The pressure within a collapsed tube, with special reference to urethral pressure

Mathematical modeling of the lower urinary tract: A review

AIMS

Understand what progress has been made toward a functionally predictive lower urinary tract (LUT) model, identify knowledge gaps, and develop from them a path forward.

METHODS

We surveyed prominent mathematical models of the basic LUT components (bladder, urethra, and their neural control) and categorized the common modeling strategies and theoretical assumptions associated with each component. Given that LUT function emerges from the interaction of these components, we emphasized attempts to model their connections, and highlighted unmodeled aspects of LUT function.

RESULTS

There is currently no satisfactory model of the LUT in its entirety that can predict its function in response to disease, treatment, or other perturbations. In particular, there is a lack of physiologically based mathematical descriptions of the neural control of the LUT.

CONCLUSIONS

Based on our survey of the work to date, a potential path to a predictive LUT model is a modular effort in which models are initially built of individual tissue-level components using methods that are extensible and interoperable, allowing them to be connected and tested in a common framework. A modular approach will allow the larger goal of a comprehensive LUT model to be in sight while keeping individual efforts manageable, ensure new models can straightforwardly build on prior research, respect potential interactions between components, and incentivize efforts to model absent components. Using a modular framework and developing models based on physiological principles, to create a functionally predictive model is a challenge that the field is ready to undertake.

Fluid mechanical modeling of the upper urinary tract

The upper urinary tract (UUT) consists of kidneys and ureters, and is an integral part of the human urogenital system. Yet malfunctioning and complications of the UUT can happen at all stages of life, attributed to reasons such as congenital anomalies, urinary tract infections, urolithiasis and urothelial cancers, all of which require urological interventions and significantly compromise patients' quality of life. Therefore, many models have been developed to address the relevant scientific and clinical challenges of the UUT. Of all approaches, fluid mechanical modeling serves a pivotal role and various methods have been employed to develop physiologically meaningful models. In this article, we provide an overview on the historical evolution of fluid mechanical models of UUT that utilize theoretical, computational, and experimental approaches. Descriptions of the physiological functionality of each component are also given and the mechanical characterizations associated with the UUT are provided. As such, it is our aim to offer a brief summary of the current knowledge of the subject, and provide a comprehensive introduction for engineers, scientists, and clinicians who are interested in the field of fluid mechanical modeling of UUT. This article is categorized under: Cancer > Biomedical Engineering Infectious Diseases > Biomedical Engineering Reproductive System Diseases > Biomedical Engineering.

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.

Urethral Pressure Measurement as a Tool for the Urodynamic Diagnosis of Detrusor Sphincter Dyssynergia

Purpose

To describe a technique for urodynamic diagnosis of detrusor sphincter dyssynergia (DSD) using urethral pressure measurements and examine potential associations between urethral pressure and bladder physiology among patients with DSD.

Methods

Multiple sclerosis (MS) and spinal cord injured (SCI) patients with known DSD diagnosed on videourodynamics (via electromyography or voiding cystourethrography) were retrospectively identified. Data from SCI and MS patients with detrusor overactivity (DO) without DSD were abstracted as control group. Urodynamics tracings were reviewed and urethral pressure DSD was defined based on comparison of DSD and control groups.

Results

Seventy-two patients with DSD were identified. Sixty-two (86%) had >20 cm H₂O urethral pressure amplitude during detrusor contraction. By comparison, 5 of 23 (22%) of control group had amplitude of >20 cm H₂O during episode of DO. Mean duration of urethral pressure DSD episode was 66 seconds (range, 10–500 seconds) and mean urethral pressure amplitude was 73 cm H₂O (range, 1–256 cm H₂O). Longer (>30 seconds) DSD episodes were significantly associated with male sex (81% vs. 50%, P=0.013) and higher bladder capacity (389 mL vs. 219 mL, P=0.0004). Urethral pressure amplitude measurements during DSD were not associated with significant urodynamic variables or neurologic pathology.

Conclusions

Urethral pressure amplitude of >20 cm H₂O during detrusor contraction occurred in 86% of patients with known DSD. Longer DSD episodes were associated with larger bladder capacity. Further studies exploring the relationship between urethral pressure measurements and bladder physiology could phenotype DSD as a measurable variable rather than a categorical observation.

Comparison of water and air charged transducer catheter pressures in the evaluation of cystometrogram and voiding pressure studies

AIMS

Air-charged (AC) and water-perfused (WP) catheters have been evaluated for differences in measuring pressures for voiding dysfunction. Typically, a two-catheter system was used. We believe that simultaneous pressure measurements with AC and WP in a single catheter will provide analogous pressures for coughs, Valsalvas, and maximum pressures in voiding pressure studies (VPS).

METHODS

This IRB approved prospective study included 50 women over age 21. AC dual TDOC catheters were utilized. The water-filling channel served as the bladder filler and the water pressure readings. Patients were evaluated with empty bladders and at volumes of 50-100 mL, 200 mL, and maximum capacity with cough and Valsalva maneuvers. Comparative analysis was performed on maximum stress peak pressures. At maximum bladder capacity, VPS was done and maximum voiding pressure was recorded.

RESULTS

Comparing coughs and Valsalva maneuvers pressures, there was significant increase in variability between AC and WP measurements with less than 50 mL volume (P < 0.001). Significant correlations were observed between AC and WP measurements for coughs and Valsalvas with bladder volume over 50 mL. Visual impression showed virtually identical tracings. Cough measurements had an average difference of 0.25 cmH₂ O (±8.81) and Valsalva measurements had an average difference of 3.15 cmH₂ O (±4.72). Thirty-eight women had usable maximum voiding pressure measurements and had a strong correlation.

CONCLUSIONS

Cystometrogram and maximum voiding pressure measurements done with either water or air charged catheters will yield similarly accurate results and are comparable. Results suggest more variability at low bladder volumes <50 mL.

Assessing the reproducibility of high definition urethral pressure profilometry and its correlation with an air-charged system

INTRODUCTION

Recently, a new urodynamic method for the assessment of stress urinary incontinence called high definition urethral pressure profilometry (HD-UPP) has been introduced. This method combines a novel microtip catheter with advanced signal processing to enable spatial data location and the reconstruction of a pressure image inside the urethra. In order to assess the reproducibility of HD-UPP data, we statistically evaluate HD-UPP datasets and compare them to data from a double balloon air-charged system.

MATERIALS AND METHODS

Both catheters are used on sedated female minipigs. Data from the microtip catheter are processed through a signal reconstruction algorithm, urodynamic features are extracted, and compared to the air-charged system. Reproducibility of HD-UPP data is assessed by statistically evaluating consecutive, intra-individual datasets.

RESULTS

HD-UPP delivers results in agreement with previous comparisons of microtip and air-charged systems. The average deviation of two consecutive, intra-individual pressure images is very low at 7 cm H₂ O.

CONCLUSIONS

HD-UPP provides physicians with detailed information on the pressure distribution inside the urethra. Through comparison with an air-charged catheter, it is shown that HD-UPP delivers results in agreement with previous studies on the comparison of microtip and air-charged catheters. It provides excellent reproducibility, as the difference between sequentially measured profiles from the same minipig is significantly lower than the one between profiles from different minipigs.

Optimum anesthesia for reliable urethral pressure profilometry in female dogs and goats

OBJECTIVES

To investigate the effects of propofol and isoflurane on urethral pressure profilometry of female dogs and goats, and to identify the method of anesthesia that least influences urethral pressure profilometry and to assess its reproducibility.

METHODS

The effects of premedication with midazolam, propofol sedation and isoflurane anesthesia were assessed in five female dogs. The effects of propofol and isoflurane were compared in seven goats, whereas in another group of 19 goats, the state of deep propofol sedation was compared with the state of recovery from propofol sedation. The coefficient of reproducibility and within-subject coefficient of variation were calculated to evaluate test-retest reproducibility.

RESULTS

In conscious female dogs, maximal urethral closure pressure and functional area were significantly higher than under propofol or isoflurane (P = 0.04), but not different from the recovery state. In six of seven goats, maximal urethral closure pressure and functional area were higher when measured under propofol sedation than under isoflurane (median maximal urethral closure pressure, 69 vs 47 cmH2 O; P = 0.03). Maximal urethral closure pressure was lower under propofol than during recovery from propofol in 17 of 19 goats (median maximal urethral closure pressure, 54 vs 66 cmH2 O; P < 0.001). The test-retest coefficient of reproducibility for goats was 28 cmH2 O, and the within-subject coefficient of variation was 16%.

CONCLUSIONS

In dogs, urethral pressure profilometry should be measured in conscious animals whenever possible. In goats, urethral pressure profilometry is least affected during recovery from propofol sedation, and it shows acceptable reproducibility under this condition.

Maximum Urethral Closure Pressure Increases After Successful Adjustable Continence Therapy (ProACT) for Stress Urinary Incontinence After Radical Prostatectomy

OBJECTIVE

To evaluate changes of the urethral pressure profile (UPP) after implantation of adjustable continence therapy (ProACT), a minimally invasive procedure in which 2 volume-adjustable balloons are placed periurethrally for treatment of male stress urinary incontinence. The working mechanism of the ProACT to achieve continence has not been fully understood. We hypothesized that successful treatment with ProACT improves urinary continence by inducing a significant increase in static urethral pressure.

MATERIALS AND METHODS

We included patients who underwent UPP before and after ProACT implantation. UPPs were initially performed with the Brown-Wickham water perfusion method and later with the T-DOC Air-Charged catheter method. Pre- and postoperative UPPs and International Prostate Symptom Scores were evaluated. UPP measurements of successfully (no or 1 precautionary pad per day) and unsuccessfully treated patients were compared.

RESULTS

Twenty-seven patients were included in the study; 23 patients were successfully and 4 patients were unsuccessfully treated. Maximum urethral closure pressure (MUCP) increased significantly from median 58.0 to 79.0 cmH2O in the successfully treated group (P = .001). Within the subgroup of unsuccessfully treated patients, MUCP did not change significantly (P = .715). The change in MUCP was statistically significantly different between the successful and unsuccessful group (P = .034). Total score of the International Prostate Symptom Scores did not change significantly after ProACT implantation (P = .097).

CONCLUSION

Successful treatment with ProACT is associated with a significant increase of MUCP. This implies that increased static urethral pressure contributes to the working mechanism of the ProACT device to achieve continence.

Signal processing in urodynamics: towards high definition urethral pressure profilometry

BACKGROUND

Urethral pressure profilometry (UPP) is used in the diagnosis of stress urinary incontinence (SUI) which is a significant medical, social, and economic problem. Low spatial pressure resolution, common occurrence of artifacts, and uncertainties in data location limit the diagnostic value of UPP. To overcome these limitations, high definition urethral pressure profilometry (HD-UPP) combining enhanced UPP hardware and signal processing algorithms has been developed. In this work, we present the different signal processing steps in HD-UPP and show experimental results from female minipigs.

METHODS

We use a special microtip catheter with high angular pressure resolution and an integrated inclination sensor. Signals from the catheter are filtered and time-correlated artifacts removed. A signal reconstruction algorithm processes pressure data into a detailed pressure image on the urethra's inside. Finally, the pressure distribution on the urethra's outside is calculated through deconvolution. A mathematical model of the urethra is contained in a point-spread-function (PSF) which is identified depending on geometric and material properties of the urethra. We additionally investigate the PSF's frequency response to determine the relevant frequency band for pressure information on the urinary sphincter.

RESULTS

Experimental pressure data are spatially located and processed into high resolution pressure images. Artifacts are successfully removed from data without blurring other details. The pressure distribution on the urethra's outside is reconstructed and compared to the one on the inside. Finally, the pressure images are mapped onto the urethral geometry calculated from inclination and position data to provide an integrated image of pressure distribution, anatomical shape, and location.

CONCLUSIONS

With its advanced sensing capabilities, the novel microtip catheter collects an unprecedented amount of urethral pressure data. Through sequential signal processing steps, physicians are provided with detailed information on the pressure distribution in and around the urethra. Therefore, HD-UPP overcomes many current limitations of conventional UPP and offers the opportunity to evaluate urethral structures, especially the sphincter, in context of the correct anatomical location. This could enable the development of focal therapy approaches in the treatment of SUI.

A Method for Recording Urethral Pressure Profiles in Female Rats

Aims

Urethral pressure profile (UPP) and leak-point pressure (LPP) measurements as well as external urethral sphincter (EUS) electromyography (EMG) and videourodynamic analyses are the primary methods for evaluating urethral function in humans. However, UPP recording in female rats, a widely used animal model, is challenging due to their small body sizes. This study reports a novel method for recording UPP in female rats.

Materials and Methods

Seventeen anesthetized female rats were studied. LPP data for 14 rats were included. The other 3 rats were excluded because of death or abnormal urogenital organs. UPP curves were recorded using a modified water-perfusion catheter system, with the lateral hole facing the 3-, 6-, 9-, and 12-o’clock positions in a randomized sequence. LPP, functional urethral length (FUL) and maximum urethral closure pressure (MUCP) were analyzed.

Results

The mean LPP was 64.39 ± 20.29 cm H₂O. The mean FUL and MUCP values at the 3-, 6-, 9-, and 12-o’clock positions were 12.90 ± 1.20, 16.70 ± 1.95, 13.90 ± 2.42, and 11.60 ± 0.97 mm, respectively, and 38.70 ± 11.85, 33.90 ± 11.82, 37.40 ± 11.95, and 71.90 ± 23.01 cm H₂O, respectively. The FUL at the 6-o’clock position and MUCP at the 12-o’clock position were significantly greater than those at the other 3 positions. The FUL and MUCP of repeated UPP recordings were not significantly different than those of the first recordings.

Conclusions

UPP recording using a modified method based on a water-perfusion catheter system is feasible and replicable in female rats. It produces UPP curves that sensitively and appreciably reflect detailed pressure changes at different points within the urethra and thus provides opportunity to evaluate urethral structures, especially the urethral sphincter, in detail. These results may enhance the utility of female rat models in research of urinary sphincter mechanisms.

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.

Towards a Treatment of Stress Urinary Incontinence: Application of Mesenchymal Stromal Cells for Regeneration of the Sphincter Muscle

Stress urinary incontinence is a significant social, medical, and economic problem. It is caused, at least in part, by degeneration of the sphincter muscle controlling the tightness of the urinary bladder. This muscular degeneration is characterized by a loss of muscle cells and a surplus of a fibrous connective tissue. In Western countries approximately 15% of all females and 10% of males are affected. The incidence is significantly higher among senior citizens, and more than 25% of the elderly suffer from incontinence. When other therapies, such as physical exercise, pharmacological intervention, or electrophysiological stimulation of the sphincter fail to improve the patient’s conditions, a cell-based therapy may improve the function of the sphincter muscle. Here, we briefly summarize current knowledge on stem cells suitable for therapy of urinary incontinence: mesenchymal stromal cells, urine-derived stem cells, and muscle-derived satellite cells. In addition, we report on ways to improve techniques for surgical navigation, injection of cells in the sphincter muscle, sensors for evaluation of post-treatment therapeutic outcome, and perspectives derived from recent pre-clinical studies.

Urethral pressure reflectometry, a novel technique for simultaneous recording of pressure and cross-sectional area in the prostatic urethra: testing in men without bothersome lower urinary tract symptoms

OBJECTIVE

Urethral pressure reflectometry (UPR) was introduced in 2005, for simultaneous measurement of pressure and cross-sectional area in the female urethra. It has shown to be more reproducible than conventional pressure measurement. Recently, it has been tested in the anal canal and the prostatic urethra. The primary aim of this study was to describe UPR in men without bothersome lower urinary tract symptoms.

MATERIAL AND METHODS

The study investigated 18 men, median age 59 (range 50-77) with UPR and pressure-flow analyses (PQ), the International Prostate Symptom Score and the Danish version of Prostate Symptom Score, flow rate, residual urine measurements, transrectal ultrasound, urethral pressure profilometry and visual analogue scale (Discomfort). UPR parameters measured were opening and closing pressure, opening and closing elastance and hysteresis, from the bladder neck to the sphincter region.

RESULTS

All UPR parameters increased significantly from the bladder neck to the sphincter region, except for the opening pressure between the prostate and the sphincter region. Seven men were obstructed according to PQ, but with no significant differences in any other standard urodynamic parameters. The hysteresis in the sphincter region was significantly lower in the obstructed group (p = 0.005). Discomfort was significantly lower with PQ compared to UPR (p = 0.04). Nine men had slight bleeding from the urethra during measurement with UPR.

CONCLUSIONS

The increase in all parameters from the bladder neck to the sphincter region is consistent with previous studies measuring the same parameters. The hysteresis may explain why seven men were obstructed according to PQ.

Urodynamic quantification of decrease in sphincter function after radical prostatectomy: relation to postoperative continence status and the effect of intensive pelvic floor muscle exercises

AIMS

We analyzed the impact of radical retropubic prostatectomy (RRP) on the urethral sphincter function as assessed by urethral pressure profilometry (UPP) and its relation to post-radical prostatectomy continence status. Furthermore, we analyzed the effect of intensive pelvic floor muscle exercises (PFME) on the urethral sphincter function.

METHODS

Sixty-six patients were included in the study. UPP was performed before RRP and 26 weeks after catheter removal. All patients were instructed in PFME, however, the intensity of PFME varied between instructions based on an information folder only (F-PFME) and intensive guidance by a physiotherapist, in addition to the folder (PG-PFME).

RESULTS

In 66 patients, pre- as well as postoperative UPP was evaluable. After surgery, the functional profile length and the maximum urethral closure pressure (MUCP) showed a median decrease of 64% and 41%, respectively. For men who had regained continence after 6 months the median MUCP was significantly higher both before and after operation as compared to men who were still incontinent. In multivariate analysis, non-nerve sparing approach was a prognostic factors for a higher relative decrease of the MUCP after RRP. Comparing the PG-PFME group with the F-PFME group there were no significant differences in changes in UPP parameters.

CONCLUSIONS

A poor preoperative MUCP seems to be an important prognostic factor for persistent incontinence after RRP. Non-nerve sparing approach seems to be an important prognostic factor for impairment of the urethral sphincter function as measured by UPP. More intensive physiotherapy seems to have no additional effect on the postoperative urethral sphincter function as measured by UPP.

Urethral pressure reflectometry; a novel technique for simultaneous recording of pressure and cross-sectional area: a study of feasibility in the prostatic urethra

What's known on the subject? and What does the study add? In the 1980s and 1990s, a method for direct measurement of pressure and cross-sectional area in women and men was developed. It was successful in terms of obtaining meaningful results in several studies. But the technique, which was based on the field gradient principle, was never implemented in the clinical setting because of technical limitations. In 2005, urethral pressure reflectometry was introduced as a new technique in female urodynamics. The technique has been shown to be more reproducible than conventional urethral pressure profilometry, when measuring incontinence in women. In 2010 it was also introduced as a new measuring technique in the anal canal. This study, adds a new and interesting technique to the field of male urodynamics. For the first time, sound waves have been used to measure pressure and cross-sectional area simultaneously, directly in the prostatic urethra. The results from this first trial with urethral pressure reflectometry are promising, in terms of obtaining meaningful physiological parameters. Our hope is that, future trials will help us to be able to identify specific areas of obstruction or rigidity in the prostatic urethra, making treatment more direct and side effects from surgery less severe. However, further studies are needed to evaluate the technique with regards to clinical usefulness in men with benign prostatic obstruction.

OBJECTIVE

Urethral Pressure Reflectometry (UPR) was introduced in 2005, and it has since been used in the female urethra for simultaneous measurement of pressure (P) and cross-sectional area (CA). It has shown to be more reproducible than conventional pressure measurement and reintroduced direct measurement of pressure and elastance in the urethra as important parameters when assessing incontinent women. To test the feasibility of UPR in the prostatic urethra.

PATIENTS AND METHODS

We tested the technique in ten male patients, median age 73 and range 51-91. Measurements were performed in the supine position, with less than 50 ml of urine in the bladder. The UPR valuables measured were opening and closing pressure, opening and closing elastance and hysteresis.

RESULTS

The PVC tube was easy to insert to the same degree as a normal KAD. Opening pressure and opening elastance were measured on all patients. The sphincter area was easily identified during measurements. UPR provides results compatible with previous techniques. A standardized method for measurements was developed.

CONCLUSION

UPR has been shown feasible in the prostatic urethra. Further studies on healthy volunteers and patients with lower urinary tract symptoms and benign prostatic obstruction (BPO) are needed, to determine if UPR has a future role in urodynamic diagnostics of male patients with BPO.

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.

Urethral pressure reflectometry vs urethral pressure profilometry in women: a comparative study of reproducibility and accuracy

OBJECTIVE

To compare urethral pressure reflectometry (UPR), a new and simple technique for simultaneous measurements of cross-sectional area (CA) and pressure in the female urethra, with urethral pressure profilometry (UPP).

PATIENTS, SUBJECTS AND METHODS

The study included 143 women (105 patients and 38 healthy volunteers); the UPR was measured using a very thin polyurethane bag in the urethra; a pump applied pre-selected pressures stepwise to the bag and for each step the CA was measured by acoustic reflectometry. Measurements were made during both inflation and deflation. The women were examined supine both while relaxed and during 'squeeze', and while upright and relaxed. The following variables were measured; the opening and closing pressure, the opening and closing elastance and the hysteresis. For UPP we used the perfusion technique with the patient supine and relaxed. All the women were assessed twice with both UPR and UPP at the same setting (short-term reproducibility) and 17 patients were assessed with both methods on two different days (long-term reproducibility).

RESULTS

The mean pressures were 51.7 and 52.9 cmH(2)O for the UPR and UPP, respectively (not significant) at a CA of 5.1 mm(2); the limit of agreement between the methods was -19.4 to +17.0 cmH(2)O (mean and 2 SD). The Pearson coefficient was - 0.16 (not significant). The variability (2 sd) of two consecutive measurements was significantly less with UPR (9.5 cmH(2)O) than UPP (13.8 cmH(2)O; P < 0.001). For the opening and closing pressures the coefficient of variation (CV) was 5.9-11.6%; for the elastances the CV was 14.3-31.2% and for the hysteresis the CV was 12.9-49.1%. In test-retest measurements, the variability of the UPR values (2 sd, 8.7 cmH(2)O) was significantly less than for UPP (15.4 cmH(2)O; P < 0.05). The discomfort of UPR was statistically less than for UPP or than a standard gynaecological examination.

CONCLUSION

Compared at the same CA, UPR measured the same pressure as UPP but the UPR was more reproducible. With the patient relaxed the opening and closing pressure, opening and closing elastance and the hysteresis can be measured while supine and upright; while squeezing, the opening pressure and elastance can be measured.

The correlation of urethral resistance pressure with maximum urethral closure pressure and stress incontinence

OBJECTIVE

Aim of the study was to correlate urethral retro resistance pressure with the maximum urethral closure pressure (MUCP) and functional urethral length (FUL) in patients with urinary incontinence and healthy individuals.

STUDY DESIGN

Two hundred and twenty patients with the complaint of urinary incontinence had a urodynamic examination including urethral pressure profiles and URP. Additionally, 15 healthy individuals without the complaint of any incontinence had their URP and urethral pressure profiles measured. The correlation of MUCP, FUL and URP were calculated using Graph Pad Instat 4.0 for windows.

RESULTS

URP correlates well with the diagnosis of urodynamic stress incontinence. Correlation coefficient between URP and MUCP is 0.9262. Healthy individuals have significantly higher values for URP and MUCP.

CONCLUSION

URP is a valuable less invasive test than conventional urethral function tests for the diagnosis of urodynamic incontinence with an excellent correlation of MUCP and URP.

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.

Possibilities of experimental verification of the validity of urethral pressure profilometry

OBJECTIVES

The aim is to define conditions for exact measurement of urethral pressure profile, to prepare an aparatus and fabricate an artificial urethra for testing measuring catethers. To examine it's qualities by experiment.

METHODS

We designed a measuring appliance and a specialized software for measuring and evaluating. An experimental phantom of urethra, made from a part of bull's urethra, was used for testing of measurement's validity with use of different measuring catethers. Measurements were 10x repeated within the same position of the catether. Reproducibility of the measurement and stability of the experimental model was tested.

RESULTS

Measuring urethra and experimental phantom of urethra succeeded, it was possible to make well reproducible measurements with different measuring catethers and to evaluate their metrologic abilities and limits. Results of our measurements confirmed appointed theoretical conditions of the measurement.

CONCLUSION

Measurements proved that it is possible to simulate the conditions that are similar to physiological conditions and that it is possible to test metrological qualities of compressive profilometry of urethra.

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.

Functional Analysis of Active Urethral Closure Mechanisms Under Sneeze Induced Stress Condition in a Rat Model of Birth Trauma

PURPOSE

We evaluated changes in the urethral closure mechanism under a sneeze induced stress condition in a rat model of birth trauma.

MATERIALS AND METHODS

Four days after vaginal distention induced by balloon catheter inflation in the vagina sneezing was induced while recording intravesical pressure with the rat under urethane anesthesia to evaluate sneeze induced leak point pressure, defined as the lowest pressure inducing fluid leakage from the urethral meatus during sneezing. Sneeze induced responses in the bladder and proximal or mid urethra were also measured using microtip transducer catheters.

RESULTS

In 5 sham operated rats no leakage was observed from the urethral meatus during sneezing, which produced an increase in intravesical pressure of up to 34 cm H(2)O. However, in 5 of 6 rats with vaginal distention leakage during sneezing was observed with a sneeze leak point pressure of 26.2 cm H(2)O. In the mid urethra microtip transducer catheters revealed that pressure increases during sneezing were greater than those in the bladder but they were significantly decreased in the 5 incontinent vaginal distention rats. However, sneeze induced responses at the proximal urethra, which were similar to those in the bladder, were not different in sham operated and incontinent vaginal distention rats.

CONCLUSIONS

Sneeze induced stress urinary incontinence in a rat model of birth trauma was caused by decreased active closure mechanisms at the mid urethra without affecting the passive transmission of abdominal pressure in the proximal urethra.

Optimization of the artificial urinary sphincter: modelling and experimental validation

The artificial urinary sphincter should be long enough to prevent strangulation effects of the urethral tissue and short enough to avoid the improper dissection of the surrounding tissue. To optimize the sphincter length, the empirical three-parameter urethra compression model is proposed based on the mechanical properties of the urethra: wall pressure, tissue response rim force and sphincter periphery length. In vitro studies using explanted animal or human urethras and different artificial sphincters demonstrate its applicability. The pressure of the sphincter to close the urethra is shown to be a linear function of the bladder pressure. The force to close the urethra depends on the sphincter length linearly. Human urethras display the same dependences as the urethras of pig, dog, sheep and calf. Quantitatively, however, sow urethras resemble best the human ones. For the human urethras, the mean wall pressure corresponds to (-12.6 +/- 0.9) cmH2O and (-8.7 +/- 1.1) cmH2O, the rim length to (3.0 +/- 0.3) mm and (5.1 +/- 0.3) mm and the rim force to (60 +/- 20) mN and (100 +/- 20) mN for urethra opening and closing, respectively. Assuming an intravesical pressure of 40 cmH2O, and an external pressure on the urethra of 60 cmH2O, the model leads to the optimized sphincter length of (17.3 +/- 3.8) mm.

Urogynaecology: Urethral retro-resistance pressure and urodynamic diagnoses in women with lower urinary tract symptoms

OBJECTIVE

This study determines whether the retrograde urethral retro-resistance pressure (URP) measurement discriminates between urodynamic diagnoses in a group of women.

DESIGN

A prospective observational study.

SETTING

Urogynaecology units of three tertiary referral teaching hospitals.

POPULATION

Women with lower urinary tract symptoms.

METHODS

Consecutive women attending the urodynamic clinics of three tertiary referral teaching hospitals were studied using a validated urinary symptom questionnaire, URP measurement and urodynamic evaluation between February and July 2004. The URP mean values were compared with urinary symptoms and urodynamic diagnoses, using the independent t test correction for multiple measurements.

MAIN OUTCOME MEASURES

Retrograde URP, urodynamic diagnoses and urinary symptoms.

RESULTS

One hundred and eighty-five women were recruited. Women with urodynamic stress incontinence (USI) have significantly lower URP than women with competent urethral sphincters (P < 0.05, independent t test). Women with mixed urodynamic incontinence had values of URP intermediate between women with detrusor overactivity (DOA) and those with USI. In the mixed group, URP mean values were not significantly different from those with DOA and competent sphincters or USI (P > 0.05, independent t test). There was no significant difference between mean URP values and different urinary symptoms (P > 0.05, independent t test).

CONCLUSIONS

There are significantly different URP measurements between women with DOA and those with USI. However, the URP is not a diagnostic tool.

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.

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.

Urodynamic study of women in urinary retention treated with sacral neuromodulation

PURPOSE

We investigated the action of sacral neuromodulation in restoring voiding function in women with urinary retention attributable to sphincter overactivity (Fowler's syndrome).

MATERIALS AND METHODS

We recruited women within retention who were able to void following neuromodulation by temporary test stimulation or a permanent implant. Urethral pressure profiles, cystometry and sphincter electromyography were performed before and after neuromodulation.

RESULTS

A total of 30 women 19 to 52 years old were recruited, including 21 with a permanent implant and 9 undergoing temporary stimulation. Mean maximum urethral closure pressure was elevated compared to expected pressure and it did not change significantly after neuromodulation. The electromyographic abnormality persisted during neuromodulation and voiding was often done with an interrupted flow. There was a slight increase in detrusor contractility.

CONCLUSIONS

This evidence suggests that neuromodulation does not restore voiding in these patients by a direct relaxant effect on the sphincter. The modest increase in detrusor pressure appears to be sufficient to overcome the resistance of the overactive sphincter.

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.

Urethral pressure measurement--problems and clinical value

Urethral pressure measurements are in use to assess urethral closure and voiding function. The lack of general agreement on an explicit definition of urethral pressure and standardisation of the methodology for measurement has limited the clinical utility of urethral pressure measurements.

Model-based estimation of male urethral resistance and elasticity using pressure-flow data

To assess urethral resistance and changes in the urethral elasticity during voiding, a lumped parameter model of the urethra was developed. The model uses pressure and flow measurements to estimate time-dependent resistance and elasticity factor. The model includes a resistance that has a function of the cross-section and urethral elasticity. Two resistivity types are compared in the constricted flow-controlling zone of the urethra: Poiseouille resistance and the Bernoulli effect. Using real pressure-flow data sets, the model was used to estimate urethral resistance and changes in urethral elasticity during voiding. Estimation of the elasticity show that in a normal patient relaxation of the urethra is a process that continues until the end of voiding. This has important implications with regard to the present methods that are used in the clinic to assess urethral obstruction or constriction. The resistance as calculated by this model, may be a useful indicator of urethral constriction and obstruction, since it is especially independent of the bladder function. Changes in the urethral elasticity during voiding which are estimated by the model add a new diagnostic parameter to pressure-flow studies.

Interactions of pulsatile upstream forcing with flow-induced oscillations of a collapsed tube: mode-locking

Interest in flow through collapsible tubes derives from their prevalence in the human body. In the circulation at least, the driving pressure for flow is pulsatile, and it is accordingly appropriate to investigate the response of a collapsible tube to a pulsatile head. A servo-controlled hydraulically powered piston pump was used to add pulsation to the head propelling aqueous flow through a silicone rubber tube. The pump was commanded to execute a sinusoidal variation of piston position at various frequencies on either side of the natural frequency of an operating point where slow (3.75 Hz) repetitive self-excited oscillations in the absence of such forcing could be guaranteed. The resulting time series were characterised by the ratio of the number of collapse cycles to the number of forcing cycles in one overall interaction waveform period. Nonlinear interaction rather than linear superposition was dominant. Many different mode-locked interactions were recorded, and are here systematised in Farey series and plots which show the extent of entrainment. A few of the time series were aperiodic over the time scales investigated, suggesting possible chaos.

A technique for measurement of related values of pressure and cross-sectional area in the male urethra

A probe for measurement of related values of cross-sectional area and pressure in the male urethra was constructed. The probe allows induction of variable pressures or fluid volumes in a distensible balloon located in the urethra and simultaneous recording of related values of cross-sectional area and pressure. Cross-sectional area is measured in the range of 11-102 mm2 using the field-gradient principle. Pressure is measured in the range of 0-250 cmH2O using tip transducers. The time constant for cross-sectional area measurement is 0.02 s and that for pressure measurement, 0.007 s. The pressures required to reach the maximal and minimal cross-sectional areas of the balloon are 2.8 and -2.4 cmH2O, respectively. The shape of the probe after its placement in the urethra was studied by transrectal ultrasound in five volunteers. The results showed that the measurement error caused by the slope of the balloon walls or the forced bending of the catheter did not exceed 5%. The method enables a description of the biomechanical properties of the male urethra at rest in terms of estimated pressure at zero cross-sectional area, elastance, and stress-relaxation and at voluntary contraction in terms of work and power as evaluated at well-defined anatomical locations.

Evaluation and treatment of incontinence after bladder neck reconstruction in exstrophy and epispadias

Twenty-five children with exstrophy/epispadias who had had at least one bladder neck operation (but no augmentation) for incontinence underwent cystometrography (CMG) and urethral pressure profile (UPP) studies. The purpose of this study was to examine all components of lower urinary tract function and to determine how the properties of the bladder and the properties of the bladder neck/urethra interacted to achieve continence or to result in incontinence in the individual child. Examination of detrusor function during filling revealed involuntary contractions in 12 children and an end-fill pressure > 10 cm H2O in 8. Of the 21 children in whom voiding could be evaluated only 6 could initiate a detrusor contraction. In the 18 incontinent children leak pressure could be measured and was > or = 15 cm H2O in 12. Five of the 7 continent children also demonstrated at least one abnormality in lower tract function. The maximum pressure of the UPP did not agree with the leak pressure and may not be a valid measure of the closing pressure of the bladder neck/urethra in this patient population. Detailed urodynamic investigation is necessary in these children to guide the next step of management and to evaluate objectively each form of treatment.

Pressure response to rapid dilation of resting urethra in healthy women

Rapid urethral dilations were performed by a balloon mounted on a double-tip transducer catheter for simultaneous measurement of pressure in urethra and bladder. The cross sectional area of the urethra was measured according to the field gradient principle. Pressure and cross sectional area were recorded synchronously. The response of the female urethra to rapid dilation is a typical stress relaxation effect with a pressure peak followed by a pressure decay over a few seconds. The peak pressure response represents the bladder pressure required in producing a corresponding urethral dilation by the ingression of urine. The increase in pressure response was statistically significant by increasing rate as well as size of dilation. The method enables experimental simulation of stress urinary incontinence in vivo which may bring further insight into the physiology of the urethral closure function and the pathophysiology of stress incontinence. For comparative studies rapid dilation should be performed under standardized circumstances.

Discriminant analysis of urethral pressure profilometry data for the diagnosis of genuine stress incontinence

Urethral pressure profilometry (UPP) has been advocated for the diagnosis of genuine stress incontinence (GSI) but no published data exist to define clearly the criteria of measurement that should be used. The aim of this study was to examine the value of UPP in the diagnosis of GSI. Data from 102 urodynamically normal women and 70 women with GSI were compared. Thirty UPP variables from the resting and stress profiles were examined. The urodynamic diagnosis was made on the basis of a pad test, uroflowmetry and videocystourethrography. Each UPP variable was examined singly and thereafter all the measurements were examined by discriminate analysis. The single most discriminatory UPP variable was 'area under the stress profile' but the overlap between normal and GSI patients was too great to allow the test to be used diagnostically. Discriminate analysis resulted in correct classification in 78% of cases. On the basis of these results, UPP is not an accurate test for the diagnosis of GSI.

Treatment of benign prostatic hyperplasia by androgen deprivation: effects on prostate size and urodynamic parameters

The possible effect of medical androgen deprivation in the treatment of benign prostatic hyperplasia has been studied in 12 patients. Six patients received the luteinizing hormone-releasing hormone agonist buserelin and 6 others received the antiandrogen cyproterone acetate. The treatment resulted in an average decrease in prostatic size of 29 per cent after 12 weeks as measured by ultrasonography. This decrease led to an increase in peak urinary flow rate, a reduction in residual urine volume and a decrease in daytime voiding frequency. However, it caused no decrease in urethral resistance but only an increase in the bladder contraction strength. After discontinuation of the treatment the prostates showed regrowth to the initial sizes within 6 to 36 weeks. The urodynamic changes were reversed as well. Although statistically significant, the urodynamic changes were minimal from a clinical viewpoint and did not lead to an unobstructed state after 12 weeks of treatment. For this reason the clinical indication for use of medical androgen deprivation in benign prostatic hyperplasia patients will remain limited for the time being.