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Biomedical subjects

R van Mastrigt

Publications and source records attributed to R van Mastrigt.

At least 73 records · Page 4Linked to original sources
PubMed1993

Cell length measurements in longitudinal smooth muscle strips of the pig urinary bladder.

In this study the length of smooth muscle cells in muscle bundles of pig urinary bladder wall was determined after dissection in Tyrode buffers with different calcium concentrations ([Ca2+]). Previous studies have shown that the length of isolated smooth muscle cells decreases with an increase in [Ca2+] in the buffer. Unlike the results in isolated cells, no significant differences in length were found between cells in strips subjected to different [Ca2+]. Cells in bundles dissected from filled bladders were significantly larger than those dissected from emptied bladders. Cells in strips from emptied bladders dissected in 1.8 mM Ca(2+)-Tyrode buffer were shorter than those obtained in Ca(2+)-free buffer. From the measurements it was concluded that: (1) Cell length in intact tissue is directly related to tissue length; series elastic structures external to the cells do not allow significant shortening of the cells. (2) Passive parallel elasticity outside the cells accounts for passive shortening when bladders are emptied manually. (3) Cell length is not related to empty bladder weight. (4) A positive relation exists between empty bladder weight and bladder capacity.

Animals↗
PubMed1993

Automated evaluation of urethral obstruction.

The measurement of detrusor pressure and flow rate during voiding is the only way to objectively measure or grade infravesical obstruction. The resulting data cannot be interpreted easily. Manual as well as automatic methods have been introduced to derive one or several factors or parameters to quantify urethral resistance. A number of these methods are described in this overview. Since automatic methods involving computers guarantee uniform, unbiased, and objective processing of data, besides enabling the use of (statistical) methods that take into account more than one or two of the measured pressure and flow rate values, emphasis is on these methods. Some clinical results obtained with such automatic methods are discussed to illustrate the clinical value and possible impact on diagnosis and evaluation of treatment of lower urinary tract disorders.

Diagnosis, Computer-Assisted↗
PubMed1991

The force recovery following repeated quick releases applied to pig urinary bladder smooth muscle.

A method for measuring several quick-releases during one contraction of a pig urinary bladder smooth muscle preparation was developed. The force recovery following quick release in this muscle type was studied by fitting a multiexponential model to 926 responses measured during the first 700 ms after release, both in the stimulated and in the unstimulated muscle. It was concluded that the force recovery in this observation window was biexponential and that the two time constants result from two fundamentally different processes. The slower time constant in the order of 0.45 s was ascribed to crossbridge cycling, and this hypothesis was supported by the considerable dependence of the amplitude associated with this time constant on the stimulus condition of the muscle. The faster time constant in the order of 0.032 s was found to be largely independent of the degree of stimulation of the muscle and was ascribed to a passive, viscoelastic process.

Animals↗
PubMed1991

The effect of oxyphenonium bromide and oxybutynin hydrochloride on detrusor contractility and reflux in children with vesicoureteral reflux and detrusor instability.

In a prospective study the effects of the anticholinergic drugs oxyphenonium bromide and oxybutynin hydrochloride on detrusor contractility and reflux were studied. Although anticholinergic properties are claimed of both drugs, only oxybutynin hydrochloride proved to decrease detrusor contractility and the degree of reflux, probably due to a direct spasmolytic effect on the detrusor. Therefore, in cases of reflux and detrusor instability treatment with oxybutynin hydrochloride is recommended.

Child↗
PubMed1991

Urodynamic assessment and quantification of prostatic obstruction before and after transurethral resection of the prostate: standardization with the aid of the computer program CLIM.

The clinical manifestations of benign prostatic hypertrophy (BPH) are ascribed entirely to the infravesical obstruction. Therefore relief of symptoms is pursued by surgical removal of obstruction, i.e. prostatectomy. On the other hand, it is generally accepted that the conventional clinical signs and symptoms do not correlate with obstruction as urodynamically defined. In the present study, objective obstruction and detrusor contractility parameters were calculated from detrusor pressure and flow rate measurements in 22 patients before and after transurethral resection of the prostate (TURP) using the computer program CLIM. The results indicate: (1) that CLIM supplies reliable obstruction and contractility parameters for preoperative assessment and follow-up in patients with BPH and (2) that greater than 25% of the patients, who underwent TURP, were objectively not obstructed. These findings form strong arguments for including CLIM parameters in the preoperative assessment to perform a TURP.

Diagnosis, Computer-Assisted↗
PubMed1990

Estimation of the maximum contraction velocity of the urinary bladder from pressure and flow throughout micturition.

The contractility of the urinary bladder can be adequately described in terms of the parameters P0 (isometric pressure) and Vmax (maximum contraction velocity). In about 12% of urodynamic evaluations of patients these clinically relevant parameters can be calculated from pressure and flow rate as measured during micturition. A method was developed of estimating Vmax for any micturition from these signals. The properties of this estimated contractility parameter were clinically tested and are discussed.

Adult↗
PubMed1990

Opening contraction energy in prostatic (compressive) obstruction.

The opening contraction energy (Eop), i.e. the energy expended by the detrusor in the opening phase of micturition, was measured in 70 males (mean age 63 +/- 9 years) with bladder outflow obstruction (compressive obstruction) due to benign prostatic hypertrophy. Significant correlations (p less than 0.001) were found between Eop and the maximum external voiding power developed by the detrusor, Wext max (rs = -0.57), between Wext max and the fraction of bladder volume voided, VV% (rs = 0.65), and between Eop and VV% (rs = -0.77) - which suggests that increasing values of Eop affect the energy which the detrusor can supply for completion and termination of voiding. It then seems the parameter Eop would be able to assess not only the opening phase of micturition, but the emptying phase as well - the greater Eop (i.e. the greater the work needed to unfold the urethral lumen and start urine flow), the lesser the muscle mechanical capability of the urinary bladder to completely void. Thus, we eventually believe that calculating the parameter Eop may prove to be a complete, though indirect, method of quantifying the degree of prostatic (compressive) obstruction of the vesical outlet by a single numerical index.

Aged↗
PubMed1989

Efficient storage of urodynamic signals by computer: application of FAN adaptive sampling.

Digital storage of urodynamic signals such as detrusor pressure and flowrate at a sufficiently high sampling rate (10 samples per second) to allow subsequent analysis requires considerable computer memory. A procedure for compressing these data by deleting redundant samples (the fan method of adaptive sampling) was tested. The method allows a flexible adaptation to specific hardware and a compromise between storage requirements and accuracy. In this study the number of samples required for adequate reconstruction of the detrusor pressure signal could be varied from 80% to 4% of the original number of samples by varying the average difference between reconstructed and original signal from 0.01 to 2 cm H2O. Fast components of the measurements (for example cough peaks) which were lost if a lower sampling rate or averaging was used to obtain equally low storage requirements were unaffected by this compression technique.

Algorithms↗
PubMed1987

Isolation and individual electrical stimulation of single smooth-muscle cells from the urinary bladder of the pig.

In contrast to striated muscle, measurements on strips of smooth muscle cannot be uniquely interpreted in terms of an array of contractile units. Therefore scaling down to the single-cell level is necessary to gain detailed understanding of the contractile process in this type of muscle. The present study describes the development of a method for isolating contractile single smooth muscle cells from pig urinary bladders. Contractile responses evoked by individual electrical stimulation were used as a measure of cell quality during development of the method. Responses were evaluated by measuring latency, contraction and relaxation times, as indicated by visible length changes, and stored on-line in a computer. Initial length, relative shortening and shortening speed were determined by measuring cell lengths in previously timed still video frames using a computer-controlled crosshair device. Increase of stimulus pulse duration resulted in improved responses, indicating that the observed shortening represented a physiological contractile response. Ultimately this method of evaluation was applied to two sets of cell preparations obtained by two different methods, one using only collagenase digestion, the other using mechanical manipulation as well. Both sets showed two main patterns of response to electrical stimulation: a pattern of contraction upon stimulation followed by enhanced contraction when stimulation was switched off (CK), and a pattern of contraction upon stimulation followed by relaxation when the stimulus was switched off (CR). The set of preparations containing the highest percentage of CR cells was found to be superior (i.e. greater initial length, shorter latency and contraction times, increased shortening and higher shortening speed). The method of isolation used for this set gives a high yield of contractile cells available for experimental use over a long span of time.

Animals↗
PubMed1987

Clinical comparison of bladder contractility parameters calculated from isometric contractions and pressure-flow studies.

Parameters describing the contractility of the urinary bladder can be calculated from both isometric contractions and pressure-flow studies. The first method has the advantage of making very little demand either on the patient or on the urodynamicist, and the disadvantage of yielding a parameter that is not clearly related to muscle physiology. The second method demands more from both patient and experimenter but yields straightforward parameters. For a group of 86 patients with mixed pathologic findings, a correlation between the two types of parameters was demonstrated, showing that both methods test, at least partly, the same mechanism.

Adult↗
PubMed1986

An evaluation of contractility parameters determined from isometric contractions and micturition studies.

In 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/l, 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.

Adult↗
PubMed1986

Urinary bladder function and its control in healthy females.

Recordings in eight healthy female volunteers of bladder (detrusor) pressure and flow rate, obtained during bladder filling and during voiding, both through the urethra and through a catheter, demonstrate that a model of bladder function in which the detrusor muscle is considered as completely passive during filling and fully activated during voiding is inadequate. Assessment of the detrusor contraction strength by a new method (described in APPENDIX A) shows that in ideal normal voidings the contraction strength rises to values of 11-24 W/m2 and is sustained or rises slightly until the bladder is empty. During unstable detrusor contractions, which even in these healthy women are observed during bladder filling and also during inhibited voidings through the urethra, the contraction is weaker. During voidings through a catheter the detrusor contraction is weak, variable, and fades away before the bladder is empty. An elementary feedback analysis demonstrates that the effect of the micturition reflex governing detrusor behavior differs according to whether or not voiding is taking place. The reflex does not lead to a simple on-off mechanism but to a more complex behavior that is consistent with the observations and that appears to be important for the understanding of pathological obstructed micturition.

Adult↗
PubMed1986

Modeling the contractility of urinary bladder smooth muscle using isometric contractions.

In the course of developing a clinical contractility index, isometric contractions of pig urinary bladder smooth muscle were analyzed in terms of phase plots (a plot of the rate of change of a variable, in this case force, as a function of the variable itself). The straight line describing the major part of the phase plots is characterized by the two parameters Fiso (the horizontal intercept) and c (the slope) of the line. It was found that changes in the geometry of the tissue sample and changes in extracellular calcium grossly influence Fiso, but not c, whereas changes in prestimulus rest time influence c, but not Fiso. It is concluded that Fiso is related to the number of available contractile units, and c is related to the limiting rate constant in the excitation-contraction coupling, which is probably determined by the release of intracellular calcium. The existence of the calcium paradox and the interpretation of the concept of facilitation or potentiation in this type of smooth muscle are discussed.

Animals↗
PubMed1986

Influence of temperature and stimulus interval variations on the propagation of contractions in the pig ureter.

The influences of ureter temperature and time interval between stimulations on the velocity of propagation of contractions in the pig ureter were studied in vitro. The propagation velocity was calculated from electromyogram signals measured at regular distances along the ureter. It was found that a temperature decrease of 3 degrees C causes a velocity decrease of nearly 5 mm/s. The influence of the interstimulus interval is much smaller: a reduction from 300 to 10 s causes a 10% drop in propagation velocity. Both phenomena can be understood from changes in the strength-duration curve describing the excitability of the tissue and clarify the discrepancies between propagation velocity measurements in vitro and in vivo.

Animals↗
PubMed1985

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

Contractility 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. Th 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.

Animals↗
PubMed1985

Electrical stimulation of smooth muscle strips from the urinary bladder of the pig.

Strips of smooth muscle from pig urinary bladders were electrically stimulated to contract. Stimulation parameters and conditions were optimized so as to obtain a maximum number of isometric contractions with maximal force. It was found that the contractions could be described mathematically by a simple model. In the model there is a constant probability for cells to pass from the non-contractile to the contractile state during stimulation; this leads to a linearly decreasing phase plot (a plot of the rate of rise of a variable as a function of the variable) for the force. 'Activation' of the cells is described by a physical step function. Isometric contractions were thus characterized by a set of three parameters: U, the time derivative of the force, extrapolated to zero force, Fiso the value of the isometric force which is approached asymptotically after infinitely long periods of stimulation and t1, the activation time. The sensitivity of these three parameters to variation of the stimulus parameters was investigated. It was found that the parameter U was consistently correlated with the stimulus parameters, suggesting that this parameter can be used to describe the effectiveness of electrical stimulation of such strips.

Animals↗
PubMed1984

Bolus propagation in pig ureter in vitro.

Pig ureters were made to propagate injected fluid boluses by electrical stimulation in vitro. The propagation velocity was determined from EMG measurements made at several points along the ureter. It was found that this velocity varied both along the ureter and as a function of time, and that it was related to the contraction pressure but not to the bolus size.

Animals↗