Some Biomechanical Aspects of Continence Function

Liquid crystal elastomer based dynamic device for urethral support: Potential treatment for stress urinary incontinence

Stress urinary incontinence (SUI) is characterized by the involuntary loss of urine due to increased intra-abdominal pressure during coughing, sneezing, or exercising. SUI affects 20-40% of the female population and is exacerbated by aging. Severe SUI is commonly treated with surgical implantation of an autologous or a synthetic sling underneath the urethra for support. These slings, however, are static, and their tension cannot be non-invasively adjusted, if needed, after implantation. This study reports the fabrication of a novel device based on liquid crystal elastomers (LCEs) capable of changing shape in response to temperature increase induced by transcutaneous IR light. The shape change of the LCE-based device was characterized in a scar tissue phantom model. An in vitro urinary tract model was designed to study the efficacy of the LCE-based device to support continence and adjust sling tension with IR illumination. Finally, the device was acutely implanted and tested for induced tension changes in female multiparous New Zealand white rabbits. The LCE device achieved 5.6% ± 1.1% actuation when embedded in an agar gel with an elastic modulus of 100 kPa. The corresponding device temperature was 44.9 °C ± 0.4 °C, and the surrounding agar temperature stayed at 42.1 °C ± 0.4 °C. Leaking time in the in vitro urinary tract model significantly decreased (p < 0.0001) when an LCE-based cuff was sutured around the model urethra from 5.2min ± 1min to 2min ±0.5min when the cuff was illuminated with IR light. Normalized leak point force (LPF) increased significantly (p = 0.01) with the implantation of an LCE-CB cuff around the bladder neck of multiparous rabbits. It decreased significantly (p = 0.023) when the device was actuated via IR light illumination. These results demonstrate that LCE material could be used to fabricate a dynamic device for treating SUI in women.

The Anatomical Pathogenesis of Stress Urinary Incontinence in Women

Stress urinary incontinence is a common disease in middle-aged and elderly women, which seriously affects the physical and mental health of the patients. For this reason, researchers have carried out a large number of studies on stress urinary incontinence. At present, it is believed that the pathogenesis of the disease is mainly due to changes related to age, childbirth, obesity, constipation and other risk factors that induce changes in the urinary control anatomy, including the anatomical factors of the urethra itself, the anatomical factors around the urethra and the anatomical factors of the pelvic nerve. The combined actions of a variety of factors lead to the occurrence of stress urinary incontinence. This review aims to summarize the anatomical pathogenesis of stress urinary incontinence from the above three perspectives.

Ameliorative effect of Abeliophyllum distichum Nakai on benign prostatic hyperplasia in vitro and in vivo

BACKGROUND/OBJECTIVES

Benign prostatic hyperplasia (BPH) is the most common prostate disease and one of the most common chronic diseases caused by aging in men. On the other hand, there has been no research on BPH using Abeliophyllum distichum Nakai (A. distichum). Therefore, this study investigated the effects of A. distichum on BPH.

MATERIALS/METHODS

A. distichum leaves were extracted with distilled water, 70% ethanol, and 95% hexane as solvents. Subsequently, the inhibitory effects of each A. distichum extract on androgen receptor (AR) signaling were evaluated in vitro. The testosterone-induced BPH model was then used to confirm the efficacy of A. distichum leaves in 70% ethanol extract (ADLE).

RESULTS

ADLE had the strongest inhibitory effect on AR signaling. A comparison of the activity of ADLE by harvest time showed that the leaves of A. distichum harvested in autumn had a superior inhibitory effect on AR signaling to those harvested at other times. In the BPH rat model, the administration of ADLE reduced the prostate size and prostate epithelial cell thickness significantly and inhibited AR signaling. Subsequently, the administration of ADLE also reduced the expression of growth factors, thereby inactivating the PI3K/AKT pathway.

CONCLUSIONS

An analysis of the efficacy of ADLE to relieve BPH showed that the ethanol extract grown in autumn exhibited the highest inhibitory ability of the androgen-signaling related factors in vitro. ADLE also inhibited the expression of growth factors by inhibiting the expression of the androgen-signaling related factors in vivo. Overall, ADLE is proposed as a functional food that is effective in preventing BPH.

Influence of ATOMS implant on the voiding phase of patients with post-prostatectomy urinary incontinence

OBJECTIVE

To assess changes in voiding phase, especially urethral resistance after post-prostatectomy urinary incontinence (PPI) treatment with the Adjustable TransObturator Male System (ATOMS).

MATERIAL AND METHODS

A longitudinal prospective study was performed on 45 men treated with ATOMS for PPI, with the intention to evaluate the changes produced by the implant on the voiding phase. Patients with preoperative urodynamic study were offered postoperative urodynamic evaluation, and both studies were compared. The following urodynamic date were evaluated: maximum voiding detrusor pressure, detrusor pressure at maximum flow rate, maximum flow rate (Qmax), voiding volume, post-void residue, bladder outlet obstruction index (BOOI), urethral resistance factor (URA), and bladder contractility index (BCI). The statistical analysis used were the mean comparison test for dependent groups (Student's t test) for parametric variables and the Wilcoxon test for non-parametric variables. The signification level was set at 95% bilateral.

RESULTS

A total of 37 patients (82.2%) used zero pads/day at the time of urodynamic postoperative evaluation and pad-test evolved from 592 ± 289 ml baseline to 25 ± 40 ml (p = 0.0001). Significant differences were observed in Qmax (15 ± 8.3 before and 11 ± 8.3 after surgery; p = 0.008), voiding volume (282 ± 130.7 before and 184 ± 99.92 after surgery). BOOI (-12 ± 23.9 before and -2 ± 21.4 after surgery; p = 0.025) and BCI (93 ± 46.4 before and 76 ± 46.0 after surgery; p = 0.044). In no case did we observe postoperative bladder outlet obstruction, according to URA parameter below 29 cm H₂ O in all cases. There was not a significant variation either in post-void urinary residual volume (15 ± 47.4 before and 14 ± 24.2 after surgery, p = 0.867).

CONCLUSIONS

The ATOMS implant induces a decrease of Qmax, voided volume, and bladder contractility and an increase of BOOI. However, our findings suggest that ATOMS device does not cause bladder outlet obstruction.

On Structure-Function Relationships in the Female Human Urethra: A Finite Element Model Approach

Remarkably little is known about urethral striated and smooth muscle and vascular plexus contributions to maintaining continence or initiating micturition. We therefore developed a 3-D, multiphysics, finite element model, based on sequential MR images from a 23-year-old nulliparous heathy woman, to examine the effect of contracting one or more individual muscle layers on the urethral closure pressure (UCP). The lofted urethra turned out to be both curved and asymmetric. The model results led us to reject the current hypothesis that the striated and smooth muscles contribute equally to UCP. While a simulated contraction of the outer (circular) striated muscle increased closure pressure, a similar contraction of the large inner longitudinal smooth muscle both reduced closure pressure and shortened urethral length, suggesting a role in initiating micturition. When age-related atrophy of the posterior striated muscle was simulated, a reduced and asymmetric UCP distribution developed in the transverse plane. Lastly, a simple 2D axisymmetric model of the vascular plexus and lumen suggests arteriovenous pressure plays and important role in helping to maintain luminal closure in the proximal urethra and thereby functional urethral length. More work is needed to examine interindividual differences and validate such models in vivo.

Systematic review and meta-analysis comparing Adjustable Transobturator Male System (ATOMS) and male Readjustment Mechanical External (REMEEX) system for post-prostatectomy incontinence

OBJECTIVE

To assess the efficacy and safety of Adjustable Transobturator Male System (ATOMS) compared to male Readjustment Mechanical External (REMEEX) system for post-prostatectomy incontinence (PPI).

MATERIAL AND METHODS

A systematic review and meta-analysis on adjustable device ATOMS compared to male REMEEX is presented. Studies on female or neurogenic incontinence were excluded. Primary objectives were evaluation of dryness (the proportion of patients with no-pad or one safety pad/day after device adjustment) and improvement between devices. Secondary objectives were complications and explant rate. They were estimated using a random-effect model. Statistical heterogeneity among studies was assessed using Cochran's Q test, Higgins's I² statistics and tau2.

RESULTS

Combined data of 29 observational studies with 1919 patients showed an equivalent proportion of patients treated with radical prostatectomy (p = .125) and previous radiation (p = .126). Dryness rate was 69.3% for ATOMS and 53.4% for male REEMEX (p = .008). Improvement rate was 90.8% for ATOMS and 80.2% for REMEEX (p = .007). Complication rate was 18.9% for ATOMS and 35.8% for REMEEX (p = .096) and explant rate was 5.5% for ATOMS and 13.9% for REMEEX (p = .027). Significant heterogeneity was evidenced, due to absence of randomized studies, variable incontinence severity baseline, difficulties for a common reporting of complications and difference in the follow-up. Differences observed between devices remained statistically significant when only studies with silicone-covered scrotal port (SSP) ATOMS and male REMEEX system II were considered.

CONCLUSIONS

Despite the absence of direct comparison and the limitations observed ATOMS appears more effective than male REMEEX to treat PPI, and with less explant rate as reported in the literature.

Functional Morphology of the Cardiac Jelly in the Tubular Heart of Vertebrate Embryos

The early embryonic heart is a multi-layered tube consisting of (1) an outer myocardial tube; (2) an inner endocardial tube; and (3) an extracellular matrix layer interposed between the myocardium and endocardium, called "cardiac jelly" (CJ). During the past decades, research on CJ has mainly focused on its molecular and cellular biological aspects. This review focuses on the morphological and biomechanical aspects of CJ. Special attention is given to (1) the spatial distribution and fiber architecture of CJ; (2) the morphological dynamics of CJ during the cardiac cycle; and (3) the removal/remodeling of CJ during advanced heart looping stages, which leads to the formation of ventricular trabeculations and endocardial cushions. CJ acts as a hydraulic skeleton, displaying striking structural and functional similarities with the mesoglea of jellyfish. CJ not only represents a filler substance, facilitating end-systolic occlusion of the embryonic heart lumen. Its elastic components antagonize the systolic deformations of the heart wall and thereby power the refilling phase of the ventricular tube. Non-uniform spatial distribution of CJ generates non-circular cross sections of the opened endocardial tube (initially elliptic, later deltoid), which seem to be advantageous for valveless pumping. Endocardial cushions/ridges are cellularized remnants of non-removed CJ.

The female continence mechanism measured by high resolution manometry: Urethral bulking versus midurethral sling

AIMS

Traditional technology to characterize urethral pressure changes during dynamic conditions is limited by slow response times or artifact-inducing withdrawal maneuvers. The 8F high-resolution manometry (HRM) catheter (ManoScan™ ESO, Covidien) has advantages of fast response times and the ability to measure urethral pressures along the urethral length without withdrawal. Our objective was to determine static and dynamic maximum urethral closure pressures (MUCPs) and resting functional urethral length (FUL) in women using HRM before and after transurethral bulking and compare results to other women who underwent midurethral sling (MUS).

METHODS

We recorded rest, cough, and strain MUCPs and FUL in 24 women before and after transurethral bulking with polydimethylsiloxane (Macroplastique®) using the HRM catheter and compared these changes to HRM values from 26 women who had the same measures before and after MUS.

RESULTS

At rest, MUCPs increased minimally after both urethral bulking and MUS (3 vs 0.4 cm H₂ O respectively, P = 0.4). Under dynamic conditions there were statistically insignificant small increases in MUCP and these increases were markedly less than after MUS (cough: 1.5 vs 63.8 cm H₂ O, P < 0.001 and strain: 11.5 vs 57.7 cm H₂ O, P < 0.001). FUL increased by 0.5 cm after transurethral bulking (P = 0.003), and decreased by 0.25 cm after MUS placement (P = 0.012).

CONCLUSIONS

The mechanism of continence after urethral bulking differs from MUS. While MUS increases dynamic MUCP, bulking may rely on increasing the length of the continence zone.

Posterior colporrhaphy does not affect the urethral closure mechanism

INTRODUCTION AND HYPOTHESIS

Studies have suggested that a posterior vaginal wall prolapse might compress the urethra and mask stress urinary incontinence (SUI), much like an anterior vaginal wall prolapse. A recent study with urethral pressure reflectometry (UPR) has shown that the urethral closure mechanism deteriorates after anterior colporrhaphy; this could explain the occurrence of postoperative de novo SUI. We hypothesized that urethral pressure would also decrease after posterior colporrhaphy.

METHODS

This was a prospective, observational study where women with posterior vaginal wall prolapse ≥stage II were examined before and after posterior colporrhaphy. We performed prolapse staging according to the Pelvic Organ Prolapse Quantification system, UPR measurements at rest, during squeezing and straining, and standardized stress tests with 300 ml saline. The women filled out International Consultation on Incontinence-Urinary incontinence (ICIQ-UI) short forms. The sample size was 18, with a power of 99.9% and a level of significance of 5%. Parameters were compared using paired t tests or Fisher's exact test, where appropriate; p values <0.05 were considered statistically significant.

RESULTS

Eighteen women with posterior vaginal wall prolapse ≥stage II were recruited. One woman did not undergo surgery. There were no changes in urethral pressure at rest (p = 0.4), during squeezing (p = 0.2) or straining (p = 0.2), before and after surgery. The results of the stress tests and ICIQ-UI short forms were the same after surgery.

CONCLUSIONS

The urethral closure mechanism is not affected by posterior colporrhaphy. Our study does not support the theory that the posterior vaginal wall prolapse compresses the urethra and masks SUI.

Relation of Urinary Retention and Functional Recovery in Stroke Patients During Rehabilitation Program

Objective

To investigate the relationship between urinary retention and short-term functional recovery in subacute stage after stroke.

Methods

The medical records of 94 patients admitted to the rehabilitation unit of Korea University Guro Hospital were reviewed retrospectively. The postvoid residual urine (PVR) was measured at least once a day using a bladder scan, and urinary retention (UR) was defined when the daily PVR volume consistently checked more than 100 mL. Clinical data and functional outcomes of patients in the rehabilitation ward were collected. Functional outcomes were measured using the Mini-Mental State Examination (MMSE), Berg Balance Scale (BBS), Functional Ambulation Category (FAC) level, Fugl-Meyer Assessment (FMA), and Modified Barthel Index (MBI) at admission (or transfer) and discharge. The data of patients with and without urinary retention were compared and analyzed.

Results

Of the 94 participants, 25 patients were classified to the UR group and 69 were classified to the non-UR group. At the initial stage of rehabilitation, the scores of MMSE, BBS, FAC, MBI were significantly worse in the UR group (p<0.05). Both groups showed significant improvements of all functional outcomes after rehabilitation (p<0.05). The non-UR group showed more prominent recovery of BBS, FAC, MBI scores (p<0.05).

Conclusion

Urinary retention in post-stroke patients is significantly related to the poor functional status at initial stage of rehabilitation, and also to poor recovery after rehabilitation.

The impact of tension-free vaginal tape on the urethral closure function: mechanism of action

AIM

To investigate if the tension-free vaginal tape (TVT) works by increasing the abdominal to urethral pressure impact ratio (APIR).

METHODS

Twenty one women with urodynamically proven stress urinary incontinence (SUI) were assessed by ICIQ-SF, pad-weighing test, incontinence diary and Urethral Pressure Reflectometry (UPR) before and after TVT. UPR was conducted during resting and increased intra-abdominal pressure (P(Abd)) by straining. Related values of P(Abd) and urethral opening pressure (P(o)) were plotted into an abdomino-urethral pressuregram. Linear regression of the values was conducted, and the slope of the line was found. The slope expresses the ratio of pressure increase in the urethra compared to the pressure increase in the abdomen and was called APIR.

RESULTS

The urethral opening pressure at rest (P(o-rest)) was unchanged after TVT, while APIR increased in all women (from 0.7 to 1.4, P < 0.0001).

CONCLUSIONS

The TVT seems to strengthen the urethral closure function by increasing the APIR while P(o-rest) is unchanged regardless of the type of pre-operative dysfunction. This confirms the theory of TVT's mechanism of action being mid-urethral support.

A faster urethral pressure reflectometry technique for evaluating the squeezing function

OBJECTIVE

Urethral pressure reflectometry (UPR) has shown to be superior in evaluating the squeeze function compared to urethral pressure profilometry. The conventional UPR measurement (step method) required up to 15 squeezes to provide one measure of the squeezing opening pressure and one measure of the squeezing elastance. The UPR technique was modified (so the examination last 7 s), requiring only one squeeze for the measurement to be made (continuous method). The aims of the study were to compare the UPR parameters measured during squeezing by the continuous method with measurements made by the step method and to measure the reproducibility of the continuous method.

MATERIAL AND METHODS

In total, 33 women were included (eight healthy and 25 with urodynamically proven stress urinary incontinence). The women were measured twice with the step method followed by five measurements with the continuous method.

RESULTS

No significant difference was seen between the mean squeezing opening pressures measured with the two methods. The squeezing elastance was significantly higher (p < 0.00001) with the continuous method (2.7 cmH₂O/mm²) than with the step method (1.9 cmH₂O/mm²). The coefficient of variation (CV) was 6.5% for the opening pressure measured with the continuous method and 14.8% for the squeezing elastance.

CONCLUSIONS

A new method for performing UPR measurements during squeezing has been described. With the new method a UPR measurement can be conducted during only one squeeze. The squeezing opening pressure is the same while the squeezing elastance is higher with the new method compared with the conventional method.

Static single channel and multichannel water perfusion pressure profilometry in a bench model of a urethra

AIMS

To determine the catheter perfusion and withdrawal rate which generate the most repeatable single (SCPP) and multichannel pressure profilometry (MCPP) profiles in a bench model.

METHODS

A bench model using a urethral substitute was developed in which SCPP and MCPP were performed using the Brown-Wickham method. One single channel and four multichannel catheters were tested using seven withdrawal rates and three perfusion rates. Repeatability was determined using spread of mean profile pressure, cross-correlation, Bland-Altman statistic, and a one-tailed Student's t-statistic. An artificial urinary sphincter (AUS) model was constructed to create a predictable intraluminal profile. MCPP data were used to generate three-dimensional (3D) images of the pressures exerted by the AUS model.

RESULTS

A withdrawal rate of 0.5 mm/sec and perfusion rate 1 ml/min produced the most repeatable SCPP profiles with a spread of mean profile pressure ≤7 cmH(2)O. For MCPP, a 10 F 6-channel catheter using a withdrawal rate of 1 mm/sec and perfusion rate of 1 ml/min produced the most similar profiles (cross-correlation = 0.99). However, the spread of MCPP was large (spread ≤44 cmH(2)O per channel). Nevertheless MCPP was able to consistently demonstrate areas of high pressure as predicted by the AUS model.

CONCLUSIONS

MCPP was not repeatable and is an unreliable measure of urethral pressure. MCPP and 3D images do demonstrate directional differences predicted from the AUS model. These may be of use for qualitative understanding and appreciation of relative relationships if not actual forces within the urethra and have application in understanding urethral function in vivo.

A case of acute kidney injury due to complex, partial, multifocal ureteral strictures

BACKGROUND

An 89-year-old man with a history of prostate cancer who had undergone radical prostatectomy 15 years ago presented with hyperkalemia (serum potassium level 6.9 mmol/l) and kidney failure (serum creatinine level 937 micromol/l [10.6 mg/dl]). Ultrasound scan of his kidneys showed mild bilateral hydronephrosis. Although placement of a bladder catheter led to an initial increase in glomerular filtration rate, the improvement was delayed and incomplete. Subsequently, the patient's glomerular filtration rate decreased acutely. This unusual biphasic course of kidney injury begged explanation.

INVESTIGATIONS

Physical examination, measurements of serum creatinine level and electrolytes, imaging of the urinary tract (ultrasound and CT scans), and nephrostograms.

DIAGNOSIS

Acute kidney injury due to upper (multiple ureteral strictures bilaterally) and lower (urethral) urinary tract obstruction.

MANAGEMENT

Placement of bladder catheter and percutaneous nephrostomy tubes followed by bilateral internal ureteral stents.

Fluid perfused urethral pressure profilometry and Valsalva leak point pressure: a comparative study in a biophysical model of the urethra

In patient studies the correlation between maximum urethral closure pressure (MUCP) and Valsalva leak point pressure (LPP) is meagre at best (r = 0.22-0.50). We therefore studied the relation between MUCP and LPP in a flexible and extensible model urethra. We applied differently sized pressure zones and different degrees of resistance to a biophysical model urethra by stepwise inflating three types of blood pressure cuff placed around the model. At each degree of resistance we measured detrusor LPP, an in vitro equivalent of Valsalva LPP. Subsequently, we recorded the Urethral Pressure Profile using a water-perfused 5F end-hole catheter at four withdrawal rates and five perfusion rates and calculated MUCP. We tested the dependence of LPP on pressure zone length and MUCP on perfusion rate, withdrawal rate and pressure zone length using analysis of variance. We tested the correlation between LPP and MUCP using Pearson's correlation coefficient and Linear Regression. LPP did not significantly depend on the pressure zone length (P = 0.80) and increased linearly with increasing cuff pressure. MUCP also increased with increasing cuff pressure, however, MUCP significantly depended (P < 0.01) on perfusion rate, withdrawal rate and pressure zone length. MUCP increased with increasing perfusion rate, and decreased with increasing withdrawal rate. In our model urethra MUCP only accurately reflected urethral resistance for a very limited number of combinations of perfusion rate and withdrawal rate. LPP reflected urethral resistance independent of the type of pressure zone.

Urethral pressure reflectometry; a novel technique for simultaneous recording of pressure and cross-sectional area in the female urethra

AIMS

Urethral pressure reflectometry (UPR) is a new and easily applicable technique for simultaneous measurements of cross-sectional area (CA) and pressure in the urethra. CAs of 1-16 mm(2) and pressures of 0-200 cm H(2)O can be measured along the entire urethra in the same setting. The method is reliable in vitro. The aim was to present the method and some clinical results from the female urethra.

METHODS

A very thin polyurethane-bag was placed in the urethra. A pump applied preselected pressures stepwise to the bag. For every step the CA was measured by acoustic reflectometry. Measurements were made both during inflation and deflation. The women were examined in different positions and with different provocations.

RESULTS

UPR was easy to perform. The obtained parameters were opening pressure, closing pressure, elastance of the opening curve and closing curve, and hysteresis.

CONCLUSIONS

UPR is feasible for measuring urethral pressure and corresponding CA. The technique is minimally invasive and with minimal impact on the urethra per se. The technique provides physiological sound parameters which add potentially important physiological/pathophysiological information about the urethra to what can be obtained on the basis of conventional urodynamic work-up. Further studies are needed to prove if this new method is useful for clinical and research purposes.

Is benign prostatic hyperplasia a risk factor for chronic renal failure?

PURPOSE

Benign prostatic hyperplasia (BPH) and chronic renal failure (CRF) are common medical conditions in older men. Based on the low prevalence of CRF in clinical trials recent American Urological Association guidelines have not recommended routine serum creatinine screening in men presenting with lower urinary tract symptoms. However, chronic renal failure is a well described complication of obstructive BPH.

MATERIALS AND METHODS

A structured MEDLINE review of the literature on the association between BPH and CRF from 1966 to 2003 was performed.

RESULTS

Most studies were referral based and did not represent the full spectrum of BPH in men. The definition of renal failure varied from a serum creatinine cutoff of 1.5 to 3.0 mg/dl. Differentiating acute and chronic renal failure, and acute and chronic urinary retention was often not done. Various combinations of chronic retention with large residual urine volumes (greater than 300 ml), detrusor instability and decreased bladder compliance were associated with chronic renal failure. Ureterovesicular junction obstruction from bladder remodeling in chronic urinary retention was the most commonly proposed mechanism for CRF. However, episodic acute urinary retention, urinary tract infections and secondary hypertension may also have a role. Studies showed significant improvement in renal function after prostate surgery but the acuity of renal failure was generally not known.

CONCLUSIONS

The extent of the association between BPH and CRF is unknown and more community based, observational studies are needed. However, an association exists and it should be considered in men presenting with obstructive BPH or CRF.

Force-length relationship in the pelvic floor muscles under transverse vaginal distension: a method study in healthy women

AIMS

The purpose of this study was to investigate whether there is a relationship between changes in the diameter of the urogenital hiatus and force developed in pelvic floor musculature. In addition, we wanted to examine the reliability of the method that measures force development in the pelvic floor in the transverse direction of the urogenital hiatus.

MATERIALS AND METHODS

Passive and total force in the pelvic floor was measured with an intra-vaginal device in 20 healthy parous volunteers. The measurements were done with a consecutively increasing diameter in the transverse plane of the urogenital hiatus. The procedure was repeated with a few days interval.

RESULTS

The measurements show an increase in force with an increasing device-diameter. The results are reliable at all the diameters tested, estimated by the within-subject day-to-day variability which was non-significant. The 40 mm diameter device is most favourable, estimated by Bland Altman plots of the test-retest measurements.

CONCLUSIONS

Force development in pelvic floor muscles increased as a function of vaginal diameter when measured in the frontal plane. The measurements were reliable at all the different diameters chosen.

The role of bladder-to-urethral reflexes in urinary continence mechanisms in rats

Urethral closure mechanisms during passive increments in intravesicular pressure (Pves) were investigated using microtip transducer catheters in urethane-anesthetized female rats. After a block of reflex bladder contractions by spinal cord transection at T8-T9, abruptly raising Pves to 20, 40, or 60 cmH2O for 2 min induced a bladder pressure-dependent contractile response in a restricted portion of the middle urethra (12.5–15 mm from the urethral orifice) that was abolished by cutting the pelvic nerves bilaterally. In pelvic nerve-intact rats, the bilateral transection of either the pudendal nerves, the nerves to the iliococcygeous/pubococcygeous muscles, or the hypogastric nerves significantly reduced (49–74%) the urethral reflex response induced by passive Pves increases, and combined transection of these three sets of nerves totally abolished the urethra-closing responses. In spinal cord-intact rats, similar urethral contractile responses were elicited during Pves elevation (20 or 40 cmH2O) and were also eliminated by bilateral pelvic nerve transection. After spinal cord and pelvic nerve transection, leak point pressures, defined as the pressure inducing fluid leakage from the urethral orifice during passive Pves elevation by either bladder pressure clamping in 2.5-cmH2O steps or direct compression of the bladder, were significantly lowered by 30–35% compared with sham-operated (spinal cord-transected and pelvic nerve-intact) rats. These results indicate that 1) passive elevation of Pves can elicit pelvic afferent nerve-mediated contractile reflexes in the restricted portion of the urethra mediated by activation of sympathetic and somatic nerves and 2) bladder-to-urethral reflexes induced by passive Pves elevation significantly contribute to the prevention of stress urinary incontinence.

Development of an experimental system for the study of urethral biomechanical function

Despite its principal mechanical function in the storage and release of urine, the biomechanical properties of the urethra have remained largely unexplored. The purpose of this study was to develop and validate an experimental model that can be used for evaluating whole urethral tissue in such a manner. Bladder-urethral specimens were excised from halothane-anesthetized female rats and mounted at in vivo length within the experimental apparatus consisting of a tissue perfusion chamber, an adjustable fluid column, and a laser micrometer. Outer diameter measurements were made at proximal, mid, and distal axial locations in response to increases in intraluminal pressure and after addition of various muscle-responsive agents. Basal smooth muscle tone and regional variations in compliance were detected through pressure-diameter responses. Chemically evoked contractile responses were measured and correspond to regional compositions of intrinsic smooth and striated muscle components. The results presented illustrate the utility of this system, which should permit a more thorough characterization of structure-function relationships and urethral biomechanical function in relation to normal and dysfunctional tissue states.

Urethral closure mechanisms under sneeze-induced stress condition in rats: a new animal model for evaluation of stress urinary incontinence

The urethral closure mechanism under a stress condition induced by sneezing was investigated in urethane-anesthetized female rats. During sneezing, while the responses measured by microtip transducer catheters in the proximal and middle parts of the urethra increased, the response in the proximal urethra was almost negligible when the bladder response was subtracted from the urethral response or when the abdomen was opened. In contrast, the response in the middle urethra during sneezing was still observed after subtracting the bladder response or after opening the abdomen. These responses in the middle urethra during sneezing were significantly reduced approximately 80% by bilateral transection of the pudendal nerves and the nerves to the iliococcygeous and pubococcygeous muscles but not by transection of the visceral branches of the pelvic nerves and hypogastric nerves. The sneeze leak point pressure was also measured to investigate the role of active urethral closure mechanisms in maintaining total urethral resistance against sneeze-induced urinary incontinence. In sham-operated rats, no urinary leakage was observed during sneeze, which produced an increase of intravesical pressure up to 37 +/- 2.2 cmH2O. However, in nerve-transected rats urinary leakage was observed when the intravesical pressure during sneezing exceeded 16.3 +/- 2.1 cmH2O. These results indicate that during sneezing, pressure increases elicited by reflex contractions of external urethral sphincter and pelvic floor muscles occur in the middle portion of the urethra. These reflexes in addition to passive transmission of increased abdominal pressure significantly contribute to urinary continence mechanisms under a sneeze-induced stress condition.

Bladder and urethral responses to pelvic nerve stimulation in the pig

OBJECTIVE

The aim of our study of the pig was to investigate the responses of smooth muscle of the bladder and the urethral sphincter to preganglionic parasympathetic stimulation, and to assess the effect on the lower urinary tract of IV administration of alpha,beta-methylene-ATP.

MATERIALS AND METHODS

In seven anaesthetised female pigs, the responses to repeated 20 s pelvic nerve stimulations before and after IV administration of 0.02 mg/kg alpha-beta-methylene-ATP, and the responses to the drug itself, were recorded in the bladder and the urethra separately.

RESULTS

In the urethral high-pressure zone, pre-stimulation pressure was a mean of 61+/-11 cmH2O. During pelvic nerve stimulation, urethral pressure declined by 48+/-9 cmH2O, while the bladder pressure increased to 30+/-18 cmH2O. The rate of pressure changes during the first 3 s of stimulation (initiation of voiding) was larger in the urethra than in the bladder (urethral pressure decrease: 13.0+/-3.1 cmH2O/s, bladder pressure increase: 3.2+/-2.5 cmH2O/s). Administration of alpha,beta-methylene-ATP was followed by a significant but temporary enlargement in the bladder response to pelvic nerve stimulation to 36+/-20 cmH2O, p = 0.028, n = 7, but no change in urethral response.

CONCLUSIONS

At least 80% of the urethral pre-stimulation pressure was exerted by the smooth muscle. The synergic activation of the detrusor and the urethral smooth muscle in response to preganglionic parasympathetic nerve stimulation was controlled by the peripheral nerves or by the neuromuscular transmission. Administration of alpha,beta-methylene-ATP increased the bladder response to pelvic nerve stimulation without changing the urethral response.

Modelized analysis of pressure-flow studies of patients with lower urinary tract symptoms due to benign prostatic enlargement

AIMS

To gain insight from an adaptable computer model of micturition into the pathophysiological phenomena occurring during voiding in men with lower urinary tract symptoms due to benign prostatic enlargement (BPE).

METHODS

By using the Valentini-Besson-Nelson (VBN) micturition model, we proceeded with an in-depth and systematic analysis of the pressure-flow studies of 71 patients (119 tracings) provided by three different institutions.

RESULTS

The modelized analysis identified and quantified several pathophysiological phenomena during voiding: compressive obstruction, variations in detrusor contraction force (enhanced or reduced), progressive relaxation of the prostatic fossa, occasional detrusor-bladder neck coupling, and sphincteric control dysfunctions. Once these phenomena were taken into account by using a set of new parameters, the computed flow rate and detrusor pressure curves became very similar to the recorded ones.

CONCLUSIONS

The accuracy of this sophisticated analysis allows us to separate and to study during each voiding the phenomena belonging to the urethra, the detrusor, the bladder neck, the prostate, and their neurologic coordination in BPE patients.

Urodynamic patterns of normal male micturition: influence of water consumption on urine production and detrusor function

PURPOSE

Urodynamic characterization of normal male micturition can be a useful standard in the analysis of data on patients complaining of voiding dysfunction. The validity of such a standard is based on the need to obtain baseline parameters of pressure flow values, an important consideration when evaluating prostatic obstruction and its treatment. While current numerical pressure flow values provide a useful summary of the voiding sequence, a more complete analysis of the pattern of normal voiding may reveal more functionally useful information concerning micturition. We establish basic experimental conditions that simulate normal voiding of physiologically produced urine by the kidneys measured at intervals representing real stages of bladder filling. We report the results of an investigation designed to study consecutive micturitions at bladder volumes determined by water consumption and endogenous circadian rhythm. Our particular focus is to examine critically the urodynamic pattern of pressure flow and obtain evidence to support the hypothesis that fluid consumption has an important role in detrusor function.

MATERIALS AND METHODS

Urodynamic studies were conducted on 39 asymptomatic male volunteers with a mean age of 25.8 years (range 21 to 31) and mean weight of 75.5 kg. (range 63 to 95). Volunteers were divided into 2 groups according to water consumption regimen of 30 ml./kg. daily (17 patients, group 1) and 60 ml./kg. daily (12, group 2). Bladder pressure was monitored via a suprapubic catheter and abdominal pressure was measured via a rectal balloon using an ambulatory system. Average duration of each monitoring period was 20.5 hours. Detrusor pressure and flow rate records from each subject were identified, and consecutive filling and voiding phases were averaged during the entire monitoring period using the onset of micturition as a time marker. The average pattern of pressure, flow rate, cumulative volume and contractility curves for each subject, as well each for group, was computed and graphically presented. For each group the average parameters of urethral opening pressure, maximum detrusor pressure, detrusor pressure at maximum flow rate, bladder capacity and bladder contraction strength were calculated and compared statistically. Numerical values are mean +/- SE.

RESULTS

Water consumption and urine production rate influenced the pattern and many of the urodynamic parameters of micturition. In both groups there was a detrusor pressure increase before voiding and numerically maximum detrusor pressure consistently occurred before micturition started. Micturition pattern showed an asymptotic relationship between pressure and flow. Doubling of water consumption increased urethral opening pressure from 51.2 +/- 3.2 to 61.5 +/- 5.1 (p <0.05), maximum detrusor pressure from 58.9 +/- 4.5 to 70.0 +/- 6.2 cm. H(2)O (p <0.01) and contractility from 15.4 +/- 1.4 to 17.7 +/- 1.4 w/m(2). There were no significant differences due to water consumption in maximum flow rate (24.4 +/- 1.4 to 25.2 +/- 1.8 ml. per second) or bladder capacity (286 +/- 20 to 329 +/- 15 ml.) but a significant increase in the number of micturitions from 5.8 +/- 0.5 to 9.8 +/- 0.5 per day (p <0.001) proportional to water consumption.

CONCLUSIONS

The configuration of the observed pressure flow characteristics of the normal male is suggestive of the "Starlings law" relationship and the pattern of the urodynamic parameters were markedly different from those reported in the current standardization literature, suggesting the need to revise the current concept of normal male micturition. Voiding pressure and contractility increased in accordance with water consumption and urine production.