Pressure changes after balloon distension of the colon wall in diverticular disease

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.

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.

Computational analysis of mechanical stress in colonic diverticulosis

Diverticulosis results from the development of pouch-like structures, called diverticula, over the colon. The etiology of the disease is poorly understood resulting in a lack of effective treatment approaches. It is well known that mechanical stress plays a major role in tissue remodeling, yet its role in diverticulosis has not been studied. Here, we used computational mechanics to investigate changes in stress distribution engendered over the colon tissue by the presence of a pouch-like structure. The objectives of the study were twofold: (1) observe how stress distribution changes around a single pouch and (2) evaluate how stress elevation correlates with the size of the pouch. Results showed that high stresses are concentrated around the neck of a pouch, and their values and propagation increase with the size of the pouch neck rather than the pouch surface area. These findings suggest that stress distribution may change in diverticulosis and a vicious cycle may occur where pouch size increases due to stress elevation, which in turn elevates stress further and so on. Significant luminal pressure reduction would be necessary to maintain stress at normal level according to our results and therapeutic approaches aimed directly at reducing stress should rather be sought after.

Management of colon stents based on Bernoulli's principle

BACKGROUND AND AIMS

The colonic self-expanding metal stent (SEMS) has been widely used for "bridge to surgery" and palliative therapy. However, if the spread of SEMS is insufficient, not only can a decompression effect not be obtained but also perforation and obstructive colitis can occur. The mechanism of occurrence of obstructive colitis and perforation was investigated by flow dynamics.

METHODS

Bernoulli's principle was applied, assuming that the cause of inflammation and perforation represented the pressure difference in the proximal lumen and stent. The variables considered were proximal lumen diameter, stent lumen diameter, flow rate into the proximal lumen, and fluid density. To model the right colon, the proximal lumen diameter was set at 50 mm. To model the left-side colon, the proximal lumen diameter was set at 30 mm.

RESULTS

For both the right colon model and the left-side colon model, the difference in pressure between the proximal lumen and the stent was less than 20 mmHg, when the diameter of the stent lumen was 14 mm or more. Both the right colon model and the left-side colon model were 30 mmHg or more at 200 mL s^-1 when the stent lumen was 10 mm or less. Even with an inflow rate of 90-110 mL s^-1, the pressure was 140 mmHg when the stent lumen diameter was 5 mm.

CONCLUSION

In theory, in order to maintain the effectiveness of SEMS, it is necessary to keep the diameter of the stent lumen at 14 mm or more.

Diet, ageing and genetic factors in the pathogenesis of diverticular disease

Diverticular disease (DD) is an age-related disorder of the large bowel which may affect half of the population over the age of 65 in the UK. This high prevalence ranks it as one of the most common bowel disorders in western nations. The majority of patients remain asymptomatic but there are associated life-threatening co-morbidities, which, given the large numbers of people with DD, translates into a considerable number of deaths per annum. Despite this public health burden, relatively little seems to be known about either the mechanisms of development or causality. In the 1970s, a model of DD formulated the concept that diverticula occur as a consequence of pressure-induced damage to the colon wall amongst those with a low intake of dietary fiber. In this review, we have examined the evidence regarding the influence of ageing, diet, inflammation and genetics on DD development. We argue that the evidence supporting the barotrauma hypothesis is largely anecdotal. We have also identified several gaps in the knowledge base which need to be filled before we can complete a model for the etiology of diverticular disease.

Pathophysiological aspects of diverticular disease of colon and role of large bowel motility

Colonic diverticular disease (diverticulosis) is one of the most common gastrointestinal disorders in Western countries. This disorder is strictly related to aging and fibre intake, and still bears a discrete amount of morbidity. Numerous etiological co-factors have to date been implicated in the pathogenesis of the disease, yet the supporting evidence is still far from absolute. The present review considers the pathophysiology of colonic diverticular disease, with a special emphasis on factors related to abnormal colonic motility.

Pathogenesis of colonic diverticula

BACKGROUND

Diverticula are herniations through the colonic wall and are therefore likely to be due to a weakness within the wall, an alteration in intracolonic pressures or a combination of these factors. This article reviews these aspects in relation to the pathogenesis of colonic diverticula.

METHODS

Medline and Science Citation Index searches were performed to locate English language articles relating to the pathogenesis of colonic diverticulosis published since 1960. Manual cross-referencing was also performed and some historical articles were included.

RESULTS AND CONCLUSION

Several theories now exist about the development of colonic diverticula. The majority of the evidence suggests that the morphological changes are the response to a lifelong consumption of a low-residue diet. However, there are complex relations between colonic structure, motility and dietary factors, and it is likely that all of these (and possibly genetic influences) play a role in the pathogenesis to a greater or lesser degree.

Diverticulosis in the defunctioned limb of a long-standing colostomy

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A regional audit of the investigation and treatment of colorectal and pelvic floor disorders (1984-1991)

The activities of a regional physiology unit established for the investigation of colorectal and pelvic floor physiology in health and disease in a clinically relevant setting has been audited and its evolution described over a period of eight years. Trends in surgical treatment of some of these disorders over the same period have also been documented in the Lothian Region. Although there has been little change in the number of patients investigated annually patterns of investigation appear to change. Sphincter manometry, proctometrography and somatosensory reflex measurements have remained the most frequently performed and useful investigations. Spinal stimulation studies increased transiently because of a collaborative investigation of bowel and bladder function in patients with spinal injuries. A considerable increase in surface EMG tests and dynamic proctography has occurred. These trends are thought to be related to interest in defining evacuation dysfunction of the rectum and related problems of the pelvic floor. Isotope proctography now rivals barium videoproctography; at the same time the use of manometric colonic motility studies has diminished. Anal ultrasonography has replaced sphincter mapping in the last year and is being applied to other aspects of anorectal pathology. The last 4 years have seen the introduction and increasing use of non-surgical therapeutic modalities for the treatment of faecal incontinence and constipation: reflex electronic sphincter stimulation, biofeedback and the use of a prokinetic agent to promote colonic motility. Concomitant changes in the surgery of constipation and reconstructive anorectal procedures have been observed. It is recommended that coloproctology units should have easy access to at least one such investigation laboratory within their catchment area together with appropriate auditing facilities.

Age-related alterations in the strength and collagen content of left colon in rats

The biomechanical properties and intestinal wall composition of left colon were studied in 4-month-old, 14-month-old, and 27-month-old male rats. The hydroxyproline content and hydroxyproline concentration in old rats were increased by 36% and 26%, respectively, compared with young rats and by 20% and 17%, respectively, compared with middle-aged rats. In middle-aged rats the maximum load increased by 21%, compared with young rats. In old rats, however, the maximum load decreased by 13%, compared with middle-aged rats. Histological examination showed that the mean crypt height was 9% higher in middle-aged rats and 12% higher in old rats than in young rats. In conclusion, an accumulation of collagenous proteins was found in old rats compared with middle-aged rats and this was accompanied by a decrease in the strength, which may deteriorate the functional integrity of the left colonic wall with age.

Strength of the colon wall in diverticular disease

Studies of the aetiology of diverticular disease of the colon have been focused on intraluminal pressure for almost three decades. It is only relatively recently that the mechanical properties of the wall of the colon have been examined. The tensile strength and elasticity of the colon decline with age and this is the most marked in the left colon which is the narrowest and thickest part. This review discusses the case that the mechanical properties of the bowel wall are key factors in the development of diverticular disease. The potential role of high fibre diets in reducing the pressure changes which may stress the colon wall in this disease is also considered.

Pressure response of human colon to intraluminal distension

Pressure response to intraluminal distension was recorded in the ascending and descending colon of six subjects awaiting closure of transverse colostomies to assess and compare compliance in different regions of the human colon. Resistance to distension was significantly greater in the descending colon at intraluminal volumes of 30 ml or greater (P less than 0.01). An equal number of postmortem studies, representing passive connective tissue resistance, demonstrated a similar but more pronounced difference (P less than 0.001), which was maintained after correction for initial intraluminal diameter differences (P less than 0.001). The differences between in vivo and postmortem results indicated an active muscular component in the response of the ascending colon to distension compared with a totally passive distal response. These results support the concept of a functional division in the human colon.

Diverticular disease

Although most often clinically silent, colonic diverticula are responsible for a large number of gastrointestinal illnesses in our society. Complications of diverticular disease, including perforation and hemorrhage, may occur in 15% to 20% of patients with diverticula during their lifetime, and although often mild and self-limiting diseases, they too frequently cause life-threatening problems that require prompt surgical intervention. Despite a cadre of sophisticated laboratory and radiologic tests that have been developed to aid in the diagnosis of complicated diverticular disease, the diagnosis and treatment of diverticulitis still relies heavily on patient history, physical examination, physician judgment, and the patient's clinical response to treatment. Thus it is important for the managing physician to fully understand the pathogenesis of diverticula, the clinical consequences and modes of presentation of complicated diverticular disease, and the array of interventions available for treatment of these problems. This monograph summarizes our knowledge of diverticular disease to date and tries to give specific guidelines for the treatment of patients with complicated diverticulitis. However, it must be understood that the presentation and severity of these complications vary widely from patient to patient. Thus one cannot take a single approach toward a patient who has diverticulitis or diverticular bleeding. Rather, successful outcomes depend on an individual approach to each patient while maintaining certain generally accepted principles of treatment.

Human colonic smooth muscle: spontaneous contractile activity and response to stretch

The length dependence of the spontaneous contractile activity of human colonic muscle was assessed in vitro. Muscle obtained from the right colon was more distensible than that of the left colon. This was true for all muscle layers. Maximum spontaneous active stress was exerted by both circular and longitudinal muscle layers of the right colon at greater degrees of stretch (p less than 0.001) than those of the left colon. The contractile frequency of longitudinally oriented strips increased with length. The contractile frequency of intertaenial longitudinally oriented strips from the right colon was lower (p less than 0.001) than that of strips from the left colon. The contractile frequency of circularly-oriented strips from the right colon (6.25 +/- 0.38 min) was higher (p less than 0.001) than that of strips from the left colon (3.35 +/- 0.35 min). The human colon appears to consist of two distinct areas based on the mechanical behaviour of the smooth muscle during spontaneous contraction.

Mechanical properties of the colon: comparison of the features of the African and European colon in vitro

The tensile properties of the colon have been examined using methods which gave repeatable results. They showed little change after storage in salt for up to five weeks. The burst strength remained unchanged along the length of the colon. The tensile strength fell distally, as the thickness of the colonic wall increased. The width at burst decreased distally as did the internal diameter. The visco-elastic property of stress relaxation was constant in all regions. The tensile property of the colon was well developed at birth, but fell with age as did the width at burst and the internal diameter. Stress relaxation was unaffected. Because there may be a mechanical abnormality of the colonic wall in diverticular disease and as Europeans are prone to this condition while Africans are not commonly affected, European and African colons were compared. The tensile strength in a Kampala group was greater than in an Edinburgh one, but fell significantly in both groups with age. The width at burst was greater in the Kampala group, but also declined with age. Stress-relaxation was similar in both groups. In view of the similar properties in childhood of colons from Edinburgh and Kampala, the strength of the adult African compared with European colons may derive later from environmental factors such as diet. There were, however, no differences between the colons with and without diverticular disease in European subjects over the age of 50 years.

Elastosis in diverticular disease of the sigmoid colon

Diverticular disease of the sigmoid colon is an increasingly common clinical problem in the ageing population of western industrialised countries but the mechanism by which the disease develops remains unknown. The muscular abnormality is the most striking and consistent feature and this has been studied by light and electron microscopy in 25 surgical specimens of uncomplicated diverticular disease and in 25 controls. This is the first ultrastructural study of human colonic muscle to be published and shows that the muscle cells in diverticular disease are normal; neither hypertrophy nor hyperplasia is present. There is, however, an increase in the elastin content of the taeniae coli by greater than 200% compared with controls: elastin is laid down between the muscle cells and the normal fascicular pattern of the taeniae coli is distorted. There is no alteration in the elastin content of the circular muscle. As elastin is laid down in a contracted form, this elastosis may be responsible for the shortening or 'contracture' of the taeniae which in turn leads to the characteristic concertina-like corrugation of the circular muscle. Such a structural change could explain the altered behaviour of the colon wall in diverticular disease and its failure to change on treatment with bran.

Diverticular rupture during colonoscopy. Fact or fancy?

Uncomplicated colonic diverticula have been regarded as weak points in the bowel wall which have a predisposition to rupture during colonoscopy. We attempted to prove or disprove this assumption. Eleven segments of diverticula-containing sigmoid colon were insufflated via a colonoscope and the rupture pressure manometrically recorded. The mean +/- SEM pressure causing serosal tear was 202 +/- 15 mm Hg and mucosal rupture 226 +/- 14 mm Hg. No diverticular blowouts occurred. Intraluminal sigmoid pressures were measured manometrically in 15 patients with and 15 patients without colonic diverticula during routine colonoscopy. The pressure recordings were read in a blinded fashion, and the values were then grouped and analyzed in those patients with and without sigmoid colon diverticula. Intrarectal, sigmoid, peak sigmoid, peak sigmoid with cough, and peak sigmoid with Valsalva pressures were similar in both groups. Furthermore, the pressure levels generated during colonoscopy were much lower than those required for colonic rupture in the cadaver colons. We conclude that the reason most colonic perforations occur in the sigmoid area is not due to diverticular blowout. Rather, excluding instances where electrocautery is used, we feel it is due to instrument trauma. Less commonly, excessive air insufflation can result in serosal laceration and mucosal rupture, whereas diverticular blowout is probably limited to the setting of acute diverticulitis.