Viscoelastic properties of the human colon

Cooled feline intestine and fresh intestine did not differ in enterotomy leak pressure testing or in gross wall thickness measurement

OBJECTIVE

To report gross anatomical gastrointestinal measurements and compare enterotomy leak pressures between fresh and cooled feline cadavers.

STUDY DESIGN

Ex vivo, randomized study.

ANIMALS

Fresh feline cadavers (n = 20).

METHODS

Jejunal segments (8 cm) were harvested on the same day as euthanasia. From each cadaver, one segment was randomly assigned to control (C), fresh enterotomy (FE), and cooled enterotomy (CE) groups. Enterotomy construction and leak testing were performed within 12 h of euthanasia for the C and FE groups and after 17-29 h of cooling for the CE group. Initial leak pressure (ILP) and maximum intraluminal pressure (MIP) were compared. Gastrointestinal wall thickness and intraluminal diameter were measured on harvested applicable gastrointestinal divisions at up to three time points: day 1 fresh, day 2 cooled, and day 3 cooled.

RESULTS

The mean (± SD) ILPs for the C, FE, and CE constructs were 600 (± 0.0), 200.3 (± 114.7), and 131.3 (± 92.6) mmHg, respectively. The C ILP was higher (p < .001) than the FE and CE ILP. The ILP (p = .11) and the MIP (p = .21) did not differ between the FE and CE constructs. Wall thickness (measured in mm) did not differ between duodenum day 1 fresh and day 2 cooled groups (p = .18) or between any jejunum day groups (p = .86). The intraluminal diameters (mean ± SD) for the duodenum, jejunum, and ileum were 5.7 (± 0.7), 5.8 (± 0.8), and 7.2 (± 2.2) mm, respectively.

CONCLUSION

No difference was appreciated between FE and CE ILP and MIP. Wall thickness measurements did not differ between days for duodenum or jejunum.

CLINICAL RELEVANCE

Cadaveric feline intestine cooled for up to 29 h may be used for determining intestinal leak pressures.

Listen to Your Gut: Key Concepts for Bioengineering Advanced Models of the Intestine

The intestine performs functions central to human health by breaking down food and absorbing nutrients while maintaining a selective barrier against the intestinal microbiome. Key to this barrier function are the combined efforts of lumen-lining specialized intestinal epithelial cells, and the supportive underlying immune cell-rich stromal tissue. The discovery that the intestinal epithelium can be reproduced in vitro as intestinal organoids introduced a new way to understand intestinal development, homeostasis, and disease. However, organoids reflect the intestinal epithelium in isolation whereas the underlying tissue also contains myriad cell types and impressive chemical and structural complexity. This review dissects the cellular and matrix components of the intestine and discusses strategies to replicate them in vitro using principles drawing from bottom-up biological self-organization and top-down bioengineering. It also covers the cellular, biochemical and biophysical features of the intestinal microenvironment and how these can be replicated in vitro by combining strategies from organoid biology with materials science. Particularly accessible chemistries that mimic the native extracellular matrix are discussed, and bioengineering approaches that aim to overcome limitations in modelling the intestine are critically evaluated. Finally, the review considers how further advances may extend the applications of intestinal models and their suitability for clinical therapies.

Mechanical experimentation of the gastrointestinal tract: a systematic review

The gastrointestinal (GI) organs of the human body are responsible for transporting and extracting nutrients from food and drink, as well as excreting solid waste. Biomechanical experimentation of the GI organs provides insight into the mechanisms involved in their normal physiological functions, as well as understanding of how diseases can cause disruption to these. Additionally, experimental findings form the basis of all finite element (FE) modelling of these organs, which have a wide array of applications within medicine and engineering. This systematic review summarises the experimental studies that are currently in the literature (n = 247) and outlines the areas in which experimentation is lacking, highlighting what is still required in order to more fully understand the mechanical behaviour of the GI organs. These include (i) more human data, allowing for more accurate modelling for applications within medicine, (ii) an increase in time-dependent studies, and (iii) more sophisticated in vivo testing methods which allow for both the layer- and direction-dependent characterisation of the GI organs. The findings of this review can also be used to identify experimental data for the readers' own constitutive or FE modelling as the experimental studies have been grouped in terms of organ (oesophagus, stomach, small intestine, large intestine or rectum), test condition (ex vivo or in vivo), number of directions studied (isotropic or anisotropic), species family (human, porcine, feline etc.), tissue condition (intact wall or layer-dependent) and the type of test performed (biaxial tension, inflation-extension, distension (pressure-diameter), etc.). Furthermore, the studies that investigated the time-dependent (viscoelastic) behaviour of the tissues have been presented.

Evaluating Performance of Circular Staplers Using Comparative Test Methods for Evidence-Based Surgery

BACKGROUND

Circular stapler anastomosis is a common surgical procedure. Despite technological advancements, anastomotic leak remains a postoperative concern. Assessment of new technologies is impeded by variations in test methods and analysis, precluding outcome reproducibility and direct comparisons of results across studies. The development of robust and reproducible preclinical test methods is critical to accelerating stapling technology advancements.

METHODOLOGY

Leak pressure, staple line perfusion and security, and device removal force were quantified for triple-row (Tri-staple EEA, TriEEA) and double-row staplers (Echelon Circular Powered, ECP). Leak and perfusion testing were performed in vivo. Device removal force and staple line security testing were performed with synthetic medium using an Instron. Data were analyzed using unpaired student's t-test or Kruskal-Wallis test, with statistical significance defined as P < .05.

RESULTS

Leak pressure was 73% higher in TriEEA vs ECP (P = .016). TriEEA staple line failure force was lower than ECP at 40 and 50 mmHg (P = .001 and P = .023, respectively). Perfusion to the staple line was higher (148%) for TriEEA than for ECP (P = .003) and the force required to remove the device from its stapled anastomosis was 78% lower for TriEEA than for ECP (P < .001).

DISCUSSION/CONCLUSIONS

This report addresses a primary limitation in stapling research by presenting novel methodologies which enhance clinical relevance and provide sufficient detail for reproduction by independent investigators. These methods are applied to a comparison between triple-row and double-row staplers to demonstrate utility of new test methods in assessing key technology design features.

Mechanobiological considerations in colorectal stapling: Implications for technology development

Technological advancements in minimally invasive surgery have led to significant improvements in patient outcomes. One such technology is surgical stapling, which has evolved into a key component of many operating rooms by facilitating ease and efficacy in resection and repair of diseased or otherwise compromised tissue. Despite such advancements, adverse post-operative outcomes such as anastomotic leak remain a persistent problem in surgical stapling and its correlates (i.e., hand-sewing), most notably in low colorectal or coloanal procedures. Many factors may drive anastomotic leaks, including tissue perfusion, microbiome composition, and patient factors such as pre-existing disease. Surgical intervention induces complex acute and chronic changes to the mechanical environment of the tissue; however, roles of mechanical forces in post-operative healing remain poorly characterized. It is well known that cells sense and respond to their local mechanical environment and that dysfunction of this "mechanosensing" phenomenon contributes to a myriad of diseases. Mechanosensing has been investigated in wound healing contexts such as dermal incisional and excisional wounds and development of pressure ulcers; however, reports investigating roles of mechanical forces in adverse post-operative gastrointestinal wound healing are lacking. To understand this relationship well, it is critical to understand: 1) the intraoperative material responses of tissue to surgical intervention, and 2) the post-operative mechanobiological response of the tissue to surgically imposed forces. In this review, we summarize the state of the field in each of these contexts while highlighting areas of opportunity for discovery and innovation which can positively impact patient outcomes in minimally invasive surgery.

Electromagnetic tool for the endoscopic creation of colon anastomoses-development and feasibility assessment of a novel anastomosis compression implant approach

BACKGROUND

Colorectal anastomoses are among the most commonly performed interventions in abdominal surgery, while associated patient trauma is still high. Most recent trends of endoscopic anastomosis devices integrate magnetic components to overcome the challenges of minimally invasive surgery. However, the mutual attraction between magnetic implant halves may increase the risk of inadvertently pinching healthy structures. Thus, we present a novel anastomosis device to improve system controllability and flexibility.

METHODS

A magnetic implant and an applicator with electromagnetic control units were developed. The interaction of magnetic implants with the electromagnets bears particular challenges with respect to the force-related dimensioning. Here, attraction forces must be overcome by the electromagnet actuation to detach the implant, while the attraction force between the implant halves must be sufficient to ensure a stable connection. Thus, respective forces were measured and the detachment process was reproducibly investigated. Patient hazards, associated with resistance-related heating of the coils were investigated.

RESULTS

Anastomosis formation was reproducibly successful for an implant, with an attraction force of 1.53 [Formula: see text], resulting in a compression pressure of [Formula: see text]. The implant was reproducibly detachable from the applicator at the anastomosis site. Coils heated up to a maximum temperature of [Formula: see text]. Furthermore, we were able to establish a neat reconnection of intestinal bowel endings using our implant.

DISCUSSION

As we achieved nearly equal compression forces with our implant as other magnetic anastomosis systems did (Magnamosis™: 1.48 N), we concluded that our approach provides sufficient holding strength to counteract the forces acting immediately postoperatively, which would eventually lead to an undesired slipping of the implant halves during the healing phase. Based on heat transfer investigations, preventive design specifications were derived, revealing that the wall thickness of a polymeric isolation is determined rather by stability considerations, than by heat shielding requirements.

Total collagen content and distribution is increased in human colon during advancing age

Background

The effect of ageing on total collagen content of human colon has been poorly investigated. The aim of this study was to determine if ageing altered total collagen content and distribution in the human colon.

Methods

Macroscopically normal ascending colon was obtained at surgery from cancer patients (n = 31) without diagnosis of diverticular disease or inflammatory bowel disease. Masson’s trichrome and Picrosirius red stains were employed to identify the total collagen content and distribution within the sublayers of the colonic wall for adult (22–60 years; 6 males, 6 females) and elderly (70 – 91years; 6 males, 4 female) patients. A hydroxyproline assay evaluated the total collagen concentration for adult (30–64 years; 9 male, 6 female) and elderly (66–91 years; 8 male, 8 female) patients.

Key results

Histological studies showed that the percentage mean intensity of total collagen staining in the mucosa, submucosa and muscularis externa was, respectively, 14(1.9) %, 74(3.2) % and 12(1.5) % in the adult ascending colon. Compared with the adults, the total collagen fibres content was increased in the submucosa (mean intensity; 163.1 ± 11.1 vs. 124.5 ± 7.8; P < 0.05) and muscularis externa (42.5 ± 8.0 vs. 20.6 ± 2.8; P < 0.01) of the elderly patients. There was no change in collagen content of the mucosa. The total collagen concentration was increased in the elderly by 16%. Sex-related differences were not found, and data were combined for analysis.

Conclusions

Greater total collagen content was found in the submucosa and muscularis externa of the elderly human male and female colon. These changes may contribute to a possible loss of function with ageing.

Local Colonic Administration of a Serine Protease Inhibitor Improves Post-Inflammatory Visceral Hypersensitivity in Rats

Dysregulation of the protease-antiprotease balance in the gastrointestinal tract has been suggested as a mechanism underlying visceral hypersensitivity in conditions such as inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS). We aimed to study the potential therapeutic role of an intracolonically administered serine protease inhibitor for the treatment of abdominal pain in a post-inflammatory rat model for IBS. An enema containing 2,4,6-trinitrobenzene sulfonic acid (TNBS) was used to induce colitis in male Sprague-Dawley rats, whereas controls received a saline solution. Colonoscopies were performed to confirm colitis and follow-up mucosal healing. In the post-inflammatory phase, the serine protease inhibitor UAMC-00050 (0.1-5 mg/kg) or its vehicle alone (5% DMSO in H2O) was administered in the colon. Thirty minutes later, visceral mechanosensitivity to colorectal distensions was quantified by visceromotor responses (VMRs) and local effects on colonic compliance and inflammatory parameters were assessed. Specific proteolytic activities in fecal and colonic samples were measured using fluorogenic substrates. Pharmacokinetic parameters were evaluated using bioanalytical measurements with liquid chromatography-tandem mass spectrometry. Post-inflammatory rats had increased trypsin-like activity in colonic tissue and elevated elastase-like activity in fecal samples compared to controls. Treatment with UAMC-00050 decreased trypsin-like activity in colonic tissue of post-colitis animals. Pharmacokinetic experiments revealed that UAMC-00050 acted locally, being taken up in the bloodstream only minimally after administration. Local administration of UAMC-00050 normalized visceral hypersensitivity. These results support the role of serine proteases in the pathophysiology of visceral pain and the potential of locally administered serine protease inhibitors as clinically relevant therapeutics for the treatment of IBS patients with abdominal pain.

A new method for assessing anal distensibility with a barostat and magnetic resonance imaging in healthy and constipated women

OBJECTIVES

Defecation requires relaxation of the internal and external anal sphincters. High anal resting pressure is associated with painful constipation, defecatory disorders, and increased healthcare utilization in constipated patients; the mechanisms are unclear. Perhaps patients with a high anal resting pressure have a less distensible canal, which impedes defecation.

METHODS

In 50 of 64 participants (33 healthy and 17 constipated women), anal pressures and distensibility were measured, respectively, with manometry and balloon distention combined with magnetic resonance imaging; rectal balloon expulsion time (BET) was also studied.

RESULTS

The BET (P = .006) was longer, and the mean (SD) rectoanal pressure gradient (-58[40] vs -34[26] mm Hg, P = .03) was more negative in constipated than healthy women; anal resting pressure was not different. During anal distention, the balloon expanded rapidly at an opening pressure of 49 (18) mm Hg, which was lower (P < .0001) than resting pressure (90 [25] mm Hg). The resting pressure was correlated with the opening pressure (r = 0.57, P < .0001) and inversely (r = -0.38, P = .007) with maximum volume but not with anal distensibility (volume-pressure slope). In healthy women, the difference (opening-resting pressure) was correlated with anal relaxation during evacuation (r = 0.35, P = .04). Anal distensibility and sensory thresholds were not different between constipated and healthy women.

CONCLUSIONS

Among healthy and constipated women, a greater anal resting pressure is correlated with greater opening pressure and lower maximum volume during distention, and, hence, provides a surrogate marker of anal distensibility. The difference (opening-resting pressure), which reflects anal relaxation during distention, is correlated with anal relaxation during evacuation. Anal resting pressure and distensibility were comparable in healthy and constipated women.

The Macro- and Micro-Mechanics of the Colon and Rectum I: Experimental Evidence

Many lower gastrointestinal diseases are associated with altered mechanical movement and deformation of the large intestine, i.e., the colon and rectum. The leading reason for patients' visits to gastrointestinal clinics is visceral pain, which is reliably evoked by mechanical distension rather than non-mechanical stimuli such as inflammation or heating. The macroscopic biomechanics of the large intestine were characterized by mechanical tests and the microscopic by imaging the load-bearing constituents, i.e., intestinal collagen and muscle fibers. Regions with high mechanical stresses in the large intestine (submucosa and muscularis propria) coincide with locations of submucosal and myenteric neural plexuses, indicating a functional interaction between intestinal structural biomechanics and enteric neurons. In this review, we systematically summarized experimental evidence on the macro- and micro-scale biomechanics of the colon and rectum in both health and disease. We reviewed the heterogeneous mechanical properties of the colon and rectum and surveyed the imaging methods applied to characterize collagen fibers in the intestinal wall. We also discussed the presence of extrinsic and intrinsic neural tissues within different layers of the colon and rectum. This review provides a foundation for further advancements in intestinal biomechanics by synergistically studying the interplay between tissue biomechanics and enteric neurons.

First translational consensus on terminology and definitions of colonic motility in animals and humans studied by manometric and other techniques

Alterations in colonic motility are implicated in the pathophysiology of bowel disorders, but high-resolution manometry of human colonic motor function has revealed that our knowledge of normal motor patterns is limited. Furthermore, various terminologies and definitions have been used to describe colonic motor patterns in children, adults and animals. An example is the distinction between the high-amplitude propagating contractions in humans and giant contractions in animals. Harmonized terminology and definitions are required that are applicable to the study of colonic motility performed by basic scientists and clinicians, as well as adult and paediatric gastroenterologists. As clinical studies increasingly require adequate animal models to develop and test new therapies, there is a need for rational use of terminology to describe those motor patterns that are equivalent between animals and humans. This Consensus Statement provides the first harmonized interpretation of commonly used terminology to describe colonic motor function and delineates possible similarities between motor patterns observed in animal models and humans in vitro (ex vivo) and in vivo. The consolidated terminology can be an impetus for new research that will considerably improve our understanding of colonic motor function and will facilitate the development and testing of new therapies for colonic motility disorders.

Biomathematical model for simulating abnormal orifice patterns in colonic crypts

Colonic polyps, which are abnormal growths in the colon, are a major concern in colon cancer diagnosis and prevention. Medical studies evidence that there is a correlation between histopathology and the shapes of the orifices in colonic crypts. We propose a biomathematical model for simulating the appearance of anomalous shapes for the orifices of colonic crypts, associated to an abnormal cell proliferation. It couples a mechanical model that is a mixed elastic/viscoelastic quasi-static model describing the deformation of the crypt orifice, with a convection-diffusion model that simulates the crypt cell dynamics in space and time. The coupling resides in the variation of pressure generated by abnormal proliferative cells that induce a mechanical force and originate the change in shape of the crypt orifice. Furthermore the model is formulated in a two-dimensional setting, for emulating the top view of the colonic mucosa, observed in vivo in colonoscopy images. The primary focus of this study is on the modeling of this complex biological phenomenon, by defining an appropriate reduced biomathematical model. Additionally, a numerical procedure to determine its solution is also addressed. The overall numerical simulations indicate that an excess of cell proliferation, in different crypt locations, creates some of the anomalous patterns of the colonic crypt orifices, observed in vivo in medical images.

A pharmacological challenge predicts reversible rectal sensorimotor dysfunctions in women with fecal incontinence

BACKGROUND

In order to understand the pathophysiology of rectal sensorimotor dysfunctions in women with fecal incontinence (FI) and rectal urgency, we evaluated the effects of a muscarinic antagonist and an adrenergic α₂ agonist on these parameters.

METHODS

Firstly, rectal distensibility and sensation were evaluated with a barostat and sinusoidal oscillation at baseline and after randomization to intravenous saline or atropine in 16 healthy controls and 44 FI patients. Thereafter, FI patients were randomized to placebo or clonidine for 4 wk; rectal compliance and sensation were revaluated thereafter. The effect of atropine and clonidine on rectal functions and the relationship between them were evaluated.

RESULTS

At baseline, compared to controls, rectal capacity was lower (P = .03) while the mean pressure (P = .02) and elastance (P = .01) during sinusoidal oscillation were greater, signifying reduced distensibility, in FI. Compared to placebo, atropine increased (P ≤ .02) the heart rate in controls and FI and reduced (P = .03) the variability in rectal pressures during sinusoidal oscillation in controls. Clonidine increased rectal compliance (P = .04) and reduced rectal capacity (P = .03) in FI. The effects of atropine and clonidine on compliance (r = .44, P = .003), capacity (r = .34, P = .02), pressures during sinusoidal oscillation (r = .3, P = .057), pressure (r = .6, P < .0001), and volume sensory thresholds (r = .48, P = .003) were correlated.

CONCLUSIONS

The effects of atropine and clonidine on rectal distensibility and sensation were significantly correlated. A preserved response to atropine suggests that reduced rectal distensibility is partly reversible, mediated by cholinergic mechanisms, and may predict the response to clonidine, providing a pharmacological challenge.

Evaluating the safety and the effects on colonic compliance of neostigmine during motility testing in patients with chronic constipation

BACKGROUND

Neostigmine, an acetyl cholinesterase inhibitor, stimulates colonic motor activity and may induce vagally mediated cardiovascular effects. Our aim was to evaluate effects of i.v. neostigmine on colonic compliance and its safety in patients with chronic constipation.

METHODS

We retrospectively reviewed medical records of a selected group of 144 outpatients with chronic constipation who were refractory to treatment. These patients had undergone intracolonic motility and compliance measurements with an infinitely compliant balloon linked to a barostat. Data abstracted included barostat balloon mean volumes with increases in pressure (4 mmHg steps from 0 to 44 mmHg) before and after i.v. neostigmine. Vital signs and oxygen saturation before and after neostigmine were recorded.

KEY RESULTS

Of the 144 patients, 133 were female, mean age was 41.0 ± 15.4 years (SD), and duration of constipation was 12.9 ± 13.8 years. Among patients who had undergone colonic transit measurement by scintigraphy, the overall colonic transit at 24 h (geometric center, GC24 [n = 115]) was 1.5 ± 0.7 (normal >1.3), and at 48 h (GC48 [n = 75]) it was 2.3 ± 0.9 (normal >1.9). Neostigmine decreased colonic compliance at lower distension pressures (e.g., 12 and 20 mmHg [both p < 0.001]), but not at 40 mmHg. There were expected minor changes in vital signs in response to neostigmine in 144 patients; however, one patient developed unresponsiveness, significant bradycardia, hypotension, and muscular rigidity that responded to 400 mcg i.v. atropine.

CONCLUSIONS & INFERENCES

Neostigmine significantly decreases colonic compliance in patients with refractory chronic constipation. Symptomatic bradycardia in response to neostigmine should be promptly reversed with atropine.

Analysis of the structural behaviour of colonic segments by inflation tests: Experimental activity and physio-mechanical model

A coupled experimental and computational approach is provided for the identification of the structural behaviour of gastrointestinal regions, accounting for both elastic and visco-elastic properties. The developed procedure is applied to characterize the mechanics of gastrointestinal samples from pig colons. Experimental data about the structural behaviour of colonic segments are provided by inflation tests. Different inflation processes are performed according to progressively increasing top pressure conditions. Each inflation test consists of an air in-flow, according to an almost constant increasing pressure rate, such as 3.5 mmHg/s, up to a prescribed top pressure, which is held constant for about 300 s to allow the development of creep phenomena. Different tests are interspersed by 600 s of rest to allow the recovery of the tissues' mechanical condition. Data from structural tests are post-processed by a physio-mechanical model in order to identify the mechanical parameters that interpret both the non-linear elastic behaviour of the sample, as the instantaneous pressure-stretch trend, and the time-dependent response, as the stretch increase during the creep processes. The parameters are identified by minimizing the discrepancy between experimental and model results. Different sets of parameters are evaluated for different specimens from different pigs. A statistical analysis is performed to evaluate the distribution of the parameters and to assess the reliability of the experimental and computational activities.

US-based Real-time Elastography for the Detection of Fibrotic Gut Tissue in Patients with Stricturing Crohn Disease

PURPOSE

To assess whether ultrasonography (US)-based real-time elastography (RTE) can be used to detect gut fibrosis.

MATERIALS AND METHODS

In this institutional review board-approved, prospective, proof-of-concept study, unaffected and affected gut segments in 10 patients with Crohn disease (four women, six men; median age, 49 years) were examined pre-, intra-, and postoperatively with US, including RTE to assess strain. Disease activity was scored by using the Limberg index on the basis of (a) bowel wall thickness and (b) size and extent of Doppler signal. After surgical resection, strain of full gut wall segments was measured with direct tensiometry. Gut wall layers, fibrosis, and collagen content were quantified histologically. Aggregated data per patient, disease status, and available measurements were assessed with mixed-effects models.

RESULTS

Unaffected versus affected gut segments yielded higher RTE (mean ± standard deviation, 169.0 ± 27.9 vs 43.0 ± 25.9, respectively) and tensiometry (mean, 77.1 ± 21.4 vs 13.3 ± 11.2, respectively) values used to assess strain (both P < .001). There was good correlation between pre-, intra-, and postoperative RTE values of unaffected (intraclass correlation coefficient, 0.572) and affected (intraclass correlation coefficient, 0.830) segments. RTE was not associated with pre- or intraoperative Limberg scores (median, 1 vs 2; P = .255 and .382, respectively). Affected internal (median, 2011 vs 1363 μm; P = .011) and external (median, 929 vs 632 μm; P = .013) muscularis propria, serosa (median, 245 vs 64 μm; P = .019), and muscularis mucosae (median, 451 vs 80 μm; P = .031) were wider than unaffected segments. Width differences of internal muscularis propria and mucularis mucosae were associated with RTE-assessed strain (P = .044 and .012, respectively) and tensiometry-assessed strain (P = .006 and .014, respectively). Masson trichrome (median, 4 vs 0; P < .001) and elastica-van Gieson (median, 805 346 μm(2) vs 410 649 μm(2); P < .001) stains and western blotting (median, 2.01 vs 0.87; P = .009) demonstrated a higher collagen content in affected versus unaffected segments and were associated with RTE-assessed strain (both P < .001) and tensiometry-assessed strain (P < .001 and 0.025, respectively).

CONCLUSION

RTE can be used to detect fibrosis in human Crohn disease. Online supplemental material is available for this article.

The effects of clonidine on symptoms and anorectal sensorimotor function in women with faecal incontinence

BACKGROUND

Women with faecal incontinence and rectal urgency have increased rectal stiffness and sensation.

AIM

To evaluate the effects of clonidine, an alpha(2) -adrenergic agonist, in faecal incontinence.

METHODS

In this open-label uncontrolled study, bowel symptoms and anorectal functions (anal pressures, rectal compliance, and sensation) were assessed before and during treatment with transdermal clonidine (0.2 mg daily, 4 weeks) in 12 women with urge-predominant faecal incontinence.

RESULTS

Clonidine reduced the frequency (17.8 +/- 3.1 before vs. 8.8 +/- 3.9 after, P = 0.03) and number of days with faecal incontinence (11.8 +/- 1.6 before vs. 6.1 +/- 1.8 after, P = 0.02), faecal incontinence symptom severity score (max = 13, 8.3 +/- 0.7 vs. 5.6 +/- 0.9, P < 0.01), and allowed patients to defer defecation for a longer duration (P = 0.03). Although overall effects on anorectal functions were not significant, the treatment-associated reduction in faecal incontinence episodes was associated with increased rectal compliance (r = -0.58, P < 0.05) and reduced rectal sensation. (r = -0.73, P = 0.007 vs. desire to defecate pressure threshold).

CONCLUSIONS

Clonidine improves symptoms in women with faecal incontinence; this improvement is associated with increased rectal compliance and reduced rectal sensitivity. A controlled study is necessary to confirm these observations.

Phenotypic variation of colonic motor functions in chronic constipation

BACKGROUND & AIMS

Colonic motor disturbances in chronic constipation (CC) are heterogeneous and incompletely understood; the relationship between colonic transit and motor activity is unclear. We sought to characterize the phenotypic variability in chronic constipation.

METHODS

Fasting and postprandial colonic tone and phasic activity and pressure-volume relationships were assessed by a barostat manometric assembly in 35 healthy women and 111 women with CC who had normal colon transit (NTC; n = 25), slow transit (STC; n = 19), and defecatory disorders with normal (DD-normal; n = 34) or slow transit (DD-slow; n = 33). Logistic regression models assessed whether motor parameters could discriminate among these groups. Among CC, phenotypes were characterized by principal components analysis of these measurements.

RESULTS

Compared with 10th percentile values in healthy subjects, fasting and/or postprandial colonic tone and/or compliance were reduced in 40% with NTC, 47% with STC, 53% with DD-normal, and 42% with DD-slow transit. Compared with healthy subjects, compliance was reduced (P

CONCLUSIONS

Fasting and/or postprandial colonic tone are reduced, reflecting motor dysfunctions, even in NTC. Colonic motor assessments allow chronic constipation to be characterized into phenotypes. Further studies are needed to evaluate the relationship among these phenotypes, enteric neuropathology, and response to treatment in CC.

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Key Words Collapse

MESH Headings

• Adult
• Catheterization
• Cholinesterase Inhibitors/administration & dosage
• Chronic Disease
• Colon/physiopathology
• Compliance/drug effects
• Constipation/physiopathology
• Defecation/physiology
• Female
• Gastric Emptying/physiology
• Gastrointestinal Motility/drug effects
• Gastrointestinal Motility/physiology
• Humans
• Logistic Models
• Male
• Manometry
• Neostigmine/administration & dosage
• Pastoral Care
• Phenotype
• Postprandial Period
• Pressure

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Grants

• P01 DK068055 NIDDK NIH HHS
• R01 DK078924 NIDDK NIH HHS
• R01 DK 78924 NIDDK NIH HHS

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Affiliation(s)

Karthik Ravi Clinical Enteric Neuroscience Translational and Epidemiological Research Program, Mayo Clinic and Mayo Foundation, Rochester, Minnesota
Adil E. Bharucha Clinical Enteric Neuroscience Translational and Epidemiological Research Program, Mayo Clinic and Mayo Foundation, Rochester, Minnesota
Michael Camilleri Clinical Enteric Neuroscience Translational and Epidemiological Research Program, Mayo Clinic and Mayo Foundation, Rochester, Minnesota
Deborah Rhoten Clinical Enteric Neuroscience Translational and Epidemiological Research Program, Mayo Clinic and Mayo Foundation, Rochester, Minnesota
Timothy Bakken Clinical Enteric Neuroscience Translational and Epidemiological Research Program, Mayo Clinic and Mayo Foundation, Rochester, Minnesota
Alan R. Zinsmeister Division of Biomedical Statistics and Informatics, Mayo Clinic and Mayo Foundation, Rochester, Minnesota

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Collaborators Collapse

Pilot study of pyridostigmine in constipated patients with autonomic neuropathy

BACKGROUND

The effects of cholinesterase inhibitors, which increase colonic motility in health, on chronic constipation are unknown. Our aims were to evaluate the efficacy of cholinesterase inhibitors for dysautonomia and chronic constipation and to assess whether acute effects could predict the long term response.

METHODS

In this single-blind study, 10 patients with autonomic neuropathy and constipation were treated with placebo (2 weeks), followed by an escalating dose of pyridostigmine to the maximum tolerated dose (i.e., 180-540 mg daily) for 6 weeks. Symptoms and gastrointestinal transit were assessed at 2 and 8 weeks. The acute effects of neostigmine on colonic transit and motility were also assessed.

RESULTS

At baseline, 4, 6, and 3 patients had delayed gastric, small intestinal, and colonic transit respectively. Pyridostigmine was well tolerated in most patients, improved symptoms in 4 patients, and accelerated the geometric center for colonic transit at 24 h by > or =0.7 unit in 3 patients. The effects of i.v. neostigmine on colonic transit and compliance predicted (P < 0.05) the effects of pyridostigmine on colonic transit.

CONCLUSIONS

Pyridostigmine improves colonic transit and symptoms in some patients with autonomic neuropathy and constipation. The motor response to neostigmine predicted the response to oral pyridostigmine.

Analysis of rectal dynamic and static compliances in patients with irritable bowel syndrome

AIMS

Our aim was to investigate whether the dynamic and static compliances differ between patients with irritable bowel syndrome (IBS) and normal subjects.

MATERIALS AND METHODS

Fifty-five IBS patients (age range 20-65 years, mean age 39.0 years, 28 women and 27 men; 36 diarrhea-predominant IBS (IBS-D) patients and 19 constipation-predominant IBS (IBS-C) patients) with symptoms that fulfilled the Rome-II criteria and 21 healthy controls (age range 25-58 years, mean age 37.8 years; 11 women and ten men) were recruited. The anorectal functions, including dynamic compliance, were evaluated via barostat tests. A power exponential model was used for the evaluation of static compliance.

RESULTS

There was no significant difference in dynamic compliance between the normal subjects and the IBS patients (10.3+/-3.1 and 8.9+/-2.9 mmHg, respectively, P>0.05). However, even though no significant difference was detected in the overall shape of the curve (beta; P>0.05), there were significant differences in the kappa and P (half) between the normal subjects and the IBS patients (P<0.05), respectively. When we compared the dynamic and static compliances between the IBS-C and IBS-D patients, there were no significant differences found (P>0.05).

CONCLUSIONS

An exponential model provided good fit to the actual data, and there were significant differences in static compliance between the normal subjects and the IBS patients. This result can reveal the altered biomechanical properties of the gut wall in IBS patients.

Lower gastrointestinal functions

The human colon serves to absorb water and electrolytes, store intraluminal contents until elimination is socially convenient, and salvage nutrients by bacterial metabolism of carbohydrates that have not been absorbed in the small intestine. The anorectum is responsible for fecal continence and defecation. This article is a broad perspective of the current status and a personal perspective of future challenges in understanding lower gastrointestinal functions in health and disease in humans.

Comparison of mathematical methods for calculating colonic compliance in humans: power exponential, computer-based and manual linear interpolation models

Measuring compliance allows differentiation of sensory changes from changes in thresholds because of altered compliance. As compliance of the colorectum is sigmoidal, a power exponential analysis was recommended. We aimed to develop and validate simpler measurements of compliance. Forty subjects (23 female, 17 male) underwent colonic barostat procedures comparing dronabinol vs placebo. Results of the effects on compliance were reported elsewhere. Compliance was determined as volume response to pressures ranging from 0 to 36 mmHg. Pressures corresponding to 10%, 50% and 90% (Pr10, Pr50 and Pr90) of maximum volume at 36 mmHg were estimated using a power exponential model, computer-based and manual linear interpolation. Data were compared and concordance evaluated. Pr50 and Pr90 were not significantly different by all methods for baseline and post-treatment. Respectively, concordance correlation coefficients were: pretreatment, 0.879, 0.464 and post-treatment, 0.879, 0.623. There is larger variation in Pr10 comparing all methods and manual calculations allow for the closest fit to the data. Concordance correlation coefficients were pretreatment = 0.189 and post-treatment = 0.322. There were no gender differences in compliance measurements. Results of compliance are highly concordant amongst all models. However, computer-based or manual interpolations appear superior to power exponential models for estimating Pr10.

Effect of aging on anorectal and pelvic floor functions in females

PURPOSE

In females, fecal incontinence often is attributed to birth trauma; however, symptoms sometimes begin decades after delivery, suggesting that anorectal sensorimotor functions decline with aging.

METHODS

In 61 asymptomatic females (age, 44 +/- 2 years, mean +/- standard error of the mean) without risk factors for anorectal trauma, anal pressures, rectal compliance, and sensation were assessed by manometry, staircase balloon distention, and a visual analog scale during phasic distentions respectively. Anal sphincter appearance and pelvic floor motion also were assessed by static and dynamic magnetic resonance imaging respectively in 38 of 61 females.

RESULTS

Aging was associated with lower anal resting (r = -0.44, P < 0.001) and squeeze pressures (r = -0.32, P = 0.01), reduced rectal compliance (i.e., r for pressure at half-maximum volume vs. age = 0.4, P = 0.001), and lower (P <or = 0.002) visual analog scale scores during phasic distentions at 16 (r = -0.5) and 24 mmHg (r = -0.4). Magnetic resonance imaging revealed normal anal sphincters in 29 females and significant sphincter injury, not associated with aging, in 9 females. The location of the anorectal junction at rest (r = 0.52, P < 0.001), squeeze (r = 0.62, P < 0.001), and Valsalva maneuver (r = 0.35, P = 0.03), but not anorectal motion (e.g., from resting to squeeze) was associated with age.

CONCLUSIONS

In asymptomatic females, aging is associated with reduced anal resting and squeeze pressures, reduced rectal compliance, reduced rectal sensation, and perineal laxity. Together, these changes may predispose to fecal incontinence in elderly females.

Time-dependent viscoelastic properties along rat small intestine

AIM: To measure the time-dependent (viscoelastic) behavior in the change of the small intestinal opening angle and to test how well the behavior could be described by the Kelvin model for a standard linear solid.

METHODS: Segments from the duodenum, jejunum, and ileum were harvested from 10 female Wistar rats and the luminal diameter, wall thickness, and opening angle over time (θ(t)) were measured from rings cut from these segments.

RESULTS: Morphometric variations were found along the small intestine with an increase in luminal area and a decrease in wall thickness from the duodenum to the ileum. The opening angle obtained after 60 min was highest in the duodenum (220.8±12.9°) and decreased along the length of the intestine to 143.9±8.9° in the jejunum and 151.4±9.4° in the ileum. The change of opening angle as a function of time, fitted well to the Kelvin model using the equation θ(t)/θo = [1-ηexp (-λt)] after the ring was cut. The computed creep rate λ did not differ between the segments. Compared to constant calculated from pig aorta and coronary artery, it showed that α agreed well (within 5%), η was three times larger than that for vascular tissue, and λ ranged ±40% from the value of the pig coronary artery and was a third of the value of pig aorta.

CONCLUSION: The change of opening angle over time for all the small intestine segments fits well to the standard linear spring-dashpot model. This viscoelastic constant of the rat small intestine is fairly homogenous along its length. The data obtained from this study add to a base set of biomechanical data on the small intestine and provide a reference state for comparison to other tissues, diseased intestinal tissue or intestinal tissue exposed to drugs or chemicals.

Contractile response to colonic distention is influenced by oscillation frequency

Static colonic mechanical properties are characterized by stepwise balloon distention. It is unclear whether the state of contractile activation affects frequency-dependent differences in biomechanical properties. Our aim was to investigate the frequency-dependence of colonic mechanical properties by sinusoidal oscillation. A descending colonic balloon was sinusoidally oscillated by 25 mL at 5, 10 and 20 cpm in randomized order for 20 min at each frequency in six healthy subjects before and after neostigmine. Volume oscillation was between 75-100 mL before, and 25-50 mL after neostigmine. Pressure waveforms were most variable shortly after commencing oscillation, reflecting an initial contractile response to distention. Elastance (i.e. pressure response to imposed volume) and hysteresivity were estimated; hysteresivity represents the proportion of energy added to the system during inflation, which cannot be recovered during deflation. Colonic elastance was frequency dependent, being highest and most variable at 10 cpm. In contrast, hysteresivity was not significantly different across frequencies. Neostigmine increased mean colonic elastance at all frequencies, and hysteresivity only at 5 cpm. Thus, colonic mechanical properties, particularly elastance are frequency-dependent. The frequency-dependence of colonic mechanical properties is worthy of future study because it may provide insights into reflex responses in health and disease.

Abnormal rectal motor physiology in patients with irritable bowel syndrome

A contentious issue is whether irritable bowel syndrome (IBS) patients have abnormal rectal motor physiology. Our aim was to determine whether IBS patients have abnormal rectal responses to low (urge producing) or high (pain producing) distension pressures. The IBS patients and healthy controls underwent five series of isobaric rectal distensions to examine volume-pressure relationships and rectal accommodation: (i) ascending stepwise distensions terminating upon report of moderate pain, (ii) phasic and (iii) tonic distensions at a single low pressure producing a moderate sensation of urge to defecate (iv) phasic and (v) tonic distensions at a single high pressure producing a moderate pain sensation. The IBS patients demonstrated a lower rectal volume-pressure ratio during repetitive single-pressure phasic distensions, and a slower rate of rectal accommodation during low (but not high) pressure tonic distensions. However, dynamic compliance during ascending stepwise distensions and the change in rectal volume during tonic distension were not significantly different from controls. Rectal abnormality was readily demonstrated by determining the volume-pressure ratio using a small number of repetitive single-pressure distensions, supporting the hypothesis that IBS patients have abnormal rectal motor physiology. We propose that a peripheral neuromuscular substrate may contribute to the pathogenesis of IBS.

Pathophysiology of adult fecal incontinence

Fecal incontinence occurs when the normal anatomy or physiology that maintains the structure and function of the anorectal unit is disrupted. Incontinence usually results from the interplay of multiple pathogenic mechanisms and is rarely attributable to a single factor. The internal anal sphincter (IAS) provides most of the resting anal pressure and is reinforced during voluntary squeeze by the external anal sphincter (EAS), the anal mucosal folds, and the anal endovascular cushions. Disruption or weakness of the EAS can cause urge-related or diarrhea-associated fecal incontinence. Damage to the endovascular cushions may produce a poor anal "seal" and an impaired anorectal sampling reflex. The ability of the rectum to perceive the presence of stool leads to the rectoanal contractile reflex response, an essential mechanism for maintaining continence. Pudendal neuropathy can diminish rectal sensation and lead to excessive accumulation of stool, causing fecal impaction, mega-rectum, and fecal overflow. The puborectalis muscle plays an integral role in maintaining the anorectal angle. Its nerve supply is independent of the sphincter, and its precise role in maintaining continence needs to be defined. Obstetric trauma, the most common cause of anal sphincter disruption, may involve the EAS, the IAS, and the pudendal nerves, singly or in combination. It remains unclear why most women who sustain obstetric injury in their 20s or 30s typically do not present with fecal incontinence until their 50s. There is a strong need for prospective, long-term studies of sphincter function in nulliparous and multiparous women.

Role of extrinsic innervation in modulating nitrergic transmission in the canine ileocolonic region

The human colon can dilate, often to life-threatening proportions. Our aim was to explore nitrergic mechanisms underlying colonic dilation in conscious dogs with enterically isolated ileocolonic loops either extrinsically innervated (n = 4) or extrinsically denervated (n = 4). We recorded phasic pressures in ileum and ileocolonic sphincter (ICS), colonic tone, compliance, and relaxation during ileal distension. By NADPH-diaphorase histochemistry, we assessed effects of extrinsic denervation and enteric isolation on nitrergic fibers. Extrinsic denervation increased phasic pressures in ileum, ICS, and colon and abolished ICS and colonic relaxation in response to ileal distension. The nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine (L-NNA) increased phasic pressures at all sites and ICS tone but did not abolish colonic relaxation during ileal distension in innervated loops. L-NNA reduced compliance and induced colonic high-amplitude propagated contractions in denervated loops. The NOS substrate donor L-arginine reversed effects of L-NNA. The number of NADPH-diaphorase fibers increased in both enterically isolated preparations. Nonnitrergic extrinsic nerve pathways mediate reflex colonic relaxation during ileal distension. Enteric isolation augments the number of NOS fibers, an effect not modified by extrinsic denervation.