The vesico-urethral pressuregram analysis of urethral function under stress

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.

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.

Mechanisms of continence and surgical cure in female and male SUI: surgical research initiatives

AIMS

To report the conclusions of the Think Tank on mechanisms of incontinence and surgical cure in female and male SUI: surgical research initiatives during the ICI-RS meeting in 2010.

METHODS

The sub-group considered five areas for future research in stress urinary incontinence (SUI); (i) epidemiology and public health efforts in SUI, (ii) the basic sciences examining the physiology and pathophysiology of the continence mechanism, (iii) diagnostic techniques and clinical assessment of SUI, (iv) the future of treatment and surgical cure, and (v) the separate issue of male SUI.

RESULTS

Roadblocks to progress were identified for each of the five directions.

CONCLUSIONS

Future research directions are suggested for each of these areas.

Differences in continence system between community-dwelling black and white women with and without urinary incontinence in the EPI study

OBJECTIVE

We sought to compare continence system function of black and white women in a population-based sample.

STUDY DESIGN

As part of a cross-sectional population-based study, black and white women ages 35-64 years were invited to have pelvic floor testing to achieve prespecified groups of women with and without urinary incontinence. We analyzed data collected from 335 women classified as continent (n = 137) and stress (n = 102) and urge (n = 96) incontinent based on full bladder stress test and symptoms. Continence system functions were compared across racial and continence groups.

RESULTS

Comparing black to white women, maximal urethral closure pressure (MUCP) was 22% higher in blacks than whites (68.0 vs 55.8 cm H(2)O, P < .0001). White and black women with stress incontinence had MUCP 19% and 23% lower than continent women. MUCP in urge incontinent white women was as low as stress incontinent whites, but blacks with urge had normal urethral function.

CONCLUSION

Black women have higher urethral closure pressures than white women. White women with urge incontinence, but not black women, have reduced MUCP.

Vaginal birth and de novo stress incontinence: relative contributions of urethral dysfunction and mobility

OBJECTIVE

To evaluate the relative contributions of urethral mobility and urethral function to stress incontinence.

METHODS

This was a case-control study with group matching. Eighty primiparous women with self-reported new stress incontinence 9-12 months postpartum were compared with 80 primiparous continent controls to identify impairments specific to stress incontinence. Eighty nulliparous continent controls were evaluated as a comparison group to allow us to determine birth-related changes not associated with stress incontinence. Urethral function was measured with urethral profilometry, and vesical neck mobility was assessed with ultrasound and cotton swab test. Urethral sphincter anatomy and mobility were evaluated using magnetic resonance imaging. The associations among urethral closure pressure, vesical neck movement, and incontinence were explored using logistic regression.

RESULTS

Urethral closure pressure (+/-standard deviation) in primiparous incontinent women (62.9+/-25.2 cm H(2)0) was lower than in primiparous continent women (83.9+/-21.0, P<.001; effect size d=0.91) who were similar to nulliparous women (90.3+/-25.0, P=.091). Vesical neck movement measured during cough with ultrasonography was the mobility measure most associated with stress incontinence; 15.6+/-6.2 mm in incontinent women compared with 10.9+/-6.2 in primiparous continent women (P<.001, d=0.76) or nulliparas (9.9+/-5.0, P=.322). Logistic regression disclosed the two-variable model (max-rescaled R(2)=0.37, P<.001) was more strongly associated with stress incontinence than either single-variable model, urethral closure pressure (R(2)=0.25, P<.001) or vesical neck movement (R(2)=0.16 P<.001).

CONCLUSION

Lower maximal urethral closure pressure is the measure most associated with de novo stress incontinence after first vaginal birth followed by vesical neck mobility.

LEVEL OF EVIDENCE

II.

Evaluation of the dynamic responses of female pelvic floor using a novel vaginal probe

The female pelvic floor (PF) provides anatomical support to many visceral organs, such as uterus, bladder, urethra, vagina, and rectum. Physiologically, the PF is made up of a number of highly coordinated muscle groups organized to respond to postural and abdominal stresses to maintain continence. In this article, we describe a new methodology for the evaluation of PF strength using a novel vaginal probe design, having force and displacement sensors. This design was derived on the basis of imaging data showing that force/displacement characteristics are important determinants of the integrity of the PF function. The prototype probe used was constructed to evaluate the dynamic responses to slow voluntary contractions as well as reflex stress contractions. Initial clinical experiments were performed on nine healthy female subjects. The probe recorded the force and displacement signals on the anterior and posterior sides of the subjects' middle vaginal wall in voluntary PF muscle contraction and cough. The time domain and frequency domain characteristics of the dynamic responses, including the force and displacement responses, of the vaginal wall were measured and the power and energy associated with the dynamic responses of the PF were analyzed showing the differences between the dynamic characteristics of the voluntary PF muscle contraction and cough. Results show that voluntary PF muscle contractions have higher amplitudes, longer duration, and higher power than reflex contractions. The design of this probe enables the measurement of force and displacement during rapidly occurring events.

Functional anatomy of the female pelvic floor

The anatomic structures in the female that prevent incontinence and genital organ prolapse on increases in abdominal pressure during daily activities include sphincteric and supportive systems. In the urethra, the action of the vesical neck and urethral sphincteric mechanisms maintains urethral closure pressure above bladder pressure. Decreases in the number of striated muscle fibers of the sphincter occur with age and parity. A supportive hammock under the urethra and vesical neck provides a firm backstop against which the urethra is compressed during increases in abdominal pressure to maintain urethral closure pressures above the rapidly increasing bladder pressure. This supporting layer consists of the anterior vaginal wall and the connective tissue that attaches it to the pelvic bones through the pubovaginal portion of the levator ani muscle, and the uterosacral and cardinal ligaments comprising the tendinous arch of the pelvic fascia. At rest the levator ani maintains closure of the urogenital hiatus. They are additionally recruited to maintain hiatal closure in the face of inertial loads related to visceral accelerations as well as abdominal pressurization in daily activities involving recruitment of the abdominal wall musculature and diaphragm. Vaginal birth is associated with an increased risk of levator ani defects, as well as genital organ prolapse and urinary incontinence. Computer models indicate that vaginal birth places the levator ani under tissue stretch ratios of up to 3.3 and the pudendal nerve under strains of up to 33%, respectively. Research is needed to better identify the pathomechanics of these conditions.

Effects of Aging on Lower Urinary Tract and Pelvic Floor Function in Nulliparous Women

OBJECTIVE

To evaluate the effects of aging, independent of parity, on pelvic organ and urethral support, urethral function, and levator function in a sample of nulliparous women.

METHODS

A cohort of 82 nulliparous women, aged 21-70 years, were recruited from the community through advertisements. Subjects underwent pelvic examination using pelvic organ prolapse quantification, urethral angles by cotton-tipped swab, and multichannel urodynamics and uroflow. Vaginal closure force was quantified using an instrumented vaginal speculum. Subjects were grouped into five age categories and analyses performed using t tests, Fisher exact tests, Kruskal-Wallace, and Pearson correlation coefficients. Multiple linear regression modeling was performed to adjust for factors that might confound the results of our primary outcomes.

RESULTS

Increasing age was associated with decreasing maximal urethral closure pressure (r=-0.758, P<.001) with a 15-cm-H(2)O decrease in pressure per decade. Pelvic organ support as measured by pelvic organ prolapse quantification did not differ by age group. Levator function as measured by resting vaginal closure force and augmentation of vaginal closure force also did not change with increasing age.

CONCLUSION

In a sample of nulliparous women between 21 and 70 years of age maximal urethral closure pressure in the senescent urethra was 40% of that in the young urethra; increasing age did not affect clinical measures of pelvic organ support, urethral support, and levator function.

LEVEL OF EVIDENCE

III.

Primer: questionnaires versus urodynamics in the evaluation of lower urinary tract dysfunction—one, both or none?

What is the role of urodynamic assessments and have we made too much use of them? Is there a correlation between symptoms and underlying pathophysiology? These questions are addressed in this article. There are disparities in the assessment of lower urinary tract dysfunction between the accuracy of symptomatic assessment and the underlying pathophysiology. This is particularly evident with voiding symptoms, in contrast to storage symptoms, and has fuelled the debates that have resulted in the abandonment of the term 'prostatism' in favor of 'lower urinary tract symptoms', whereas the term 'overactive bladder syndrome' has been embraced as a storage symptom complex. Clearly, voiding disorders principally affect men, whilst storage disorders are more common in women. Much has been written and spoken about regarding the use of symptomatic assessment versus urodynamics in the assessment of lower urinary tract symptoms in men, whilst there has been a clearer consensus on the potential usefulness of urodynamics in the assessment of storage disorders, and so this article focuses principally on the latter topic.

A critical review of diagnostic criteria for evaluating patients with symptomatic stress urinary incontinence

The first paper in this section is a review by several highly respected authors of diagnostic criteria for evaluating patients with symptomatic stress urinary incontinence, and is followed by a review of the role of urgency and its measurement in the overactive bladder symptom syndrome, with emphasis on current concepts and future prospects. These are two important papers, which point the reader in the direction of a greater understanding of these conditions. The concept of alpha-blockade before a trial without catheter after acute urinary retention is revisited by authors from the UK, who used tamsulosin in a randomized controlled trial. They found that it is appropriate to recommend tamsulosin for such use in this condition.

Pathophysiology of adult urinary incontinence

The anatomic structures that prevent stress incontinence, urinary incontinence during elevations in abdominal pressure, can be divided into 2 systems: a sphincteric system and a supportive system. The action of the vesical neck and urethral sphincteric mechanisms at rest constrict the urethral lumen and keep urethral closure pressure higher than bladder pressure. The striated urogenital sphincter, the smooth muscle sphincter in the vesical neck, and the circular and longitudinal smooth muscle of the urethra all contribute to closure pressure. The mucosal and vascular tissues that surround the lumen provide a hermetic seal, and the connective tissues in the urethral wall also aid coaptation. Decreases in striated muscle sphincter fibers occur with age and parity, but the other tissues are not well understood. The supportive hammock under the urethra and vesical neck provides a firm backstop against which the urethra is compressed during increases in abdominal pressure to maintain urethral closure pressures above rapidly increasing bladder pressure. The stiffness of this supportive layer is presumed to be important to the degree to which compression occurs. This supporting layer consists of the anterior vaginal wall and the connective tissue that attaches it to the pelvic bones through the pubovaginal portion of the levator ani muscle and also the tendinous arch of the pelvic fascia. Activation of the levator muscle during abdominal pressurization is important to this stabilization process. The integrity of the connection between the vaginal wall and tendinous arch also plays an important role.

Mechanisms of female urinary continence under stress: frequency spectrum analysis

Intravesical and urethral pressure signals during cough and Valsalva maneuvers for 15 continent women were analyzed with frequency spectrum analysis. Clear modulation of the urethral pressure changes by the intravesical pressure rise during stress maneuvers was demonstrated in the frequency bands of 14 and 7 Hz for cough and Valsalva, respectively. The linearity between the urethral and intravesical pressure signals was strong for cough, but relatively weaker for Valsalva. The observed linearity lead to the formulation of a modified continence equation to mathematically quantify stress leak point pressure (sLPP): sLPP=MUCP/(1-alpha1)+RBP. This algebraic equation demonstrated that sLPP depends on pressure transmission, resting bladder pressure, and maximum urethral closure pressure. The equation was validated with excellent theoretical predictions for the 15 continent subjects (R(2)=0.98 and 0.97 for cough and Valsalva leak point pressure, respectively) and good but somewhat weaker predictions for 46 stress incontinent women (R(2)=0.79 and 0.48, respectively). It has been shown that pressure transmission plays the most important role in female continence function, while it may be attributable to passive structural origin as evidenced by the minimal time delay between the two pressure signals, in the order of a few milliseconds. It can be concluded that coughing seems to have a more mechanical, rather than neuromuscular basis for its signal dynamics. This study suggests that a complete assessment of female stress continence function requires comprehensive urodynamic information in terms of pressure transmission, maximum urethral closure pressure, and resting bladder pressure.

The functional anatomy of the female pelvic floor and stress continence control system

This paper provides an overview of the functional anatomy of the structures responsible for controlling urinary continence under stress. The stress continence control system can be divided into two parts: the system responsible for bladder neck support, and the system responsible for sphincteric closure. Age- and injury-related changes in each of these systems are discussed. Understanding the pathophysiology of incontinence on the anatomical level will help to lead to identification of specific defects, thereby allowing better individualized treatment for the incontinent patient.

Principles of urodynamics pressure measurement and its implication to female continence function

Urodynamic pressure measurements using catheters have been widely used among clinicians. More often objective interpretation of urodynamic pressure measurements requires fundamental understanding of pressure measurement techniques due to many measurement artifacts. In this study we developed a simplified compound thick-walled cylinder model to investigate the mechanical nature of urodynamic pressure measurement as well as pressure transmission. Efficacy of collagen implantation was also explored. Lamé's formulation was used to find analytical solutions. Pressure transmission can be related to catheter caliber and the compressibility of the urethral tissue (poisson ratio) in a simple mathematical form. The theoretical pressure transmission ratio will be 133% with the additional incompressibility assumption, reflecting the passive structural transmission of intraabdominal pressure increase. The relationship between the pressure measurement error and the catheter caliber was found to be linear (r2 = 0.94 +/- 0.04) and two or more pressure measurements need to be used to find the uninstrumented pressure. It was predicted that collagen implantation treatment might improve the pressure transmission ratio maximally by 33%.

A pelvic muscle precontraction can reduce cough-related urine loss in selected women with mild SUI

OBJECTIVES

To test the hypothesis that selected older women with mild-to-moderate stress urinary incontinence (SUI) can learn to demonstrate significantly reduced urine loss in 1 week by intentionally contracting the pelvic floor muscles before and during a cough (a skill we have termed "The Knack").

DESIGN

A prospective, randomized, single-blind interventional study.

SETTING

The Older American Independence Center, a federally sponsored research program affiliated with the University of Michigan in Ann Arbor, Michigan.

PARTICIPANTS

Twenty-seven women with a mean (SD) age of 68.0 (5.5) years, self-reported SUI, and demonstrable urine loss during a deep cough.

INTERVENTION

Women were randomized to an immediate intervention group (Group I: n=13) who were taught the Knack after their first clinic visit, or a wait-listed control group (Group II: n=14) who were taught the Knack after 1 month.

MEASUREMENTS

At 1 week after instruction, we tested the efficacy of the Knack in a standing stress test by (1) comparing the volumes of cough-related urine loss leaked by all subjects, with and without use of the Knack, and (2) comparing the volumes of cough-related urine loss leaked by Group I, using the Knack, with Group II, which had not yet been taught the Knack.

RESULTS

Intra-individual results showed that at 1-week follow-up, the Knack was used to reduce urine loss resulting from a medium cough by an average of 98.2%, compared with that of a similar cough performed 1 minute before without the Knack (P=.009); likewise urine loss was reduced by an average of 73.3% (P=.003) in a deep cough. Reduction in urine loss was not significantly correlated with a digital measure of pelvic floor muscle strength.

CONCLUSION

Within 1 week, selected older women with mild-to-moderate SUI can acquire the skill of using a properly-timed pelvic floor muscle contraction to significantly reduce urine leakage during a cough.