Biomechanics of the gastrointestinal tract

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.

Sensory and Biomechanical Responses to Distension of the Normal Human Rectum and Sigmoid Colon

“…Unfortunately, the compliance parameter expresses merely the difference in luminal dimensions between pressure steps. Hence, the parameter does not take into account the actual degree of stretch that occurs under luminal pressure loading and the variation in the unstressed size of the organ [7]. The CSA distensibility parameter used in this study accounts for these deficiencies.…”

“…In older studies, rectal compliance was estimated using simultaneous measurements of rectal pressure and volume [2, 8]. Pressure-volume data may, however, be biased since elongation of the bag in the axial direction is likely to occur [7, 8]. The compliance defined as the slope of the pressure-volume curve varies throughout the colon; it is greater in the transverse colon than in the sigmoid colon [22].…”

“…where T is the circumferential wall tension, r is the bag radius, and ΔP is the transmural pressure [7, 23]. The transmural pressure was considered to be equal to the difference between bag pressure and the resting pressure assuming that the pressure within the colon at rest is the same as the intra-abdominal pressure.…”

“…Unfortunately, the studies attempting to describe the biomechanical properties of the colon and rectum report a wide range in compliance [1, 4, 5]. Tests based on volume measurements are not optimal since they provide no direct measure of variables useful in plane stress and strain analysis [7]. This is further emphasized by the fact that the distal GI tract is tubular rather than globular.…”

A Study on Anchoring Ability of Three-Leg Micro Intestinal Robot

“…The biomechanical features mostly rely on the smooth muscles of the muscularis externa layer. Various experiments [9][10][11][12][13] have attempted to model the passive behavior of the intestinal walls and the friction between the intestinal walls and contents. Due to the complexity of the responses under mechanical stimulation, no model has been able to perfectly demonstrate the mechanical interaction needed for traveling through the small bowel.…”