Abstract As the function of the gastrointestinal tract is to a large degree mechanical, it has become increasingly popular to acquire distensibility data in motility research based on various parameters. Hence it is important to know on which geometrical and mechanical assumptions the various parameters are based. Currently, compliance and tone derived from pressure‐volume curves are by far the most often used parameters. However, pressure‐volume relations obtained in tubular organs must be carefully interpreted as they provide no direct measure of luminal cross‐sectional area and other variables useful in plane stress and strain analysis. Thus, erroneous conclusions concerning tissue distensibility may be deduced. Other parameters, such as wall tension, stress and strain, give more useful information about mechanical behaviour. Distensibility data procure significance in fluid mechanics and in the study of tone, peristaltic reflexes, and mechanoreceptor kinematics. Such data are needed for the determination of the interaction between stimulus, electrical responses in neurons and the mechanical behaviour of the gut. Furthermore, from a clinical perspective, investigation of visco‐elastic properties is important because GI diseases are associated with growth and remodelling. For example, prestenotic dilatation, increased collagen synthesis, dysmotility and altered distensibility are common features of obstructive diseases. The purpose of this review is to discuss the physiological and clinical importance of acquiring biomechanical data, distensibility parameters and interpretation of these results and their associated errors. We will also discuss some aspects of the relationship between morphology, growth and biomechanics. Finally, we will outline a number of techniques to study the mechanical properties of the GI tract.

Biomechanics of the gastrointestinal tract

As the function of the gastrointestinal tract is to a large degree mechanical, it has become increasingly popular to acquire distensibility data in motility research based on various parameters. Hence it is important to know on which geometrical and mechanical assumptions the various parameters are based. Currently, compliance and tone derived from pressure-volume curves are by far the most often used parameters. However, pressure-volume relations obtained in tubular organs must be carefully interpreted as they provide no direct measure of luminal cross-sectional area and other variables useful in plane stress and strain analysis. Thus, erroneous conclusions concerning tissue distensibility may be deduced. Other parameters, such as wall tension, stress and strain, give more useful information about mechanical behaviour. Distensibility data procure significance in fluid mechanics and in the study of tone, peristaltic reflexes, and mechanoreceptor kinematics. Such data are needed for the determination of the interaction between stimulus, electrical responses in neurons and the mechanical behaviour of the gut. Furthermore, from a clinical perspective, investigation of visco-elastic properties is important because GI diseases are associated with growth and remodelling. For example, prestenotic dilatation, increased collagen synthesis, dysmotility and altered distensibility are common features of obstructive diseases. The purpose of this review is to discuss the physiological and clinical importance of acquiring biomechanical data, distensibility parameters and interpretation of these results and their associated errors. We will also discuss some aspects of the relationship between morphology, growth and biomechanics. Finally, we will outline a number of techniques to study the mechanical properties of the GI tract.

https://www.springer.com/productFlyer_978-1-85233-520-5.pdf?SGWID=0-0-1297-2180540-0

Biomechanics of the Gastrointestinal Tract

Changes in Contractile Properties in Hypertrophic Rat Urinary Bladder

The bladder wall is composed of passive (collagen, elaftin) and active (smooth muscle) elements. Some of the smooth muscle cells have properties of “pacemakers” in that they show spontaneous activity at rest. Moreover, when these cells are stretched, the resting membrane potentials decrease and the frequency of action potentials increase. It has been further demonstrated that both in vitro muscle strips and in vivo bladder preparations show spontaneous activity which may generate both tonic and phasic changes in bladder wall forces. The rate and duration of stretch both affect the force that the cell can generate. Thus, the filling pressureivolume curve obtained by systometry represents an interaction between the active and passive elements of the bladder wall. Since the cystornetric curve is time dependent, it is impossible to compare cystometrograms unless this time dependency is taken into account. With these principles in mind it is possible to standardize the terminology for characterizing detrusor activity during the collection phase as outlined in this report.

Bladder compliance and detrusor activity during the collection phase

A variety of conditions encountered in urology result in bladder dysfunction and the need for bioengineered tissue substitutes. Traditionally, a number of synthetic materials and natural matrices have been used in experimental and clinical settings. However, the production of functional bladder tissue replacements remains elusive. The urinary bladder sustains considerable structural deformation during its normal function and represents an ideal model tissue in which to study the effects of biomechanical simulation on tissue morphogenesis, differentiation, and function. However, the actual role of mechanical forces within the bladder has received little attention. A strategy in which in vitro-generated tissue constructs are conditioned by exposure to the same mechanical forces as they would encounter in vivo could potentially be used both in the development of functional tissue replacements and to further study the role of biomechanical signalling. The purpose of this review is to examine the role and structure-function relationship of the urinary bladder and, through consultation of the literature available on mechanotransduction and tissue engineering of alternative tissues, to determine the factors that need to be considered when biomechanically engineering a functional bladder.

Review: tissue engineering of the urinary bladder: considering structure-function relationships and the role of mechanotransduction.

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.

Visco-elastic properties of the bladder wall.

https://repub.eur.nl/pub/14867/4747663.pdf

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

To analyse pressure decay curves, as recorded in stepwise cystometry, an electronic device was constructed. This device offers an alternative for similar analyses by a digital computer. A prototype of

A. van der Zwart

Papers

Visco-elastic properties of the bladder wall.

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

An Electronic Device for Quick Analysis of Exponential Decay Curves