W. A. van Duyl

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.

Drug Clearance by Continuous Haemodiafiltration

SummaryWith continuous arteriovenous haemodiafiltration (CAVHD), time-averaged clearance rates are higher than with intermittent haemodialysis. Indeed, drug removal rates may be high enough to warrant dose adjustment. In this study we measured the rate of drug clearance by CAVHD for 7 commonly used antibiotics: cefuroxime, cefotaxime, ceftazidime, imipenem, ciprofloxacin, tobramycin and vancomycin. By combining our data on clearance rates by CAVHD with literature data on drug distribution volumes and nonrenal clearance rates, we developed guidelines for drug dosage in intensive care patients treated by CAVHD. Dose adjustments during CAVHD treatment were deemed necessary for cefuroxime, ceftazidime, tobramycin and vancomycin.

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.

Spontaneous contractions in urinary bladder smooth muscle: Preliminary results

Spontaneous rhythmic contraction patterns in bladder tissue have been analysed in time and space by using a new experimental technique. These rhythmic contractions appear to be composed of frequency components which are multiples of a basic frequency. Distributions of the activity are also more or less synchronized in space. The physiological significance of the spontaneous activity is related to the potentiality of small regional contractions to become an epicentre for the development of large contractions leading to detrusor instability. The level of spontaneous activity is suggested as a parameter to define the state of the bladder along a bladder‐performance scale with the fully passive and fully activated states as extreme modes of performance.

Micromotions of bladder wall in chronic pelvic pain (CPP): A pilot study

Abstract: The aim of the study was to investigate the occurrence and duration of micromotions of the bladder wall. Thirty women with CPP and 7 healthy women underwent micromotion detection (MMD). A latex balloon provided with eight electrodes was placed within the bladder through the urethra and filled with saline up to 200 ml. Micromotions (MM), pressure within the balloon, abdominal pressure and respiratory excursions of the abdomen were registered simultaneously. A significant difference in duration as well as frequency of occurrence was found for MM activity between subjects with CPP and controls. For the occurrence of variations in detrusor presure, the difference between groups tended towards significance. We conclude that there are indications that the bladder is involved in CPP.

Step-wise cystometry of urinary bladder. New dynamic procedure to investigate viscoelastic behavior

Abstract Step-wise cystometry has been developed to analyze the pressure-relaxation phenomena of the bladder in mongrel dogs. The results show that a mathematical model consisting of two exponentials and a constant can befitted to the measurements. This model is interpreted in a mechanical model of the bladder wall in terms of viscoelasticity.

A model for both the passive and active properties of urinary bladder tissue related to bladder function

Herein we propose a new mechanical model for interpretation of volume‐pressure relationships of the bladder in both the collection and in the evacuation phase. Contractile tissue is ascribed plastic properties. The static volume‐pressure relation is related to a plasto/contractile‐elastic tissue component. In contrast to other models, the elastic element in series with the contractile element corresponds to tissue elasticity, which also determines the static volume–pressure relation. Viscoelasticity is more relevant in the evacuation phase than in the collection phase.

A New Clinical Parameter for the Assessment of the Contractility of the Urinary Bladder

In clinical urodynamic investigations there is a need for the assessment of the contractility of the bladder. A method, based on isometric cystometry, is proposed and evaluated in normal subjects. The method, adopted from cardiovascular research, is based on Hill’s equation and observations on the elastic behaviour of bladder tissue. The reproducibility of the results has been tested.

A mathematical model of continuous arterio-venous hemodiafiltration (CAVHD)

Continuous arterio-venous hemodiafiltration (CAVHD) differs from conventional hemofiltration and dialysis by the interaction of convection and diffusion, the use of very low dialysate flow rates and by the deterioration of membrane conditions during the treatment. In order to study the impact of these phenomena on diffusive transport, we developed a mathematical model of the kinetics of CAVHD solute transport from plasma water to dialysate. The model yields an expression of the diffusive mass transfer coefficient, Kd, as a function of blood, filtrate and dialysate flow rates and solute concentrations, which can be measured in the clinical setting. This paper gives a description of the model derivation. Kd is demonstrated to vary depending on dialysate flow and duration of treatment.

Stress relaxation of the human cervix: a new tool for diagnosis of cervical incompetence

A method is described for determination of the stress-relaxation characteristics of the cervix uteri of non-gravid women after almost stepwise dilatation of the cervical canal by a water-filled balloon. The stress relaxation is followed by measurement of the pressure decay in the same balloon. Application of this atraumatic technique to women with a normal cervix and women known to have an incompetent cervix yields diagnostic ranges of various parameters, in particular a time constant and the elastic ratio. The technique seems promising for easy detection of cervical incompetence, allowing suitable measures to be taken for prevention of immature deliveries. A mechanical model of the tissue of the ostium internum has further been developed on the basis of the measured characteristics.