Tim Idzenga

Is the impaired flow after hypospadias correction due to increased urethral stiffness

PURPOSEnA low flow rate without clinical symptoms is commonly found in boys after hypospadias correction. Urethral calibration usually shows no abnormalities. We investigated whether this impairment might be caused by increased neo-urethral wall stiffness.nnnMETHODSnFrom polyvinyl alcohol cryogel two models of the urethra were made, hypospadias and control; both had a constant and equal inner diameter and equal compliance. The hypospadias model had a less compliant distal segment mimicking the distal neo-urethra after hypospadias correction. In both models, flow rate was recorded as a function of bladder pressure. To test whether the length of the less compliant segment had an effect on the flow rate, both models were shortened by cutting off 1-cm segments.nnnRESULTSnIn a physiological range of bladder pressures (10-130 cmH(2)O) the mean flow rate (+/-1 SEM) in the hypospadias model was 2.8+/-0.3 ml/s, significantly lower (P<0.05) than in the control model (5.4+/-0.6 ml/s). Shortening of the hypospadias model showed some increase in flow rate, but this was not statistically significant. In the control model there was also no significant variation in flow rate.nnnCONCLUSIONnA low-compliant segment of a urethral model reduced the flow rate. Extrapolating these results to asymptomatic boys with a low urinary flow rate after hypospadias repair might justify a watchful waiting policy.

Development of a noninvasive method to diagnose bladder outlet obstruction based on decorrelation of sequential ultrasound images

OBJECTIVEnTo develop an ultrasound (US)-based method for noninvasive diagnosing of bladder outlet obstruction, and the relationship between decorrelation of sequential US images and the degree of obstruction in a urethra model was studied.nnnMATERIALS AND METHODSnA flexible model of a male urethra was constructed from 15% aqueous solution of polyvinyl alcohol cryogel. To create 4 different degrees of obstruction, polyvinyl alcohol rings representing the prostate were placed around the model. Each model was perfused at different flow rates (1-15xa0mL/s) with an aqueous solution containing scattering particles mimicking urine. At each flow rate, 10 sequential US images were acquired. The average correlation coefficients between the images were calculated and plotted as a function of the degree of obstruction and the flow rate.nnnRESULTSnThe average correlation decreased approximately linearly with an increase in the degree of obstruction. This decrease in correlation (decorrelation) might be due to turbulence caused by the obstruction. A higher degree of obstruction creates more turbulence and results in a higher decorrelation between sequential US images.nnnCONCLUSIONnQuantification of the decorrelation between sequential US images may provide us with a new approach to noninvasively diagnose bladder outlet obstruction.

Dependence of ultrasound decorrelation on urine scatter particle concentration for a non-invasive diagnosis of bladder outlet obstruction

We investigated the influence of scattering particles concentration on the decorrelation of ultrasound signals for urinary flow imaging in a urethra model. A flexible urethra model made from PolyVinyl Alcohol (PVA) was perfused at flow rate of 10 ml/s with five diluted urine solutions prepared from morning urine samples of 4 healthy volunteers and seven aqueous solutions containing silica gel as scattering particles. During flow, ten ultrasound RadioFrequency (RF) data sets were acquired for each solution at a pulse repetition frequency of 5 kHz. Correlation coefficients between each two sequential RF-data sets were calculated as a function of particle concentration. The results depict that average correlation increases with an increase in particle concentration. The curves derived from the urine samples of the volunteers displayed a behavior similar to that of the silica particle aqueous solutions. Therefore, we conclude that urinary flow imaging using the decorrelation method in patients might be feasible.

Variability and repeatability of perineal sound recording in a population of healthy male volunteers

In a population of 16 healthy male volunteers we studied the variability and repeatability of perineal sound recording as a non‐invasive method for diagnosing bladder outlet obstruction.

Toward an Acoustic Noninvasive Diagnosis of Urinary Bladder Outlet Obstruction

On average, in aging males, the prostate enlarges (benign prostatic enlargement or BPE) and may cause bladder outlet obstruction (BOO). The internationally standardized method for diagnosing BOO is based on measurements of urinary flow rate and bladder pressure, using a catheter inserted into the bladder via the urethra. This method is invasive, time-consuming, and uncomfortable for the patient. We are developing a novel diagnostic method based on perineal recording of sound during urinary flow. Although it is known that (some aspects of) the recorded sound are (among others) related to the degree of obstruction, an exact and unique relation allowing derivation of the degree of obstruction from the sound recording is not known. In a biophysical model of the urethra, we found that the weighted average frequency, the standard deviation, and the skewness of the power spectrum are monotonically related to the degree of obstruction. The standard deviation was the most significant predictor of BOO (89% correct). Based on this model study, we are confident that a simple noninvasive acoustic method for diagnosing BOO caused by BPE can be developed. This would lower the threshold for urodynamic testing of patients with lower urinary tract symptoms resulting in higher therapeutic efficacy.

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 (rxa0=xa00.22–0.50). 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 (Pxa0=xa00.80) and increased linearly with increasing cuff pressure. MUCP also increased with increasing cuff pressure, however, MUCP significantly depended (Pxa0<xa00.01) 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.

Noninvasive Diagnosis of Bladder Outlet Obstruction in Patients with Lower Urinary Tract Symptoms Using Ultrasound Decorrelation Analysis

PURPOSEnWe developed a noninvasive method to diagnose bladder outlet obstruction. An ultrasound based decorrelation method was applied in male patients with lower urinary tract symptoms.nnnMATERIALS AND METHODSnIn 60 patients ultrasound data were acquired transperineally while they were voiding while sitting. Each patient also underwent a standard invasive pressure flow study.nnnRESULTSnHigh frequent sequential ultrasound images were successfully recorded during voiding in 45 patients. The decorrelation (decrease in correlation) between subsequent ultrasound images was higher in patients with bladder outlet obstruction than in unobstructed patients and healthy volunteers. ROC analysis resulted in an AUC of 0.96, 95% specificity and 88% sensitivity. A linear relationship was fitted to the decorrelation values as a function of the degree of obstruction represented by the bladder outlet obstruction index, measured in the separate pressure flow studies.nnnCONCLUSIONSnIt is possible to noninvasively diagnose bladder outlet obstruction using the ultrasound decorrelation technique.

Noninvasive estimation of the pressure profile in the male urethra using ultrasound imaging

PURPOSEnDecreased prostatic compliance as a result of benign prostatic enlargement can result in bladder outlet obstruction. This changes the urethral pressure profile during voiding. In this study, the authors propose noninvasive estimation of this pressure profile. In four soft tissue mimicking models of the urethra with increasing degree of obstruction, the authors measured deformation of the wall during flow, using ultrasound imaging. Combined with estimates of the model compliance, the authors were able to estimate the pressure profile.nnnMETHODSnFirst, the compliances (Youngs moduli) of the four models were derived by applying static luminal pressure and measuring the resulting strain of the tissue using an ultrasound imaging system. Next, continuous flow was applied to the models and the strain in the urethral wall was measured similarly. The luminal pressure profile was estimated from the strain (measured under continuous flow conditions) and the derived compliance (measured under static pressure conditions). The estimated pressures up- and downstream of the obstruction were compared with the corresponding measured pressures. In the obstructed region, the strain gradient was estimated using linear regression.nnnRESULTSnThe luminal pressure values estimated from the ultrasound data up- and downstream of the obstruction were not significantly different from the corresponding measured pressures. The general pressure profile showed a decrease along the length of the obstruction followed by a small increase after the obstruction. The strain gradient in the obstructed region reflected the decrease in urethral pressure and increased with flow rate and degree of obstruction.nnnCONCLUSIONSnThe results from this model study illustrate the feasibility of noninvasive estimation of the urethral pressure profile using ultrasound. This offers the prospect of a noninvasive, ultrasound based diagnostic tool for assessment of bladder outlet obstruction in men with lower urinary tract symptoms.

Perineal sound recording for diagnosis of bladder outlet obstruction.

Objectives: Elderly men are prone to developing lower urinary tract symptoms (LUTS) possibly caused by bladder outlet obstruction (BOO). The most frequently used method to diagnose this condition is an invasive and time-consuming pressure-flow study. We are developing a novel non-invasive method to diagnose BOO in men with LUTS based on perineal sound recording. Methods: A biophysical model urethra was made from polyvinyl alcohol (PVA) cryogel with viscoelastic properties comparable to those of the male pig urethra. To this model different degrees of obstruction were applied and sound was recorded at different positions downstream of the obstruction. In a study in 16 healthy male volunteers the variability and repeatability of perineal sound recording was tested. Results: In the model three parameters, derived from the frequency spectrum of the recorded sound (i.e., weighted average frequency, standard deviation and skewness) are uniquely related to the degree of obstruction (linear regression, P<0.001). The variability of perineal sound recording in healthy male volunteers was found to be smaller within volunteers than between volunteers (Kruskal-Wallis, P<0.001) and the repeatability was comparable to that of the maximum flow rate. Conclusions: We conclude that perineal sound recordings are significantly different between volunteers. In combination with the unique relations found in the model-experiments these results increase the probability that perineal sound recording can be used as a simple and cheap non-invasive method to diagnose BOO. Clinical testing of this method is therefore strongly indicated.

Diagnosing Bladder Outlet Obstruction Using Non-invasive Decorrelation-Based Ultrasound Imaging: A Feasibility Study in Healthy Male Volunteers

A feasibility study on the applicability of an ultrasound decorrelation method to urinary flow imaging was carried out in 20 healthy male volunteers, to provide a basis for a non-invasive approach to diagnose bladder outlet obstruction. Each volunteer voided five times in a flow meter in standing position. During each voiding, ultrasound radiofrequency frames were acquired transperineally at different flow rates. The results indicated that the decrease in correlation (decorrelation) of ultrasound radiofrequency signals had no unique relation with flow rate, but decreased distinctively with urinary flow velocity. In most of the healthy volunteers, the decorrelation was small because of the low flow velocity. However, because of the different flow velocities in volunteers, the variation in slope between volunteers was statistically significant. Therefore, it is probably possible to use the decorrelation method to differentiate between healthy persons and patients with obstruction.