Effect of crural myotomy on the incidence and mechanism of gastroesophageal reflux in cats

Understanding the GERD Barrier

Gastroesophageal reflux disease (GERD) is steadily increasing in incidence and now affects 18% to 28% of the population in the United States. A thorough understanding of the pathophysiology underlying this disease is necessary to improve the current standard of care. Most GERD pathophysiology models focus on the lower esophageal sphincter (LES) as the key element which prevents esophageal reflux. More recent research has highlighted the crural diaphragm (CD) as an additional critical component of the GERD barrier. We now know that the CD actively relaxes when the distal esophagus is distended and contracts when the stomach is distended. Crural myotomy in animal models increases esophageal acid exposure, highlighting the CD's vital role. There are also multiple physiological studies in patients with symptomatic hiatal hernia that demonstrate CD dysfunction is associated with GERD. Finally, computer models integrating physiological data predict that the CD and the LES each contribute roughly 50% to the GERD barrier. This more robust understanding has implications for future procedural management of GERD. Specifically, effective GERD management mandates repair of the CD and reinforcement of the LES. Given the high rate of hiatal hernia recurrences, it seems that novel antireflux procedures should target this essential component of the GERD barrier. Future research should focus on methods to maintain crural integrity, decrease hiatal hernia recurrence, and improve long-term competency of the GERD barrier.

Respiratory disease and the oesophagus: reflux, reflexes and microaspiration

Gastro-oesophageal reflux is associated with a wide range of respiratory disorders, including asthma, isolated chronic cough, idiopathic pulmonary fibrosis, chronic obstructive pulmonary disease and cystic fibrosis. Reflux can be substantial and reach the proximal margins of the oesophagus in some individuals with specific pulmonary diseases, suggesting that this association is more than a coincidence. Proximal oesophageal reflux in particular has led to concern that microaspiration might have an important, possibly even causal, role in respiratory disease. Interestingly, reflux is not always accompanied by typical reflux symptoms, such as heartburn and/or regurgitation, leading many clinicians to empirically treat for possible gastro-oesophageal reflux. Indeed, costs associated with use of acid suppressants in pulmonary disease far outweigh those in typical GERD, despite little evidence of therapeutic benefit in clinical trials. This Review comprehensively examines the possible mechanisms that might link pulmonary disease and oesophageal reflux, highlighting the gaps in current knowledge and limitations of previous research, and helping to shed light on the frequent failure of antireflux treatments in pulmonary disease.

GABAB receptors as drug targets to treat gastroesophageal reflux disease

For many years, acid-suppressive therapy has been at the forefront of treating gastroesophageal reflux disease (GERD), yet despite the advent of the proton pump inhibitors (PPIs) some patients continue to experience persistent GERD symptoms. Therapeutic (non-surgical) options for such patients are currently limited. To tackle this clinical issue, research efforts have begun to focus on 'reflux inhibition' as a potential therapeutic target - i.e. inhibition of transient lower esophageal relaxations (TLESRs), the predominant mechanism of gastroesophageal reflux. Preclinical research has identified a number of drug targets through which TLESRs can be modulated, and the gamma-aminobutyric acid (GABA) type B (GABA(B)) receptor has emerged as one of the most promising. Studies with baclofen, a well-known agonist of this receptor, have demonstrated that reflux inhibition is a valid concept in the clinical setting in that reducing the incidence of TLESRs improves GERD symptoms. But baclofen is associated with significant central nervous system (CNS) side effects, rendering it undesirable for use as a treatment for GERD. Further development work has yielded a number of novel GABA(B) receptor agonists with reduced CNS side effect profiles, and clinical trials are currently being performed with several agents. Compounds that target TLESRs may therefore present a new add-on treatment for patients with persistent GERD symptoms despite PPI therapy.

Pharmacological dissection of the human gastro-oesophageal segment into three sphincteric components

Quantifications of gastro-oesophageal anatomy in cadavers have led some to identify the lower oesophageal sphincter (LOS) with the anatomical gastric sling-clasp fibres at the oesophago-cardiac junction (OCJ). However, in vivo studies have led others to argue for two overlapping components proximally displaced from the OCJ: an extrinsic crural sphincter of skeletal muscle and an intrinsic physiological sphincter of circular smooth-muscle fibres within the abdominal oesophagus. Our aims were to separate and quantify in vivo the skeletal and smooth muscle sphincteric components pharmacologically and clarify the description of the LOS. In two protocols an endoluminal ultrasound-manometry assembly was drawn through the human gastro-oesophageal segment to correlate sphincteric pressure with the anatomic crus. In protocol I, fifteen normal subjects maintained the costal diaphragm at inferior/superior positions by full inspiration/expiration (FI/FE) during pull-throughs. These were repeated after administering atropine to suppress the cholinergic smooth-muscle sphincter. The cholinergic component was reconstructed by subtracting the atropine-resistant pressures from the full pressures, referenced to the anatomic crus. To evaluate the extent to which the cholinergic contribution approximated the full smooth-muscle sphincter, in protocol II seven patients undergoing general anaesthesia for non-oesophageal pathology were administered cisatracurium to paralyse the crus. The smooth-muscle sphincter pressures were measured after lung inflation to approximate FI. The cholinergic smooth-muscle pressure profile in protocol I (FI) matched closely the post-cisatracurium smooth-muscle pressure profile in protocol II, and the atropine-resistant pressure profiles correlated spatially with the crural sling during diaphragmatic displacement. Thus, the atropine-resistant and cholinergic pressure contributions in protocol I approximated the skeletal and smooth muscle sphincteric components. The smooth-muscle pressures had well-defined upper and lower peaks. The upper peak overlapped and displaced rigidly with the crural sling, while the distal peak separated from the crus/upper-peak by 1.1 cm between FI and FE. These results suggest the existence of separate upper and lower intrinsic smooth-muscle components. The 'upper LOS' overlaps and displaces with the crural sling consistent with a physiological LOS. The distal smooth-muscle pressure peak defines a 'lower LOS' that likely reflects the gastric sling/clasp muscle fibres at the OCJ. The distinct physiology of these three components may underlie aspects of normal sphincteric function, and complexity of sphincter dysfunction.

Feline lower esophageal sphincter sling and circular muscles have different functional inhibitory neuronal responses

The lower esophageal sphincter (LES) has a circular muscle component exhibiting spontaneous tone that is relaxed by nitric oxide (NO) and a low-tone sling muscle that contracts vigorously to cholinergic stimulation but with little or no evidence of NO responsiveness. This study dissected the responses of the sling muscle to nitrergic innervation in relationship to its cholinergic innervation and circular muscle responses. Motor responses were induced by electrical field stimulation (EFS; 1-30 Hz) of muscle strips from sling and circular regions of the feline LES in the presence of cholinergic receptor inhibition (atropine) or NO synthase inhibition [NG-nitro-L-arginine (L-NNA)+/-atropine]. This study showed the following. First, sling muscle developed less intrinsic resting tone compared with circular muscle. Second, with EFS, sling muscle contracted (most at <or=10 Hz), whereas circular muscle relaxed >50% by 5 Hz. Third, on neural blockade with atropine or L-NNA+/-atropine, 1) sling muscle, although predominantly influenced by excitatory cholinergic stimulation, had a small neural NO-mediated inhibition, with no significant non-NO-mediated inhibition and 2) circular muscle, although little affected by cholinergic influence, underwent relaxation predominantly by neural release of NO and some non-NO inhibitory influence (at higher EFS frequency). Fourth, the sling, precontracted with bethanecol, could relax with NO and some non-NO inhibition. Finally, the tension range of both muscles is similar. In conclusion, sling muscle has limited NO-mediated inhibition to potentially augment or replace sling relaxation effected by switching off its cholinergic excitation. Differences within the LES sling and circular muscles could provide new directions for therapy of LES disorders.

Topography of the gastro-oesophageal junction in the dog revisited: possible clinical implications

The topographical anatomy of the gastro-oesophageal junction was evaluated in six Greyhounds and six Beagles with particular emphasis on the inter-relationship of anatomic structures and landmarks. Significant variation existed between individuals, and a standard topography could not be identified. It was not possible to document the consistent presence of an intra-abdominal oesophagus in either breed examined; in the majority of cases the oesophagus was contained entirely within the thoracic cavity such that no portion of the oesophagus could be subject to abdominal pressures. This has implications for understanding the pathogenesis of hiatal hernia associated gastro-oesophageal reflux disease.

Feline esophagitis secondary to gastroesophageal reflux disease: clinical signs and radiographic, endoscopic, and histopathological findings

Chronic esophagitis due to gastroesophageal reflux (GER) is rarely reported in the cat. This paper describes the clinical signs and diagnostic findings, including radiographic, endoscopic, and histopathological abnormalities, in three young, purebred, male cats with esophagitis presumed to be secondary to GER. Clinical signs included regurgitation, dysphagia, and weight loss. Contrast radiography revealed GER, esophageal dilatation, and decreased motility. Endoscopy showed hyperemia, increased vascularity, ulcers, erosion, and an abnormal lower esophageal sphincter. Histopathological lesions included squamous hyperplasia and dysplasia, erosions, ulcers, and an inflammatory infiltrate of lymphocytes, plasma cells, and neutrophils. Long-term follow-up demonstrated progression of the disease in two of the cats.

The diaphragm: two physiological muscles in one

To the respiratory physiologist or anatomist the diaphragm muscle is of course the prime mover of tidal air. However, gastrointestinal physiologists are becoming increasingly aware of the value of this muscle in helping to stop gastric contents from refluxing into the oesophagus. The diaphragm should be viewed as two distinct muscles, crural and costal, which act in synchrony throughout respiration. However, the activities of these two muscular regions can diverge during certain events such as swallowing and emesis. In addition, transient crural muscle relaxations herald the onset of spontaneous acid reflux episodes. Studying the motor control of this muscular barrier may help elucidate the mechanism of these episodes. In the rat, the phrenic nerve divides into three branches before entering the diaphragm, and it is possible to sample single neuronal activity from the crural and costal branches. This review will discuss our recent findings with regard to the type of motor axons running in the phrenic nerve of the rat. In addition, we will outline our ongoing search for homologous structures in basal vertebrate groups. In particular, the pipid frogs (e.g. the African clawed frog, Xenopus laevis) possess a muscular band around the oesophagus that appears to be homologous to the mammalian crural diaphragm. This structure does not appear to interact directly with the respiratory apparatus, and could suggest a role for this region of the diaphragm, which was not originally respiratory.

Individual inactivation of the sphincteric component of the gastroesophageal barrier causes reflux esophagitis in piglets

BACKGROUND/PURPOSE

The lower esophageal sphincter and the diaphragmatic crural sling form the gastroesophageal barrier. This work shows that division of the sphincteric component alone suffices to induce reflux esophagitis in piglets.

METHODS

Male piglets underwent either sham operation (n = 7) or extramucosal myotomy of the gastroesophageal junction (n = 8). Before and 1 week after the operation, pull-through manometry was performed under sedation. Pressures taken on the 4 quadrants at 20 1-mm intervals on both time endpoints were compared by pairwise Wilcoxon tests. The distal esophagus was studied histologically after 8 weeks.

RESULTS

The pressure profiles did not change after sham operation. In contrast, they were significantly flattened in the distal half of the high-pressure zone after myotomy reflecting disappearance of the sphincteric component of the barrier. Esophagitis was seen in all myotomized piglets but in none from the sham group.

CONCLUSIONS

Lower esophageal sphincter myotomy alone with preservation of the crural sling induces reflux esophagitis in piglets. This animal, widely available and not too costly, is an excellent model for gastroesophageal research.

Excess gastroesophageal reflux in patients with hiatus hernia is caused by mechanisms other than transient LES relaxations

BACKGROUND & AIMS

Esophageal acid exposure is higher in gastroesophageal reflux disease (GERD) patients with hiatus hernia than in those without. We investigated the effect of a sliding hiatus hernia on the mechanisms underlying spontaneous gastroesophageal reflux over 24 hours.

METHODS

Twelve GERD patients with and 10 GERD patients without hiatus hernia were studied for 24 hours. Combined esophageal pH and manometric recordings of the pharynx, lower esophageal sphincter (LES), and stomach were performed using a multiple-lumen assembly incorporating a Dent sleeve connected to a portable water-perfused manometric system and a pH glass electrode.

RESULTS

Patients with hiatus hernia had greater esophageal acid exposure (7.6% vs. 3.3%; P < 0.01) and more reflux episodes (3.1 vs. 1.8/h; P < 0.001) than those without. LES pressure, the incidence of transient LES relaxations (TLESRs), and the proportion of TLESRs associated with acid reflux were comparable in both groups. Both groups had equal numbers of reflux episodes associated with TLESRs and swallow-associated prolonged LES relaxations. Patients with hiatus hernia had more reflux associated with low LES pressure, swallow-associated normal LES relaxations, and straining during periods with low LES pressure.

CONCLUSIONS

The excess reflux in GERD patients with hiatus hernia compared with those without is caused by malfunction of the gastroesophageal barrier during low LES pressure, swallow-associated normal LES relaxations, deep inspiration, and straining.

Gastroesophageal reflux after combined lower esophageal sphincter and diaphragmatic crural sling inactivation in the rat

This study tests the hypothesis that either selective or combined destruction of the lower esophageal sphincter and the diaphragmatic crural sling should induce reflux in the rat. Pull-through perfusion manometry was performed before and after lower esophageal myectomy, crural myotomy, or both. pH monitoring was used to detect reflux. Unmanipulated rats served as controls. Paired t tests were used for comparison of pre- and postoperative pressure values and contingency tables with Fisher's tests for examining the association between the interventions and the appearance of reflux. Esophageal myectomy decreased only sphincteric pressure from 25.9+/-15.5 to 9+/-6 mm Hg (P < 0.01), whereas crural myotomy decreased only sling pressure from 26.2+/-13.3 to 7.3+/-3.9 mm Hg (P < 0.01). Simultaneous performance of both procedures decreased sphincteric and crural pressures from 20.4+/-7.5 to 7.6+/-4.3 mm Hg (P < 0.01) and from 45.9+/-20.6 to 18.2+/-7.4 mm Hg (P < 0.01), respectively. None of the control, myectomy, or myotomy animals showed reflux upon pH-metry but 5/8 rats in which both procedures were performed had prolonged acid exposure. No esophagitis was seen. In conclusion, normal rats do not have reflux. Selective destruction of either the sphincter or the crural sling does not induce reflux, despite causing flattening of their respective manometric profiles. Conversely, combined inactivation of both components is significantly associated with reflux.

A comparative study of esophageal and anorectal motility in myotonic dystrophy

Myotonic dystrophy may be associated with visceral abnormalities involving smooth muscle, the pathogenesis of which is not clear. Our aim was to evaluate the involvement of smooth and striated muscles at both ends of the gastrointestinal tract. Esophageal and anorectal manometric studies were performed in 13 patients and healthy controls. There was a correlation between: (1) the resting pressure in the upper esophageal sphincter and in the lower anal canal, (2) the amplitude and the coordination of contraction primary waves in the proximal and in the distal esophagus, and (3) the resting pressure in the higher anal canal and in the lower one. These results suggest that both ends of the gastrointestinal tract are disturbed in a similar fashion, both quantitatively and qualitatively and that there is a relationship between smooth and striated visceral muscle involvement in myotonic dystrophy.

Basic considerations in gastroesophageal reflux disease

The cause of foregut symptoms is often quite uncertain until a comprehensive evaluation has been performed. The critical elements of this evaluation include historic, radiographic, endoscopic, and physiologic data, and most importantly, the insight of a mature diagnostician. Patients who are not evaluated in a comprehensive way are at risk for serious postoperative problems; surgeons who perform interventions without appropriate diagnostic support may have to deal with these unhappy patients. In the long run, a complete workup provides the guidance for treatment and is cost-effective.

Motor events underlying gastro-oesophageal reflux in ambulant patients with reflux oesophagitis

Information on the mechanism of gastro-oesophageal reflux in patients with reflux disease is limited largely to studies in resting recumbent subjects. Evidence exists that both posture and physical activity may influence reflux. The aim of this study was to investigate reflux mechanisms in ambulant patients with reflux oesophagitis. Concurrent ambulatory oesophageal manometry and pH monitoring were performed in 11 ambulant patients with erosive oesophagitis. Lower oesophageal sphincter (LOS) pressure was monitored with a perfused sleeve sensor. Recordings were made for 90 min before and 180 min after a meal. At set times patients sat in a chair or walked. LOS pressure was < or = 2 mmHg at the time of reflux for 98% of reflux episodes. Transient LOS relaxation was the most common pattern overall and the predominant pattern in seven patients, whilst persistently absent basal LOS pressure was the most common pattern in four patients. The pattern of LOS pressure was not altered by the presence of hiatus hernia or by walking. Straining occurred at the onset of 31% of acid reflux episodes but often followed the development of an oesophageal common cavity. The occurrence of straining was not influenced by walking. In ambulant patients with reflux oesophagitis: (1) LOS pressure is almost always absent at the time of reflux, usually because of transient LOS relaxation, (2) persistently absent basal LOS pressure is an important mechanism of reflux in a few patients, (3) straining may help to induce acid reflux in a variable proportion of occasions and may in some instances be a response to gas reflux, and (4) walking does not influence the occurrence of reflux or its mechanisms.

Esophageal shortening induced by short-term intraluminal acid perfusion in opossum: a cause for hiatus hernia?

BACKGROUND/AIMS

Reflux esophagitis and hiatal hernia commonly coexist, yet a cause and effect relationship remains unclear. This study examined whether acute acid-induced esophageal injury induces longitudinal esophageal shortening in the opossum model.

METHODS

Esophageal length was measured continuously using a specially designed strain gauge transducer in anesthetized opossums while the midesophagus was perfused intraluminally with either normal saline or 100 mmol/L HCl. After a stabilization period, the test solution was perfused for 150 minutes. The effect of bilateral cervical vagotomy and atropine (60 microns/kg intravenously) were determined in separate groups. Parallel studies in which resting lower esophageal sphincter pressure was measured before and after prolonged intraesophageal acid perfusion were performed.

RESULTS

Esophageal acid perfusion induced acute epithelial injury as determined histologically. This was associated with significant esophageal shortening compared with saline-perfused controls and was not affected by vagotomy or atropine. In contrast, acid perfusion invariably induced a decrease in resting lower esophageal sphincter pressure.

CONCLUSIONS

Acute acid-induced esophageal mucosal injury induces longitudinal esophageal shortening that does not involve vagal pathways or cholinergic neurons. This raises the possibility that esophagitis could contribute to the development of hiatal hernia by inducing esophageal long axis shortening.