Development of a device to standardize leak point pressure experiments in rats

The objective of this study was to test a custom device aimed at increasing repeatability of abdominal leak point pressure (LPP) measurements in rodents.

The device consisted of a soft-tipped force applicator with a force sensor which was moved in the vertical direction by a linear actuator, laser crosshairs for accurate positioning, and a hand-held wired remote control system. One expert and two novice experimenters acquired LPP measurements using manual and device methods by applying a gradually increasing force with the finger or the device, respectively, until a leak was visually observed at the urethral meatus. The device was tested at fast, medium, and slow speeds. A leak sensor was also tested to determine presence of a leak and reaction time of the user. The change in bladder pressure due to the externally applied force (LPP) was the primary outcome.

There were no significant differences in mean LPP value when compared across experiments (expert, novice), method (manual, device), or speeds. The pooled variance of LPP was significantly decreased (P < 0.05) compared to the manual method when using the device at medium speed; however the slower speed showed no further improvement over the medium speed. The wet sensor detected leaks 385 +/- 187 msec earlier than users' reaction.

Use of the device can decrease variability of the experiment but does not alter mean values. Reaction time, inherent in both the manual and device methods, has the potential for a significant impact on LPP outcomes.