Central mechanisms of lower esophageal sphincter control

Baroreflex Sensitivity in Patients With Laryngopharyngeal Dysfunction-The Overwhelmed Vagus Hypothesis

Importance

The autonomic nervous system maintains internal stability by concurrently prioritizing and managing different functions. It is currently not known whether dysfunction at the aerodigestive junction could overwhelm autonomic control and impair other functions.

Objective

To compare baroreflex sensitivity, a prognostically significant index of the autonomic system's ability to stabilize blood pressure, between patients with predominantly esophagogastric (digestive) and patients with predominantly laryngopharyngeal (aerodigestive) symptoms.

Design, Setting, and Participants

A cross-sectional study, between 2018 and 2019, of adults undergoing esophagal manometry or transnasal panendoscopy was carried out in a specialist center. The analysis took place between 2023 and 2024.

Main Outcomes and Measures

Heart rate and blood pressure were recorded and baroreflex sensitivity and heart rate variability were derived. Esophageal physiology was assessed with high-resolution manometry.

Results

There were 30 and 23 patients in the digestive and aerodigestive groups, respectively. The mean (SD) age was 61 (15) years and there were 26 women and 27 men. Compared with patients in the digestive group, more patients in the aerodigestive group had voice or throat symptoms and fewer had classic reflux symptoms (odds ratio [OR], 5.65; 95% CI, 1.82-17.5; OR, 2.07; 95% CI, 1.28-3.33; and OR, 0.60; 95% CI, 0.38-0.95, respectively). Patients in the aerodigestive group had higher mean (SD) resting heart rate (93 [17] vs 75 [13] min-1; difference of means, -18 min-1; 95% CI, -26 to -10), lower resting mean (SD) arterial pressure (94 [16] vs 104 [23] mm Hg, OR, 10; 95% CI, -1 to 21), lower mean (SD) baroreflex sensitivity (3.77 [0.79] vs 9.76 [2.92] s-3mm Hg-1; OR, 6.0 s-3mmHg-1; 95% CI, 4.7-7.2), and lower mean (SD) parasympathetic-spectrum heart rate variability (0.68 [0.15] vs 1.30 [0.53]; OR, 0.62; 95% CI, 0.39-0.85). There was a correlation between reduced lower esophageal relaxation (integrated relaxation pressure) and reduced baroreflex sensitivity (r = -0.33; 95% CI, -0.58 to -0.03).

Conclusions

In this cross-sectional study of adults undergoing esophageal manometry or transnasal panendoscopy, patients with laryngopharyngeal symptoms had reduced baroreflex sensitivity, indicating diminished vagal control compared with patients with esophagogastric symptoms. The overwhelmed vagus hypothesis may explain these responses by considering autonomic functions as competing consumers of the finite regulatory resources of a common controller. The regulatory demands of maintaining a safe airway with concurrent laryngopharyngeal sensorimotor dysfunction, superadded to baseline demands for dual speech and aerodigestive control, could overwhelm and force the system to deprioritize less immediate functions like esophageal relaxation and the baroreflex. Measuring baroreflex sensitivity, now possible in routine clinical practice, could enable phenotyping and objective outcome assessment for laryngopharyngeal dysfunction. A neurophysiological model for considering laryngopharyngeal sensorimotor dysfunction could in turn move patient care toward a more holistic autonomic health footing.

Chronic REM-sleep deprivation induced laryngopharyngeal reflux in rats: A preliminary study

OBJECTIVE

The aim of this study was to investigate the relationship of chronic REM-sleep deprivation with laryngopharyngeal reflux (LPR) and its mechanism.

METHODS

Forty healthy male SD rats (body weight 250-280 g) were randomly divided into four groups. The first three ones were test group, which underwent REM-sleep deprivation with different duration of time by modified multiplatform water surface method. The last group was the control one having normal sleep. All the animals were performed Dx-pH monitoring when finishing sleep deprivation, and sacrificed to study the gastric residual rate (GRR) and small intestine peristalsis (SPR) rate by charcoal meal method.

RESULTS

At prone position, the reflux incidence in the test groups fairly increased with the duration of sleep deprivation (p<0.05). The total number of reflux episodes at prone position in the test group rats with 3 months duration of sleep deprivation was significantly increased compared with that in the control ones (p<0.05). GRR in rats experiencing sleep deficiency for different duration all reduced significantly when compared to the control group (p<0.05). GRR and SPR presented continuous decline tendency with the duration of sleep deprivation (p>0.05).

CONCLUSIONS

It is suggested that chronic sleep deficiency could cause LPR in rats, which might result from the uncoordinated digestive tract motility caused by dysfunction of central nervous system after chronic REM-sleep deprivation. Our results implied that chronic REM-sleep deprivation might be one of the causes of LPR. Addressing sleep problems might help to decrease the prevalence of LPR and enhance its treatment efficacy.

Gastrointestinal dysfunction after spinal cord injury

The gastrointestinal tract of vertebrates is a heterogeneous organ system innervated to varying degrees by a local enteric neural network as well as extrinsic parasympathetic and sympathetic neural circuits located along the brainstem and spinal axis. This diverse organ system serves to regulate the secretory and propulsive reflexes integral to the digestion and absorption of nutrients. The quasi-segmental distribution of the neural circuits innervating the gastrointestinal (GI) tract produces varying degrees of dysfunction depending upon the level of spinal cord injury (SCI). At all levels of SCI, GI dysfunction frequently presents life-long challenges to individuals coping with injury. Growing attention to the profound changes that occur across the entire physiology of individuals with SCI reveals profound knowledge gaps in our understanding of the temporal dimensions and magnitude of organ-specific co-morbidities following SCI. It is essential to understand and identify these broad pathophysiological changes in order to develop appropriate evidence-based strategies for management by clinicians, caregivers and individuals living with SCI. This review summarizes the neurophysiology of the GI tract in the uninjured state and the pathophysiology associated with the systemic effects of SCI.

Adolescent rumination syndrome

Rumination syndrome is the non-purposeful regurgitation of recently ingested food from the stomach to the mouth, where it is either expelled or reswallowed. Adolescent rumination syndrome (ARS) is a rare condition of which many physicians are unaware. Patients often are misdiagnosed or undergo costly testing, and as a result, diagnosis and treatment are often delayed. While ARS is not life-threatening, it does have medical and emotional effects on the patient and the patient's family. Diagnosis of ARS is based upon the Rome III diagnostic criteria. Antroduodenal manometry, while not required for a diagnosis, can be helpful to confirm the diagnosis. The pathogenesis of this disorder is complex and not well understood. However, because of its behavioral component, treatment of ARS requires a multidisciplinary approach that includes both medical management of symptoms and implementation of strategies that address behavioral, psychological, and general quality-of-life components of the disorder.

Adolescent rumination syndrome

Adolescent Rumination Syndrome (ARS) is a relatively uncommon disorder, defined by the involuntary regurgitation of recently ingested food from the stomach to the mouth, where it is either expelled or re-swallowed. Although the disorder itself is not life-threatening, it typically has a significant medical and psychosocial impact on the patient and family. There continues to be limited awareness about the clinical presentation, diagnosis, and treatment of ARS among clinicians. As such, adolescents presenting with symptoms of ARS often are misdiagnosed and typically undergo avoidable, extensive, invasive, and costly testing. This article seeks to increase awareness and knowledge about ARS, and to provide the clinician with practical guidelines regarding the pathogenesis, assessment, diagnosis, and treatment of ARS.

Acid peptic diseases: pharmacological approach to treatment

Acid peptic disorders are the result of distinctive, but overlapping pathogenic mechanisms leading to either excessive acid secretion or diminished mucosal defense. They are common entities present in daily clinical practice that, owing to their chronicity, represent a significant cost to healthcare. Key elements in the success of controlling these entities have been the development of potent and safe drugs based on physiological targets. The histamine-2 receptor antagonists revolutionized the treatment of acid peptic disorders owing to their safety and efficacy profile. The proton-pump inhibitors (PPIs) represent a further therapeutic advance due to more potent inhibition of acid secretion. Ample data from clinical trials and observational experience have confirmed the utility of these agents in the treatment of acid peptic diseases, with differential efficacy and safety characteristics between and within drug classes. Paradigms in their speed and duration of action have underscored the need for new chemical entities that, from a single dose, would provide reliable duration of acid control, particularly at night. Moreover, PPIs reduce, but do not eliminate, the risk of ulcers in patients taking NSAIDs, reflecting untargeted physiopathologic pathways and a breach in the ability to sustain an intragastric pH of more than 4. This review provides an assessment of the current understanding of the physiology of acid production, a discussion of medications targeting gastric acid production and a review of efficacy in specific acid peptic diseases, as well as current challenges and future directions in the treatment of acid-mediated diseases.

Autonomic neural control of the airways

The airways and lungs are innervated by both sympathetic and parasympathetic nerves. Cholinergic parasympathetic innervation is well conserved in the airways while the distribution of noncholinergic parasympathetic and adrenergic sympathetic nerves varies considerably amongst species. Autonomic nerve function is regulated primarily through reflexes initiated upon bronchopulmonary vagal afferent nerves. Central regulation of autonomic tone is poorly described but some key elements have been defined.

Baclofen improves symptoms and reduces postprandial flow events in patients with rumination and supragastric belching

BACKGROUND & AIMS

In patients with clinically suspected rumination, esophageal impedance manometry differentiates episodes of rumination (involuntary straining with intragastric pressure increases) from aerophagia/supragastric belching. Treatment options are limited and focused on behavioral therapy. Baclofen, an agonist of the γ-aminobutyric acid B receptor, increases lower esophageal sphincter pressure and decreases swallowing rate. We investigated its effects in these patients.

METHODS

High-resolution manometry-impedance recordings were taken from 12 patients (8 women; mean age, 45 years; range, 18-89 years) with clinically suspected rumination or supragastric belching before and during treatment with baclofen (10 mg, 3 times daily). After 30 minutes of recordings, patients received a 1000-kcal solid meal; recordings were then continued for 1 hour. Patients were asked to register symptoms with an event marker. The number of symptoms registered and number and type of flow events were compared before and during treatment.

RESULTS

An average of 20 symptom markers (range, 14-34) were recorded at baseline (10 [range, 4-25] for belching and 9 [range, 0-11] for regurgitation). This was significantly reduced to 6 (range, 2-22) (3 [range, 1-15] for belching and 1 [range, 0-13] for regurgitation) during baclofen treatment (P = .01). The number of flow events (473 at baseline [42 reflux, 192 rumination, 188 supragastric belching, and 42 aerophagia]) was significantly reduced to 282 (32 reflux, 99 rumination, 123 supragastric belching, and 13 aerophagia) during baclofen therapy (P = .02). The reduction in flow events correlated with the increase in lower esophageal sphincter pressure (r = -0.62; P = .03) and reduction in swallowing frequency (r = 0.64; P = .02).

CONCLUSIONS

Baclofen is an effective treatment for patients with rumination or supragastric belching/aerophagia.

Alterations confined to the gastro-oesophageal junction: the relationship between low LOSP, TLOSRs, hiatus hernia and acid pocket

The gastro-oesophageal junction is a specialised segment of the gut designed to prevent reflux of gastric contents into the oesophagus. This task is fulfilled by two structures, i.e. the lower oesophageal sphincter and the crural diaphragm, which generate a high pressure zone. Especially during low pressure at the junction, as in case of long-lasting transient lower oesophageal sphincter relaxations, reflux can occur but mainly if a positive pressure gradient exists between stomach and the oesphagogastric junction. Although patients with gastro-oesophageal reflux disease have increased oesophageal acid exposure compared to controls, the number of transient relaxations is not increased compared to healthy controls. Instead, the risk to have acid reflux is at least doubled in patients, especially in those with a hiatal hernia, most likely as a result of the supradiaphragmatic position of the acid pocket. In hiatal hernia patients, the acid pocket is indeed often trapped in the hernia above the diaphragm. Which factors exactly determine the physical composition (liquid or gas) and the proximal extent of the refluxate however requires further research.

Neuro-regulation of lower esophageal sphincter function as treatment for gastroesophageal reflux disease

The junction between the esophagus and the stomach is a specialized region, composed of lower esophageal sphincter (LES) and its adjacent anatomical structures, the gastric sling and crural diaphragm. Together these structures work in a coordinated manner to allow ingested food into the stomach while preventing reflux of gastric contents across the esophago-gastric junction (EGJ) into the esophagus. The same zone also permits retrograde passage of air and gastric contents into esophagus during belching and vomiting. The precise coordination required to execute such a complicated task is achieved by a finely-regulated high-pressure zone. This zone keeps the junction between esophagus and stomach continuously closed, but is still able to relax briefly via input from inhibitory neurons that are responsible for its innervation. Alterations of the structure and function of the EGJ and the LES may predispose to gastroesophageal reflux disease (GERD).

Achalasia

Achalasia is a rare motor disorder of the oesophagus, characterised by the absence of peristalsis and impaired swallow-induced relaxation. These motor abnormalities result in stasis of ingested food in the oesophagus, leading to clinical symptoms, such as dysphagia, regurgitation of food, retrosternal pain and weight loss. Although it is well demonstrated that loss of myenteric oesophageal neurons is the underlying problem, it still remains unclear why these neurons are preferentially attacked and destroyed by the immune system. This limited insight into pathophysiology explains the fact that treatment is limited to interventions aimed at reducing the pressure of the lower oesophageal sphincter. The most successful therapies are clearly pneumatic dilatation and Heller myotomy with short-term success rates of 70-90%, declining to 50-65% after more than 15 years. The challenge for the coming years will undoubtedly be to get more insight into the underlying disease mechanisms and to develop a treatment to restore function.

Pseudoachalasia in a patient after truncal vagotomy surgery successfully treated by subsequent pneumatic dilations

Pseudoachalasia is a difficult condition for the clinician to differentiate from idiopathic achalasia even by manometry, radiological studies or endoscopy. Its etiology is usually associated with tumors. In most cases, the diagnosis is made after surgical explorations. The proposed pathogenesis of the disease is considered as mechanical obstruction of the distal esophagus or infiltration of the malignancy that affects the inhibitory neurons of the meyenteric plexus in the majority of cases. Surgery has been reported as a cause of pseudoachalasia. We report a 70-year-old man who suffered from deglutination disorder caused by pseudo-achalasia after truncal vagotomy. The patient was symptom-free after a nine-year follow-up and complete recovery of esophageal motility status from pseudoachalasia after pneumatic dilations. We also reviewed the literature of pseudoachalasia.

The lower oesophageal sphincter

The lower oesophageal sphincter (LOS) is a specialized segment of the circular muscle layer of the distal oesophagus, accounting for approximately 90% of the basal pressure at the oesophago-gastric junction. Together with the crural diaphragm, it functions as an antireflux barrier protecting the oesophagus from the caustic gastric content. During swallowing or belching, the LOS muscle must relax briefly in order to allow passage of food or intragastric air. These swallow-induced and prolonged transient lower oesophageal sphincter relaxations (TLOSRs) respectively result from activation of the inhibitory motor innervation of the sphincter. Both in man and animals, the main neurotransmitter released by the inhibitory neurones is nitric oxide. The two typical examples of dysfunction of the LOS are achalasia and gastro-oesophageal reflux disease (GORD). Achalasia is characterized by reduction or even absence of the inhibitory innervation to the LOS, leading to impaired LOS relaxation with dysphagia and stasis of food in the oesophagus. On the contrary, GORD results from failure of the antireflux barrier, with increased exposure of the oesophagus to gastric acid. This leads to symptoms such as heartburn and regurgitation, and in more severe cases to oesophagitis, Barrett's oesophagus and even carcinoma. To date, TLOSRs are recognized as the main underlying mechanism, and may represent an important target for treatment. More insight in the pathogenesis of both diseases will undoubtedly lead to new treatments in the near future.

Gastroesophageal reflux in familial dysautonomia: correlation with crisis frequency and sensory dysfunction

OBJECTIVES

Familial dysautonomia (FD), a genetic disorder resulting in sensory and autonomic nervous system dysfunction, is associated with a high frequency of gastroesophageal reflux (GER). In this study the authors attempted to determine if GER prevalence correlated with dysautonomic crisis frequency and small fiber sensory dysfunction.

METHODS

Of an initial population of 252 FD patients who had survived past their seventh year and were alive during the year of study from June 1, 2001 to June 1, 2002, 174 (69.0%) had sufficient data in their patient files to be included in this retrospective analysis. Subjects were stratified into three groups: those with no GER, those medically treated for GER and those surgically treated for GER with fundoplication. Data were obtained regarding frequency and severity of dysautonomic crises and sensory function including pain sensation, cold and warm thresholds and vibration perception.

RESULTS

There were no significant differences among the three groups regarding age or severity of sensory dysfunction. However, dysautonomic crises were significantly more frequent in FD patients who were presumed to have more intractable GER, as they had required fundoplication (P < 0.05).

CONCLUSIONS

The data confirm the high incidence of GER in the FD population and demonstrate that GER is independent of severity of sensory dysfunction. In addition, the authors demonstrate that fundoplication does not alleviate the central autonomic cause of retching, the dysautonomic crisis.

Involvement of cannabinoid receptors in gut motility and visceral perception

From a historical perspective to the present day, all the evidence suggests that activation of cannabinoid receptors (CBRs) is beneficial for gut discomfort and pain, which are symptoms related to dysmotility and visceral perception. CBRs comprise G-protein coupled receptors that are predominantly in enteric and central neurones (CB1R) and immune cells (CB2R). In the last decade, evidence obtained from the use of selective agonists and inverse agonists/antagonists indicates that manipulation of CB1R can alter (1) sensory processing from the gut, (2) brain integration of brain-gut axis, (3) extrinsic control of the gut and (4) intrinsic control by the enteric nervous system. The extent to which activation of CB1R is most critical at these different levels is related to the region of the GI tract. The upper GI tract is strongly influenced by CB1R activation on central vagal pathways, whereas intestinal peristalsis can be modified by CB1R activation in the absence of extrinsic input. Actions at multiple levels make the CB1R a target for the treatment of functional bowel disorders, such as IBS. Since low-grade inflammation may act as a trigger for occurrence of IBS, CB2R modulation could be beneficial, but there is little supporting evidence for this yet. The challenge is to accomplish CBR activation while minimizing adverse effects and abuse liabilities. Potential therapeutic strategies involve increasing signaling by endocannabinoids (EC). The pathways involved in the biosynthesis, uptake and degradation of EC provide opportunities for modulation of CB1R and some recent evidence with inhibitors of EC uptake and metabolism suggest that these could be exploited for therapeutic gain.

Achalasia presenting after operative and nonoperative trauma

Achalasia has been described following fundoplication and is attributed to vagal nerve damage during surgery. Similarly, other traumatic events to the distal esophagus may be linked to the development of achalasia. Operative and nonoperative trauma as a possible factor in the development of achalasia was studied. A retrospective analysis of patients with achalasia (n = 64) at our institution was performed. Collected data included age, gender, symptoms, and history of operative and nonoperative traumatic events. Comparisons were made to a group of patients with similar symptoms but normal esophageal manometry (n = 73). Achalasia was diagnosed by manometry in 125 patients over a 6-year period. All patients with complete medical records (n = 64) were studied. A history of operative or nonoperative trauma to the upper gastrointestinal tract prior to the development of symptomatic achalasia was present in 16 of 64 (25%). Significantly fewer patients (9.5%) with symptoms of dysphagia, but normal manometry and upper endoscopy, had precedent trauma to the upper gastrointestinal tract (P < 0.05). All cases of nonoperative trauma occurred in motor vehicle accidents. Cases of operative trauma included coronary artery bypass surgery (n = 4), bariatric surgery (n = 2), fundoplication (n = 3), heart/lung transplantation (n = 1), and others (n = 5). Patients with proven achalasia and a history of trauma were more likely to have chest pain (RR, 4.5; P = 0.012) but less likely to have regurgitation (RR, 0.51; P = 0.01) or nausea/vomiting (RR, 0.0; P = 0.27) than those without a history of antecedent trauma. In this series, significantly more patients with achalasia had a history of preceding trauma than did patients with similar symptoms and normal esophageal manometry. Following trauma, patients may be at increased risk for developing achalasia, possibly from neuropathic dysfunction due to vagal nerve damage. Patients with posttraumatic achalasia may have symptoms which differ from those of other achalasia patients.