Multimodal pain stimulations in patients with grade B oesophagitis

Pancreatic QST Differentiates Chronic Pancreatitis Patients into Distinct Pain Phenotypes Independent of Psychiatric Comorbidities

BACKGROUND & AIMS

Quantitative sensory testing (QST) has been previously used to study pain in chronic pancreatitis (CP) but included methods that are not suitable for clinical purposes. The aims of this study were to determine if pancreatic QST (P-QST) can differentiate patients into distinct pain phenotypes and to determine the association of these with their clinical pain and psychiatric comorbidities.

METHODS

A multicenter cross-sectional study was conducted where patients completed validated questionnaires assessing quality of life (QoL), depression and anxiety scores as well as clinical pain symptoms followed by P-QST which included a cold pressor test, repetitive pinprick stimuli and pressure stimulation of the upper abdominal (T10) and control dermatomes. P-QST categorized patients into pain phenotypes based on a previously established nomogram. QoL, clinical pain and psychiatric assessment scores were compared across these groups.

RESULTS

A total of 179 patients were enrolled with a mean age of 54.1±13.6 years among whom 59% were males and 42% had an alcoholic etiology. P-QST showed no hyperalgesia in 91 (51%), segmental hyperalgesia in 50 (28%) and widespread hyperalgesia in 38 (21%) patients. Patients with widespread hyperalgesia had significantly higher pain intensity scores (P = .03) and rates of constant pain (P = .002) as well as decreased QoL (P < .001) and physical functioning (P =.03) in comparison with the other two pain phenotypes. In contrast, psychiatric comorbidities were similar across all groups.

CONCLUSIONS

P-QST may serve as a novel unbiased pain assessment tool in CP as it categorizes patients into distinct pain phenotypes independent of their psychiatric comorbidities.

Rationale for and Development of the Pancreatic Quantitative Sensory Testing Consortium to Study Pain in Chronic Pancreatitis

OBJECTIVES

Abdominal pain is the primary symptom of chronic pancreatitis (CP), but pain is difficult to assess, and objective methods for pain assessment are lacking. The characterization of the sensory component of pain as a surrogate for nociception can be achieved by sensory testing using standardized stimuli. Herein, we describe the rationale for and development of an international consortium to better understand and characterize CP pain.

METHODS

A collaboration was initially formed between the University of Aalborg, Johns Hopkins University, and the University of Pittsburgh. This group refined the protocol for pancreatic quantitative sensory testing (P-QST) and then expanded the collaboration with plans for incorporating P-QST into prospective studies.

RESULTS

The collaboration has successfully developed a P-QST nomogram. Chronic pancreatitis patients identified with P-QST as having widespread hyperalgesia had higher pain intensity scores, higher prevalence of constant pain, and decreased quality of life. Psychiatric comorbidities were independent of pain phenotypes. Multiple studies are underway to validate these findings and evaluate their utility in clinical trials.

CONCLUSIONS

Development of the P-QST Consortium will facilitate collaborative efforts to use P-QST as a means for evaluation and characterization of pain in CP patients, and optimize methods to guide individualized pain management approaches.

The role of serotonin in the control of esophageal sensitivity assessed by multimodal stimulation in health

BACKGROUND

Esophageal hypersensitivity is considered an important pathophysiological mechanism in refractory gastroesophageal reflux disease (GERD) patients. Serotonin (5-HT) plays an important role in the regulation of GI (gastrointestinal) secretion, motility and sensitivity. Previous studies found that altered 5-HT availability has no clear effects on esophageal/GI sensations. Our aim was therefore to investigate the role of 5-HT in esophageal sensitivity in healthy volunteers (HV).

METHODS

Esophageal sensitivity to thermal, mechanical, electrical, and chemical stimuli was assessed in 3 different placebo-controlled studies. In the first study, the effect of citalopram (40 mg; 5-HT reuptake inhibitor; intravenous) was investigated (n = 14). In the second study, the effect of buspirone (20 mg; 5HT1A agonist; oral) was investigated (n = 10). In the third study, acute tryptophan depletion (ATD) was used to decrease 5-HT levels to investigate the effect of reduced 5-HT availability on esophageal sensitivity (n = 15).

KEY RESULTS

No difference was observed in esophageal sensitivity after the administration of citalopram or buspirone (all p > 0.06). In contrast, pain perception threshold to chemical stimulation was increased after ATD (p = 0.017, Cohen's d+ = 0.67). No effect was found on the first perception or pain tolerance threshold. ATD had no influence on esophageal sensitivity to thermal, mechanical, and electrical stimulation compared with placebo.

CONCLUSIONS AND INFERENCES

ATD, which induces 5-HT depletion, significantly decreased pain perception threshold during chemical stimulation, without affecting sensitivity to mechanical, thermal, or electrical stimulation. These findings confirm the involvement of 5-HT in the control of esophageal acid sensitivity, but identifying the receptors involved requires more ligands and studies.

A clinically feasible method for the assessment and characterization of pain in patients with chronic pancreatitis

BACKGROUND AND AIMS

Pain is the primary symptom of chronic pancreatitis (CP), but methods for sensory testing and pain characterization have not previously been validated for clinical use. We present a clinically feasible method for the assessment and characterization of pain mechanisms in patients with CP based on quantitative sensory testing (QST).

METHODS

This was a cross-sectional, multicenter study of 122 control subjects without pancreatic disease and another 60 patients with painful CP. All subjects underwent standardized QST assessments including a cold pressor test, a conditioned pain modulation paradigm, repetitive pin-prick stimuli (temporal summation) and pressure stimulation of the upper abdominal (pancreatic) and control dermatomes. The effects of age and gender on QST assessment parameters were investigated and normative reference values based on quartile regression were derived and implemented in algorithms to categorize patients according to their patterns of central pain processing (normal vs. segmental sensitization vs. widespread sensitization).

RESULTS

Absolute pressure thresholds were subject to clinically relevant gender effects (all p < 0.001), while the remainder of QST parameters were unaffected by age and gender. The algorithm with the best discriminatory capacity showed good separation between patients and controls (p < 0.001); 50% of patients had normal central pain processing, 23% had evidence of segmental sensitization and 27% had evidence of widespread sensitization.

CONCLUSION

We show normative reference values for a clinically feasible method for assessment and characterization of pain mechanisms in patients with CP. Application of this method streamlines the evaluation of pancreatic pain and may be used to inform treatment. CLINICALTRIALS.

GOV ID

NCT03434392.

The infusion of menthol into the esophagus evokes cold sensations in healthy subjects but induces heartburn in patients with gastroesophageal reflux disease (GERD)

Recent studies in animal models have reported that some afferent fibers innervating the esophagus express the cold receptor TRPM8. In the somatosensory system the stimulation of TRPM8 leads to cold sensations and in certain circumstances alleviates pain. It is therefore hypothesized in this paper that the esophageal infusion of the TRPM8 activator menthol evokes cold sensations from the esophagus and alleviates heartburn in humans. The esophageal infusion of menthol (3 mM, 20 min) evoked cold sensations in 11 of 12 healthy subjects. In striking contrast, the esophageal infusion of menthol evoked heartburn in 10 of 10 patients with gastroesophageal reflux disease (GERD). In healthy subjects the cold sensation evoked by menthol was perceived only as a minor discomfort as evaluated by the visual analog scale (VAS score 1.9 ± 0.3 on the scale 1-10). However, in patients with GERD the menthol-induced heartburn was perceived as painful (VAS score 5.6 ± 0.6, P < 0.01 compared to healthy subjects). It is concluded that the sensations evoked by esophageal infusion of menthol change from relatively nonpainful cold sensations in healthy subjects to painful heartburn sensations in patients with GERD. These qualitative and quantitative changes indicate substantial alterations in afferent signaling mediating sensations from the esophagus in patients with GERD.

The optimal order of stimulation modalities and reproducibility of the multimodal esophageal stimulation paradigm

BACKGROUND

Esophageal hypersensitivity can be triggered by different stimuli. We use a multimodal stimulation model to study esophageal sensitivity to four sensory modalities: thermal, mechanical, electrical, and chemical stimulation. The optimal order of these stimulations needs further validation.

METHODS

Esophageal sensitivity to thermal (heated saline solution), mechanical (balloon distention), electrical (block pulses with electrodes), and chemical stimulation (acid solution, 0.1 N HCl) was assessed in 10 subjects. In one session, thermal stimulation was performed first, followed by mechanical stimulation ("original protocol"). In a second session, mechanical stimulation was performed first, followed by temperature stimulation ("reversed protocol"). Besides, the impact of balloon distention speed (25 mL/min vs 50 mL/min) during mechanical stimulation was evaluated. Secondly, in order to establish reproducibility, independent control sessions of multimodal stimulations in 15 healthy volunteers were used retrospectively.

KEY RESULTS

A significant difference in pain perception threshold for thermal stimulation was found between the original and reversed protocol (P = 0.046), indicating that mechanical stimulation can sensitize the esophagus to thermal stimulation. Balloon distention rate had no impact on sensitivity thresholds for mechanical stimulation. Concerning the reproducibility, there were no differences for thermal, mechanical, electrical, and chemical stimulation in any of the control sessions.

CONCLUSIONS

The optimal order of the multimodal stimulation protocol was to start with the thermal stimulation, followed by mechanical, electrical, and chemical stimulation. The optimal balloon distention rate was 25 mL/min. Multimodal esophageal stimulation generates reproducible perception scores in health and therefore provides a reliable method to assess esophageal sensitivity changes after interventions that may alter esophageal sensitivity.

Pathophysiology and treatment of achalasia in a muscle mechanical perspective

This review provides a biomechanical perspective on the pathophysiology and treatment of achalasia. The esophagus is efficient in transporting ingested material to the stomach in healthy subjects. A fine balance exists between the peristaltic forces generated in the esophageal body (which herein is defined as the preload) and the resistance in the outlet, the esophago-gastric junction (which is defined as the afterload). Achalasia is a rare esophageal disease that progressively over many years challenges esophageal efficacy. Clinical features and current literature are interpreted using well-known muscle mechanics models and terms from cardiac mechanophysiology. The preload, afterload, length-tension, and strain softening concepts in particular are useful for understanding the remodeling induced by achalasia. The concepts are also useful in understanding the treatment that aim to reduce the lower esophageal sphincter pressure that does not relax sufficiently in achalasia. These treatments cover endoscopic or laparoscopic myotomy, pneumatic balloon dilation, and Botox injections. In addition to the intended reduction of the afterload for aboral transport of ingested materials, the treatments tend to induce gastroesophageal reflux in some patients because they obliterate an important component in the reflux barrier.

What Is the Future of Impedance Planimetry in Gastroenterology?

The gastrointestinal (GI) tract is efficient in transporting ingested material to the site of delivery in healthy subjects. A fine balance exists between peristaltic forces, the mixing and delivery of the contents, and sensory signaling. This fine balance is easily disturbed by diseases. It is mandatory to understand the pathophysiology to enhance our understanding of GI disorders. The inaccessibility and complex nervous innervation, geometry and mechanical function of the GI tract make mechanosensory evaluation difficult. Impedance planimetry is a distension technology that assesses luminal geometry, mechanical properties including muscle dynamics, and processing of nociceptive signals from the GI tract. Since standardized models do not exist for GI muscle function in vivo, models, concepts, and terminology must be borrowed from other medical fields such as cardiac mechanophysiology. The review highlights the impedance planimetric technology, muscle dynamics assessment, and 3 applied technologies of impedance planimetry. These technologies are the multimodal probes that assesses sensory function, the functional luminal imaging probe that dynamically measures the geometry of the lumen it distends, and Fecobionics that is a simulated feces providing high-resolution measurements during defecation. The advanced muscle analysis and 3 applied technologies can enhance the quality of future interdisciplinary research for gaining more knowledge about mechanical function, sensory-motor disorders, and symptoms. This is a step in the direction of individualized treatment for GI disorders based on diagnostic subtyping. There seems to be no better alternatives to impedance planimetry, but only the functional luminal imaging probe is currently commercially available. Wider use depends on commercialization of the multimodal probe and Fecobionics.

Impaired conditioned pain modulation in youth with functional abdominal pain

Functional abdominal pain (FAP) is associated with enhanced pain responsiveness. Although impaired conditioned pain modulation (CPM) characterizes adults with a variety of chronic pain conditions, relatively little is known about CPM in youth with FAP. This study assessed CPM to evoked thermal pain in 140 youth (ages 10-17), 63 of whom had FAP and 77 of whom were healthy controls. Multilevel models demonstrated weaker CPM effects in youth with FAP than in healthy youth, as evident in slower within-person decreases in pain ratings during the conditioning phase. Weaker CPM effects were associated with greater somatic symptom severity and functional disability. Pain responses in youth with FAP were heterogeneous, with 43% of youth showing an unexpected increase in pain ratings during the conditioning phase, suggesting sensitization rather than CPM-related pain inhibition. These findings highlight directions for future research on the emergence and maintenance of FAP in youth.

Patients with Barrett's esophagus are hypersensitive to acid but hyposensitive to other stimuli compared with healthy controls

BACKGROUND

Esophageal hyposensitivity has been observed in Barrett's esophagus and may contribute to its pathophysiology. However, studies are few, in particular those assessing different sensory modalities. We aimed to compare esophageal sensitivity to multimodal stimulation in patients with Barrett's esophagus and in healthy controls.

METHODS

Twenty-three patients with Barrett's esophagus and 12 healthy controls were examined. A multimodal probe was placed in the lower esophagus. Mechanical, thermal, and electrical stimulation was applied followed by an acid perfusion test with 0.1 N hydrochloric acid.

KEY RESULTS

Compared with controls, patients were hyposensitive to mechanical distension, heat, and electrical stimulation (all P<.05), but hypersensitive to acid (mean tolerated acid volume 57% lower, P=.001). A linear correlation between acid hypersensitivity and lower baseline impedance was found (P<.001). Patients had longer esophageal acid exposure time than controls (median acid exposure time 18 vs 5%, P=.03). Asymptomatic patients (no reflux symptoms at baseline) were hyposensitive to mechanical distension, electrical stimulation, and acid perfusion (all P<.05) compared with symptomatic patients.

CONCLUSIONS & INFERENCES

Patients with Barrett's esophagus exhibited acid hypersensitivity but hyposensitivity to other stimuli. Lower mucosal baseline impedance, a likely surrogate marker for impaired mucosal integrity, may explain the selective hypersensitivity to acid. On the other hand, the concurrent hyposensitivity may theoretically be explained by changes in central pain modulation. Patients with Barrett's esophagus seem to compose symptomatic and asymptomatic subgroups, showing different esophageal sensory profiles.

Ravages of Diabetes on Gastrointestinal Sensory-Motor Function: Implications for Pathophysiology and Treatment. Curr Gastroenterol Rep. 2016;18:6. [PMID: 26768896 DOI: 10.1007/s11894-015-0481-x]

Symptoms related to functional and sensory abnormalities are frequently encountered in patients with diabetes mellitus. Most symptoms are associated with impaired gastric and intestinal function. In this review, we discuss basic concepts of sensory-motor dysfunction and how they relate to clinical findings and gastrointestinal abnormalities that are commonly seen in diabetes. In addition, we review techniques that are available for investigating the autonomic nervous system, neuroimaging and neurophysiology of sensory-motor function. Such technological advances, while not readily available in the clinical setting, may facilitate stratification and individualization of therapy in diabetic patients in the future. Unraveling the structural, mechanical, and sensory remodeling in diabetes disease is based on a multidisciplinary approach that can bridge the knowledge from a variety of scientific disciplines. The final goal is to increase the understanding of the damage to GI structures and to sensory processing of symptoms, in order to assist clinicians with developing an optimal mechanics based treatment.

Brain changes in diabetes mellitus patients with gastrointestinal symptoms

Diabetes mellitus is a common disease and its prevalence is increasing worldwide. In various studies up to 30%-70% of patients present dysfunction and complications related to the gut. To date several clinical studies have demonstrated that autonomic nervous system neuropathy and generalized neuropathy of the central nervous system (CNS) may play a major role. This systematic review provides an overview of the neurodegenerative changes that occur as a consequence of diabetes with a focus on the CNS changes and gastrointestinal (GI) dysfunction. Animal models where diabetes was induced experimentally support that the disease induces changes in CNS. Recent investigations with electroencephalography and functional brain imaging in patients with diabetes confirm these structural and functional brain changes. Encephalographic studies demonstrated that altered insular processing of sensory stimuli seems to be a key player in symptom generation. In fact one study indicated that the more GI symptoms the patients experienced, the deeper the insular electrical source was located. The electroencephalography was often used in combination with quantitative sensory testing mainly showing hyposensitivity to stimulation of GI organs. Imaging studies on patients with diabetes and GI symptoms mainly showed microstructural changes, especially in brain areas involved in visceral sensory processing. As the electrophysiological and imaging changes were associated with GI and autonomic symptoms they may represent a future therapeutic target for treating diabetics either pharmacologically or with neuromodulation.

Protease-Activated Receptor-2 Up-Regulates Transient Receptor Potential Vanilloid 4 Function in Mouse Esophageal Keratinocyte

BACKGROUND

The reflux of pancreatic-duodenal fluids is implicated in the pathophysiology of proton-pump inhibitor-resistant gastroesophageal reflux disease (GERD). Protease-activated receptor-2 (PAR-2) is activated by proteases, the pancreatic enzyme, trypsin, and the activated PAR-2 enhances transient receptor potential vanilloid 4 (TRPV4) function in neurons. TRPV4 stimulates ATP exocytosis in conjunction with the vesicular nucleotide transporter, which mediates mechano-transduction and vagal stimulation. The aim of the present study was to verify whether the activated PAR-2 up-regulates TRPV4 function in mouse esophageal keratinocytes, which may link to the pathophysiology in PPI-resistant GERD.

METHODS

TRPV4 and PAR-2 expressions were detected by RT-PCR, immunostaining, and western blotting in mouse esophageal keratinocytes. The functional response of TRPV4 to esophageal keratinocytes was analyzed using a Ca(2+) imaging system. Cellular ATP release was examined by luciferase-luciferin reaction. TRPV4 phosphorylation was studied by immunoprecipitation and western blotting.

RESULTS

PAR-2 and TRPV4 mRNAs and proteins were expressed in esophageal keratinocytes. Pre-treatment with trypsin significantly increased the responses to TRPV4 activator in esophageal keratinocytes, probably via the phosphorylation of serine residue of TRPV4 by protein kinase C and resulted in cellular ATP release from the cells.

CONCLUSIONS

Activated PAR-2 with trypsin exposure up-regulated TRPV4 function and increased ATP release in mouse esophageal keratinocytes. This mechanism might be related to the pathophysiology of GERD, especially non-erosive GERD.

Association between individual response to food taste and gastroesophageal symptoms

OBJECTIVE

Taste is an important element in food preferences. Gastroesophageal reflux disease (GERD) is related to lifestyles including eating habits. We aimed to investigate the relationship between responses to specific tastes and GERD.

METHODS

Altogether 280 patients including 170 men with a mean age of 58.6 years were included in the study to determine the relationship between their liking for specific tastes and GERD using a new self-administered questionnaire (responses to various tastes and participants' sensitivity to taste and hot food and on the frequency of stomatitis). Another self-administrated questionnaire was administrated for a diagnosis of GERD (the frequency scale for the symptoms of GERD cut-off score of 10). Furthermore, 142 of 280 patients who had received esophagogastroduodenoscopy (EGD) were investigated on the association between endoscopic esophagitis and their favorite tastes.

RESULTS

In the association analyses between responses to specific tastes and GERD, the group liking salty food and the group with a high frequency of stomatitis had a significantly higher incidence of GERD (salty food: odds ratio [OR] 2.059, 95% confidence interval [CI] 1.215-3.488, P = 0.0073; stomatitis: OR 2.861, 95% CI 1.558-5.253, P = 0.0007, respectively). In association analyses with endoscopic esophagitis, the groups liking salty and sour food had a significantly higher incidence rate of endoscopic esophagitis (salty: OR 2.718, 95% CI 1.330-5.555, P = 0.0061; sour: OR 3.267, 95% CI 1.491-7.160, P = 0.0031, respectively).

CONCLUSIONS

Sensitivity and response to specific food taste were associated with GERD. The results of a preference to hot or salty food and endoscopic esophagitis suggest that physical stimuli are important for esophageal injuries.

Neurophysiology of the esophagus

The following, from the 12th OESO World Conference: Cancers of the Esophagus, includes commentaries on the methods and characteristics of esophageal afferents in humans; the pitfalls in characterization of mechanosensitive afferents; the sensitization of esophageal afferents in human studies; the brain source modeling in the understanding of the esophagus-brain axis; the use of evoked brain potentials in the esophagus; and measuring descending inhibition in animal and human studies.

Systematic mechanism-orientated approach to chronic pancreatitis pain

Pain in chronic pancreatitis (CP) shows similarities with other visceral pain syndromes (i.e., inflammatory bowel disease and esophagitis), which should thus be managed in a similar fashion. Typical causes of CP pain include increased intrapancreatic pressure, pancreatic inflammation and pancreatic/extrapancreatic complications. Unfortunately, CP pain continues to be a major clinical challenge. It is recognized that ongoing pain may induce altered central pain processing, e.g., central sensitization or pro-nociceptive pain modulation. When this is present conventional pain treatment targeting the nociceptive focus, e.g., opioid analgesia or surgical/endoscopic intervention, often fails even if technically successful. If central nervous system pain processing is altered, specific treatment targeting these changes should be instituted (e.g., gabapentinoids, ketamine or tricyclic antidepressants). Suitable tools are now available to make altered central processing visible, including quantitative sensory testing, electroencephalograpy and (functional) magnetic resonance imaging. These techniques are potentially clinically useful diagnostic tools to analyze central pain processing and thus define optimum management approaches for pain in CP and other visceral pain syndromes. The present review proposes a systematic mechanism-orientated approach to pain management in CP based on a holistic view of the mechanisms involved. Future research should address the circumstances under which central nervous system pain processing changes in CP, and how this is influenced by ongoing nociceptive input and therapies. Thus we hope to predict which patients are at risk for developing chronic pain or not responding to therapy, leading to improved treatment of chronic pain in CP and other visceral pain disorders.

New therapies for non-cardiac chest pain

After excluding a cardiac cause, potent anti-reflux therapy should be administered to patients with non-cardiac chest pain since gastroesophageal reflux disease (GERD) is the most common underlying mechanism of this disorder. If GERD is an unlikely cause of patient's symptoms, an esophageal motor disorder should be excluded. Spastic motility disorders can be treated with a smooth muscle relaxant (such as calcium channel blocker, nitrate, or phosphodiesterase 5 inhibitors). Alternatively, spastic motility disorders may respond to anti-spasmodics, pain modulators, botulinum toxin injection into the distal esophagus, and/or surgery. Patients with functional chest pain have recently seen an expanded treatment armamentarium including medications such as trazadone, tricyclic anti-depressants, selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, pregabalin, and/or ramelteon.

Evaluation of esophageal sensation

Dramatic progress has been made over the past decade in the sophistication and availability of equipment to test esophageal motility and sensation. High-resolution esophageal manometry and impedance have moved from the research clinic into clinical practice. Some of the testing is costly and time consuming, and requires extensive experience to perform the testing and properly interpret the results. These sensory studies are valuable in the interpretation of clinical problems, and provide important research information. Clinicians should evaluate the research studies to advance their understanding of the pathophysiology of the esophagus.

Do patients with functional chest pain have neuroplastic reorganization of the pain matrix? A diffusion tensor imaging study

Background and aims

In functional chest pain (FCP) of presumed esophageal origin central nervous system hyperexcitability is generally believed to play an important role in pain pathogenesis. However, this theory has recently been challenged. Using magnetic resonance diffusion tensor imaging, the aim was to characterize any microstructural reorganization of the pain neuromatrix in FCP patients.

Methods

13 FCP patients and 20 matched healthy controls were studied in a 3T MR scanner. Inclusion criteria were relevant chest pain, normal coronary angiogram and normal upper gastrointestinal evaluation. Apparent diffusion coefficient (ADC) (i.e. mean diffusivity of water) and fractional anisotropy (FA) (i.e. directionality of water diffusion as a measure of fiber organization) values were assessed in the secondary sensory cortex, cingulate cortex, insula, prefrontal cortex, and amygdala.

Results

Overall, including all regions, no difference in ADC and FA values was found between the patients and controls (P = 0.79 and P = 0.23, respectively). Post-hoc tests revealed no difference in ADC and FA values of the individual regions. However, a trend of patients having increased ADC in the mid insula grey matter and increased FA in the mid insula white matter was observed (both P = 0.065).

Conclusions

This explorative study suggests that microstructural reorganization of the central pain neuromatrix may not be present in well-characterized FCP patients.

Implications

This finding, together with recent neurophysiologal evidence, challenges the theory of visceral hypersensitivity due to changes in the central nervous system in FCP patients.

Gastrointestinal sensitivity and gastroesophageal reflux disease

This paper reports on gastrointestinal sensitivity, including on the role of refluxate volume on the perception of reflux symptoms; experimental pain models that mimic mechanisms and symptoms of pain associated with esophageal diseases; the potential role of the acid receptor TRPV1 in the genesis of gastroesophageal reflux disease (GERD) symptoms; and roles for ATP and the purine and pyrimidine receptor subfamilies P1, P2X, and P2Y in the pathogenesis of GERD symptoms.

Perception and pain thresholds for cutaneous heat and cold, and rectal distension: associations and disassociations

BACKGROUND

Hypersensitivity to somatic or visceral pain has been reported in numerous clinical conditions such as fibromyalgia or the irritable bowel syndrome, and general hypersensitivity has been proposed to be the underlying mechanism. However, cross-modal relationships especially between somatic and visceral pain have rarely been investigated even in healthy volunteers. Furthermore, psychological influences on pain have rarely been characterized across modalities.

METHODS

Sixty-one healthy participants underwent testing of perception and pain thresholds for cutaneous thermode heat and cold, as well as for rectal balloon distension. Psychological testing for anxiety, depression, and pain experience (including catastrophizing and coping) as well as cardiac interoception was performed. Measurement quality and the correlations between the different modalities were examined.

KEY RESULTS

Significant correlations existed between the perception thresholds for cold/heat (τB  = -0.28, p = 0.002) and cold/distension (τB  = -0.21, p = 0.03) and for the pain thresholds for cold/heat (r = -0.61, p < 0.001) and heat/distension (r = 0.33, p = 0.01). No association was found between pain thresholds and anxiety, depression, psychological experience with and processing of pain, or cardiac interoception. Retest reliabilities for pain measurements were satisfying after short intertrial intervals (all intraclass correlation coefficients >0.8), but less so after longer intervals. The individuals contributing to the respective correlations differ between measurements.

CONCLUSIONS & INFERENCES

Moderate associations were found for pain thresholds across modalities. The strength of the associations and their stability over time warrants further investigation and might serve to increase the understanding of conditions affecting multiple pain modalities.

Exploration of the effects of gender and mild esophagitis on esophageal pain thresholds in the normal and sensitized state of asymptomatic young volunteers

BACKGROUND

Clinical data suggest gender differences in gastrointestinal pain, but very little experimental data exist. Esophageal painful thresholds to mechanical, thermal, electric, and chemical stimuli can be measured with the esophageal multimodal pain model. The aim was to measure the effect of gender and mild esophagitis on esophageal pain perception.

METHODS

Thirty-five healthy asymptomatic volunteers [19 men, median age 29 (22-56 years)] underwent upper GI endoscopy, 24 h pH/impedance measurement, and multimodal esophageal pain stimulation before and after sensitization with acid. Stimulus intensities at painful thresholds were recorded.

KEY RESULTS

Men had higher pain thresholds (PT) to mechanical stimulation (mean volume: men 20.9 ± 10 mL vs women 15.2 ± 6.8 mL, P = 0.02) and more men tolerated the maximum acid challenge (58% vs 20%, P = 0.03). There were no differences between genders for PT to (1) thermal stimulation [mean stimulation time (men, women): heat; 20 ± 5 s vs 21 ± 6 s or cold; 33.3 ± 20.1 s vs 20.7 ± 21.4 s, P > 0.2], (2) electrical current (mean current: men 17.6 ± 9.2 mA vs women 12.9 ± 3.7 mA, P = 0.11), or (3) acid volume [median volume: men 200 (20;200) mL vs women 133 (40;200) mL, P = 0.2]. Fifteen asymptomatic subjects had mild esophagitis (10 men, all Los Angeles A). There were no differences in esophageal PT between subjects with normal endoscopy or mild esophagitis (all P > 0.3).

CONCLUSIONS & INFERENCES

The effects of gender and mild esophagitis on esophageal multimodal pain perception have been measured in asymptomatic volunteers. The study suggests that gender, not mild esophagitis, tends to influence mechanical and chemical esophageal pain.

Randomized clinical trial: inhibition of the TRPV1 system in patients with nonerosive gastroesophageal reflux disease and a partial response to PPI treatment is not associated with analgesia to esophageal experimental pain

OBJECTIVE

Many patients with nonerosive reflux disease (NERD) have insufficient relief on proton pump inhibitors (PPIs). Some patients have a hypersensitive esophagus and may respond to transient receptor potential vanilloid 1 (TRPV1) antagonists. Aim. To investigate the effect of the TRPV1 antagonist AZD1386 on experimental esophageal pain in NERD patients.

MATERIAL AND METHODS

Enrolled patients had NERD and a partial PPI response (moderate-to-severe heartburn or regurgitation ≥3 days/week before enrolment despite ≥6 weeks' PPI therapy). Fourteen patients (21-69 years, 9 women) were block-randomized into this placebo-controlled, double-blinded, crossover study examining efficacy of a single dose (95 mg) of AZD1386. On treatment days, each participant's esophagus was stimulated with heat, distension, and electrical current at teaching hospitals in Denmark and Sweden. Heat and pressure pain served as somatic control stimuli. Per protocol results were analyzed.

RESULTS

Of 14 randomized patients, 12 were treated with AZD1386. In the esophagus AZD1386 did not significantly change the moderate pain threshold for heat [-3%, 95% confidence interval (CI), -22;20%], distension (-11%, 95% CI, -28;10%), or electrical current (6%, 95% CI, -10;25%). Mean cutaneous heat tolerance increased by 4.9°C (95% CI, 3.7;6.2°C). AZD1386 increased the maximum body temperature by a mean of 0.59°C (95% CI, 0.40-0.79°C), normalizing within 4 h.

CONCLUSIONS

AZD1386 had no analgesic effect on experimental esophageal pain in patients with NERD and a partial PPI response, whereas it increased cutaneous heat tolerance. TRPV1 does not play a major role in heat-, mechanically and electrically evoked esophageal pain in these patients. ClinicalTrials.gov identifier: D9127C00002.

The pain system in oesophageal disorders: mechanisms, clinical characteristics, and treatment

Pain is common in gastroenterology. This review aims at giving an overview of pain mechanisms, clinical features, and treatment options in oesophageal disorders. The oesophagus has sensory receptors specific for different stimuli. Painful stimuli are encoded by nociceptors and communicated via afferent nerves to the central nervous system. The pain stimulus is further processed and modulated in specific pain centres in the brain, which may undergo plastic alterations. Hence, tissue inflammation and long-term exposure to pain can cause sensitisation and hypersensitivity. Oesophageal sensitivity can be evaluated ,for example, with the oesophageal multimodal probe. Treatment should target the cause of the patient's symptoms. In gastro-oesophageal reflux diseases, proton pump inhibitors are the primary treatment option, surgery being reserved for patients with severe disease resistant to drug therapy. Functional oesophageal disorders are treated with analgesics, antidepressants, and psychological therapy. Lifestyle changes are another option with less documentation.

The esophageal multimodal pain model: normal values and degree of sensitization in healthy young male volunteers

BACKGROUND

Sensory changes are thought to be involved in gastro-esophageal reflux disease (GERD). The esophageal multimodal pain model can be used to investigate sensations in response to distension, heat, electric current and acid.

AIMS

The aim of this study was to provide normal values for this model in the normal state and in the acid induced sensitized state.

METHODS

Fifty-three healthy men (20-38 years old) underwent esophageal stimulation with distension, heat and electrical current before and after sensitization with 0.1 N HCl acid. Stimulus intensities at painful and non-painful thresholds and referred pain areas were measured. The percentage of individual participants sensitized to each modality was calculated. In 22 subjects the pre-acid tests were repeated on three subsequent visits.

RESULTS

To reach moderate pain, subjects tolerated mean distension of 29.1 ± 11 mL, heat stimulation time of 141 ± 33 s, and mean current of 17.6 ± 6.4 mA. After acid exposure, significantly reduced thresholds were observed for mechanical (24%), heat (11%) and electrical (14%) stimulation (P values < 0.05). The percentage of subjects sensitized, defined as reductions in thresholds of ≥10% or ≥20% after acid perfusion, was as follows: for distension 77%/62%, for heat 48%/28%, and for current 58%/44%. The model showed good reliability (intra-class correlations >0.6).

CONCLUSIONS

Normal values for healthy young men are now provided for the normal and the sensitized state. The percentage of subjects sensitized after acid stimulation are thoroughly documented, and depends on stimulation type and the cut-off value chosen.

Transient receptor potential vanilloid 4 (TRPV4)-dependent calcium influx and ATP release in mouse oesophageal keratinocytes

Gastro-oesophageal reflux disease (GERD) is a multi-factorial disease that may involve oesophageal hypersensitivity to mechanical or heat stimulus as well as acids. Intraganglionic laminar endings (IGLEs) are the most prominent terminal structures of oesophageal vagal mechanosensitive afferents and may modulate mechanotransduction via purinergic receptors. Transient receptor potential channel vanilloid 4 (TRPV4) can detect various stimuli such as warm temperature, stretch and some chemicals, including 4α-phorbol 12,13-didecanoate (4α-PDD) and GSK1016790A. TRPV4 is expressed in many tissues, including renal epithelium, skin keratinocytes and urinary bladder epithelium, but its expression and function in the oesophagus is poorly understood. Here, we show anatomical and functional TRPV4 expression in mouse oesophagus and its involvement in ATP release. TRPV4 mRNA and protein were detected in oesophageal keratinocytes. Several known TRPV4 activators (chemicals, heat and stretch stimulus) increased cytosolic Ca2+ concentrations in cultured WT keratinocytes but not in TRPV4 knockout (KO) cells. Moreover, the TRPV4 agonist GSK1016790A and heat stimulus evoked TRPV4-like current responses in isolated WT keratinocytes, but not in TRPV4KO cells. GSK1016790A and heat stimulus also significantly increased ATP release from WT oesophageal keratinocytes compared to TRPV4KO cells. The vesicle-trafficking inhibitor brefeldin A (BFA) inhibited the ATP release. This ATP release could be mediated by the newly identified vesicle ATP transporter, VNUT, which is expressed by oesophageal keratinocytes at the mRNA and protein levels. In conclusion, in response to heat, chemical and possibly mechanical stimuli, TRPV4 contributes to ATP release in the oesophagus. Thus, TRPV4 could be involved in oesophageal mechano- and heat hypersensitivity.

Randomised clinical trial: the efficacy of a transient receptor potential vanilloid 1 antagonist AZD1386 in human oesophageal pain

BACKGROUND

Many patients with gastro-oesophageal reflux disease (GERD) are hypersensitive to heat and acid and may respond insufficiently to standard treatment. Antagonists of the heat and acid receptor 'transient receptor potential vanilloid 1'(TRPV1) are a potential drug class for GERD treatment.

AIM

To investigate the effect of a TRPV1 antagonist (AZD1386) on experimentally induced oesophageal pain.

METHODS

Twenty-two healthy men (20-31 years) participated in this randomised, placebo-controlled, double-blinded, crossover study examining the effects of a single-dose oral AZD1386 (30 and 95 mg). Subjects were block-randomised. On treatment days, participants were stimulated with painful heat, distension, electrical current and acid in the oesophagus. Heat and pressure pain on the forearm were somatic control stimuli.

DATA ANALYSIS

intention-to-treat.

RESULTS

A total of 21 participants completed the protocol and 1 voluntarily discontinued. In the oesophagus, both 30 and 95 mg of AZD1386 increased pain thresholds to heat stimuli 23% [95% confidence interval (CI): 10-38%] and 28%, respectively (CI: 14-43%). The skin heat tolerance was increased 2.1 °C (CI: 1.1-3.2 °C) after 30 mg AZD1386 and 4.0 °C (CI: 3.0-5.0 °C) after 95 mg. Heat analgesia persisted for 2.5 h. Pain thresholds to the other stimuli were unaffected by AZD1386. 50% reported 'feeling cold' and body temperature increased in all subjects exposed to 30 and 95 mg AZD1386 (mean increase 0.4±0.3 °C and 0.7±0.3 °C, respectively, P<0.05).

CONCLUSIONS

AZD1386 increased oesophageal and skin heat pain thresholds and had a safe adverse-event profile. This drug class may have a potential for treatment of GERD.

Proximal and distal esophageal sensitivity is decreased in patients with Barrett’s esophagus

AIM: To investigate sensations to multimodal pain stimulation in the metaplastic and normal parts of the esophagus in patients with Barrett’s esophagus (BE).

METHODS: Fifteen patients with BE and 15 age-matched healthy volunteers were subjected to mechanical, thermal and electrical pain stimuli of the esophagus. Both the metaplastic part and the normal part (4 and 14 cm, respectively, above the esophago-gastric junction) were examined. At sensory thresholds the stimulation intensity, referred pain areas, and evoked brain potentials were recorded.

RESULTS: Patients were hyposensitive to heat stimulation both in the metaplastic part [median stimulation time to reach the pain detection threshold: 15 (12-34) s vs 14 (6-23) s in controls; F = 4.5, P = 0.04] and the normal part of the esophagus [median 17 (6-32) s vs 13 (8-20) s in controls; F = 6.2, P = 0.02]. Furthermore, patients were hyposensitive in the metaplastic part of the esophagus to mechanical distension [median volume at moderate pain: 50 (20-50) mL vs 33 (13-50) mL in controls; F = 5.7, P = 0.02]. No indication of central nervous system abnormalities was present, as responses were comparable between groups to electrical pain stimuli in the metaplastic part [median current evoking moderate pain: 13 (6-26) mA vs 12 (9-24) mA in controls; F = 0.1, P = 0.7], and in the normal part of the esophagus [median current evoking moderate pain: 9 (6-16) mA, vs 11 (5-11) mA in controls; F = 3.4, P = 0.07]. Furthermore, no differences were seen for the referred pain areas (P-values all > 0.3) or latencies and amplitudes for the evoked brain potentials (P-values all > 0.1).

CONCLUSION: Patients with BE are hyposensitive both in the metaplastic and normal part of esophagus likely as a result of abnormalities affecting peripheral nerve pathways.

Different effects of morphine and oxycodone in experimentally evoked hyperalgesia: a human translational study

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT * Previous studies using short-lasting experimental pain stimulations in healthy volunteers have shown differences in opioid effects regarding visceral pain stimulations. However, these differences can be more pronounced in patients due to a sensitized pain system. Therefore, the aim of the present study was to mimic the clinical situation by investigating opioid effects on experimental pain in healthy volunteers after experimentally evoked hyperalgesia. WHAT THIS STUDY ADDS? * We now know that morphine and oxycodone exerts different effects in the sensitized pain system as we found a greater analgesic effect of oxycodone in response to skin, muscle and oesophageal pain stimulation. This supports clinicians' experiences that oxycodone can be superior to morphine in the treatment of some pain conditions. The evoked hyperalgesia bridged findings from studies in healthy volunteers to patients, and new fundamental knowledge on different analgesic effects in hyperalgesia was found. AIM Similar analgesics may have different analgesic potencies especially in patients in whom the pain system is sensitized. The aim was to investigate different opioid effects on experimental pain after the sensitized pain system was mimicked evoking hyperalgesia in healthy volunteers. METHODS Twenty-four healthy volunteers were randomized to treatment with morphine (30 mg orally) and oxycodone (15 mg orally) or placebo in a double-blind crossover study. Hyperalgesia was induced by oesophageal perfusion with acid and capsaicin. Several exploratory endpoints were studied using skin heat, muscle pressure and oesophageal mechanical, heat and electrical stimulation. Effects on pain from deeper structures were considered most important. RESULTS Different analgesic potencies were found. Oxycodone had a greater analgesic effect than morphine attenuating pain from: (i) heat stimulation of skin (P= 0.016); difference between the means of 0.39 degrees C, 95% CI 0.22, 2.09. (ii) muscle pressure (P < 0.001); difference between the means of 11.93kPa, 95% CI 5.4, 18.5. (iii) oesophageal heat stimulation (P < 0.001); difference between the means of 38.54 cm(2), 95% CI 15.37, 61.71 and (iv) oesophageal electrical stimulation (P= 0.016); difference between the means of 6.69mA, 95% CI 1.23, 12.13. CONCLUSION After sensitization of the pain system different analgesic potencies of morphine and oxycodone were found in response to skin, muscle and oesophageal pain stimulation, in which oxycodone had a greater effect. As similar differential analgesic potencies of the two opioids have been found in patients with chronic pain, the experimental hyperalgesia model bridged findings from studies in healthy volunteers to patients.

Esophageal sensation and esophageal hypersensitivity - overview from bench to bedside

Noxious stimuli in the esophagus activate nociceptive receptors on esophageal mucosa, such as transient receptor potential, acid-sensing ion channel and the P2X family, a family of ligand-gated ion channels responsive to ATP, and this generates signals that are transmitted to the central nervous system via either spinal nerves or vagal nerves, resulting in esophageal sensation. Among the noxious stimuli, gastric acid and other gastric contents are clinically most important, causing typical reflux symptoms such as heartburn and regurgitation. A conventional acid penetration theory has been used to explain the mechanism of heartburn, but much recent evidence does not support this theory. Therefore, it may be necessary to approach the causes of heartburn symptoms from a new conceptual framework. Hypersensitivity of the esophagus, like that of other visceral organs, includes peripheral, central and probably psychosocial factor-mediated hypersensitivity, and is known to play crucial roles in the pathoegenesis of nonerosive reflux disease, functional heartburn and non-cardiac chest pain. There also are esophagitis patients who do not perceive typical symptoms. This condition is known as silent gastroesophageal reflux disease. Although the pathogenesis of silent gastroesophageal reflux disease is still not known, hyposensitivity to reflux of acid may possibly explain the condition.

Acid hypersensitivity in patients with eosinophilic oesophagitis

OBJECTIVE

Painful symptoms are prevalent in patients with eosinophilic oesophagitis but experimental data are sparse. The aim of this study was to compare the pain response to experimental oesophageal stimulation in 14 patients with eosinophilic oesophagitis and 15 healthy volunteers.

MATERIAL AND METHODS

A multimodal probe was placed in the oesophagus. The participants were subjected to mechanical, thermal and electrical pain stimuli followed by perfusion with 0.1 M HCl. Pain scores, referred pain areas and evoked brain potentials to electrical stimulation of the oesophagus were recorded.

RESULTS

Patients tolerated significantly less acid perfused in the oesophagus (median 123 versus 200 ml; P = 0.02) and felt the burning sensation evoked by the acid earlier (median 2.0 versus 5.0 min; P = 0.01). Eight patients had coexisting gastro-oesophageal reflux disease. Six patients had pure eosinophilic oesophagitis, and this group felt the acid earlier than those with concomitant reflux or the healthy volunteers (median 0.8 versus 2.0 and 5.0 min; P = 0.03). There were no differences between patients and controls in the responses to mechanical or thermal stimulation (P > 0.4). Furthermore, no differences were found for the proxies of central nervous system sensitization (response to electrical stimulations, referred pain areas or evoked brain potentials; P > 0.1).

CONCLUSIONS

Patients with eosinophilic oesophagitis are hypersensitive to acid perfused in the oesophagus, and pathophysiologic findings are likely confined to the peripheral tissue. Reflux from physiological acid may play a role in the symptoms of eosinophilic oesophagitis.

An endoscopic method for thermal and chemical stimulation of the human oesophagus

Previous methods for visceral thermal stimulation have lacked control of the temperature rate and visual inspection of the organ. The aims of this study was to develop a method for linear control of heat stimulation in the human oesophagus combined with endoscopy, to assess the reproducibility of this method and to investigate sensitivity to thermal stimulation of the distal oesophagus before and after acid perfusion. A probe with a 2.8 mm endoscope inside was constructed permitting heat and chemical stimulation. Three different temperature ramps were applied in the distal oesophagus in 12 healthy subjects by recirculation of heated water in a bag. Endoscopy of the oesophageal mucosa was performed prior to experimental stimulation. The temperature, the time of stimulation and the area under the temperature curve (AUC) were measured at the pain detection threshold. Thermal stimulation was repeated after perfusion of the oesophagus with acid. The method was tested on two subsequent days to assess reproducibility. All subjects had a normal endoscopic examination. Day-to-day reproducibility was good for the three temperature ramps (intra-class correlations >0.6). The subjects tolerated less heat stimulation, a decrease in AUC (P = 0.0003), a decrease in time to pain detection threshold (P = 0.005) and decreased temperature at pain detection threshold (P = 0.0001) after acid perfusion. The slow ramp was the most sensitive, showing a decrease in AUC of 29%. The present method was easily implemented and showed good reproducibility. It can potentially be used in basic experiments, drug and clinical studies as it provides a controllable thermal stimulus.

Role of neuropathic pain mechanisms in the pathogenesis of pain in chronic pancreatitis

Abdominal pain is a major clinical symptom in patients with chronic pancreatitis. Alleviation of abdominal pain is important in the treatment of chronic pancreatitis. More and more studies show that the pain in chronic pancreatitis is similar to neuropathic pain. In this article, we will review the role of neuropathic pain mechanisms in the pathogenesis of pain in chronic pancreatitis by describing the clinical features of the pain, peripheral sensitization, central sensitization and changes in electroencephalogram. Understanding of the mechanisms responsible for pain in chronic pancreatitis may have important implications for the treatment of the disease.

Sensory testing of the human gastrointestinal tract

The objective of this appraisal is to shed light on the various approaches to screen sensory information in the human gut. Understanding and characterization of sensory symptoms in gastrointestinal disorders is poor. Experimental methods allowing the investigator to control stimulus intensity and modality, as well as using validated methods for assessing sensory response have contributed to the understanding of pain mechanisms. Mechanical stimulation based on impedance planimetry allows direct recordings of luminal cross-sectional areas, and combined with ultrasound and magnetic resonance imaging, the contribution of different gut layers can be estimated. Electrical stimulation depolarizes free nerve endings non-selectively. Consequently, the stimulation paradigm (single, train, tetanic) influences the involved sensory nerves. Visual controlled electrical stimulation combines the probes with an endoscopic approach, which allows the investigator to inspect and obtain small biopsies from the stimulation site. Thermal stimulation (cold or warm) activates selectively mucosal receptors, and chemical substances such as acid and capsaicin (either alone or in combination) are used to evoke pain and sensitization. The possibility of multimodal (e.g. mechanical, electrical, thermal and chemical) stimulation in different gut segments has developed visceral pain research. The major advantage is involvement of distinctive receptors, various sensory nerves and different pain pathways mimicking clinical pain that favors investigation of central pain mechanisms involved in allodynia, hyperalgesia and referred pain. As impairment of descending control mechanisms partly underlies the pathogenesis in chronic pain, a cold pressor test that indirectly stimulates such control mechanisms can be added. Hence, the methods undoubtedly represent a major step forward in the future characterization and treatment of patients with various diseases of the gut, which provides knowledge to clinicians about the underlying symptoms and treatment of these patients.

Central neuronal mechanisms of gastric electrical stimulation in diabetic gastroparesis

OBJECTIVE

The mechanisms underlying symptom improvement in gastric electrical stimulation (GES) are not fully understood. Modulation of the central nervous system excitability may be involved. The objective of the study was to investigate the central effects of GES, including the possible modulation of the visceral sensory nervous system.

MATERIAL AND METHODS

A gastric electrical stimulator was implanted in seven diabetic patients with medically refractory gastroparesis. A double-blinded protocol was used to investigate the patients at baseline and one month after recovery with the stimulator turned on and off (1-month periods). The following assessments were carried out: mechanical, thermal and electrical stimulations with sensory recordings in the esophagus and duodenum, and standardized, self-administered, daily symptom questionnaires.

RESULTS

No difference was found between baseline and the on- and off periods in overall gut pain thresholds across all stimulus modalities in the esophagus (p=0.63), duodenum (p=0.19) or esophagus and duodenum combined (p=0.76). No difference in the sensory response to mechanical stimulation was found in the esophagus before (all p>0.31) and after (all p>0.43) smooth muscle relaxation with butylscopolamine. Similar findings were observed in the duodenum. No differences were found in thermal sensitivity (esophagus (p=0.67) and duodenum (p=0.17)), sensory response to electrical stimulation (esophagus (p=0.57) and duodenum (p=0.52)) or induced somatic referred pain areas (esophagus (p=0.75) and duodenum (p=0.51)). No difference was seen in the induced somatic referred pain areas or self-reported symptoms.

CONCLUSIONS

No evidence was found for GES-induced modulation of the visceral sensory system and central excitability. However, GES has been proven to modulate the central nervous system in animal studies, necessitating further human experiments in order unambiguously to establish the possible central effects of GES.

Multichannel intraluminal impedance measurement of gastroesophageal reflux in patients with different stages of morbid obesity. Obes Surg. 2009;19:1522-1529. [PMID: 18648896 DOI: 10.1007/s11695-008-9624-6]

BACKGROUND

Obesity is now one of the world's major chronic diseases. The etiology of the severe comorbid conditions associated with morbid obesity is not fully understood, and in particular the relationship between gastroesophageal reflux and obesity.

METHODS

Sixty-seven patients were enrolled in this prospective study. Patients and control individuals were divided into four subgroups according to their body mass index (BMI). Esophageal motility was assessed using a conventional water-perfused esophageal manometry catheter, and 24-h pH-metry was carried out using multichannel intraluminal impedance equipment.

RESULTS

In the group with the highest BMI (>50), contraction amplitudes in the middle and distal esophagus were significantly higher in comparison both with the control group and groups with a lower BMI (P < 0.05). Lower esophageal sphincter pressure was reduced in the majority of patients with morbid obesity and differed significantly from the control group (P < 0.001). Significant differences between the control group and the patient groups were also observed on 24-h pH-metry (P < 0.05). The 24-h impedance measurements distinguished between acid and nonacid status and between the upright and recumbent positions. The total number of reflux episodes differed significantly between the control and patient groups and between groups III and IV, with lower and higher BMI values (P < 0.008 and P < 0.05, respectively).

CONCLUSIONS

The impedance data obtained in this study confirm that patients with morbid obesity are at risk of developing gastroesophageal reflux disease. However, there is no evidence of a direct correlation between the severity of reflux and the extent of obesity.

The Role of Angina Pectoris in Chronic Pain After Coronary Artery Bypass Graft Surgery

Visceral nociception readily sensitizes the central nervous system, causing referred somatic pain and hyperalgesia via somato-visceral convergence. Hyperalgesia in the perioperative period may increase vulnerability to subsequent development of chronic pain. The study aim is to investigate the role of angina pectoris, an ischemic visceral pain, in long-term pain after coronary artery bypass surgery (CABG). We sent questionnaires to 369 patients who underwent CABG surgery in 2003. Questions were asked about angina pectoris and other pain in the period before surgery, the first week postoperatively (= acute pain), and the period after 3 months after surgery (= chronic pain). We obtained results from 256 patients (response rate = 69%). The point prevalence of chronic pain after CABG was 27% after a mean follow-up of 16 months (SD +/- 3 months). Patients with chronic pain after CABG had more angina pectoris than those without chronic pain: Before surgery (P = .07), early on postoperatively (P = .004), and more than 3 months after surgery (P = .000004). We found cumulative prevalences of chronic pain after CABG at 3 months of 39%, and of 32% after 6 months. Other predictive factors for chronic pain after CABG were acute postoperative pain (P = .00002) and younger age (P = .002). Angina pectoris is associated with chronic pain after CABG surgery. Other predictive factors include acute postoperative pain and younger age.

PERSPECTIVE

The influence of postoperative angina pectoris for chronic pain after CABG surgery has not been described in the literature to date. Visceral nociception may play an important role in the development of chronic pain after surgery and should be taken into account in future studies.

Assessment of experimental pain from skin, muscle, and esophagus in patients with chronic pancreatitis

OBJECTIVES

Comprehensive experimental methods are of major relevance assessing pain mechanisms in patients with chronic pain. Chronic pancreatitis is thought to involve the sensory response in other visceral organs and somatic tissue. We, therefore, aimed at exploring the pain mechanisms in chronic pancreatitis (CP) using a multimodal and multitissue stimulation approach.

METHODS

Ten patients (mean age, 50 years) with CP and 13 healthy controls (mean age, 35 years) participated. None of the patients took analgesics regularly. All were exposed to multimodal (mechanical, thermal, and electrical) experimental pain in the skin, muscles, and esophagus.

RESULTS

The patients were hyposensitive to mechanical stimulations of the skin (P = 0.001), but there were no differences in the pain to thermal and electrical stimulations. In the muscle and esophagus, no differences in pain thresholds were found. The difference between single and repeated stimulations reflecting the degree of central sensitization was 17% in controls and 36% in patients (P = 0.001). The referred pain area to electrical stimulation was 30.1 cm2 in the patients and 7.7 cm2 for the controls (P = 0.02).

CONCLUSIONS

The findings suggest that the balance among central hyperexcitability, neuroplastic changes, and descending pain-modulating pathways may explain the pain response to experimental multimodal stimulations in CP. This will likely also reflect the clinical pain mechanisms and may have important impact in selection of treatment, where drugs with potential effects on these mechanisms should be used.

Gut sensations in diabetic autonomic neuropathy

The pathogenesis of gastrointestinal symptoms in diabetes mellitus is complex and multi-factorial. Diabetes induced peripheral and central changes in the neuronal pain matrix may be of importance and were explored using a new multi-modal and multi-segmental sensory testing approach. The sensitivity to mechanical, thermal and electrical stimulations in the oesophagus and duodenum was assessed in 12 type-1 diabetic patients with proven autonomic neuropathy and severe gastrointestinal symptoms using a comprehensive stimulation device aiming to activate different gut nerves and pain mechanisms. Twelve healthy subjects served as controls. The sensory response and the somatic referred pain areas were recorded. In the diabetic patients an overall hyposensitivity to the combination of all stimulations was found in the oesophagus and duodenum (P=0.02). Post hoc analysis revealed hyposensitivity to mechanical stimulations in the oesophagus (P=0.006) and duodenum (P=0.002), and to thermal (P<0.001) and electrical (P=0.005) stimulations in the oesophagus and duodenum combined. The hyposensitivity in the gut was accompanied by a 46% increase in the somatic referred pain areas (P=0.04) indicating central neuronal changes. The multi-modal and multi-segmental sensory testing approach indicates that the sensory nerves are widely affected in the GI tract and generalized to nerves in all layers of the gut. Changes in the neuronal pain matrix including interactions between peripheral and central pain mechanisms may be involved in the pathogenesis of gastrointestinal symptoms in long-standing diabetes. Future targets in the treatment of gastrointestinal symptoms in diabetic patients with autonomic neuropathy could be based on modulation of the central nervous system excitability.

Review article: acidity and volume of the refluxate in the genesis of gastro-oesophageal reflux disease symptoms

BACKGROUND

A number of mechanisms, other than acid reflux, may be responsible for the symptoms of gastro-oesophageal reflux disease.

AIM

To assess the importance of non-acid reflux mechanisms.

METHODS

This review is based on presentations and discussion at a workshop, where specialists in the field analysed data relating to these mechanisms.

RESULTS

Weakly acidic reflux, pH (4-7), detected with impedance-pHmetry is associated with regurgitation and atypical gastro-oesophageal reflux disease symptoms. It is not clear whether pepsin and trypsin can elicit symptoms, but bile can elicit heartburn. The magnitude of reflux-induced oesophageal distension can be determined by high frequency ultrasonography and is not reduced by proton pump inhibition, suggesting that persisting symptoms 'on' a proton pump inhibitor may still be due to oesophageal distension by non-acidic reflux. Exaggerated longitudinal muscle contraction can induce non-acid-related heartburn. Preliminary studies showed a positive effect of baclofen, surgery or endoscopic procedures to reduce weakly acidic reflux.

CONCLUSION

Mechanisms other than acid reflux are involved in some of the symptoms of gastro-oesophageal reflux disease. Controlled outcome studies are needed to clarify their roles and the indications for antireflux procedures in patients with persistent symptoms whilst 'on' a proton pump inhibitor.

Pain in chronic pancreatitis: the role of reorganization in the central nervous system

BACKGROUND & AIMS

In various chronic pain conditions cortical reorganization seems to play a role in the manifestations. The aim of this study was to investigate cortical reorganization in patients with pain caused by chronic pancreatitis.

METHODS

Twelve healthy subjects and 10 patients with chronic pancreatitis were included. The esophagus, stomach, and duodenum were stimulated electrically at the pain threshold using a nasal endoscope. The electroencephalogram was recorded from 64 surface electrodes and event-related brain potentials (EPs) were obtained.

RESULTS

As compared with healthy subjects, the patient group showed decreased latencies of the early EP components (N1, P < .001; P1, P = .02), which is thought to reflect the exogenous brain pain processing specifically. Source analysis showed that the dipolar activities corresponding to the early EPs were located consistently in the bilateral insula, in the anterior cingulate gyrus, and in the bilateral secondary somatosensory area. The bilateral insular dipoles were localized more medial in the patient group than in the healthy subjects after stimulation of all 3 gut segments (P < .01). There also were changes in the cingulate cortex where the neuronal source was more posterior in patients than in controls to stimulation of the esophagus (P < .05).

CONCLUSIONS

The findings indicate that pain in chronic pancreatitis leads to changes in cortical projections of the nociceptive system. Such findings also have been described in somatic pain disorders, among them neuropathic pain. Taken together with the clinical data this suggests a neuropathic component in pancreatic pain, which may influence the approach to treatment.

Differential effect of opioids in patients with chronic pancreatitis: an experimental pain study

OBJECTIVE

Animal experiments and clinical observations have indicated a different working profile of oxycodone compared to morphine, and it has previously been shown that oxycodone attenuates visceral pain better than morphine. The objective of this study was to test the effects of oxycodone and morphine on experimental pain in patients with pain caused by chronic pancreatitis.

MATERIAL AND METHODS

Ten patients took part in this blinded, cross-over study. The analgesic effects of morphine (30 mg, oral), oxycodone (15 mg, oral) and placebo were tested against multimodal (mechanical, thermal and electrical) experimental pain in the skin, muscles and oesophagus. Pain was assessed at baseline and 30, 60 and 90 min after drug administration.

RESULTS

In the skin and muscles, oxycodone was more effective than placebo and morphine on mechanically (skin: F=12.4, p<0.001, muscle: F=11.0, p<0.001) and thermally (skin: F=8.5, p<0.001) evoked pain. In oesophageal heat pain, the effect of morphine was equal to that of placebo, while oxycodone attenuated pain better than both morphine and placebo (F=9.5, p<0.001). Both morphine and oxycodone were more effective in attenuating mechanical pain in the oesophagus than placebo (F=8.6, p<0.001). After electrical stimulation no differences were seen between the opioids and placebo in any tissue studied.

CONCLUSIONS

Oxycodone was a stronger analgesic than morphine in several pain modalities in the skin, muscle and oesophagus.

Contribution of sensitivity, volume and tone to visceral perception in the upper gastrointestinal tract in man: emphasis on testing

Upper gastrointestinal (GI) symptoms occur frequently in the general population, making them among the most common indications responsible for patients consulting the healthcare system. Consequently, understanding and characterization of the upper GI symptoms is important for the diagnosis and assessment of organ dysfunction. In practice, assessment of clinical symptoms is difficult and it is still to a large extent unclear how sensitivity, volume and tone contribute to visceral perception in the upper GI tract. The goal of advanced research in upper GI symptoms is to obtain a better understanding of the mechanisms involved in transduction, transmission, and perception under normal and pathophysiological conditions. An important step towards this goal is understanding the information provided by and the inherent limitations of the currently available measuring techniques. This article focuses on the sensory testing of the oesophagus, and methods and concepts used to assess the relation between gastric volumes or tone and upper GI symptoms. It also summarizes the contributions of these techniques towards identifying the components responsible for the generation of upper GI symptoms.

Mechanisms of hypersensitivity in IBS and functional disorders

General introduction The concept of visceral hypersensitivity is accepted as being germane to several functional gastrointestinal disorders (FGIDs). The causes or risk factors associated with this hypersensitivity are unclear. This article addresses the proposed mechanisms leading to hypersensitivity: from genetic to inflammatory disorders, from central to peripheral alterations of function. However, in order to place visceral hypersensitivity in a more global perspective as an aetiological factor for FGIDs, it also provides a review of recent evidence regarding the role of other peripheral mechanisms (the intraluminal milieu), as also genetic factors in the pathophysiology of these disorders. The article has been divided into five independent sections. The first three sections summarize the evidence of visceral hypersensitivity as a biological marker of functional gut disorders, the peripheral and central mechanisms involved, and the role of inflammation on hypersensitivity. In opposition to visceral hypersensitivity as an isolated phenomenon in functional gut disorders, the last two sections focus on the importance of peripheral mechanisms, like motor disturbances, specifically those resulting on altered transport of intestinal gas, and alterations of the intraluminal milieu and genetics.