Gastric stimulation: influence of electrical parameters on gastric emptying in control and diabetic rats

BACKGROUND: The aim of this study was to test the effect of different pulse frequencies and amplitudes during gastric stimulation (GS) on gastric emptying in the rat. METHODS: GS was performed in 2 groups of laparotomized rats: healthy control animals, and rats with acute diabetes. The effects of four pulse frequencies (0.5, 1, 10, 20 Hz) and three pulse amplitudes (5, 20, 40 mA) were tested. The volumes emptied from the stomach after the oro-gastric instillation of a nutrient solution were compared to those obtained in animals without GS. Intragastric pH values were assessed under basal conditions and after GS. RESULTS: In both groups, GS increased emptied volumes compared to conditions without stimulation (p < 0.05) for pulse frequencies above 0.5 Hz. Increases in pulse frequencies accelerated gastric emptying (p < 0.01) with a plateau at around 10 Hz. The increase in pulse amplitudes resulted in larger emptied volumes only when the pulse frequency was 1 Hz (p < 0.04) while the opposite effect was observed at 20 Hz (p < 0.04). The most effective combinations to enhance gastric emptying compared to baseline conditions were 10 Hz with 5 or 20 mA. The overall effect of GS on gastric emptying compared to baseline conditions without stimulation, was greater in diabetic than in controls rats (p < 0.05). During stimulation, intragastric pH values were not different from basal conditions during fasting or after a meal in control and diabetic rats. CONCLUSIONS: Although both pulse frequency and amplitude should be considered during GS, frequency appears to be the most critical point. The possibility of increasing gastric emptying by electrical stimulation in diabetic rats suggests potential clinical applications for this method

Motility and absorption in the autotransplanted canine jejunoileum

Transplantation of the upper gut will soon become a clinical reality, yet little is known about the effects on enteric physiology. This study addresses relevant and complementary long-term objectives with respect to the physiology of the transplanted jejunoileum, particularly neural and humoral control of the upper gastrointestinal tract

Control mechanisms of mammalian pepsinogen secretion

The objective of this thesis was to delineate aspects of the control mechanisms of mammalian pepsinogen secretion. In order to accomplish this goal, a comprehensive study was undertaken which would establish an historical perspective of the subject, validate appropriate methodology and then seek to answer specific questions regarding the physiology and pathophysiology of pepsinogen secretion. More specifically, the objectives of this thesis were: 1. To review the historical background of the subject of pepsinogen in the context of the physiology of digestion with specific emphasis on the work and lives of the two major initial proponents of pepsinogen research (Schwann and Langley). 2. To provide a contemporary overview and evaluation of the current status of pepsinogen pathophysiology. 3. To modify and adapt experimental models necessary for the study of pepsinogen and acid secretion in mammalian gastric mucosa and cells. 4. To establish and validate a pepsinogen assay sensitive and reproducible enough for use in mammalian mucosa! and cellular secretory systems. 5. To delineate the fundamental (second messenger) control mechanisms (cyclic AMP and calcium calmodulin) of pepsinogen secretion in the isolated gastric gland model. 6. To define whether the process of pepsinogen secretion is independent of acid secretion in intact mucosa! preparations. 7. To identify different classes of pharmacological agents which would inhibit pepsinogen secretion and/or release. 8. To identify whether conditions present in critically ill patients liable to mucosal "stress ulceration" might influence the release of pepsinogen

Developments in the technique of sphincter of Oddi manometry and investigation of sphincter of Oddi dysfunction

MDThe hazardous technique of endoscopic manometry precludes the investigation of "normal volunteers" required to advance our knowledge of the physiology and pathophysiology of the sphincter of Oddi, a suitable animal model is required. Large and small animal models have been proposed, as yet no one model has been accepted as being representative of the human sphincter of Oddi. Furthermore no animal model of sphincter of Oddi dysfunction has been developed. In this thesis a porcine animal model of sphincter of Oddi function has been developed. The importance of selecting the appropriate anaesthetic agent, enflurane, has been proven. The effect of cholecystectomy on the porcine sphincter of Oddi is shown to have no overall significant effect on sphincter motility when compared to a sham laparotomy group. However, two of the seven pigs after cholecystectomy showed a paradoxical rise in sphincter basal pressure after cholecystokinin infusion, these animal may represent porcine sphincter of Oddi dysfunction. Although substance P is found throughout the intestinal tract including the sphincter of Oddi of man and pig its action was hitherto unknown. In this thesis exogenous substance P was shown to stimulate the sphincter of Oddi in vivo. In this thesis the first development in sphincter of Oddi manometry catheter design in nearly twenty years is presented. A superior nine lumen catheter has been evaluated in porcine model and subsequently used to assess sphincter of Oddi asymmetry in man. Two retrospective studies are reported in this thesis; an audit of the largest U. K. series, and a study assessing the relationship of sphincter of Oddi motility and duodenal activity. Tachyoddia dissociated from the duodenal migrating motor complex was associated with a raised sphincter of Oddi basal pressure and may be a part of sphincter of Oddi dysfunction

Optical mapping and optogenetics in cardiac electrophysiology research and therapy:a state-of-the-art review

State-of-the-art innovations in optical cardiac electrophysiology are significantly enhancing cardiac research. A potential leap into patient care is now on the horizon. Optical mapping, using fluorescent probes and high-speed cameras, offers detailed insights into cardiac activity and arrhythmias by analysing electrical signals, calcium dynamics, and metabolism. Optogenetics utilizes light-sensitive ion channels and pumps to realize contactless, cell-selective cardiac actuation for modelling arrhythmia, restoring sinus rhythm, and probing complex cell–cell interactions. The merging of optogenetics and optical mapping techniques for ‘all-optical’ electrophysiology marks a significant step forward. This combination allows for the contactless actuation and sensing of cardiac electrophysiology, offering unprecedented spatial–temporal resolution and control. Recent studies have performed all-optical imaging ex vivo and achieved reliable optogenetic pacing in vivo, narrowing the gap for clinical use. Progress in optical electrophysiology continues at pace. Advances in motion tracking methods are removing the necessity of motion uncoupling, a key limitation of optical mapping. Innovations in optoelectronics, including miniaturized, biocompatible illumination and circuitry, are enabling the creation of implantable cardiac pacemakers and defibrillators with optoelectrical closed-loop systems. Computational modelling and machine learning are emerging as pivotal tools in enhancing optical techniques, offering new avenues for analysing complex data and optimizing therapeutic strategies. However, key challenges remain including opsin delivery, real-time data processing, longevity, and chronic effects of optoelectronic devices. This review provides a comprehensive overview of recent advances in optical mapping and optogenetics and outlines the promising future of optics in reshaping cardiac electrophysiology and therapeutic strategies

Effects of hyperglycaemia on small intestinal and anorectal motor function in humans

This thesis presents studies which relate to the effects of changes in the blood glucose concentration on the organisation and control of motility in the small intestine and anorectum. The motor mechanisms by which acute hyperglycaemia slows small intestinal transit in healthy humans were investigated. Hyperglycaemia (blood glucose concentration -15mmol/l) stimulated phase III activity, but there was overall suppression of small intestinal pressure waves' when compared to euglycaemia- These results indicate that marked hyperglycaemia has major effects on small intestinal motility in normal subjects. The observed suppression of small intestinal motility provides a possible mechanism for the slowing of small intestinal transit during hyperglycaemia. Among the candidate mechanisms mediating the effects of hyperglycaemia on small intestinal motility is modification of tonic inhibition mediated by enteric nerves containing nitric oxide, The effects of a specific inhibitor of nitric oxide (NO) synthase, NG-monomethyl-L-arginine (L-NMMA), on small intestinal motor activity, were evaluated in healthy human volunteers. Administration of L-NMMA was associated with stimulation of small intestinal phase III activity and a reduction in the duration of phase I activity. These results indicate that NO mechanisms are involved in the initiation of small intestinal phase III activity- Disordered defaecation occurs commonly in patients with diabetes mellitus and is associated with heterogenous anorectal motor and sensory dysfunctions' These abnormalities may potentially be due to hyperglycaemia, rather than irreversible neural dysfunction. In healthy humans, measurements of anorectal motility and sensation were performed, during euglycaemia (4mmol/l) and hyperglycaemia (8mmol/l and 12mmol/l). At a blood glucose concentration of 12mmol/l the number of spontaneous internal anal sphincter relaxations was greater and the strength of the external anal sphincter less when compared to euglycaemia. The threshold for perception of rectal balloon distension was lower at a blood glucose of 12mmol/l when compared to 4mmol/l. These observations demonstrate that acute changes in the blood glucose concentration affect both the smooth and striated muscle of the anal sphincter, as well as rectal sensation, and suggest that hyperglycaemia may contribute to incontinence in patients with diabetes mellitus. Autonomic nervous system dysfunction occurs frequently in patients with diabetes mellitus and is associated with disordered gastrointestinal motor function. The possibility that the blood glucose concentration may affect cardiovascular autonomic (parasympathetic and sympathetic) function was evaluated in healthy human volunteers by performing paired studies during euglycaemia and hyperglycaemia (∼15mmol/l). Hyperglycaemia was associated with changes in cardiovascular parasympathetic function. This observation indicates that acute changes in the blood glucose concentration affect cardiovascular autonomic function, which may be important in mediating the effects of hyperglycaemia on gastrointestinal motor function. The studies reported in this thesis provide new insights into the control of gastrointestinal motility in healthy humans and effects of changes in the blood glucose concentration. The latter observations are likely to be relevant to an understanding of gastrointestinal motor function in patients with diabetes mellitus.Thesis (M.Med.Sc.)-- University of Adelaide, Dept. of Medicine, 199

Assessment of chronic pain in companion animals : development and concurrent validation of neurophysiological methods

La douleur est une expérience complexe impliquant des composantes sensorielles et de perception (émotionnelle, affective, cognitive). Elle est associée au stress, de la souffrance et une dégradation de la qualité de la vie. Les affections douloureuses chroniques telles que l'arthrose et le cancer des os touchent les chats et les chiens. La douleur dans ces conditions implique de nombreux mécanismes affectant les systèmes nerveux périphérique et central, qui génèrent et entretiennent une douleur pathologique. Les tests sensoriels quantitatifs (TSQ) sont des outils pour quantifier la composante sensorielle de la douleur, qui peuvent aussi être utilisés pour éluder les mécanismes de la douleur impliquée. Les travaux initiaux sur les chats et les chiens souffrant d'arthrose ont permis de développer et de valider certaines méthodes de TSQ; cependant, quelques questions sont restées sans réponse chez les chats souffrant de l'arthrose, et cette méthodologie n'a pas été encore explorée chez les chiens atteints d’ostéosarcome. Nos hypothèses de recherche étaient: 1) les chats arthrosiques sont affectés par des modifications neurophysiologiques caractéristiques de la sensibilisation centrale, pouvant être détectées par les TSQ et répondant à l'administration d'analgésiques à action centrale; et 2) l’ostéosarcome provoque une sensibilisation périphérique et centrale avec des mécanismes descendants d’inhibition de la douleur déficients chez le chien. Nos objectifs étaient : 1) chez les chats souffrant d'arthrose, de fournir des évidences sur la thérapie basée sur les mécanismes neurophysiologiques à l'aide de TSQ; et 2) de tester la capacité d'un protocole TSQ à démontrer la sensibilisation périphérique et centrale chez les chiens atteints de cancer des os, y compris un test de modulation de la douleur conditionnée, et de tester l’efficacité d’un protocole d’analgésique palliatif par paliers chez ces patients. En utilisant les TSQ statiques et dynamiques chez les chats arthrosiques, nous avons démontré que les analgésiques à action centrale tels que le tramadol peuvent renverser la sensibilisation centrale mesurée par la sommation temporelle de la douleur. Cet effet n’a pas été observé après l’administration d’analgésique à action périphérique tel que les antiinflammatoires non stéroïdiens comme le meloxicam. Ces résultats 3 soulignent l’importance d’une approche de traitement fondée sur les mécanismes de la douleur chronique. Le protocole TSQ développé pour les chiens a révélé que ceux atteints de cancer des os manifestaient de l'hyperalgésie primaire et secondaire et de l’allodynie dynamique au brossage par rapport aux chiens en bonne santé. Un test de modulation de la douleur conditionnée pouvant être facilement appliqué a été mis au point et a démontré la capacité de différencier les chiens sains des chiens cancéreux. En utilisant cette méthodologie, il s’est avéré que cette dernière population démontrait un système descendant d’inhibition de la douleur déficient. Ces études ont fourni des preuves des similitudes dans le profil sensoriel entre les malades humains et les animaux de compagnie affectés par l'arthrose, ainsi que les ostéosarcomiques. Les TSQ sont utiles dans la recherche vétérinaire sur la douleur et doivent être accompagnés des normes les plus strictes en matière de soins des animaux et de conception, de conduite et de compte-rendu des études.Pain is a complex experience involving sensory and perceptual components. It causes stress, suffering and decreased quality of life. Chronic painful conditions such as osteoarthritis (OA) and bone cancer affect cats and dogs. Pain in these conditions results from numerous mechanisms affecting the peripheral and central nervous systems which generate and maintain pathological pain in affected individuals. Quantitative sensory testing (QST) are means to quantify the sensory component of pain. In combination with observed analgesic efficacy, they can be used to study mechanisms of pain. Initial work on cats and dogs with OA has helped to develop and validate some QST methods; however, questions remained unanswered in cats with OA, and this methodology was not yet explored in dogs with bone cancer. Our main hypotheses were: 1) osteoarthritic cats are affected by neurophysiological changes characteristic of central sensitization which can be detected by QST and the concomitant administration of centrally-acting analgesics; and 2) bone cancer in dogs causes peripheral and central sensitization with deficient descending modulating mechanisms. Our main objectives were: 1) to provide evidence of mechanism-based therapy in cats with OA using QST; and 2) to test the ability of a QST protocol to provide evidence of peripheral and central sensitization in dogs with bone cancer including the development and validation of a conditioned pain modulation test, and to test the efficacy of a step-wise palliative analgesic protocol in these patients. Using static and dynamic QST in osteoarthritic cats, we demonstrated that centrally-acting analgesics such as tramadol can reverse central sensitization as measured by facilitated temporal summation of pain, while the same is not observed when a peripherally-acting analgesic such as non-steroidal anti-inflammatory drug, meloxicam, is administered. These findings highlight the importance of mechanism-based approach for the treatment of chronic pain. The QST protocol developed for use in dogs revealed that dogs with bone cancer are affected by primary and secondary hyperalgesia and brush allodynia when compared 5 with healthy dogs. A conditioned pain modulation test which can be easily applied into clinical practice was developed and demonstrated ability to differentiate between healthy and cancerous dogs. Using this methodology, the latter population was found to be affected by deficient descending modulating systems. These studies provided evidence of the similarities in sensory profile between people and companion animals affected by OA- and bone cancer-related pain. The use of QST is valuable in veterinary pain research and should be accompanied by the highest standards of animal care and study design, conduct and reporting

Peripheral and central mechanisms in acid induced visceral pain hypersensitivity in the human oesophagus

PhDIntroduction: Gastro-oesophageal reflux disease (GORD) affects 40% of Western populations. Many symptoms persist despite the resolution of inflammation or acid exposure. In these patients, visceral pain hypersensitivity (VPH), modulated peripherally and centrally, is believed to be important. Study 1: Full thickness human oesophageal samples were collected from 10 patients undergoing oesophagectomy. Using immunohistochemistry, the samples were stained with PGP 9.5, synapthophysin, TRPV1, TRPV4 and ASIC3. Within healthy areas of the human oesophagus, immunoreactive nerve fibres and ganglia were identified in the sub-epithelium and myenteric plexus. Within the epithelium, nerve endings were absent; however, ASIC3 was reliably identified in epitheliocytes. Study 2: Oesophageal biopsy samples from 36 individuals were collected during upper GI endoscopy; erosive oesophagitis, non-erosive reflux disease and controls. Symptoms were profiled using symptom severity scores, adapted from a validated questionnaire. Oesophageal mucosal biopsies were taken 3-5 cm above the lower oesophageal sphincter. Specific features of oesophageal mucosal epithelial ASIC3 were identified by immunohistochemistry, which were associated positively with an increase in symptom severity. Study 3: Oesophageal VPH can be induced in healthy volunteers using an established model of acid infusion. In total, 85 retrospective infusions from 57 volunteers were studied, and VPH was present in 70%. The model was shown to be safe and reproducible, but reliability of the model for drug studies was only valid provided control measures were observed. Study 4: Pregabalin is a centrally acting calcium channel blocker currently used for somatic neuropathic pain and partial seizures. Using the model described in study 3, a prospective, double-blinded, cross-over, placebo-controlled study in 15 healthy volunteers was performed. After an initial screening visit, the volunteers were randomised to either pregabalin or placebo. Pregabalin prevented or attenuated VPH at 30 and 90 minutes after acid sensitisation. Conclusion: The evidence for central sensitisation was further consolidated with the pregabalin study and peripheral sensitisation by the ASIC3 study. The evidence is important in the detection of predominant mechanisms underlying the symptoms of patients with GORD for both cohort development and targeted treatment

Oesophageal hypersensitivity in patients with gastro-oesophageal reflux symptoms: Prevalence and novel treatments

Background Gastro oesophageal reflux disease (GORD) is a leading cause of morbidity and economic importance worldwide. It is currently defined by the Montreal definition as a condition, which develops when the reflux of gastric content causes troublesome symptoms or complications. This definition based on symptoms is all encompassing, and further classification is made based on macroscopic mucosal injury as seen on gastroscopy, increased distal oesophageal acid and non acid exposure, based on 24 hour pH and impedance pH testing, and reflux symptom association. Thus, GORD may be sub classified into the following conditions – erosive reflux disease (ERD), non erosive reflux disease (NERD), reflux hypersensitivity (RH), functional heartburn (FH) and functional chest pain (FCP). Treatment of GORD is with acid suppression therapy, anti reflux therapy and pain modulation. The pathophysiology of GORD is thought to occur in a spectrum, with varying contributions from direct mucosal injury to peripheral sensitization and central sensitization. Further efforts to phenotype GORD populations, investigate mechanisms of symptom evolution and treatments are driven by a significant proportion of patients who are refractory to currently available therapies. Aims The aim of this body of work was to phenotype patients with RH, the least studied subtype of GORD, to investigate the effect of ONO 8539, a novel antagonist to the Prostaglandin E 1 receptor thought to be involved in pain perception on acid induced oesophageal pain hypersensitivity in patients with NERD, to investigate the effect of transcutaneous vagal nerve stimulation (tVNS) on an oesophageal pain model in healthy volunteers, and to investigate the effect of slow deep breathing on oesophageal pain hypersensitivity in patients with NERD. Methods I investigated the above aims in a retrospective cohort study on patients referred to the gastro intestinal physiology unit of the Royal London Hospital for investigation of typical GORD symptoms, a double blind placebo controlled two period cross over study in patients with NERD, a single blind sham controlled two period cross over study in healthy volunteers and single blind sham controlled parallel study in patients with NERD respectively. The first study was done as a service evaluation exercise and the latter three studies had ethical approval from the National Research and Ethics Service (NRES), QMUL Ethics and NRES respectively. Results I demonstrated that phenotypic characteristics in patients with RH were distinct from NERD and FH/FCP. This was the largest cohort of RH patients evaluated, and this body of work will contribute to further research on mechanisms, pathophysiology and treatments in RH. In my second study, I was not able to demonstrate an anti nociceptive effect of ONO 8539 versus placebo on oesophageal pain hypersensitivity in patients with NERD. In my third study, I was able to demonstrate an increase in anti nociceptive parasympathetic tone, and an increase in pain tolerance threshold with tVNS compared to sham stimulation in an oesophageal pain hypersensitivity model in healthy volunteers. In my final study, I was able to demonstrate an increase in parasympathetic tone, but no improvement in lag time to pain perception with a slow deep breathing protocol compared to a sham breathing protocol in a Modified Bernstein test model of distal oesophageal acid infusion in patients with NERD. Conclusions This body of work improves upon current knowledge of the phenotypic characteristics of RH, adding further weight to the definition of RH as a distinct condition. tVNS and deep slow breathing were shown to increase parasympathetic tone in healthy volunteers and patients with NERD respectively. The anti nociceptive effect of raising parasympathetic tone was only demonstrated in the healthy volunteer model of oesophageal pain hypersensitivity. The performance of the MBT model used in the two patient studies was not as reliable as the healthy volunteer model, and a new oesophageal pain hypersensitivity model for patients with NERD was propose

CARDIAC RHYTHM DURING MECHANICAL VENTILATION AND WEANING FROM VENTILATION

The transition from mechanical ventilation (MV) to spontaneous ventilation during weaning is associated with hemodynamic alterations and autonomic nervous system (ANS) alterations (reflected by heart rate variability [HRV]). Although cardiac dysrhythmias are an important manifestation of hemodynamic alterations, development of dysrhythmias during MV and weaning and subsequent impact on length of MV has received little attention. The purposes of this dissertation were to 1) evaluate the relationship of heart rate variability (HRV) during weaning to the development of cardiac dysrhythmias and 2) determine the relationship of cardiac dysrhythmias to length of MV. A convenience sample of 35 patients (66.7% men; mean age 53.3 years) who required MV was enrolled in this study. Continuous 3-lead electrocardiographic data were collected for 24 hours at baseline during MV and for the first 2 hours during the initial weaning trial. HRV was evaluated using spectral power analysis. Twenty- seven patients out of 30 were exposed to a combination of pressure support (8-15 cm H2O) and continuous positive airway pressure 5 cm H2O during weaning trial. Three patients self- extubated and received supplemental oxygen through either a partial rebreathing or non-rebreathing mask. Low frequency (LF) power HRV decreased, while high frequency (HF) and very low frequency (VLF) power HRV did not change during weaning. Multiple regression analyses showed that LF and HF HRV were significant predictors of occurrence of ventricular and supraventricular ectopic beats during weaning, while VLF power predicted occurrence of ventricular ectopic beats only. The mean of occurrence of supraventricular ectopic beats per hour during weaning was double the mean at baseline, while the mean of ventricular ectopic beats per hour did not change. Mean number of supraventricular ectopic beats per hour during weaning was a significant predictor of length of MV. This dissertation has fulfilled an important gap in the evidence base for cardiac dysrhythmias during weaning from MV. Cardiac dysrhythmias and HRV alterations should be systemically evaluated during MV and weaning trials in order to decrease length of MV