Hypertrophic smooth muscle in the partially obstructed opossum esophagus. The model: histological and ultrastructural observations

Role of mechanoregulation in mast cell-mediated immune inflammation of the smooth muscle in the pathophysiology of esophageal motility disorders

Major esophageal disorders involve obstructive transport of bolus to the stomach, causing symptoms of dysphagia and impaired clearing of the refluxed gastric contents. These may occur due to mechanical constriction of the esophageal lumen or loss of relaxation associated with deglutitive inhibition, as in achalasia-like disorders. Recently, immune inflammation has been identified as an important cause of esophageal strictures and the loss of inhibitory neurotransmission. These disorders are also associated with smooth muscle hypertrophy and hypercontractility, whose cause is unknown. This review investigated immune inflammation in the causation of smooth muscle changes in obstructive esophageal bolus transport. Findings suggest that smooth muscle hypertrophy occurs above the obstruction and is due to mechanical stress on the smooth muscles. The mechanostressed smooth muscles release cytokines and other molecules that may recruit and microlocalize mast cells to smooth muscle bundles, so that their products may have a close bidirectional effect on each other. Acting in a paracrine fashion, the inflammatory cytokines induce genetic and epigenetic changes in the smooth muscles, leading to smooth muscle hypercontractility, hypertrophy, and impaired relaxation. These changes may worsen difficulty in the esophageal transport. Immune processes differ in the first phase of obstructive bolus transport, and the second phase of muscle hypertrophy and hypercontractility. Moreover, changes in the type of mechanical stress may change immune response and effect on smooth muscles. Understanding immune signaling in causes of obstructive bolus transport, type of mechanical stress, and associated smooth muscle changes may help pathophysiology-based prevention and targeted treatment of esophageal motility disorders.NEW & NOTEWORTHY Esophageal disorders such as esophageal stricture or achalasia, and diffuse esophageal spasm are associated with smooth muscle hypertrophy and hypercontractility, above the obstruction, yet the cause of such changes is unknown. This review suggests that smooth muscle obstructive disorders may cause mechanical stress on smooth muscle, which then secretes chemicals that recruit, microlocalize, and activate mast cells to initiate immune inflammation, producing functional and structural changes in smooth muscles. Understanding the immune signaling in these changes may help pathophysiology-based prevention and targeted treatment of esophageal motility disorders.

Esophageal Symptoms and Lumbosacral Back Pain

BACKGROUND AND AIMS

Esophageal symptoms, that is, heartburn, regurgitation, dysphagia, and chest pain are common in the general population. Also common are symptoms of back pain related to pathology in the lumbosacral spine. The right crus of the diaphragm that forms the esophageal hiatus, originates from lumbar spine, may be affected by lumbar spine pathology resulting in esophageal symptoms. We studied whether there was an association between esophageal symptoms and spine symptoms.

METHODS

Two patient groups of 150 each were investigated: group 1 (ES); patients referred to the esophageal manometry study for assessment of esophageal symptoms, group 2 (SC); patients undergoing screening colonoscopy (control group). Both groups completed standardized questionnaires assessing esophageal and spine symptoms.

RESULTS

Back pain was reported by 74% of patients in the ES group as compared to 55% of patients in the SC group. Thirty percent of patients in the SC group reported one or more esophageal symptoms and these patients were regrouped with the ES group, resulting in 2 groups, ES1 and SC1, with and without esophageal symptoms, respectively. The ES1 group was 3.3 times more likely to experience back pain compared to the SC1 group (95% confidence interval: 1.95-5.46). Thoracolumbar was the most common site of pain in both groups. Pain score was greater for the group with esophageal symptoms compared to controls. Narcotic intake for most patients in the ES1 group was for back pain.

CONCLUSION

A strong association between esophageal symptoms and thoracolumbar back pain raises the possibility that structural and functional changes in the esophageal hiatus muscles related to thoracolumbar spine pathology lead to esophageal dysmotility and symptoms.

Three-Dimensional Pressure Profile of the Lower Esophageal Sphincter and Crural Diaphragm in Patients with Achalasia Esophagus

BACKGROUND & AIMS

Smooth muscles of the lower esophageal sphincter (LES) and skeletal muscle of the crural diaphragm (esophagus hiatus) provide the sphincter mechanisms at the esophagogastric junction (EGJ). We investigated differences in the 3-dimensional (3D) pressure profile of the LES and hiatal contraction between healthy subjects and patients with achalasia esophagus.

METHODS

We performed a prospective study of 10 healthy subjects (controls; 7 male; mean age, 60 ± 15 years; mean body mass index, 25 ± 2) and 12 patients with a diagnosis of achalasia (7 male; mean age, 63 ± 13 years; mean body mass index, 26 ± 1), enrolled at a gastroenterology clinic. Participants underwent 3D high-resolution manometry (3DHRM) with a catheter equipped with 96 transducers (for the EGJ pressure recording). A 0.5-mm metal ball was taped close to the transducer number 1 of the 3DHRM catheter. EGJ pressure was recorded at end-expiration (LES pressure) and at the peak of forced inspiration (hiatal contraction). Computed tomography (CT) scans were performed to localize the circumferential location of the metal ball on the catheter. Esophagus, LES, stomach, right and left crus of the diaphragm, and spine were segmented in each CT scan slice images to construct the 3D morphology of the region.

RESULTS

The metal ball was located at the 7 o'clock position in all controls. The circumferential orientation of metal ball was displaced 45 to 90 degrees in patients with achalasia compared with controls. The 3D-pressure profile of the EGJ at end-expiration and forced inspiration revealed marked differences between the groups. The LES turns to the left as it entered from the chest into the abdomen, forming an angle between the spine and LES. The spine-LES angle was smaller in patients with achalasia (104°) compared with controls (124°). Five of the 10 subjects with achalasia had physical breaks in the left crus of the diaphragm CONCLUSIONS: Besides LES, the 3D pressure profile of the EGJ can indicate anatomic and functional abnormalities of the crural diaphragm muscle in patients with achalasia esophagus. Further studies are needed to define the nature of hiatal and crural diaphragm dysfunction in patients with achalasia of the esophagus.

Clinical impact of peroral endoscopic myotomy for esophageal motility disorders on esophageal muscle layer thickness

Background and study aims  Previously, we reported that esophageal muscle layer thickness was associated with technical complexity of peroral endoscopic myotomy (POEM). However, there are no data regarding the mid-term effects of POEM procedures on esophageal muscle layer thickness. Therefore, we conducted this study to elucidate mid-term effects of POEM procedures, and to examine whether postoperative changes in esophageal muscle layer thickness were related to particular clinico-pathological features in patients with esophageal motility disorders. Patients and methods  Seventy-four consecutive patients with esophageal motility disorders who underwent POEM at Kobe University Hospital from April 2015 to December 2016 were prospectively recruited into this study. First, we investigated the esophageal muscle layer thickness values obtained at 1 year after POEM. Second, we evaluated the effects of a reduction in muscle layer thickness on various clinico-pathological features. Results  At 1 year after POEM, mean thickness of the inner circular muscle at 0 cm, 5 cm, and 10 cm from the esophagogastric junction was 1.06 ± 0.45 mm, 0.99 ± 0.36 mm, and 0.97 ± 0.44 mm, respectively. Among all sites, muscle layer thickness had significantly decreased after POEM. However, univariate logistic regression analysis demonstrated that no clinical factors were associated with esophageal muscle layer thickness after POEM procedure. Conclusions  We demonstrated for the first time that thickness of the esophageal muscle layer was significantly decreased after POEM. This result reveals that changes in esophageal muscle layer thickness caused by esophageal motility disorders are reversible.

Catheter-based high-frequency intraluminal ultrasound imaging is a powerful tool to study esophageal dysmotility patients

High-resolution manometry (HRM) is currently the most important diagnostic test for esophageal motility disorders, providing information on the contraction pattern of the circular muscle layer, which helps classify these esophageal motor diseases. However, with the increasing development of ultrasound, other techniques, such as high-frequency intraluminal ultrasound (HFIUS), have gained importance. This technique uses a flexible shaft with a central wire integrated into a standard endoscope, which facilitates real-time sonography. Its main utility is to provide anatomical information on the structure of the esophageal wall, including both the circular and longitudinal layers that constitute the esophageal muscularis propria. Increasing knowledge about these motility disorders has led to the hypothesis that, in addition to an abnormal contraction pattern of the circular muscle, an overall increased muscle thickness and an abnormal longitudinal muscle contraction could be added as pathophysiological factors. The increase in muscle thickness could be an important indicator of the severity of diseases, such as achalasia, distal esophageal spasm, or hypercontractile esophagus. More studies are required before definitive conclusions can be reached, but HFIUS employed simultaneously with HRM could provide a more complete and precise evaluation of these esophageal motor disorders.

Consequences of bariatric surgery on oesophageal function in health and disease

Obesity is a continuing epidemic with substantial associated morbidity and mortality. Owing to the limitations of lifestyle modifications and pharmacological options, bariatric surgery has come to the forefront as an efficient method of achieving sustained weight loss and decreasing overall mortality in comparison with nonsurgical interventions. The most frequently performed bariatric operations are either purely restrictive, such as laparoscopic adjustable gastric band (LAGB) and laparoscopic sleeve gastrectomy (LSG), or restrictive-malabsorptive, such as the Roux-en-Y gastric bypass (RYGB). Each operation results in weight loss, but can also have unintended effects on the health of the oesophagus. Specifically, operations might lead to oesophageal dilation or the development of GERD. LAGB is the best-studied procedure with notable evidence for postoperative worsening of GERD and pseudo-achalasia, which increases lower oesophageal pressure and causes aperistalsis. In some studies, LSG initiates not only a worsening of GERD, but also the formation of de novo GERD in patients without preoperative GERD symptoms. RYGB demonstrates the most profound evidence for improvement of GERD symptoms and preservation of oesophageal motility. Future high-quality studies will be required to better understand the interaction between bariatric surgery and oesophageal disease.

Selective inhibition of nitric oxide synthase causes increased muscle thickness in rat esophagus

AIM

Achalasia is a primary motor dysfunction of esophagus which can be created experimentally by nitric oxide synthase (NOS) inhibition. Although several theories have been suggested, mechanism of increased esophageal muscle thickness in achalasia is still unclear. An experimental study was performed to evaluate the esophageal muscle thickness after selective inhibition of NOS in rats.

MATERIALS AND METHODS

Wistar albino rats (n=18) weighing 150-200g of both sexes were included in the study. After anesthetization with ketamine hydrochloride, esophageal body and distal esophagus were sampled in control group (CG, n=6). In sham group (SG, n=6), intraperitoneal saline (1ml) injection was performed for 21days. l-NAME (l-nitroarginin metyl ester, selective inhibitor of NOS) group (LNAMEG, n=6) received 100mg/kg/d l-NAME intraperitoneally for 21days. The esophageal body and distal esophagus were removed for histopathological analysis in each group. All samples were evaluated for total and circular muscle thickness with hemotoxylene-eosine (HE) staining.

RESULTS

None of the samples showed pathologic finding in esophageal mucosa. There was no difference between CG and SG for total and circular muscle thickness in esophageal body and distal esophagus. LNAMEG had higher median levels of both total and circular muscle thickness than CG and SG in esophageal body (P<0.05). However, in distal esophageal segments, only total muscle thickness was statistically higher in LNAMEG than CG and SG (P<0.05).

CONCLUSION

Selective inhibition of NOS causes increased total smooth muscle thickness in esophageal body and distal esophagus. However, this effect could not detected in circular muscle in the distal esophagus. We suggest that NOS inhbition not only increases esophageal peristalsis but also causes muscle hypertrophy in esophagus.

Gastroesophageal reflux disease after bariatric procedures

GERD is a significant comorbidity in bariatric patients preoperatively and postoperatively. Surgeons should be aware of appropriate evaluation, procedures choices, and management options. Revision surgery for reflux symptoms is common and appropriate anatomy and outcomes should be considered when offering these interventions to our patients. Patient selection is important to ensure avoiding postoperative development or worsening of GERD.

Megaesophagus in a line of transgenic rats: a model of achalasia

Megaesophagus is defined as the abnormal enlargement or dilatation of the esophagus, characterized by a lack of normal contraction of the esophageal walls. This is called achalasia when associated with reduced or no relaxation of the lower esophageal sphincter (LES). To date, there are few naturally occurring models for this disease. A colony of transgenic (Pvrl3-Cre) rats presented with megaesophagus at 3 to 4 months of age; further breeding studies revealed a prevalence of 90% of transgene-positive animals having megaesophagus. Affected rats could be maintained on a total liquid diet long term and were shown to display the classic features of dilated esophagus, closed lower esophageal sphincter, and abnormal contractions on contrast radiography and fluoroscopy. Histologically, the findings of muscle degeneration, inflammation, and a reduced number of myenteric ganglia in the esophagus combined with ultrastructural lesions of muscle fiber disarray and mitochondrial changes in the striated muscle of these animals closely mimic that seen in the human condition. Muscle contractile studies looking at the response of the lower esophageal sphincter and fundus to electrical field stimulation, sodium nitroprusside, and L-nitro-L-arginine methyl ester also demonstrate the similarity between megaesophagus in the transgenic rats and patients with achalasia. No primary cause for megaesophagus was found, but the close parallel to the human form of the disease, as well as ease of care and manipulation of these rats, makes this a suitable model to better understand the etiology of achalasia as well as study new management and treatment options for this incurable condition.

Review article: the impact of bariatric surgery on gastrointestinal motility

BACKGROUND

Obesity is a major medical problem worldwide. Different treatment modalities have emerged to treat obese patients, but the best long-term results are achieved with bariatric surgery. Currently, the interventions most commonly performed are laparoscopic adjustable gastric banding (LAGB), Roux-en-Y- gastric bypass (RYGB) and sleeve gastrectomy.

AIM

To review the gastrointestinal motor complications associated with each of these types of bariatric interventions and the clinical implications of such complications.

METHODS

Search of medical database (PubMed) on English-language articles from January 1996 to March 2011. The search terms used were laparoscopic adjustable gastric banding (LAGB), sleeve gastrectomy (LSG), roux-en-Y-gastric bypass (RYGB), using the AND operator with the terms: complications, motility, GERD, reflux, gastric emptying, esophagitis, dysphagia.

RESULTS

Of the three bariatric interventions reviewed, LAGB was the most studied. Most studies reported short follow-up, of ≤ 1 year. Oesophageal motor dysfunction is the most common motility complication following the bariatric interventions that were reviewed and is mainly observed after LAGB. Some data suggest that oesophageal motor function testing predicts development of post-operative symptoms and oesophageal dilation. RYGB offers protection from gastro-oesophageal reflux. Sleeve gastrectomy was the least studied and was associated with an acceleration of gastric emptying.

CONCLUSIONS

The effects of these interventions on GI motility should be considered when selecting patients for bariatric surgery. There is scant information regarding the overall effect of sleeve gastrectomy on gastro-oesophageal reflux patterns and oesophageal motility.

Morphometric evaluation of oesophageal wall in patients with nutcracker oesophagus and ineffective oesophageal motility

The pathogenesis of nutcracker oesophagus (NE) and ineffective oesophageal motility (IEM) is unclear. Damage to the enteric nervous system or smooth muscle can cause oesophageal dysmotility. We tested the hypothesis that NE and IEM are associated with abnormal muscular or neural constituents of the oesophageal wall. Oesophageal manometry was performed in patients prior to total gastrectomy for gastric cancer. The oesophageal manometries were categorized as normal (n = 7), NE (n = 13), or IEM (n = 5). Histologic examination of oesophageal tissue obtained during surgery was performed after haematoxylin and eosin (H&E) and trichrome staining. Oesophageal innervation was examined after immunostaining for protein gene product-9.5 (PGP-9.5), choline acetyltransferase (ChAT) and neuronal nitric oxide synthase (nNOS). There were no significant differences in inner circular smooth muscle thickness or degree of fibrosis among the three groups. Severe muscle fibre loss was found in four of five patients with IEM. The density of PGP-9.5-reactive neural structures was not different among the three groups. The density of ChAT immunostaining in the myenteric plexus (MP) was significantly greater in patients with NE (P < 0.05) and the density of nNOS immunostaining in the circular muscle (CM) was significantly greater in IEM patients (P < 0.05). The ChAT/nNOS ratio in both MP and CM was significantly greater in NE patients. NE may result from an imbalance between the excitatory and inhibitory innervation of the oesophagus, because more than normal numbers of ChAT-positive myenteric neurones are seen in NE. Myopathy and/or increased number of nNOS neurones may contribute to the hypocontractile motor activity of IEM.

Smooth muscle remodeling of the gastroesophageal junction after endoluminal gastroplication

BACKGROUND

Endoluminal gastroplication has been shown to reduce symptoms of gastroesophageal reflux disease and to induce focal hypertrophy of the gastroesophageal junction (GEJ) muscularis propria. Despite suture loss, some patients have persistent symptomatic resolution.

OBJECTIVE

This study was designed to examine the durability of smooth muscle hypertrophy after suture removal.

DESIGN

Seven pigs underwent upper endoscopy with endoscopic ultrasonography (EGD/EUS) at baseline to evaluate GEJ muscularis propria layer. Endoluminal gastroplication was performed at week 1 with placement of 2 sutures at the GEJ. Repeat EGD/EUS was performed at week 3 and week 5. Three of the 7 pigs were killed for histologic analysis. The remaining 4 pigs had sutures removed and survived for 9, 11, and 13 weeks; serial weekly EGD/EUS was performed until the animal was killed.

RESULTS

The GEJ muscularis propria thickness by EUS was 1.1+/-0.1 mm at baseline, 4.7+/-1.9 mm at week 3, and 4.4+/-1.1 mm at week 5. The muscularis propria thickness by histologic examination in the 3 animals with sutures intact were 6.2+/-0.3 mm near the suture site and 4.7+/-0.5 mm at the opposing wall to the suture site. For the 4 animals with sutures removed, the measurements were 6.9+/-0.2 mm (suture site) and 4.7+/-0.5 mm (opposing wall), respectively.

CONCLUSIONS

The GEJ smooth muscle cell hypertrophy induced by endoluminal gastroplication persisted after removal of mucosal sutures. These changes may be responsible for persistent symptomatic response despite suture loss in patients.

Prevalence of increased esophageal muscle thickness in patients with esophageal symptoms

BACKGROUND

Patients with achalasia, diffuse esophageal spasm (DES), and nutcracker esophagus have a thicker muscularis propria than normal subjects. The goal of our study was to determine the prevalence of increased muscle thickness in a group of unselected patients referred to the esophageal function laboratory for evaluation of the symptoms.

METHODS

We studied 40 normal subjects and 94 consecutive patients. Manometry and ultrasound images were recorded concurrently, using a special custom-built catheter. Esophageal muscle thickness and muscle cross-sectional area were measured at 2 and 10 cm above the lower esophageal sphincter (LES). Patients were assigned manometric diagnosis and determination was made if they had increased muscle thickness and muscle cross-sectional area.

RESULTS

Nearly all patients with well-defined spastic motor disorders, i.e., achalasia, DES, and nutcracker esophagus, revealed (a) an increase in the muscle thickness/cross-sectional area, (b) increase in esophageal muscle thickness/cross-sectional area was also seen, albeit at a lower prevalence rate, in patients with less well-characterized manometric abnormalities, i.e., hypertensive LES, impaired LES relaxation, and ineffective esophageal motility, and (c) 24% of patients with esophageal symptoms but normal manometry were also found to have an increase in muscle thickness/cross-sectional area. Dysphagia was more likely, and heartburn less likely in patients with increased muscle thickness, but there were no differences in chest pain and regurgitation symptoms between the groups.

CONCLUSION

We describe, for the first time, increased muscle thickness in patients with esophageal symptoms and normal manometry. We suggest that increased esophageal muscle thickness is likely to be an important marker of esophageal motor dysfunction.

A model for gastric banding in the treatment of morbid obesity: the effect of chronic partial gastric outlet obstruction on esophageal physiology

OBJECTIVE

This work establishes an animal model for nonadjustable gastric banding and characterizes the effect of gastric banding on esophageal physiology.

SUMMARY BACKGROUND DATA

Obstruction at the esophagogastric junction (EGJ) results in esophageal dilation and aperistalsis. Although laparoscopic gastric banding as a primary treatment of morbid obesity has been widely accepted, the effects of this therapy on esophageal function remain unknown.

METHODS

Twenty-five opossums were randomly divided into sham (n = 5), EGJ band (n = 5), and gastric band (n = 15) groups. Gastric and EGJ bands were surgically placed, and esophageal manometry was performed prebanding, at 2-week intervals during the banding period (up to 14 weeks), and 2 and 4 weeks after band removal.

RESULTS

Manometric measures were equivalent prior to banding in all groups. There were no changes in LES or esophageal pressures during the study period in the sham group. During banding, there was a 36% decrease in baseline mean resting lower esophageal sphincter pressure in the gastric band group (P = 0.003). Mean distal esophageal peristaltic pressure decreased from baseline by 36% in gastric band animals (P < 0.001). The incidence of esophageal motility disorder during the study period for sham, EGJ band, and gastric band groups, was 2.9%, 42.1%, and 31.3%, respectively (P = 0.001, P = 0.381, pairwise comparisons of gastric band vs. sham and gastric band versus EGJ groups, respectively). Immediately prior to band removal, the probability of an abnormal peristaltic sequence with each swallow was 1%, 38%, and 16% for sham, EGJ, and gastric band groups, respectively (P < 0.005, pairwise comparisons of band groups with sham).

CONCLUSIONS

Nonadjustable gastric banding results in impaired esophageal body motility, a reduction in esophageal peristaltic pressure, and a reduction in resting lower esophageal sphincter pressure. These findings suggest that gastric banding causes esophageal outlet obstruction and subsequent decompensation of peristaltic function as well as a compromise of the native antireflux mechanism.

Oesophageal wall stress and muscle hypertrophy in high amplitude oesophageal contractions

Excessive wall stress is a known stimulus for muscle growth. We recently reported a thickened muscularis propria in patients with high amplitude oesophageal contractions (HAEC). The goal of this study was to determine oesophageal wall stress in normal subjects and patients with HAEC. A manometry catheter equipped with a high frequency ultrasound (US) transducer was used to record pressure and US images simultaneously in 10 healthy subjects and 11 patients with HAEC. Recordings were obtained at 2 and 10 cm above the lower oesophageal sphincter during water swallows. The changes in circumferential wall stress during oesophageal contraction in both groups are relatively small because of an increase in the wall thickness-to-radius ratio during contraction. Patients show a greater muscle thickness than normal subjects at rest and at the peak of contraction. The wall stress in patients is elevated at the 2 cm but not at the 10-cm level as compared to normal subjects. Wall strain is not different between the two groups. Increase in wall thickness during oesophageal contraction maintains low wall stress. A greater wall stress in patients with HAEC may be a stimulus for the increased wall thickness.

Gastroesophageal junction smooth muscle remodeling after endoluminal gastroplication

OBJECTIVES

Endoluminal gastroplication (ELGP) is an endoscopic mucosal suturing procedure for the treatment of gastroesophageal reflux disease. The antireflux mechanism of the mucosal suture remains poorly understood. The aim of this study is to investigate any morphologic changes in the smooth muscle layer induced by the mucosal sutures placed at the gastroesophageal junction.

METHODS

ELGPs were performed using endoscopic suturing devices with placement of two or three circumferential sutures within 2 cm of the squamocolumnar junction. Eight patients with subsequent symptom resolution underwent endoscopic ultrasound (EUS) to evaluate the muscularis propria layer at the gastroesophageal junction. A swine model was used for EUS and histopathologic correlation study. Six control and 15 ELGP pigs were evaluated with EUS and histological examination of the gastroesophageal junction smooth muscle layer.

RESULTS

Focal thickening of the muscularis propria layer near the suture region (2.3 +/- 0.4 mm vs 1.4 +/- 0.3 mm, p < 0.01) was found in eight patients with symptomatic resolution. In ELGP pigs, the smooth muscle layer thickness increased by 2.6 mm near the suture site by EUS. By histology, the total and circular smooth muscle layer thickness increased by 2.1 mm and 1.9 mm, respectively.

CONCLUSIONS

Focal thickening of smooth muscle layer occurs at the gastroesophageal junction after ELGP in patients with gastroesophageal reflux disease. This finding was reproduced in a swine model and localized hypertrophy was found to be entirely due to an increase in the circular smooth muscle layer.

Hypertrophy of the muscularis propria of the lower esophageal sphincter and the body of the esophagus in patients with primary motility disorders of the esophagus

OBJECTIVES

Patients with diffuse esophageal spasm (DES) and nutcracker esophagus/high amplitude esophageal contraction (HAEC) have a thicker esophageal muscularis propria than do healthy subjects. The goals of this study were to determine the esophageal muscle cross-sectional area (MCSA), a measure of muscle mass, in patients with achalasia of the esophagus; and to compare it with that in patients with DES, patients with HAEC, and normal subjects.

METHODS

Using a high-frequency ultrasound probe catheter, concurrent manometry and ultrasound images of the esophagus were recorded in four subject groups: normal volunteers, patients with HAEC, patients with DES, and patients with achalasia of the esophagus. Recordings were obtained from the lower esophageal sphincter (LES) and multiple sites in the esophagus 2, 4, 6, 8, and 10 cm above the LES.

RESULTS

The LES and esophageal muscle thickness as well as esophageal MCSA were greater in all three patient groups than in the normal subject group. Muscle thickness and MCSA were observed to be greatest in patients with achalasia, which were greater than in patients with DES, which were greater than in those with HAEC, which in turn were greater than in normal subjects.

CONCLUSIONS

We propose that an increase in the MCSA is an important feature of patients with primary motility disorders of the esophagus. The degree of increase in muscle mass may be an important determinant of the type and the severity of esophageal motor dysfunction.

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.

Evaluation of early events in the creation of amyenteric opossum model of achalasia

Benzyldimethyltetradecylammonium chloride (BAC) has previously been used to create amyenteric rat jejunal models. Fifteen opossums (D. virginiana) were injected with 10-15 mL 4 mM BAC or saline in the distal oesophagus and along with controls underwent oesophagoscopy, manometry and barium oesophagrams. Atropine and sodium nitroprusside were studied in six of the BAC-treated and five controls using oesophageal manometry. Histologically several neuronal markers, B-NADPH-diaphorase and acetylcholine esterase histochemical staining were used. NADPH-diaphorase activity was assayed at the lower oesophageal sphincter (LOS) and 3 and 5 cm above LOS in both groups. Oesophagoscopy of the treated animals showed no mucosal inflammation, or strictures. Manometrically, LOS pressures were significantly higher in the BAC-treated group (25.7 +/- 8.6 mmHg) when compared to controls (8.7 +/- 1.8 mmHg). The oesophageal contraction amplitudes were similar in both groups. While sodium nitroprusside (SNP) significantly reduced the LOS pressure, atropine did not alter the resting LOS pressure in the BAC-treated animals. Histologically at the LOS the treated group showed: (i) absence of myenteric neurons, in contrast to prominent NADPH-diaphorase and other neuron and peptide markers in the control and (ii) increase in the number of nerve bundles that were not positive for AchE. No differences were seen in the oesophageal body between the groups. The NADPH-diaphorase assay showed a significant decrease of activity in the BAC-treated LOS, but no differences in the oesophageal body compared to controls. Several of these radiologic, manometric and histological observations resemble features of achalasia and the mechanism of the tonic pressure increase at this early time point appears to be due to a non-cholinergic mechanism.

Role of altered responsiveness of hypertrophic smooth muscle in manometric abnormalities of the obstructed opossum oesophagus

The movements of the obstructed oesophagus are abnormal, but whether this relates to the disease causing the obstruction, to the altered load conditions or to abnormal neuromuscular functions in hypertrophic smooth muscle is unclear. In an opossum model of chronic oesophageal obstruction, we compared the mechanical responsiveness of hypertrophic smooth muscle in vitro to in vivo manometric function. Related to their greater thickness, strips of hypertrophic muscle generated greater force in response to electrical stimulation and to stretch than control strips. Hypertrophic muscle often generated repetitive contractions; spread of contractions orad from the stimulus site was common in hypertrophic oesophageal bands. On manometry, the obstructed oesophagus generated abnormally high pressures proximally, and highly variable pressure amplitudes in the middle and distally; pressure waves often occurred simultaneously throughout the oesophagus, were repetitive or multi-peaked and led to a lasting rise of oesophageal pressure. Alterations in the intrinsic neuromuscular functions of hypertrophic smooth muscle including generation of greater force, repetitive or spontaneous contractions, and retrograde spread of contractions explain many, but not all, of the manometric abnormalities seen in the chronically obstructed oesophagus.

Etiology of intestinal damage in gastroschisis. III: Morphometric analysis of the smooth muscle and submucosa

The response of intestinal smooth muscle to injury may explain some of the motility derangement observed in infants with gastroschisis. An experimental model of gastroschisis was created and a detailed analysis of the intestinal muscle layer was undertaken to study this response. An abdominal wall defect and evisceration of the bowel were carried out in fetal lambs at 80 days' gestation (full term, 145 days), with delivery at 100 days or 135 days. Smooth muscle cell size and number were determined by detailed morphometric analysis, proliferative rate was determined using proliferating cell nuclear antigen staining, and collagen content was determined by morphometry after Verhoeff van Gieson staining. Compared with controls, there was a significant increase in cell number (hyperplasia) in the gastroschisis animals at 100 days and an increase in size (hypertrophy) at 135 days. The proliferation rate of smooth muscle was significantly lower and the submucosal collagen thickness was significantly greater in the gastroschisis animals during both periods. These data suggest that gastroschisis is characterised by initial hyperplasia, with subsequent diminution in smooth muscle proliferation. The hypertrophy may reflect a response to injury in which cell growth instead of proliferation occurs. The persistent elevation in collagen throughout gestation in animals with gastroschisis may be a reflection of this hyperplastic response in the smooth muscle cells and an important factor in the bowel-wall thickening. This deranged pattern of growth may lead to the clinical problems observed in human infants with this disease.

Dynamic imaging of obstructed opossum esophagus. From altered load to altered contractility

We studied by barium contrast the dynamics of experimental obstruction in the opossum esophagus. Immediately after banding the gastroesophageal junction, entrapment of the bolus between the band and the peristaltic contraction led to esophageal bulging, forceful retropulsion of the bolus at the band, and the repeated triggering of peristaltic contractions by the retropelled bolus. In ensuing weeks, triggering of contractions became more difficult and contractions led to bizarre "corkscrew" movements of the increasingly distended and tortuous esophagus. A tight contraction ring that moved very slowly retrograde was occasionally observed in the chronically distended esophagus. Computer-assisted analysis showed that the area and perimeter of the bolus were abnormally large in chronic obstruction and that during its passage through the esophagus the compactness of the bolus increased no longer. Configurational analysis of the cone that the peristaltic contraction shapes at the tail of the barium column showed this to narrow progressively on passage through the normal esophagus and, paradoxically, to widen in both acute and chronic obstruction.

Biomechanical wall properties and collagen content in the partially obstructed opossum esophagus

A specially designed probe was used to investigate biomechanical wall properties of the esophagus in opossums with distal esophageal banding. A balloon was stepwise inflated and deflated 6 cm above the lower esophageal sphincter before the banding and at 2 weeks postoperatively. After animals were killed, collagen content of the esophageal wall was determined. Preoperatively, cross-sectional area and wall tension at maximal inflation of the balloon, compliance, and hysteresis were 108.04 +/- 7.23 mm2, 5.8 +/- 0.3 cm H2O/m, 0.664 +/- 0.081 mm2/cm H2O, and 101.14 +/- 18.89 mm2, respectively. Postoperatively, the parameters increased to 357.45 +/- 54.22 mm2 (P < 0.001), 10.5 +/- 1.4 cm H2O/m (P < 0.001), 2.402 +/- 0.420 mm2/cm H2O (P < 0.001), and 225.86 +/- 44.56 mm2 (P < 0.05), respectively. The collagen content was 0.065 +/- 0.004 and 0.104 +/- 0.009 mg/mg dry defatted weight in the mid and distal normal esophagus, respectively, compared with 0.110 +/- 0.012 and 0.121 +/- 0.012 mg/mg in the banded group (P < 0.05 in the middle part). A positive correlation was shown between the maximal cross-sectional area and the collagen content in the mid-esophagus (P < 0.05). In conclusion, biomechanical wall properties were altered significantly, indicating dilatation and decreased ability of the esophageal wall to resist intraluminal pressure.

Hypertrophic smooth muscle in the partially obstructed opossum esophagus. Excitability and electrophysiological properties

Partial obstruction of the opossum esophagus leads to thickening of the circular muscle, hypertrophy of smooth muscle cells, and diminution of the extracellular space. The pharmacological and electrophysiological properties of this hypertrophied muscle were studied. Carbachol produced phasic and tonic contractions of the circular muscle. The EC50 for tonic contractions was greater for hypertrophied than for normal muscle (21.1 +/- 3.9 mumol/L vs. 4.8 +/- 2.2 mumol/L; P less than 0.05). The resting membrane potential difference of hypertrophied muscle (-50.8 +/- 0.2 mV) was similar to that of normal muscle (-50.0 +/- 0.2 mV). Electrical stimulation of intrinsic nerves in the normal muscle produced a hyperpolarization followed by a depolarization of smooth muscle membrane potential. Hypertrophied muscle responded either with an attenuated hyperpolarization or no hyperpolarization, both of which were followed by a depolarization. The space constant in the long axes of the hypertrophied circular muscle cells was greater than normal (4.4 +/- 0.2 mm vs. 3.4 +/- 0.1 mm; P less than 0.001). The threshold potential for initiation of action potentials was more negative for hypertrophied (-43.2 +/- 0.4 mV) than for normal circular muscle (-41.6 +/- 0.2 mV; P less than 0.005). These data indicate that alterations in neuromuscular function accompany the hypertrophy of esophageal smooth muscle.