtip catheter (a) placed in the vagina and the UEC-meter (b) in the urethra. Below are copies of leakage (H) and pressure recordings. Note the stepwise increase in cough strength. CILPP was defined as the mean of the lowest single pressure that produced leakage and the highest single pressure recorded without concomitant leakage. The lowest pressure producing leakage in a series of three Valsalva maneuvers defined the VLPP.

Results:
CILPP verified leakage in 37/40 and 38/39 patients at 200 ml and at 90% of maximum bladder capacity, respectively. The corresponding figures for VLPP were 29/40 and 37/39. Thus at 200 ml, the sensitivity of CILPP was significantly higher than the sensitivity of VLPP. At 200 ml, the specificity of CILPP was 0.73 (8/11) and the overall accuracy 0.88 (45/51). The corresponding figures for VLPP were 0.82 (9/11) and 0.75 (38/51). Increasing bladder volume to 90% of maximum capacity did not alter the specificity of either measure. Raising the volume did, however, increase the overall accuracy of both CILPP and VLPP to 0.92. Mean pressure levels at leakage for CILPP were significantly lower at 90% of maximum bladder capacity than at 200 ml: 90.7 cm H2O compared with 103.2 cm H2O (p=0.0085). VLPP levels were significantly lower than mean CILPP levels at corresponding volumes, but there was no statistically significant difference between VLPP levels at 200 ml and 90% of bladder capacity: 72.5 cm H2O and 68.6 cm H2O respectively.

Conclusion:
The sensitivity of CILPP is high over a wide range of bladder volumes whereas VLPP requires a large bladder volume to attain an acceptable detection rate. The specificity of CILPP and VLPP allows differentiation between patients with stress incontinence and controls.