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Ron van Mastrigt

Publications and source records attributed to Ron van Mastrigt.

13 recordsLinked to original sources
PubMed2006

Development of a CFD urethral model to study flow-generated vortices under different conditions of prostatic obstruction.

A novel, non-invasive method to diagnose bladder outlet obstruction involves the recording of noise with a contact microphone pressed against the perineum (between anus and scrotum). This noise results from flow-generated vortices caused by prostatic obstruction. We developed a computational fluid dynamic (CFD) urethral model including urethral geometry to study the relation between generated noise and the degree of obstruction. This model comprised a bladder, bladder neck, prostate and urethra. Calculations were carried out at four bladder pressures, five degrees of obstruction and three obstruction shapes. For each of the sixty simulations, the velocity and pressure distributions along the urethra were calculated including wall shear stresses to localize flow transition from disturbed to normal. Negative pressures at the obstruction outlet induced recirculation of flow. The location of transition was independent of the applied bladder pressure, but it depended primarily on the degree and secondarily on the shape of the obstruction. Based on the presented results, we hypothesize that the location of the maximum amplitude of perineal noise mainly depends on the degree and shape of the prostatic obstruction. Our future aim is to test our hypothesis in male patients and to extend the presented model to 3D with a viscoelastic urethral wall to calculate the fluid-wall interaction.

Humans↗
PubMed2006

A biophysical model of the male urethra: comparing viscoelastic properties of polyvinyl alcohol urethras to male pig urethras.

AIMS: We aim at developing a non-invasive method for grading and diagnosing urinary bladder outlet obstruction, based on noise recording with a perineal contact microphone during voiding. We found that the noise production during voiding depends amongst others on the viscoelastic properties of the urethral wall. To further test our method, we need a realistic biophysical model of the male urethra. METHODS: We made various model urethras with different viscoelastic properties from a 10% aqueous solution of polyvinyl alcohol cryogel. We measured the viscoelastic properties of each model and compared them to those of the male pig urethra. The male pig urethra was used, as it is physiologically comparable to the human male urethra. The viscoelastic properties of both model and pig urethras were measured by applying strain to the urethral wall in a stepwise manner and recording the pressure response. We fitted the step-response of a mechanical model to this pressure response and derived the viscoelastic properties from the coefficients of this response. RESULTS: A uniform model urethra that was freeze-thawed three times, with a Y-shaped flow channel was found to best represent the male pig urethra. CONCLUSIONS: We consider the three times freeze-thawed model urethra with a Y-shaped flow channel the best model of the human male urethra. And we therefore use this model urethra for studying the relation between noise recording during urine flow and the degree of bladder outlet obstruction.

Animals↗
PubMed2006

Is it possible to improve elderly male bladder function by having them drink more water? A randomized trial of effects of increased fluid intake/urine output on male lower urinary tract function.

OBJECTIVES: Several animal studies have shown that bladder performance improves as a result of diuresis. Whether increased urine output also has beneficial effects on elderly male bladder function and lower urinary tract symptoms is unknown. METHODS: We performed a randomized placebo-controlled trial of 141 men, 55 to 75 years of age, with moderate lower urinary tract symptoms. The experimental group drank 1.5 L of extra water daily. The control group consumed one tablespoon of placebo syrup daily. After 6 months, we evaluated bladder contractility, voided volumes, and the severity of lower urinary tract symptoms. The actual increase in water consumption was measured using the deuterium urine dilution method. RESULTS: Water consumption in the intervention group increased by 359 mL (95% confidence interval [CI] 171 to 548) per 24 hours compared with the control group. At 6 months, no statistically significant effect was found in the maximal flow rate (0.9 mL/s, 95% CI -0.4 to 2.2) compared with placebo. A statistically significant effect was found for bladder pressure (20 cm H2O, 95% CI 6 to 34) and bladder wall stress (1.9 N/cm2, 95% CI 0.3 to 3.5). In addition, it showed that the experimental group had greater maximal (44 mL, 95% CI -1 to 90) and average (26 mL, 95% CI 1 to 51) voided volumes per urination. The subjective effect parameters improved in both groups, but no statistically significant differences were found between the two groups. CONCLUSIONS: It seems possible to improve some aspects of male bladder function by drinking more water. However, the effects are too small to be clinically relevant.

Aged↗
PubMed2006

Sacral neuromodulation in women with idiopathic detrusor overactivity incontinence: decreased overactivity but unchanged bladder contraction strength and urethral resistance during voiding.

PURPOSE: We evaluated the effect of sacral (S3) nerve neuromodulation on voiding in women with idiopathic detrusor overactivity incontinence. MATERIALS AND METHODS: Urodynamic measurements in all patients implanted in 1990 to 2003 were reconsidered. Patients were included if these measurements, which were done at baseline and after 6 months, could be analyzed completely and reliably. Maximum detrusor pressure, amplitude of the highest involuntary detrusor contraction and end fill volume were used as parameters characterizing the degree of detrusor overactivity. Urethral resistance and bladder contraction strength during voiding were characterized by the bladder outlet obstruction index, the urethral resistance factor, average pressure, the slope of the low pressure side of the pressure flow plot, the bladder contractility index and the bladder contraction strength parameter. RESULTS: A total of 33 women were included. Detrusor overactivity parameters were significantly improved at followup. In addition, the supine position of the patient during filling in followup measurements proved less provocative with respect to overactivity than the standing position in the majority of measurements at baseline. Consequently bladder volumes at which voiding was initiated were considerably higher at followup. Changes in the parameters characterizing urethral resistance and bladder contraction strength during voiding were not unambiguous. However, exactly those parameters that appeared volume independent in a previous study were not significantly different. CONCLUSIONS: Our study confirmed the depressant effect of sacral (S3) nerve neuromodulation on detrusor overactivity. No effect on urethral resistance and bladder contraction strength during voiding could be demonstrated using volume independent parameters.

Adult↗
PubMed2005

Perineal noise recording as a non-invasive diagnostic method of urinary bladder outlet obstruction: a study in polyvinyl alcohol and silicone model urethras.

AIMS: At present, an invasive pressure flow study is recommended to diagnose urinary bladder outlet obstruction. This method induces the risk of urinary tract infection and urethral trauma. We studied perineal noise recording as an alternative, non-invasive diagnostic method in three flexible/extensible model urethras and two silicone tubes. METHODS: The flexible/extensible model urethras were made of a 10% aqueous solution of polyvinyl alcohol (PVA) and differed in wall- stiffness, the silicone tubes differed in diameter and wall-thickness. Three degrees of obstruction were applied by inflating a cuff placed around the PVA-urethras and by compressing the silicone tubes with an adjustable clamp. Noise, produced during flow, was recorded at three positions distal to the obstruction using a piëzoceramic contact microphone. RESULTS: The average amplitude of the noise and the essential frequency of the power spectrum of each noise recording depended significantly on the degree of obstruction, the position of the microphone and the wall-stiffness in PVA-urethras and the diameter in silicone tubes. CONCLUSIONS: Based on the results of this study perineal noise recording shows good potential as an alternative method for diagnosing bladder outlet obstruction.

Data Interpretation, Statistical↗
PubMed2004

Afferent bladder nerve activity in the rat: a mechanism for starting and stopping voiding contractions.

The objective of this work was to study the relation between afferent bladder nerve activity and bladder mechanics and the mechanisms that initiate and terminate bladder contractions. Bladder nerve activity, pressure and volume were recorded during the micturition cycle in the rat. The highest correlation was found between afferent nerve activity and stress (pressure x volume). Afferent nerve activity depended linearly on stress within 6%, and both slope and offset were independent of the bladder-filling rate. The levels of afferent bladder nerve activity at the onset and cessation of efferent firing to the bladder were highly reproducible with coefficients of variation of <or=17%. We propose a model in which afferent activity is proportional to bladder wall stress, and bladder contraction is initiated when afferent activity exceeds a threshold due to an increasing pressure and volume. The contraction continues until afferent activity drops below a threshold again as a result of a decreasing volume.

Animals↗
PubMed2003

A flow rate cut-off value as a criterion for the accurate non-invasive measurement of bladder pressure using a condom-type catheter.

We developed a condom-type catheter to non-invasively measure the bladder pressure during interruption of the flow rate. The aim of the present study was to establish a minimum flow rate value at which a reliable bladder pressure measurement can be made with this catheter. We reanalysed data from 43 patients who completed a pressure-flow study and a non-invasive test. The patients voided without straining. During the test, we simultaneously measured the bladder pressure (invasively) and the condom pressure (non-invasively). The pressure increase in the condom after interruption of the flow rate was analysed in 40 of the 43 patients. A plot of the difference between the bladder pressure and the maximum condom pressure as a function of the flow rate revealed that in 70% of the patients who voided with a maximum flow rate exceeding 5.4 ml/s, the condom pressure accurately reflected the bladder pressure (+/-14 cmH2O). We conclude that to accurately and non-invasively measure the bladder pressure with a condom-type catheter, the maximum flow rate should exceed 5.4 ml/s.

Catheterization↗
PubMed2003

Causes for variability in repeated pressure-flow measurements.

OBJECTIVES: To study the causes for the variation between measurements, which is considerable, in maximal flow rate (Qmax) and the associated detrusor pressure (PdetQmax). Because of the central role of Qmax and PdetQmax in the diagnosis of bladder outlet obstruction, this is reason for concern. METHODS: Spectral analysis was carried out on two consecutive urodynamic measurements in 131 patients. The parameters for bladder outlet resistance and bladder contraction strength were determined, and difference plots were made to study the systematic variations. Logistic regression analysis was used to study whether the differences represent true changes of the function of the lower urinary tract. RESULTS: Signal components in the detrusor pressure and the flow rate signal with frequencies of 1 Hz or greater may be considered noise. Filtering out these frequencies changes the estimates of Qmax and PdetQmax, but not the between-measurement difference in them. Bladder contractility and bladder outlet resistance were systematically lower in the second measurement. Both the systematic and nonsystematic between-measurement variations were statistically significant predictors for postvoid residual urine volume. CONCLUSIONS: The nonsystematic between-measurement variability in Qmax and PdetQmax apparently reflects true variability in the physiologic state of the bladder outlet. It therefore does not discredit the pressure-flow study as the preferred method in the diagnosis of bladder outlet obstruction. Rather, the pressure-flow study is the only currently available method to study and quantify the apparent within-patient variability in bladder outlet resistance and bladder contractility.

Analysis of Variance↗
PubMed2003

Weak correlation between bladder outlet obstruction and probability to void to completion.

OBJECTIVES: To investigate the weak correlation between bladder outlet obstruction (BOO), as diagnosed using the provisional International Continence Society nomogram for the definition of BOO in men, and postvoid residual urine volume. METHODS: The relationship between voiding to completion and several indexes for bladder outlet resistance and bladder contractility was studied in 131 pressure flow studies in male patients using multivariate logistic regression analysis. RESULTS: The International Continence Society nomogram and the related BOO index weakly predict for postvoid residual urine volume (areas under the receiver operating characteristic curve 0.63 and 0.64, respectively). The BOO index primarily measures bladder outlet resistance. If the nomogram or BOO index is augmented with bladder contractility information, the postvoid residual urine volume can be predicted significantly better (eg, area under the receiver operating characteristic curve [0.89] for the combination of the BOO index and bladder contractility information). CONCLUSIONS: The weak correlation between BOO and postvoid residual urine volume is related to the fact that emptying the bladder to completion depends on bladder contractility, as well as bladder outlet resistance. It is possible to estimate the probability to void to completion quite accurately on the basis of bladder outlet resistance and bladder contractility. We named this probability "relative bladder outlet resistance." A high probability of a postvoid residual urine volume may be assumed to indicate "relative BOO." By its very nature, the correlation between "relative BOO" and postvoid residual urine volume is good.

Area Under Curve↗
PubMed2003

Bladder outlet resistance.

PURPOSE: We developed a method to objectively compare methods for the quantification of bladder outlet resistance. MATERIALS AND METHODS: We studied unselected voiding cystometries from 131 male patients. Several models proposed for bladder outlet resistance were fitted to the lowest monotonically increasing part (bottom) of the pressure flow plots. In conjunction with a parameter for bladder contractility, the model parameters were used as predictors of post-void residual greater than 20% of filled volume. RESULTS: The pressure decrease in relaxed bladder outlet was best described by a linear function of the flow rate. The flow rate independent and dependent parts of that function were statistically significant predictors for residual. However, they could be combined into 1 index that was as efficient as the 2 numbers separately in predicting residual. This index is the average pressure of the bottom of the pressure flow plot. CONCLUSIONS: We describe how different models for the quantification of bladder outlet resistance can be compared objectively on the basis of their ability to predict a significant post-void residual. Using this criterion in an unselected group of measurements, the average pressure of the bottom of the pressure flow plot performed best as an index for bladder outlet resistance quantification. It combines (or weights) 2 components (dependent and independent flow rates) without losing its power to predict post-void residual.

Humans↗
PubMed2002

Pre-selection of patients for pressure-flow analysis based on the maximum flow rate.

OBJECTIVE: To study the effects of the application of flow rate prescreening to select men for invasive pressure-flow studies, notably the reduction of invasive pressure-flow measurements that can be achieved and the proportion of men in whom, on the basis of the application of a prescreening, an invasive measurement is unjustly not indicated (false negatives). In addition, the variables on which these effects depend are studied. MATERIALS AND METHODS: Two hundred and sixty-two pressure-flow measurements in 131 patients (2 measurements/patient) and 89 free-flow measurements that preceded the invasive measurements in some patients were studied. A mathematical model was developed based on the outcomes of the invasive measurements. By means of the model the effects of several flow rate prescreening scenarios were estimated. A comparison of the model predicted and actually observed effects of flow rate prescreening was made for those measurements that were preceded by a free-flow rate measurement. RESULTS: The application of a free-flow rate prescreening may result in a reduction of the number of invasive measurements of 20-30% at a 5% false negative rate. The reduction that may be achieved at an assumed constant false negative rate depends on the distribution of the maximum flow rate in the population and on the definition of bladder outlet obstruction used. When the measurement selection procedure was applied to the free-flow rate measurements that were available in 89 patients, a 21% reduction in invasive measurement indications was found (25% expected). Four patients (4.5%) would have been unjustly excluded from invasive procedures (maximally 5% expected), three of these four patients were borderline obstructed. CONCLUSION: Considering the bother and risk to the patient and the cost of invasive measurements we think that a 20-30% gain in efficiency at a 5% risk of unjustly declaring a patient unobstructed makes a flow rate prescreening procedure cost effective in the diagnosis of bladder outlet obstruction.

Algorithms↗
PubMed2002

Relative bladder outlet obstruction.

PURPOSE: Currently bladder outlet obstruction in males is defined by the provisional International Continence Society nomogram which is partly based on expert opinion and partly on measurements before and after transurethral prostate resection. Recently there has been some interest in the development of a similar nomogram for females. MATERIALS AND METHODS: We studied the possibility of defining bladder outlet obstruction based on a sign that it causes, namely post-void residual urine. RESULTS: The probability of relative post-void residual urine exceeding 20% of bladder capacity was modeled in males and females using 1 parameter, that is URA/w20 or the ratio of the obstruction parameter urethral resistance factor (URA)-to-the bladder contractility parameter Watts factor at 20% (w20). URA/w20 represents relative bladder outlet resistance or bladder outlet resistance normalized to bladder contractility. Above a threshold of URA/w20 = 6.8 in females and 8.2 in males a relative post-void residual exceeding 20% was noted in 90% of measurements. These thresholds may be used to define relative obstruction. The provisional International Continence Society nomogram for obstruction in males was transformed into an identical nomogram for females by equating the probabilities of post-void residual urine in each gender. The latter differed from that in men, in that the lines demarcating the zones were horizontal or flow rate independent but the intercepts were approximately the same at 20 and 40 cm. water. CONCLUSIONS: Instead of defining obstruction as an absolute level of bladder outlet resistance we suggest that it is better to define it relatively, that is as a level of bladder outlet resistance that depends on bladder contractility.

Female↗