Imaging and modelling of digestion in the stomach and the duodenum

Navigating the human gastrointestinal tract for oral drug delivery: Uncharted waters and new frontiers

Many concepts of oral drug delivery are based on our comprehension of human gastrointestinal physiology. Unfortunately, we tend to oversimplify the complex interplay between the various physiological factors in the human gut and, in particular, the dynamics of these transit conditions to which oral dosage forms are exposed. Recent advances in spatial and temporal resolution of medical instrumentation as well as improved access to these technologies have facilitated clinical trials to characterize the dynamic processes within the human gastrointestinal tract. These studies have shown that highly relevant parameters such as fluid volumes, dosage form movement, and pH values in the lumen of the upper GI tract are very dynamic. As a result of these new insights into the human gastrointestinal environment, some common concepts and ideas of oral drug delivery are no longer valid and have to be reviewed in order to ensure efficacy and safety of oral drug therapy.

Inhomogeneities in the propagation of the slow wave in the stomach

The propagation of the slow wave in the stomach and its role in inducing sweeping peristaltic contractions toward the pylorus, essential for a proper digestion and emptying, have been studied for many years. Irregularities in the timing or in the pattern of propagation of the slow wave have been known to induce various gastric malfunctions and, recently, several types of gastric dysrhythmias have been described which could lead to gastric contraction abnormalities. In this study, Du et al. have analyzed the disturbances caused by a simple transmural incision in a human stomach, performed to obtain a biopsy of the muscle, on the propagation pattern of the slow wave. In addition, they show that such an incision may by itself also induce new types of gastric dysrhythmias. These results are important in demonstrating that the function of the stomach can easily be disturbed by such procedures. This mini-review describes several ways in which inhomogeneities in propagation may affect the conduction pattern of the slow wave, including the genesis of several dysrhythmias, and what is currently known about their impact on gastric contraction and digestion.

Geometric Mixing, Peristalsis, and the Geometric Phase of the Stomach

Mixing fluid in a container at low Reynolds number— in an inertialess environment—is not a trivial task. Reciprocating motions merely lead to cycles of mixing and unmixing, so continuous rotation, as used in many technological applications, would appear to be necessary. However, there is another solution: movement of the walls in a cyclical fashion to introduce a geometric phase. We show using journal-bearing flow as a model that such geometric mixing is a general tool for using deformable boundaries that return to the same position to mix fluid at low Reynolds number. We then simulate a biological example: we show that mixing in the stomach functions because of the “belly phase,” peristaltic movement of the walls in a cyclical fashion introduces a geometric phase that avoids unmixing.

Self-assembled structures formed during lipid digestion: characterization and implications for oral lipid-based drug delivery systems

There is increasing interest in the use of lipid-based formulations for the delivery of poorly water-soluble drugs. After ingestion of the formulation, exposure to the gastrointestinal environment results in dispersion and digestion processes, leading to the production of amphiphilic digestion products that form self-assembled structures in the aqueous environment of the intestine. These structures are crucial for the maintenance of drug in a solubilized state prior to absorption. This review describes the structural techniques used to study such systems, the structures formed in assembled 'equilibrium' compositions where components are combined in expected ratios representative of the endpoint of digestion, structures formed using dynamic in vitro 'non-equilibrium' digestion models where the composition and hence structures present change over time and observations from ex vivo aspirated samples. Possible future directions towards an improved understanding of the structural aspects of lipid digestion are proposed.

Imaging gastric structuring of lipid emulsions and its effect on gastrointestinal function: a randomized trial in healthy subjects

BACKGROUND

Efficient fat digestion requires fat processing within the stomach and fat sensing in the intestine. Both processes also control gastric emptying and gastrointestinal secretions.

OBJECTIVE

We aimed to visualize the influence of the intragastric stability of fat emulsions on their dynamics of gastric processing and structuring and to assess the effect this has on gastrointestinal motor and secretory functions.

DESIGN

Eighteen healthy subjects with normal body mass index (BMI) were studied on 4 separate occasions in a double-blind, randomized, crossover design. Magnetic resonance imaging (MRI) data of the gastrointestinal tract and blood triglycerides were recorded before and for 240 min after the consumption of the following 4 different fat emulsions: lipid emulsion 1 (LE1; acid stable, 0.33 μm), lipid emulsion 2 (LE2; acid stable, 52 μm), lipid emulsion 3 (LE3; acid unstable, solid fat, 0.32 μm), and lipid emulsion 4 (LE4; acid unstable, liquid fat, 0.38 μm).

RESULTS

Intragastric emulsion instability was associated with a change in gastric emptying. Acid-unstable emulsions exhibited biphasic and faster emptying profiles than did the 2 acid-stable emulsions (P ≤ 0.0001). When combined with solid fat (LE3), different dynamics of postprandial gallbladder volume were induced (P ≤ 0.001). For acid-stable emulsions, a reduction of droplet size by 2 orders of magnitude [LE1 (0.33 μm) compared with LE2 (52 μm)] delayed gastric emptying by 38 min. Although acid-stable (LE1 and LE2) and redispersible (LE4) emulsions caused a constant increase in blood triglycerides, no increase was detectable for LE3 (P < 0.0001). For LE3, MRI confirmed the generation of large fat particles during gastric processing, which emptied into and progressed through the small intestine.

CONCLUSIONS

MRI allows the detailed characterization of the in vivo fate of lipid emulsions. The acute effects of lipid emulsions on gastric emptying, gallbladder volume, and triglyceride absorption are dependent on microstructural changes undergone during consumption. Gastric peristalsis and secretion were effective at redispersing pools of liquid fat in the stomach. This trial was registered at clinicaltrials.gov as NCT01253005.

The imaging and modelling of the physical processes involved in digestion and absorption

The mechanical activity of the gastro-intestinal tract serves to store, propel and digest food. Contractions disperse particles and transform solids and secretions into the two-phase slurry called chyme; movements of the intestine deliver nutrients to mucosal sites of absorption, and from the submucosa into the lymphatic and portal venous circulation. Colonic motor activity helps to extract fluid and electrolytes from chyme and to compound and compact luminal debris into faeces for elimination. We outline how dynamic imaging by ultrasound and magnetic resonance can demonstrate intestinal flow processes critical to digestion like mixing, dilution, swelling, dispersion and elution. Computational fluid mechanics enables a numerical rendition of the forces promoting digestion: pressure and flow fields, the shear stresses dispersing particles or the effectiveness of bolus mixing can be calculated. These technologies provide new insights into the mechanical processes that promote digestion and absorption.

Slow wave conduction patterns in the stomach: from Waller's foundations to current challenges

This review provides an overview of our understanding of motility and slow wave propagation in the stomach. It begins by reviewing seminal studies conducted by Walter Cannon and Augustus Waller on in vivo motility and slow wave patterns. Then our current understanding of slow wave patterns in common laboratory animals and humans is presented. The implications of slow wave arrhythmic patterns that have been recorded in animals and patients suffering from gastroparesis are discussed. Finally, current challenges in experimental methods and techniques, slow wave modulation and the use of mathematical models are discussed.

Self-assembly structure formation during the digestion of human breast milk

An infant's complete diet, human breast milk, is the basis for its survival and development. It contains water-soluble and poorly water-soluble bioactive components, metabolic messages, and energy, all of which are made bioavailable during the digestion process in the infant's gastrointestinal tract. Reported is the first discovery of highly geometrically organized structures formed during the digestion of human breast milk under simulated in vivo conditions using small-angle X-ray scattering and cryogenic transmission electron microscopy. Time of digestion, pH, and bile salt concentration were found to have symbiotic effects gradually tuning the oil-based environment inside the breast milk globules to more water-like structures with high internal surface area. The structure formation is necessarily linked to its function as carriers for poorly water-soluble molecules in the digestive tract of the infant.

Behaviour of whey protein emulsion gel during oral and gastric digestion: effect of droplet size

A set of whey protein stabilized-emulsion gels with different droplet size distributions (D4,3 = ∼1, 6 and 12 μm) was produced, and the mechanical properties of the gels in the linear viscoelastic region and at large deformation were measured, along with the physicochemical and structural changes of the gels during oral mastication and gastric digestion. The gels containing 1 μm oil droplets had an aggregated particle structure with proteins coating at oil droplets whereas the gels containing 12 μm oil droplets had a particle-filled structure with spatially continuous matrix. During oral processing, the release of oil droplets from the gels increased as the droplet size increased, with coalescence being seen in gels containing oil droplets of 6 and 12 μm diameter. Under gastric digestion, high degrees of coalescence and phase separation of oil droplets occurred in the gels containing 6 and 12 μm oil droplets because of oil droplet release from the gel matrix; this led to slow gastric emptying. The gels were finally broken down into peptide aggregates and oil droplets (or free oil). The gels, containing 1 μm oil droplets disintegrated into various particles of several to several tens of microns with a low degree of oil droplet release and coalescence. Protein breakdown was slower in these gels, suggesting that the protein structures of the gel matrices were affected by the sizes of the incorporated oil droplets.

A standardised static in vitro digestion method suitable for food - an international consensus

Simulated gastro-intestinal digestion is widely employed in many fields of food and nutritional sciences, as conducting human trials are often costly, resource intensive, and ethically disputable. As a consequence, in vitro alternatives that determine endpoints such as the bioaccessibility of nutrients and non-nutrients or the digestibility of macronutrients (e.g. lipids, proteins and carbohydrates) are used for screening and building new hypotheses. Various digestion models have been proposed, often impeding the possibility to compare results across research teams. For example, a large variety of enzymes from different sources such as of porcine, rabbit or human origin have been used, differing in their activity and characterization. Differences in pH, mineral type, ionic strength and digestion time, which alter enzyme activity and other phenomena, may also considerably alter results. Other parameters such as the presence of phospholipids, individual enzymes such as gastric lipase and digestive emulsifiers vs. their mixtures (e.g. pancreatin and bile salts), and the ratio of food bolus to digestive fluids, have also been discussed at length. In the present consensus paper, within the COST Infogest network, we propose a general standardised and practical static digestion method based on physiologically relevant conditions that can be applied for various endpoints, which may be amended to accommodate further specific requirements. A frameset of parameters including the oral, gastric and small intestinal digestion are outlined and their relevance discussed in relation to available in vivo data and enzymes. This consensus paper will give a detailed protocol and a line-by-line, guidance, recommendations and justifications but also limitation of the proposed model. This harmonised static, in vitro digestion method for food should aid the production of more comparable data in the future.

Intragastric volume changes after intake of a high-caloric, high-fat standard breakfast in healthy human subjects investigated by MRI

The aim of this magnetic resonance imaging (MRI) study was to investigate gastric emptying after intake of a high-caloric and high-fat standard meal as recommended by FDA and EMA for food-effect bioavailability and fed bioequivalence studies. Twelve healthy human subjects (7 male, 5 female) received the standard meal after an overnight fast. MRI was performed before as well as 15, 25, 35, 45, 55, 65, 105, 195, 275, and 375 min after meal intake using strong T2-weighted sequences and chemical shift imaging. In addition, 30 min after the beginning of meal intake subjects ingested 240 mL of water representing the recommended coadministration of water during drug intake. Gastric content volume was assessed using T2-weighted images, and fat fraction was estimated using a calculation of fat fraction in chemical shift imaging. In addition, the existence of a mechanism allowing fast gastric emptying of water in the fed state was investigated. After a lag phase of 50-90 min, gastric content volume decreased constantly with a rate of 1.7 mL/min. The water ingested 30 min after the start of the meal intake directly reached the antrum and subsequently was emptied quickly from the human stomach. Complete gastric emptying within 6 h was observed in only one out of 12 subjects. The fat fraction of the intragastric chyme decreased from 9.5% directly after meal intake to 6.3% at the end of the experiments. Moreover, the fat fraction in fundus was significantly higher compared to the antrum. This study contributes fundamental data for the assessment of food effects of solid oral dosage forms.

Effect of gel structure on the gastric digestion of whey protein emulsion gels

This study aimed to characterize and determine the disintegration of emulsion gels in a human gastric simulator (HGS) and the physicochemical characteristics of gastric digesta. Using thermal treatment at 90 °C, whey protein emulsion gels with different structures and gel strengths were formed by varying the ionic strength. Simulated boluses of soft (containing 10 mM NaCl) and hard (200 mM NaCl) gels, which had similar particle sizes to those of human subjects, were created for gastric digestion. Soft gels disintegrated faster than hard gels in the HGS. The boluses of both gels gradually disintegrated into particles of size ∼10 μm. With further digestion, the protein matrix of the soft gel particles dissolved, the proteins were disrupted mainly by proteolysis and large quantities of oil droplets were released. In contrast, for the hard gel particles, although all proteins were hydrolysed after 240 min the breakdown of the particles was slow and no oil droplets were released after 300 min. The differences in the breakdown of soft and hard gels in the HGS were attributed to the structures of the emulsion gel, which may result in different sets of peptides in the digestion. In addition, coalescence of the oil droplets was observed only for the soft gel.

Designing food structures for nutrition and health benefits

In addition to providing specific sensory properties (e.g., flavor or textures), there is a need to produce foods that also provide functionality within the gastrointestinal (GI) tract, over and above simple nutrition. As such, there is a need to understand the physical and chemical processes occurring in the mouth, stomach, small intestine, and large intestine, in addition to the food structure-physiology interactions. In vivo techniques and in vitro models have allowed us to study and simulate these processes, which aids us in the design of food microstructures that can provide functionality within the human body. Furthermore, it is important to be aware of the health or nutritional needs of different groups of consumers when designing food structures, to provide targeted functionality. Examples of three groups of consumers (elderly, obese, and athletes) are given to demonstrate their differing nutritional requirements and the formulation engineering approaches that can be utilized to improve the health of these individuals. Eating is a pleasurable process, but foods of the future will be required to provide much more in terms of functionality for health and nutrition.

Gastrointestinal tone; its genesis and contribution to the physical processes of digestion

BACKGROUND

Myogenic tone has long been recognised as an important component of gastrointestinal motility. Recent work has clarified the cellular mechanisms that engender tone and the neurogenic and mechanical stimuli that modulate it but has also highlighted cellular and regional specialisation in these mechanisms within the GI tract. Smooth muscle in all segments of the gut has the capability of latching, i.e. can generate ongoing specific rather than tetanic tone. This is likely modulated by both direct and indirect input from agonists such as acetylcholine and mechanoreceptors, the latter originating in ICC-IM, smooth muscle cells or elements of the ENS. Tonic contraction can occur in the absence of phasic contractions or concurrent with them, and it can modulate wall compliance and the capacity of particular segments, thereby affecting the level of on-flow and mixing, both luminal and adjacent to the mucosa.

PURPOSE

The review seeks to provide an overview of our understanding of the mechanism by which tone is generated and maintained, highlighting its modulation by neurogenic and mechanical stimuli, its mechanical consequences in the walls of the various segments of the gastrointestinal tract and its contribution to flow and mixing of contained digesta.

Mapping and modeling gastrointestinal bioelectricity: from engineering bench to bedside

A key discovery in gastrointestinal motility has been the central role played by interstitial cells of Cajal (ICC) in generating electrical slow waves that coordinate contractions. Multielectrode mapping and multiscale modeling are two emerging interdisciplinary strategies now showing translational promise to investigate ICC function, electrophysiology, and contractions in the human gut.

Early Effect of Single-dose Sitagliptin Administration on Gastric Emptying: Crossover Study Using the (13)C Breath Test

Background/Aims

The gastrointestinal motility effects of endogenous incretin hormones enhanced by dipeptidyl peptidase-IV (DPP-IV) inhibitors have not yet been sufficiently investigated. The aim of this study was to determine whether single pre-prandial sitagliptin, the DPP-IV inhibitor, administration might have an effect on the rate of liquid gastric emptying using the ¹³C-acetic acid breath test.

Methods

Ten healthy male volunteers participated in this randomized, two-way crossover study. The subjects fasted for overnight and were randomly assigned to receive 50 mg sitagliptin 2 hours before ingestion of the liquid test meal (200 kcal per 200 mL, containing 100 mg ¹³C-acetate) or the test meal alone. Under both conditions, breath samples were collected for 150 minutes following the meal. Liquid gastric emptying was estimated by the values of the following parameters: the time required for 50% emptying of the labeled meal (T_1/2), the analog to the scintigraphy lag time for 10% emptying of the labeled meal (T_lag), the gastric emptying coefficient and the regression-estimated constants (β and κ), calculated by using the ¹³CO₂ breath excretion curve using the conventional formulae. The parameters between the 2 test conditions were compared statistically.

Results

No significant differences in the calculated parameters, including T_1/2, T_lag, gastric emptying coefficient or β and κ, were observed between the 2 test conditions.

Conclusions

The present study revealed that single-dose sitagliptin intake had no significant influence on the rate of liquid gastric emptying in asymptomatic volunteers.

Antral recirculation in the stomach during gastric mixing

We investigate flow in the stomach during gastric mixing using a numerical simulation with an anatomically realistic geometry and free-surface flow modeling. Because of momentum differences between greater and lesser curvatures during peristaltic contractions, time-averaged recirculation is generated in the antrum, with retropulsive flow away from the pylorus and compensation flow along the greater curvature toward the pylorus. Gastric content in the distal stomach is continuously transported to the distal antrum by the forward flow of antral recirculation, and it is then mixed by the backward retropulsive flow. Hence, the content inside the antral recirculation is well mixed independently of initial location, whereas the content outside the recirculation is poorly mixed. Free-surface modeling enables us to analyze the effects of posture on gastric mixing. In the upright, prone, and right lateral positions, most of the antrum is filled with content, and the content is well mixed by antral recirculation. In contrast, in the supine and left lateral positions, most of the content is located outside antral recirculation, which results in poor mixing. The curved, twisted shape of the stomach substantially supports gastric mixing in fluid mechanical terms.

Right recumbent position on gastric emptying of water evidenced by 13C breath testing

AIM: To compare the impact of the right recumbent position with the sitting position on gastric emptying of water.

METHODS: In eight healthy male volunteers, the 13C acetate breath test was performed twice to assess gastric emptying of 100 mL tap water. Subjects were seated in one test and lying on their right side in the other. In both positions, pulmonary ¹³CO₂ exhalation curves were obtained by plotting breath data against time. Percent gastric retention curves were created by analyzing data using the Wagner-Nelson protocol.

RESULTS: No significant posture effect was found in pulmonary ¹³CO₂ output curves (P = 0.2150), whereas a significant effect was seen in gastric retention curves (P = 0.0315). The percent retention values at 10 min and 15 min were significantly smaller when subjects were in the right recumbent position compared with the seated position (P < 0.05). Our results verified the accelerating effect of the right recumbent position on gastric emptying of non-nutritive solutions. Concerning clinical implications, this study suggests that placing patients with acute pain on their right side after oral administration of analgesic drugs in solution is justified as an effective practice for rapid pain relief. For patients with gastrointestinal reflux symptoms, sleeping in the right recumbent position may reduce nocturnal symptoms, as delayed gastric emptying can cause reflux symptoms.

CONCLUSION: Gastric emptying of water occurs more quickly when a subject lies on the right side compared with sitting.

Digestion of kiwifruit fiber

Dietary fiber affects the digestion and absorption of nutrients in the gastrointestinal tract. Moreover, it is generally believed that fiber largely escapes digestion in the human small intestine and is therefore mainly a substrate for microbial fermentation in the hindgut. Kiwifruit is a food naturally high in dietary fiber, yet the impact of dietary kiwifruit on nutrient availability has not been reported. The digestion of kiwifruit has been investigated but only in in vitro digestion studies. With its naturally high nonstarch polysaccharide content, it would be expected that kiwifruit would possess the characteristics of a good source of fiber for nutrition and health. Kiwifruit contains soluble and nonsoluble fiber components, both of which would be expected to affect the physical attributes of digesta as it transits the gastrointestinal tract. This chapter summarizes fiber digestion in general and current knowledge of kiwifruit fiber digestion in the gastrointestinal tract.

Nutritional translation blended with food science: 21st century applications

This paper, based on the symposium "Real-World Nutritional Translation Blended With Food Science," describes how an integrated "farm-to-cell" approach would create the framework necessary to address pressing public health issues. The paper describes current research that examines chemical reactions that may influence food flavor (and ultimately food consumption) and posits how these reactions can be used in health promotion; it explains how mechanical engineering and computer modeling can study digestive processes and provide better understanding of how physical properties of food influence nutrient bioavailability and posits how this research can also be used in the fight against obesity and diabetes; and it illustrates how an interdisciplinary scientific collaboration led to the development of a novel functional food that may be used clinically in the prevention and treatment of prostate cancer.

Vagal sensory innervation of the gastric sling muscle and antral wall: implications for gastro-esophageal reflux disease?

BACKGROUND

The gastric sling muscle has not been investigated for possible sensory innervation, in spite of the key roles the structure plays in lower esophageal sphincter (LES) function and gastric physiology. Thus, the present experiment used tracing techniques to label vagal afferents and survey their projections in the lesser curvature.

METHODS

Sprague-Dawley rats received injections of dextran biotin into the nodose ganglia. Fourteen days postinjection, animals were euthanized and their stomachs were processed to visualize the vagal afferent innervation. In different cases, neurons, muscle cells, or interstitial cells of Cajal (ICC) were counterstained.

KEY RESULTS

The sling muscle is innervated throughout its length by vagal afferent intramuscular arrays (IMAs) associated with ICC. In addition, the distal antral attachment site of the sling muscle is innervated by a novel vagal afferent terminal specialization, an antral web ending. The muscle wall of the distal antrum is also innervated by conventional IMAs and intraganglionic laminar endings, the two types of mechanoreceptors found throughout stomach smooth muscle.

CONCLUSIONS & INFERENCES

The innervation of sling muscle by IMAs, putative stretch receptors, suggests that sling sensory feedback may generate vago-vagal or other reflexes with vagal afferent limbs. The restricted distribution of afferent web endings near the antral attachments of sling fibers suggests the possibility of specialized mechanoreceptor functions linking antral and pyloric activity to the operation of the LES. Dysfunctional sling afferents could generate LES motor disturbances, or normative compensatory sensory feedback from the muscle could compromise therapies targeting only effectors.

Advancing gastric emptying studies: standardization and new parameters to assess gastric motility and function

For many years, gastric emptying (GE) studies were performed using various local protocols and different radiolabeled meals. This lack of standardization and normal values made the test results unreliable and difficult to compare from one site to another. A recent consensus has been published that now provides guidance and standardization on how to perform a radiolabeled solid-meal GE study. It is widely recognized, however, that simple measurement of total GE of a solid meal often does not provide an answer to the etiology of symptoms for a large number of patients who present with functional dyspepsia. Advances in our understanding of the different roles of the fundus and antrum and their complex interaction with the proximal small bowel and central nervous system have led to the development of new methods to study gastric motility. This review describes how a more comprehensive approach to studying GE is needed and how this will lead to better diagnosis and treatment for patients referred for GE studies.

Upper gastrointestinal dysmotility after spinal cord injury: is diminished vagal sensory processing one culprit?

Despite the widely recognized prevalence of gastric, colonic, and anorectal dysfunction after spinal cord injury (SCI), significant knowledge gaps persist regarding the mechanisms leading to post-SCI gastrointestinal (GI) impairments. Briefly, the regulation of GI function is governed by a mix of parasympathetic, sympathetic, and enteric neurocircuitry. Unlike the intestines, the stomach is dominated by parasympathetic (vagal) control whereby gastric sensory information is transmitted via the afferent vagus nerve to neurons of the nucleus tractus solitarius (NTS). The NTS integrates this sensory information with signals from throughout the central nervous system. Glutamatergic and GABAergic NTS neurons project to other nuclei, including the preganglionic parasympathetic neurons of the dorsal motor nucleus of the vagus (DMV). Finally, axons from the DMV project to gastric myenteric neurons, again, through the efferent vagus nerve. SCI interrupts descending input to the lumbosacral spinal cord neurons that modulate colonic motility and evacuation reflexes. In contrast, vagal neurocircuitry remains anatomically intact after injury. This review presents evidence that unlike the post-SCI loss of supraspinal control which leads to colonic and anorectal dysfunction, gastric dysmotility occurs as an indirect or secondary pathology following SCI. Specifically, emerging data points toward diminished sensitivity of vagal afferents to GI neuroactive peptides, neurotransmitters and, possibly, macronutrients. The neurophysiological properties of rat vagal afferent neurons are highly plastic and can be altered by injury or energy balance. A reduction of vagal afferent signaling to NTS neurons may ultimately bias NTS output toward unregulated GABAergic transmission onto gastric-projecting DMV neurons. The resulting gastroinhibitory signal may be one mechanism leading to upper GI dysmotility following SCI.

A novel 3D shape context method based strain analysis on a rat stomach model

The stomach has the ability to change its geometry and volume during digestion. Thus, the stomach shape changes dynamically due to changes in contents and due to pressure from adjacent organs. Full-field strain analysis is therefore important for accurate estimation of the true deformation in this highly non-homogeneous, anisotropic organ. The aim of this study is to introduce a modified non-rigid image registration based 3D shape context method combined with a full-field strain analysis method to describe a distension-induced 3D gastric deformation. The geometry of a normal rat stomach at distension pressures from 0.05 kPa to 0.8 kPa were obtained by ultrasonic scanning. The full-field strain distribution of the 3D gastric model between the reference state and the distended state were computed on the basis of the improved 3D shape context method and full-field strain analysis method. The registered surface showed a good agreement with the real deformed surface for all distension states. However, the errors increased with the distension pressure due to increasing dissimilarity between the deformed and the reference surface. The strain distributions on the stomach surface were non-uniform with the largest deformation in the non-glandular part and the greater and lesser curvature when the pressure was higher than 0.2 kPa. The wall stiffness of the non-glandular part was softer than that of the glandular part. The modelling analysis method which is closely allied with the non-rigid image registration and strain analysis provides a kinematically possible deformation mode of the gastric wall. This method can be potentially used for clinical data estimating the kinematical properties of the human visceral organs in health and disease.

Dissolution testing of oral modified-release dosage forms

Objectives

The in-vivo performance of oral modified-release dosage forms is determined by the interplay of various physiological- and dosage-form-derived parameters. Thus it is often a challenge to predict the in-vivo drug-release behaviour from modified-release dosage forms based solely on in-vitro release rates.

Key findings

For a long time the most common procedure to obtain in-vitro/in-vivo correlations for modified-release formulations was to apply test conditions typically used for quality control on a retrospective basis. Such so-called ‘compendial approaches’ are typically not biorelevant with respect to volumes, composition and physicochemical properties of the test media and also do not take into consideration the mechanical and hydrodynamic forces that may influence dosage-form behaviour during passage through the gastrointestinal tract.

Summary

This review provides an overview of physiological conditions relevant to in-vivo drug release and of dissolution models which, based on current scientific findings on human gastrointestinal physiology, have been developed to enable a better prediction of the in-vivo performance of oral MR dosage forms.

Patterns of trunk spine growth in two congeneric species of acanthocephalan: investment in attachment may differ between sexes and species

Acanthocephalans have evolved a hooked proboscis and some taxa have trunk spines to attach to their definitive hosts. These structures are generated before being used, thus a key question is how investment in attachment could optimally be allocated through the ontogeny. The number and arrangement of hooks and spines are never modified in the definitive host, but it is unclear whether these structures grow during adult development. A comparison of the size of trunk spines between cystacanths and adults of Corynosoma cetaceum and C. australe indicated that spines grow in both species, but only in females, which also had significantly larger spines than males. This sexual dimorphism did not result from pure allometry because the body of females was smaller, and did not grow more than that of males. However, having a longer lifespan, females would need to withstand the extreme flow conditions prevailing in marine mammals for longer, inducing different investment and development schedules for spines. Patterns of spine growth also differed between species: fore-trunk spines grew in both species, but hind-trunk spines did only in C. cetaceum. In conclusion, investment strategies on attachment may differ, not only between congeneric species of acanthocephalan, but also between sexes of the same species.

Bedside ultrasound assessment of gastric content: an observational study

PURPOSE

There is a growing interest in the use of bedside ultrasonography to assess gastric content and volume. It has been suggested that the gastric antrum in particular can be assessed reliably by sonography. The aim of this observational study was to provide a qualitative description of the sonographic characteristics of the gastric antrum when the stomach is empty and following the ingestion of clear fluid, milk, and solid content.

CLINICAL FEATURES

Six healthy volunteers were examined on four different occasions (24 scanning sessions): following a period of eight hours of fast and following ingestion of 200 mL of apple juice, 200 mL of 2% milk, and a standard solid meal (sandwich and apple juice). Examinations were performed following a standardized scanning protocol by two clinical anesthesiologists with previous experience in gastric sonography. For each type of gastric content, the sonographic characteristics of the antrum and its content are described and illustrated with figures.

CONCLUSIONS

Bedside sonography can determine the nature of gastric content (nil, clear fluid, thick fluid/solid). This qualitative information by itself may be useful to assess risk of aspiration, particularly in situations when prandial status is unknown or uncertain.

Role of RhoA and its effectors ROCK and mDia1 in the modulation of deformation-induced FAK, ERK, p38, and MLC motogenic signals in human Caco-2 intestinal epithelial cells

Repetitive deformation enhances intestinal epithelial migration across tissue fibronectin. We evaluated the contribution of RhoA and its effectors Rho-associated kinase (ROK/ROCK) and mammalian diaphanous formins (mDia1) to deformation-induced intestinal epithelial motility across fibronectin and the responsible focal adhesion kinase (FAK), extracellular signal-regulated kinase (ERK), p38, and myosin light chain (MLC) signaling. We reduced RhoA, ROCK1, ROCK2, and mDia1 by smart-pool double-stranded short-interfering RNAs (siRNA) and pharmacologically inhibited RhoA, ROCK, and FAK in human Caco-2 intestinal epithelial monolayers on fibronectin-coated membranes subjected to 10% repetitive deformation at 10 cycles/min. Migration was measured by wound closure. Stimulation of migration by deformation was prevented by exoenzyme C3, Y27632, or selective RhoA, ROCK1, and ROCK2 or mDia1 siRNAs. RhoA, ROCK inhibition, or RhoA, ROCK1, ROCK2, mDia1, and FAK reduction by siRNA blocked deformation-induced nuclear ERK phosphorylation without preventing ERK phosphorylation in the cytoplasmic protein fraction. Furthermore, RhoA, ROCK inhibition or RhoA, ROCK1, ROCK2, and mDia1 reduction by siRNA also blocked strain-induced FAK-Tyr(925), p38, and MLC phosphorylation. These results suggest that RhoA, ROCK, mDia1, FAK, ERK, p38, and MLC all mediate the stimulation of intestinal epithelial migration by repetitive deformation. This pathway may be an important target for interventions to promote mechanotransduced mucosal healing during inflammation.

Modeling the fluid dynamics in a human stomach to gain insight of food digestion

During gastric digestion, food is disintegrated by a complex interaction of chemical and mechanical effects. Although the mechanisms of chemical digestion are usually characterized by using in vitro analysis, the difficulty in reproducing the stomach geometry and motility has prevented a good understanding of the local fluid dynamics of gastric contents. The goal of this study was to use computational fluid dynamics (CFD) to develop a 3-D model of the shape and motility pattern of the stomach wall during digestion, and use it to characterize the fluid dynamics of gastric contents of different viscosities. A geometrical model of an averaged-sized human stomach was created, and its motility was characterized by a series of antral-contraction waves of up to 80% relative occlusion. The flow field within the model (predicted using the software Fluent™) strongly depended on the viscosity of gastric contents. By increasing the viscosity, the formation of the 2 flow patterns commonly regarded as the main mechanisms driving digestion (i.e., the retropulsive jet-like motion and eddy structures) was significantly diminished, while a significant increase of the pressure field was predicted. These results were in good agreement with experimental data previously reported in the literature, and suggest that, contrary to the traditional idea of a rapid and complete homogenization of the meal, gastric contents associated with high viscous meals are poorly mixed. This study illustrates the capability of CFD to provide a unique insight into the fluid dynamics of the gastric contents, and points out its potential to develop a fundamental understanding and modeling of the mechanisms involved in the digestion process.

Development of a simple model device for in vitro gastric digestion investigation

There have been some reports in the literature of model gastric digestion systems to mimic the dynamic physiological processes within the gastrointestinal tract. However, such devices often require the specification of many control parameters making routine digestion tests unfeasible. This paper introduces a simple in vitro digestion device, comprising of a water-jacketed glass vessel into which a spherical Teflon probe of variable diameter can be inserted. The probe is controlled by a texture analyser to simulate the kinetics of a food digestion process. Using this device under well controlled hydrodynamic flow and biochemical conditions key digestion parameters such as pH, food particle size, protein release, lipid release, cloudiness, etc, can be determined. Feasibility tests of the model device have been conducted using roasted and non-roasted peanuts particles. The status of peanut digestion was examined by the changes in particle size distribution and the mean particle size. Significant differences of surface microstructure have also been observed for peanut particles after the digestion. The influence of parameters such as food to gastric juice ratio, the probe speed and pepsin concentration have been examined in this work. Initial results confirm that all these factors influence the kinetic process of gastric digestion considerably and should be well regulated in any in vitro digestion investigations. We propose that the model device has the advantages of easy control and operation and furthermore could be an ideal tool for routine in vitro gastric digestion studies.

Quantification of the effects of the volume and viscosity of gastric contents on antral and fundic activity in the rat stomach maintained ex vivo

AIMS

The aim of this study was to examine the effect of varying the rheological properties of perfusate on the volume and muscular activity of the various compartments of the rat stomach.

METHODS

Image analysis was used to quantify the activity of the ex vivo stomach preparations when perfused according to a ramp profile.

RESULTS

The area of the fundus increased to a greater extent than that of the body when watery or viscous material was perfused. However, initial distension of the corpus was greater and occurred more rapidly when viscous material was perfused. Only the fundus expanded when perfusion followed the administration of verapamil. The frequency of antrocorporal contractions decreased significantly and the amplitude of antrocorporal contractions increased significantly with increase in gastric volume. The velocity of antrocorporal contractions did not vary with gastric volume but varied regionally in some preparations being faster distally than proximally. Neither the frequency, amplitude or velocity of antrocorporal contractions differed when pseudoplastic rather than watery fluid was perfused. However, the characteristics of antrocorporal contractions changed significantly when the stomach was perfused with material with rheological characteristics that induce different patterns of wall tension to those normally encountered. Hence, the mean frequency and speed of propagation of antrocorporal contractions increased and their direction of propagation became inconstant.