R. van Mastrigt

The prognostic value of bladder contractility in transurethral resection of the prostate

The contractility of the bladder as quantified by a parameter of approximated power per bladder surface area based on the Hill equation (Wmax) was calculated for 29 patients before and 3 months after transurethral resection of the prostate. There was no significant change in this parameter as a result of the operation. Patients who still had a significant amount of residual urine postoperatively had decreased contractility before and after surgery so that the postoperative condition could have been predicted preoperatively. In many patients a fading contraction was observed, that is detrusor contractility decreased during voiding, which gave rise to a significantly increased volume of residual urine. In most patients this pattern was restored to normal after relief of the obstruction, indicating that it was not related to structural changes in the detrusor muscle. A preoperative fading contraction had no predictive value towards the outcome of the operation.

Active mechanical properties of the smooth muscle of the urinary bladder

Strips of pig bladder have been maximally stimulatedin vitro at 37°C via electrodes placed in the muscle, in order, particularly, to measure the dependence of the resulting active force on the velocity of shortening and on length changes. The active isometric force and the passive viscoelastic force are approximately, but not precisely, additive. The active isometric force, like the steady (equilibrium) passive force, is a function of the extension of the strip above its rest length, which is increased after subjection to a high passive force. The steady passive force increases quasiexponentially with this extension, of which it is therefore a measure. The active isometric force Fiso increases approximately linearly with the extension until it approaches a maximum in the region where it and the steady passive force are comparable in size. The maximum is partly obscured by rest-length changes. The dependence of the active force F on the speed of shortening of the strip has been measured in a new way, with a correction for passive viscoelastic effects. For a given strip the ratio F/Fiso is, approximately, a function of the contraction velocity only. The function is similar to that of the classical Hill equation but not identical, possibly for geometrical reasons. The results imply that a velocity parameter v*, analogous to Hill’s parameter b, is approximately constant for each strip, independent of changes of length and rest length.

Visco-EIastic Properties of the Bladder Wall

Stepwise cystometry is a new method proposed to analyse the visco-elastic properties of the bladder. It is based on a mathematical analysis of the pressure decay after a stepwise filling. By assumption of a mechanical visco-elastic model of bladder tissue and a model of the geometry, the derived parameters are interpreted as elasticity and viscosity moduli. Static cystometry is involved in this new procedure. From analysis by stepwise cystometry it is concluded that static cystometry attained by following a slow-filling procedure is unacceptable in studying elastic behaviour.

Urodynamic Investigation of the Wide Ureter

Pressure flow studies constitute a valuable advancement in the investigation of wide ureters without reflux. However, these studies do not in themselves allow the determination of the adequacy of urine transport into the bladder. Radiological examination during perfusion is necessary to assess peristalsis and antiperistalsis, to determine the outflow to the bladder and to judge the geometric changes. Case studies reveal that it is difficult to assess the outflow to the bladder from measurements of renal pelvic pressure and of inflow.

An Evaluation of Contractility Parameters Determined from Isometric Contractions and Micturition Studies

SummaryIn a group of 110 patients of mixed pathology 218 micturitions were investigated. Using an on-line computer, two contractility parameters were calculated: the parameter U/1, which is derived from the isometric pressure rise in the detrusor before micturition actually started, and the parameter wmax, which is derived from flow and pressure during micturition. It was found that neither of the parameters conforms to the definition of an ideal contractility parameter. Both parameters are subject to the influence of the urethral resistance or the degree of neurogenic stimulation of the bladder, and both measure to some degree the actual performance of the detrusor during a given micturition instead of its myogenic properties. Nevertheless, by dividing patients into groups according to these two measured values, it was shown that clinically relevant types of detrusor behaviour can be distinguished.

CHANGES IN BLADDER CONTRACTILITY AND COMPLIANCE DUE TO URETHRAL OBSTRUCTION: A LONGITUDINAL FOLLOWUP OF GUINEA PIGS

PURPOSE We established the longitudinal changes in bladder contractility and compliance as a result of urethral obstruction using a guinea pig model. MATERIALS AND METHODS Obstruction was induced in guinea pigs by a silver ring around the urethra. Urodynamic studies were performed longitudinally in individual animals. Bladder contractility and compliance were calculated from the measured bladder pressure and urine flow rate. RESULTS Bladder contractility developed in distinct phases. It reached a maximum 200% increase after an average of 3.25 weeks concomitant with an almost 2-fold increase in urethral resistance, remained 150% to 200% increased during weeks 4 to 7 and then decreased to starting levels again, while urethral resistance remained almost 2-fold increased. Bladder compliance decreased by 80% during the first 3 weeks and continued to decrease to 5% of its original value after 10 to 11 weeks. CONCLUSIONS Our data indicate that as a result of obstruction bladder function passes through a specific sequence of stages, including first a compensatory increase in contractility, then a stabilization phase and finally a decompensation state. In contrast bladder compliance shows a continuous decrease. The data suggest that for assessing how far a bladder has deteriorated due to obstruction a combination of functional and structural data may be warranted.

THE VARIABLE OUTFLOW RESISTANCE CATHETER:: A NEW METHOD TO MEASURE BLADDER PRESSURE NONINVASIVELY

PURPOSE In a previous study an external condom catheter was used to measure noninvasively bladder pressure during interruption of the flow rate. The pressure increase in the condom sometimes caused a sphincter contraction that made bladder pressure measurement unreliable. Therefore, we developed a new variable outflow resistance catheter to measure noninvasively bladder pressure without interrupting the flow rate. MATERIALS AND METHODS The new catheter consists of an incontinence condom connected to a set of various outflow tubes and a pressure transducer. A remotely controlled pneumatic valve was fitted over each tube to interrupt flow through it. We measured isovolumetric pressure, maximum flow rate, and pressure and flow rates at various outflow resistances in 9 healthy male volunteers. RESULTS We derived a mathematical equation to estimate isovolumetric pressure from the pressure and flow rate values measured at various outflow resistances. The difference in the estimated and truly measured mean isovolumetric pressures plus or minus standard deviation was 0 +/- 6 cm. water. CONCLUSIONS The new variable outflow resistance catheter may be used to measure isovolumetric bladder pressure noninvasively without interrupting the flow rate. It has been previously shown that a combination of this pressure and a separately measured maximum flow rate may be used to diagnose bladder outlet obstruction noninvasively.

A computer program for on-line measurement, storage, analysis and retrieval of urodynamic data

A computer program is presented which allows for direct connection of a minicomputer to a urodynamic set-up. The program stores measured pressure and flow data in a random access disc file with minimal intervention of the urodynamicist, and enables the direct application of a number of methods of analysis to the data. The program is modular, and other analysis methods are easily added. Results of analyses are stored in the same disc file, and both results and measured data can be quickly and easily retrieved. The program is written in FORTRAN; hardware-dependent functions (analog input, graphics display, and random access disc storage) are implemented in subroutines (partly assembler) which can easily be replaced.

Contractility parameters of the guinea pig bladder in situ: similarity to human bladder contractility.

The parameters P(isv) (active isovolumetric detrusor pressure) and Vmax (maximum shortening velocity), which characterize the contractility of the detrusor muscle, were determined in guinea pigs. To this end it was necessary to develop a method of measuring flow rates in these small animals. The values found were used to calculate the contractility parameter Wmax. Thirteen animals were used. The results found for P(isv) and Vmax were 43.0 +/- 3.7 cm. H2O and 20.2 +/- 3.7 mm. per second, respectively. The latter corresponded to about 0.38 muscle lengths per second, which is similar to values reported for bladder strips from other species. Previous work showed that in vitro P(isv) decreased with increasing bladder volume over a wide range of volumes. In vivo P(isv) seemed to be independent of bladder volume. This suggests that neurogenic stimulation intensifies as volume increases. Vmax also was independent of volume. Wmax appeared to be suitable for detecting differences in the contractility of the bladders of different animals. Values were not significantly different in isovolumetric and nonisovolumetric contractions. Normalized to the size of the bladder, the Wmax values indicated that the power generated by the guinea pig bladder is similar to the power generated by the human bladder.

In vitro comparison of isometric and stop-test contractility parameters for the urinary bladder

SummaryContractility parameters in the urinary bladder can be calculated from isometric contractions (no extra patient load as compared to routine cystometry) or from stop-tests (more accurate, simpler analysis). A stop-test involves a voluntarily interrupted micturition with pressure and flow measurement. In a series of measurements in vitro on pig urinary bladder strips, parameters of the first type, obtained either by analyzing isometric contractions in terms of the Hill model, or by making phase plots, were compared to parameters of the second type. A good correlation was found. The parameter correlating best with the maximal contraction velocity of the bladder, normalized for differences in initial muscle length, as obtained from stop-test, is the isometric contraction force, which can be obtained from an isometric contraction by either of the two analysis techniques. Clinically, making phase plots seems more promising than analyzing contractions in terms of the Hill model.