The use of fibre optic sensing technology with intraluminal impedance catheter for functional gastrointestinal motility disorders

Author accepted manuscript made available with permission from Engineers Australia.We present a composite impedance fibre optic manometry catheter for monitoring functional gastrointestinal disorders (FGID). The catheter uses a dual lumen silicone extrusion to separate each technology and has been validated in ex-vivo animal models

Identification of a rhythmic firing pattern in the enteric nervous system that generates rhythmic electrical activity in smooth muscle

The enteric nervous system (ENS) contains millions of neurons essential for organization of motor behavior of the intestine. It is well established that the large intestine requires ENS activity to drive propulsive motor behaviors. However, the firing pattern of the ENS underlying propagating neurogenic contractions of the large intestine remains unknown. To identify this, we used high-resolution neuronal imaging with electrophysiology from neighboring smooth muscle. Myoelectric activity underlying propagating neurogenic contractions along murine large intestine [also referred to as colonic migrating motor complexes, (CMMCs)] consisted of prolonged bursts of rhythmic depolarizations at a frequency of ∼2 Hz. Temporal coordination of this activity in the smooth muscle over large spatial fields (∼7 mm, longitudinally) was dependent on the ENS. During quiescent periods between neurogenic contractions, recordings from large populations of enteric neurons, in mice of either sex, revealed ongoing activity. The onset of neurogenic contractions was characterized by the emergence of temporally synchronized activity across large populations of excitatory and inhibitory neurons. This neuronal firing pattern was rhythmic and temporally synchronized across large numbers of ganglia at ∼2 Hz. ENS activation preceded smooth muscle depolarization, indicating rhythmic depolarizations in smooth muscle were controlled by firing of enteric neurons. The cyclical emergence of temporally coordinated firing of large populations of enteric neurons represents a unique neural motor pattern outside the CNS. This is the first direct observation of rhythmic firing in the ENS underlying rhythmic electrical depolarizations in smooth muscle. The pattern of neuronal activity we identified underlies the generation of CMMCs

Predicting the Activation States of the Muscles Governing Upper Esophageal Sphincter Relaxation and Opening

Copyright © 2016 the American Physiological SocietyThe swallowing muscles that influence upper esophageal sphincter (UES) opening are centrally controlled and modulated by sensory information. Activation and deactivation of neural inputs to these muscles, including the intrinsic cricopharyngeus (CP) and extrinsic submental (SM) muscles, results in their mechanical activation or deactivation, which changes the diameter of the lumen, alters the intraluminal pressure, and ultimately reduces or promotes flow of content. By measuring the changes in diameter, using intraluminal impedance, and the concurrent changes in intraluminal pressure, it is possible to determine when the muscles are passively or actively relaxing or contracting. From these “mechanical states” of the muscle, the neural inputs driving the specific motor behaviors of the UES can be inferred. In this study we compared predictions of UES mechanical states directly with the activity measured by electromyography (EMG). In eight subjects, pharyngeal pressure and impedance were recorded in parallel with CP- and SM-EMG activity. UES pressure and impedance swallow profiles correlated with the CP-EMG and SM-EMG recordings, respectively. Eight UES muscle states were determined by using the gradient of pressure and impedance with respect to time. Guided by the level and gradient change of EMG activity, mechanical states successfully predicted the activity of the CP muscle and SM muscle independently. Mechanical state predictions revealed patterns consistent with the known neural inputs activating the different muscles during swallowing. Derivation of “activation state” maps may allow better physiological and pathophysiological interpretations of UES function

Activation of intestinal spinal afferent endings by changes in intra‐mesenteric arterial pressure

Author manuscript made available following 12 month embargo from date of publication (25 June 2015) in accordance with publisher copyright policy.KEY POINTS: A major class of mechano-nociceptors to the intestine have mechanotransduction sites on extramural and intramural arteries and arterioles ('vascular afferents'). These sensory neurons can be activated by compression or axial stretch of vessels. Using isolated preparations we showed that increasing intra-arterial pressure, within the physiological range, activated mechano-nociceptors on vessels in intact mesenteric arcades, but not in isolated arteries. This suggests that distortion of the branching vascular tree is the mechanical adequate stimulus for these sensory neurons, rather than simple distension. The same rises in pressure also activated intestinal peristalsis in a partially capsaicin-sensitive manner indicating that pressure-sensitive vascular afferents influence enteric circuits. The results identify the mechanical adequate stimulus for a major class of mechano-nociceptors with endings on blood vessels supplying the gut wall; these afferents have similar endings to ones supplying other viscera, striated muscle and dural vessels. ABSTRACT: Spinal sensory neurons innervate many large blood vessels throughout the body. Their activation causes the hallmarks of neurogenic inflammation: vasodilatation through the release of the neuropeptide calcitonin gene-related peptide and plasma extravasation via tachykinins. The same vasodilator afferent neurons show mechanical sensitivity, responding to crushing, compression or axial stretch of blood vessels - responses which activate pain pathways and which can be modified by cell damage and inflammation. In the present study, we tested whether spinal afferent axons ending on branching mesenteric arteries ('vascular afferents') are sensitive to increased intravascular pressure. From a holding pressure of 5 mmHg, distension to 20, 40, 60 or 80 mmHg caused graded, slowly adapting increases in firing of vascular afferents. Many of the same afferent units showed responses to axial stretch, which summed with responses evoked by raised pressure. Many vascular afferents were also sensitive to raised temperature, capsaicin and/or local compression with von Frey hairs. However, responses to raised pressure in single, isolated vessels were negligible, suggesting that the adequate stimulus is distortion of the arterial arcade rather than distension per se. Increasing arterial pressure often triggered peristaltic contractions in the neighbouring segment of intestine, an effect that was mimicked by acute exposure to capsaicin (1 μm) and which was reduced after desensitisation to capsaicin. These results indicate that sensory fibres with perivascular endings are sensitive to pressure-induced distortion of branched arteries, in addition to compression and axial stretch, and that they contribute functional inputs to enteric motor circuits

Characterization of Esophageal Physiology Using Mechanical State Analysis

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution and reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.The esophagus functions to transport swallowed fluids and food from the pharynx to the stomach. The esophageal muscles governing bolus transport comprise circular striated muscle of the proximal esophagus and circular smooth muscle of the distal esophagus. Longitudinal smooth muscle contraction provides a mechanical advantage to bolus transit during circular smooth muscle contraction. Esophageal striated muscle is directly controlled by neural circuits originating in the central nervous system, resulting in coordinated contractions. In contrast, the esophageal smooth muscle is controlled by enteric circuits modulated by extrinsic central neural connections resulting in neural relaxation and contraction. The esophageal muscles are modulated by sensory information arising from within the lumen. Contraction or relaxation, which changes the diameter of the lumen, alters the intraluminal pressure and ultimately inhibits or promotes flow of content. This relationship that exists between the changes in diameter and concurrent changes in intraluminal pressure has been used previously to identify the "mechanical states" of the circular muscle; that is when the muscles are passively or actively, relaxing or contracting. Detecting these changes in the mechanical state of the muscle has been difficult and as the current interpretation of esophageal motility is based largely upon pressure measurement (manometry), subtle changes in the muscle function during peristalsis can be missed. We hypothesized that quantification of mechanical states of the esophageal circular muscles and the pressure-diameter properties that define them, would allow objective characterization of the mechanisms that govern esophageal peristalsis. To achieve this we analyzed barium swallows captured by simultaneous videofluoroscopy and pressure with impedance recording. From these data we demonstrated that intraluminal impedance measurements could be used to determine changes in the internal diameter of the lumen comparable with measurements from videofluoroscopy. Our data indicated that identification of mechanical state of esophageal muscle was simple to apply and revealed patterns consistent with the known neural inputs activating the different muscles during swallowing

Manometric demonstration of duodenal/jejunal motor function consistent with the duodenal brake mechanism

© 2020 John Wiley & Sons Ltd Background: High-resolution manometric studies below the stomach are rare due to technical limitations of traditional manometry catheters. Consequently, specific motor patterns and their impact on gastric and small bowel function are not well understood. High-resolution manometry was used to record fed-state motor patterns in the antro-jejunal segment and relate these to fasting motor function. Methods: Antro-jejunal pressures were monitored in 15 healthy females using fiber-optic manometry (72 sensors at 1cm intervals) before and after a high-nutrient drink. Key Results: Postprandial motility showed a previously unreported transition point 18.8cm (range 13-28cm) beyond the antro-pyloric junction. Distal to the transition, a zone of non-propagating, repetitive pressure events (11.5±0.5cpm) were dominant in the fed state. We have named this activity, the duodeno-jejunal complex (DJC). Continuous DJC activity predominated, but nine subjects also exhibited intermittent clusters of DJC activity, 7.4±4.9/h, lasting 1.4±0.55minutes, and 3.8±1.2minutes apart. DJC activity was less prevalent during fasting (3.6±3.3/h; P=.04). 78% of fed and fasting state propagating antro-duodenal pressure events terminated proximally or at the transition point and were closely associated with DJC clusters. Conclusions and Inferences: High-resolution duodeno-jejunal manometry revealed a previously unrecognized transition point and associated motor pattern extending into the jejunum, consistent with the duodenal brake previously identified fluoroscopically. Timing suggests DJC activity is driven by chyme stimulating duodenal mucosal chemosensors. These findings indicate that the duodenum and proximal jejunum consists of two major functional motor regions

Discriminating movements of liquid and gas in the rabbit colon with impedance manometry

This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving'. © 2017 John Wiley & Sons, Inc. All rights reserved. This author accepted manuscript is made available following 12 month embargo from date of publication (Dec 2017) in accordance with the publisher’s archiving policyBackground High‐resolution impedance manometry is a technique that is well established in esophageal motility studies for relating motor patterns to bolus flow. The use of this technique in the colon has not been established. Methods In isolated segments of rabbit proximal colon, we recorded motor patterns and the movement of liquid or gas boluses with a high‐resolution impedance manometry catheter. These detected movements were compared to video recorded changes in gut diameter. Using the characteristic shapes of the admittance (inverse of impedance) and pressure signals associated with gas or liquid flow we developed a computational algorithm for the automated detection of these events. Key Results Propagating contractions detected by video were also recorded by manometry and impedance. Neither pressure nor admittance signals alone could distinguish between liquid and gas transit, however the precise relationship between admittance and pressure signals during bolus flow could. Training our computational algorithm upon these characteristic shapes yielded a detection accuracy of 87.7% when compared to gas or liquid bolus events detected by manual analysis. Conclusions & inferences Characterizing the relationship between both admittance and pressure recorded with high‐resolution impedance manometry can not only help in detecting luminal transit in real time, but also distinguishes between liquid and gaseous content. This technique holds promise for determining the propulsive nature of human colonic motor patterns

Spiking neural networks for robot locomotion control

Research Doctorate - Doctor of Philosophy (PhD)Spiking neural networks (SNNs) are computational models of biological neurons and the synapses that connect them. They are chosen for their characteristic property of information exchange via the timing of events called spikes, in contrast to earlier-developed models such as sigmoid neural networks which have no explicit timing component. SNNs are often applied to tasks in artificial intelligence by using existing models of biological neural networks that were used in neuroscience in the past, and that are detailed enough to contain the timing-property. Neurons can be modelled at many levels of detail, and often a neuron model is chosen with scant consideration of the most appropriate level of detail for the given task. This thesis presents a novel spiking neuron model developed to retain the timing-property, including proposed favourable characteristics for application to artificial intelligence tasks, while removing the unnecessary detail for achieving those characteristics that current SNN models contain. The result is a computationally powerful neuron model with an analytically solvable spiking-time calculation. While SNNs have been applied to various tasks in artificial intelligence, including robot control, the types of control problems faced have been primarily of a stable nature. This thesis focuses on unstable control problems, that is, problems where the dynamics governing the motion of the robot under control are such that small disturbances, inaccuracies, or pauses in control can lead to a rapid acceleration away from a desired state. Concretely, simulation experiments are conducted (i) on a planar underactuated inverted double-pendulum called the Acrobot for the swing-up and balance task which, combined with linear quadratic regulation (LQR) control for balance, was able to achieve the task, and (ii) to a 1.5m tall biped for the distance locomotion task, where it walked 16m without collapsing. In the interests of automatically developing bipedal dynamic walking behaviour, via the stochastic tuning of spiking neural network parameters, a new spherical-foot model is presented that exhibits favourable dynamical properties. Existing physical biped robot morphologies can be clustered into three main groups based on their feet and ankle configurations. One group contains large flat feet with actuated ankles, and is most often seen in environments and tasks requiring moving in both sagittal (forward-backward) and coronal (left-right) planes, such as robotic soccer. The second group contains point feet with no ankles, and finds success in fast locomotion such as running, where coronal motion is limited. The third group consists of passive-dynamic walkers, that contain rounded feet and are able to walk in the sagittal plane along a slight decline without any control input. In this thesis a new biped feet-angle configuration is proposed which is a marriage of these groups, with relatively small (second group) rounded feet capable of smooth continuous ground contact (third group), and actuated ankles (first group) that aid in standing balance control. An analysis of this novel type of foot configuration is presented here for the planar case, and a controller for standing balance is included

Balance Control of a Simulated Inverted Pendulum on a Circular Base

Balance control of a simulated inverted pendulum attached to a circular base is presented. This type of platform is analogous to a biped robot with circular soled feet in single support phase. Circular feet have been shown to be more energy efficient than flat feet during walking, and in this paper we present another advantage, where circular feet do not suffer from ground separation when applying a large torque at the ankle.