Conversion of urodynamic pressures measured simultaneously by air-charged and water-filled catheter systems.

AIMS: The objective of this study was to compare the simultaneous responses of water-filled (WFC) and air-charged (ACC) catheters during simulated urodynamic pressures and develop an algorithm to convert peak pressures measured using an ACC to those measured by a WFC. METHODS: Examples of cough leak point pressure and valsalva leak point pressure data (n = 4) were obtained from the literature, digitized, and modified in amplitude and duration to create a set of simulated data that ranged in amplitude from 15 to 220 cm H2 O (n = 25) and duration from 0.1 to 3.0 sec (n = 25) for each original signal. Simulated pressure signals were recorded simultaneously by WFCs, ACCs, and a reference transducer in a specially designed pressure chamber. Peak pressure and time to peak pressure were calculated for each simulated pressure signal and were used to develop an algorithm to convert peak pressures recorded with ACCs to corresponding peak pressures recorded with WFCs. The algorithm was validated with additional simulated urodynamic pressure signals and additional catheters that had not been utilized to develop the algorithm. RESULTS: ACCs significantly underestimated peak pressures of more rapidly changing pressures, as in coughs, compared to those measured by WFCs. The algorithm corrected 90% of peak pressures measured by ACCs to within 5% of those measured by WFCs when simultaneously exposed to the same pressure signals. CONCLUSIONS: The developed algorithm can be used to convert rapidly changing urodynamic pressures, such as cough leak point pressure, obtained using ACC systems to corresponding values expected from WFC systems.

Somatomotor and sensory urethral control of micturition in female rats.

In rats, axons of external urethral sphincter (EUS) motoneurons travel through the anastomotic branch of the pudendal nerve (ABPD) and anastomotic branch of the lumbosacral trunk (ABLT) and converge in the motor branch of the sacral plexus (MBSP). The aim of the present study was to determine in female rats the contribution of these somatomotor pathways and urethral sensory innervation from the dorsal nerve of the clitoris on urinary continence and voiding. EUS electromyographic (EMG) activity during cystometry, leak point pressure (LPP), and voiding efficiency (VE) were assessed in anesthetized virgin Sprague-Dawley female rats before and after transection of the above nerve branches. Transection of the MBSP eliminated EUS EMG, decreased LPP by 50%, and significantly reduced bladder contraction duration, peak pressure, intercontraction interval, and VE. Transection of the ABPD or ABLT decreased EUS EMG discharge and LPP by 25% but did not affect VE. Transection of the dorsal nerve of the clitoris did not affect LPP but reduced contraction duration, peak pressure, intercontraction interval, and VE. We conclude that somatomotor control of micturition is provided by the MBSP with axons travelling through the ABPD and ABLT. Partial somatomotor urethral denervation induces mild urinary incontinence, whereas partial afferent denervation induces voiding dysfunction. ABPD and ABLT pathways could represent a safeguard ensuring innervation to the EUS in case of upper nerve damage. Detailed knowledge of neuroanatomy and functional innervation of the urethra will enable more accurate animal models of neural development, disease, and dysfunction in the future.

Quantitative evaluation of electrodes for external urethral sphincter electromyography during bladder-to-urethral guarding reflex.

PURPOSE: Accuracy in the recording of external urethral sphincter (EUS) electromyography (EMG) is an important goal in the quantitative evaluation of urethral function. The aim of this study was to quantitatively compare electrode recordings taken during tonic activity and leak point pressure (LPP) testing. METHODS: Several electrodes, including the surface electrode (SE), concentric electrode (CE), and wire electrode (WE), were placed on the EUS singly and simultaneously in six female Sprague-Dawley rats under urethane anesthesia. The bladder was filled via a retropubic catheter while LPP testing and EUS EMG recording were done. Quantitative baseline correction of the EUS EMG signal was performed to reduce baseline variation. Amplitude and frequency of 1-s samples of the EUS EMG signal were measured before LPP (tonic activity) and during peak LPP activity. RESULTS: The SE, CE, and WE signals demonstrated tonic activity before LPP and an increase in activity during LPP, suggesting that the electrodes accurately recorded EUS activity during tonic activity and during the bladder-to-EUS guarding reflex, regardless of the size or location of detection areas. SE recordings required significantly less baseline correction than both CE and WE recordings. The activity in CE-recorded EMG was significantly higher than that of the SE and WE both in single and simultaneous recordings. CONCLUSIONS: These electrodes may be suitable for testing EUS EMG activity. The SE signal had significantly less baseline variation and the CE detected local activity more sensitively than the other electrodes, which may provide insight into choosing an appropriate electrode for EUS EMG recording.

Effects of sphincterotomy and pudendal nerve transection on the anal sphincter in a rat model.

PURPOSE: Our objective was to define anal resting pressure and electromyography of the normal rat anal sphincter and investigate the short-term effects of both mechanical trauma to the anal sphincter muscles and pudendal nerve transection. METHODS: Forty-five virgin female Sprague-Dawley rats were randomly allotted to three groups: controls (n = 21), sphincterotomy (n = 12), and pudendal nerve transection (n = 12). Anal pressure was monitored using a saline-filled balloon connected to a pressure transducer. Anal pressure and electromyography of the anal sphincter with use of a needle electrode were recorded both before and after injury or succinylcholine administration. RESULTS: Anal pressure data were consistent with rhythmic pressure contractions. Succinylcholine significantly reduced both pressure and electromyography signals. Electromyography amplitude and frequency decreased after nerve transection but not after sphincterotomy. The histology showed that the rat anal anatomy has muscular components that compare with human anatomy. The sphincterotomy group showed injury to the anal sphincters and the sphincter anatomy of the nerve transection group appeared similar to the control group. The anal pressure wave appears to be created by synergistic activity of both striated and smooth muscle of the anal sphincter. CONCLUSION: The female rat is a suitable and reliable model for studying effect of direct and indirect injury to the anal sphincters.

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

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

Feasibility of fluid volume conductance to assess bladder volume.

AIM: Ambulatory urodynamics has the potential to provide measurements of bladder function during activities of daily living; however, no method of real-time continuous bladder volume measurement exists. The present study was conducted to determine the feasibility of using fluid volume conductance to continuously assess bladder volume. METHODS: Prototype devices consisted of four electrodes mounted on a polymer body. Each was tested in an in vitro organ bath system using latex vessels filled to 500 ml with saline matching the conductivity of urine. One device was selected and used to test the effects of fluid concentration (25%, 50%, 100%, 200%, and 400% physiological saline) in latex vessels as well as the effects of fluid concentration (25%, 50%, 100%, 200%, and 400% Tyrodes solution) and temperature (32, 37, and 42 degrees C) in excised pig bladders. RESULTS: Conductance demonstrated a linear increase at low volumes but approached an asymptotic value at high volumes. Conductivity increased with increased temperature or concentration. With the exception of the differences between 25% and 50% concentrations, 32 degrees C and 37 degrees C, and 37 degrees C and 42 degrees C temperatures, each concentration and temperature produced statistically different conductance measurements from all others. CONCLUSIONS: The conductance method is sensitive to changes in both concentration and temperature of the intravesical solution, likely due to changes in solution conductivity. Clinical application of conductance for measurement of bladder volume will require real-time conductivity compensation for the dynamically varying properties of urine. However, improved sensitivity at high volumes is necessary before this method has the potential to provide real-time bladder volume measurement for use in ambulatory urodynamics.