Relationship between ultrasonically detected phasic antral contractions and antral pressure

Analysis of Intestinal Movements with Spatiotemporal Maps: Beyond Anatomy and Physiology

Over 150 years ago, methods for quantitative analysis of gastrointestinal motor patterns first appeared. Graphic representations of physiological variables were recorded with the kymograph after the mid-1800s. Changes in force or length of intestinal muscles could be quantified, however most recordings were limited to a single point along the digestive tract.In parallel, photography and cinematography with X-Rays visualised changes in intestinal shape, but were hard to quantify. More recently, the ability to record physiological events at many sites along the gut in combination with computer processing allowed construction of spatiotemporal maps. These included diameter maps (DMaps), constructed from video recordings of intestinal movements and pressure maps (PMaps), constructed using data from high-resolution manometry catheters. Combining different kinds of spatiotemporal maps revealed additional details about gut wall status, including compliance, which relates forces to changes in length. Plotting compliance values along the intestine enabled combined DPMaps to be constructed, which can distinguish active contractions and relaxations from passive changes. From combinations of spatiotemporal maps, it is possible to deduce the role of enteric circuits and pacemaker cells in the generation of complex motor patterns. Development and application of spatiotemporal methods to normal and abnormal motor patterns in animals and humans is ongoing, with further technical improvements arising from their combination with impedance manometry, magnetic resonance imaging, electrophysiology, and ultrasonography.

Gastrointestinal Ultrasound in Functional Disorders of the Gastrointestinal Tract - EFSUMB Consensus Statement

Abdominal ultrasonography and intestinal ultrasonography are widely used as first diagnostic tools for investigating patients with abdominal symptoms, mainly for excluding organic diseases. However, gastrointestinal ultrasound (GIUS), as a real-time diagnostic imaging method, can also provide information on motility, flow, perfusion, peristalsis, and organ filling and emptying, with high temporal and spatial resolution. Thanks to its noninvasiveness and high repeatability, GIUS can investigate functional gastrointestinal processes and functional gastrointestinal diseases (FGID) by studying their behavior over time and their response to therapy and providing insight into their pathophysiologic mechanisms. The European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) has established a Task Force Group consisting of GIUS experts, which developed clinical recommendations and guidelines on the role of GIUS in several acute and chronic gastrointestinal diseases. This review is dedicated to the role of GIUS in assisting the diagnosis of FGID and particularly in investigating patients with symptoms of functional disorders, such as dysphagia, reflux disorders, dyspepsia, abdominal pain, bloating, and altered bowel habits. The available scientific evidence of GIUS in detecting, assessing, and investigating FGID are reported here, while highlighting sonographic findings and its usefulness in a clinical setting, defining the actual and potential role of GIUS in the management of patients, and providing information regarding future applications and research.

Ultrasound imaging for assessing functions of the GI tract

OBJECTIVE

In the following review we outline how ultrasound can be used to measure physiological processes in the gastrointestinal tract.

APPROACH

We have investigated the potential of ultrasound in assessing gastrointestinal physiology including original research regarding both basic methodology and clinical applications.

MAIN RESULTS

Our main findings show the use of ultrasound to study esophageal motility, measure volume and contractility of the stomach, assess motility, wall thickness, and perfusion of the small bowel, and evaluate wall vascularization and diameters of the large bowel.

SIGNIFICANCE

Ultrasound is a widely accessible technology that can be used for both scientific and clinical purposes. Being radiation-free and user friendly, the examination can be frequently repeated enabling longitudinal studies. Furthermore, it does not influence normal GI physiology, thus being useful to estimate motility and subtle changes in physiology. Accordingly, ultrasound scanning and physiological measurements may make a big difference for the scientist and the doctor; and for the patients who receive an efficient work-up.

An activating gucy2c mutation causes impaired contractility and fluid stagnation in the small bowel

OBJECTIVE

Familial GUCY2C diarrhoea syndrome (FGDS) is caused by an activating mutation in the GUCY2C gene encoding the receptor guanylate cyclase C in enterocytes. Activation leads to increased secretion of fluid into the intestinal lumen. Twenty percent of the patients have increased risk of Crohn's disease and intestinal obstruction (CD, 20%) and the condition resembles irritable bowel syndrome with diarrhoea. We aimed to describe fluid content, contractility, peristaltic activity and bowel wall thickness in the intestine in fasting FGDS patients, using ultrasound, with healthy volunteers serving as controls.

METHODS

Twenty-three patients with FGDS and 22 healthy controls (HC) were examined with a Logiq E9 scanner in a fasting state. Bowel wall thickness was measured and fluid-filled small bowel loops were counted using three-dimensional (3D) magnetic positioning navigation. The HC ingested 500 ml PEG solution, an electrolyte balanced, non-absorbable solution, in order to investigate the contractions of the small bowel.

RESULTS

The fasting 23 FGDS patients had significantly higher number of fluid-filled small bowel segments compared to 22 fasting HC, p < 0.001. A high number of non-occlusive contractions in the ileum was observed, which was significant when compared to HC after ingesting PEG solution, p < 0.016. An increase in intestinal wall thickness or other signs of CD were not observed.

CONCLUSIONS

FGDS is characterised by multiple, fluid-filled small bowel loops with incomplete contractions and fluid stagnation in fasting state. These findings may play a role in the increased risk of bowel obstruction as well as IBS-like symptoms observed in these patients.

Ultrasonography in gastroenterology

Ultrasonography (US) is a safe and available real-time, high-resolution imaging method, which during the last decades has been increasingly integrated as a clinical tool in gastroenterology. New US applications have emerged with enforced data software and new technical solutions, including strain evaluation, three-dimensional imaging and use of ultrasound contrast agents. Specific gastroenterologic applications have been developed by combining US with other diagnostic or therapeutic methods, such as endoscopy, manometry, puncture needles, diathermy and stents. US provides detailed structural information about visceral organs without hazard to the patients and can play an important clinical role by reducing the need for invasive procedures. This paper presents different aspects of US in gastroenterology, with a special emphasis on the contribution from Nordic scientists in developing clinical applications.

[Contribution of ultrasonography for the preoperative assessment of gastric contents]

The assessment of the risk of pulmonary aspiration of gastric contents may be difficult in the preoperative period, apart from typical circumstances. The development of ultrasonography in anesthesia and critical care has led to consider ultrasonic imaging of gastric contents for preoperative risk assessment of "full" stomach in clinical practice. Ultrasonography of the body of the stomach allows direct visualization of the gastric contents. However, the stomach is often difficult to identify, particularly when it is empty. Moreover, quantitative assessment of gastric volume is delicate, and no standardized method of ultrasonography of the body of the stomach for preoperative assessment of gastric contents was described. On the contrary, ultrasonography of the antral cross-sectional area, which was initially described for the assessment of gastric emptying as an alternative method to repeated measurements of the variations of antropyloric volume after ingestion of a test meal, is easy to perform and is highly reproducible through using the aorta and the left lobe of the liver as internal landmarks. Qualitative assessment of the gastric antrum allows easily diagnosis of a "full" stomach. The measurement of antral area may allow a more accurate estimate of the presence or absence of gastric contents at risk of lung injury in the event of regurgitation and aspiration (gastric volume >0.8 ml/kg and/or with solid particles), defining the "risk" stomach. The use of antral ultrasonography may help the anesthesiologist to assess the risk of pulmonary aspiration according to clinical history of the patient, in order to choose an appropriate strategy minimizing the occurrence of this complication.

Sonographic assessments of gastrointestinal and biliary functions

Ultrasound has been established as a routine work-up imaging method in abdominal diseases. It assesses the morphology of intra-abdominal organs and depicts the normal and pathological anatomy of the gastrointestinal tract as well as of the biliopancreatic system. Ultrasound is the method of choice for visualisation of motion sequences since it is, in contrast to other imaging methods, a real-time method. The non-invasiveness and the repeatability of the method are important advantages when performing investigations of functional processes. Therefore, ultrasound is most suited for functional studies. Up to now, functional ultrasound and its potential have been undervalued. Functional ultrasound provides a widely available method to increase our understanding of functional processes and motility. The authors review the options of functional ultrasound and discuss its practical relevance.

Strain measurement during antral contractions by ultrasound strain rate imaging: influence of erythromycin

Strain rate imaging (SRI) is a non-invasive ultrasound (US) modality that enables the study of mechanical deformation (strain) with high spatial and temporal resolution. A total of 244 contractions in seven healthy volunteers were studied by SRI on two separate days to characterize radial strain of antral contractions in the fasting and fed states and to assess the influence of intravenous erythromycin. Gastric accommodation and emptying were assessed by 2D ultrasonography. The perception of hunger was registered by the participants. The strain increased from early to late phase II and phase III activity by (median) 18%, 58% and 82%, respectively, P < 0.05. Erythromycin infusion in phase I induced contractions with median strain of 35%, but did not increase postprandial strain. Both fasting and postprandially, lumen-occlusive contractions with erythromycin were more frequent than in naturally occurring contractions, 69%vs 48%, P = 0.036 and 40%vs 5%, P < 0.001 respectively. All subjects had rumbling in their abdomens when intraluminal air was detected sonographically (85% of all phase III contractions) and that rumbling was perceived by the participant as maximal awareness of hunger. SRI enabled detailed strain measurement of individual antral contractions. Erythromycin initiated fasting antral contractions and increased the number of lumen-occlusive contractions.

Vagal activation by sham feeding improves gastric motility in functional dyspepsia

Antral hypomotility and impaired gastric accommodation in patients with functional dyspepsia have been ascribed to vagal dysfunction. We investigated whether vagal stimulation by sham feeding would improve meal-induced gastric motor function in these patients. Fourteen healthy volunteers and 14 functional dyspepsia patients underwent a drink test twice, once with and once without simultaneous sham feeding. After ingesting 500 mL clear meat soup (20 kcal, 37 degrees C) in 4 min, sham feeding was performed for 10 min by chewing a sugar-containing chewing gum while spitting out saliva. Using two- and three-dimensional ultrasound, antral motility index (contraction amplitude x frequency) and intragastric volumes were estimated. Without sham feeding, functional dyspepsia patients had lower motility index than healthy volunteers (area under curve 8.0 +/- 1.2 vs 4.4 +/- 1.0 min(-1), P = 0.04). In functional dyspepsia patients, but not in healthy volunteers, motility index increased and intragastric volume tended to increase by sham feeding (P = 0.04 and P = 0.06 respectively). The change in motility index was negatively correlated to the change in pain score (r = -0.59, P = 0.007). In functional dyspepsia patients, vagal stimulation by sham feeding improves antral motility in response to a soup meal. The result supports the view that impaired vagal stimulation is implicated in the pathogenesis of gastric motility disturbances in functional dyspepsia.

Biomagnetic characterization of spatiotemporal parameters of the gastric slow wave

Certain gastric disorders affect spatiotemporal parameters of the gastric slow wave. Whereas the electrogastrogram (EGG) evaluates electric potentials to determine primarily temporal parameters, fundamental physical limitations imposed by the volume conduction properties of the abdomen suggest the evaluation of gastric magnetic fields. We used a multichannel superconducting quantum interference device magnetometer to study the magnetogastrogram (MGG) in 20 normal human subjects before and after a test meal. We computed the frequency and amplitude parameters of the gastric slow wave from MGG. We identified normal gastric slow wave activity with a frequency of 2.6 +/- 0.5 cycles per minute (cpm) preprandial and 2.8 +/- 0.3 cpm postprandial. In addition to frequency and amplitude, the use of surface current density mapping applied to the multichannel MGG allowed us to visualize the propagating slow wave and compute its propagation velocity (6.6 +/- 1.0 mm s(-1) preprandial and 7.4 +/- 0.4 mm s(-1) postprandial). Whereas MGG and EGG signals exhibited strong correlation, there was very little correlation between the MGG and manometry. The MGG not only records frequency dynamics of the gastric slow wave, but also characterizes gastric propagation. The MGG primarily reflects the underlying gastric electrical activity, but not its mechanical activity.

Morphology and motor function of the gastrointestinal tract examined with endosonography

Endosonography is a useful tool for studying the morphology and motor function of the gastrointestinal tract. Intraluminal ultrasonography is the common denomination of ultrasound examinations using intracorporal transducers which are inserted into the GI tract. Thus, the visceral wall and adjacent structures can be imaged in detail. This review describes the usefulness of endosonography in gastroenterology, in particular with respect to studies of the biomechanical and motor function of the gastrointestinal tract. New techniques such as 3-D EUS, elastography and strain rate imaging are discussed.

Mechanosensory properties in the human gastric antrum evaluated using B-mode ultrasonography during volume-controlled antral distension

The aims of this study were to evaluate gastric antral mechanical behavior and distension-induced sensorimotor responses in the human gastric antrum using transabdominal ultrasound scanning. Ten healthy volunteers underwent volume-controlled ramp inflation of a bag located in the antrum with volumes up to 125 ml. The active and passive circumferential tensions and stresses were calculated from measurements of pressure, diameter, and wall thickness before and during the administration of the anticholinergic drug butylscopolamine. The bag distensions elicited contractions in the antrum and sensory responses below the pain threshold. Butylscopolamine abolished the contractions and significantly reduced the sensory response. The length-tension diagram known from in vitro studies of smooth muscle strips could be reproduced as tension-volume diagrams in the human gastric antrum. The number of induced contractions and the contraction pressure amplitude (afterload) showed a parabolic behavior as function of the distension volume (preload), with maximum approximately at 70 ml. At the sensation threshold, the luminal circumference showed the lowest variation coefficient (13-25%), whereas the variation coefficient was more than 100% for the pressure, tensions, and stresses. We conclude that the muscle length-tension diagram and typical preload-afterload curves ad modem the Frank-Starling cardiac law can be obtained in the human gastric antrum. The sensory responses were most closely associated with the luminal circumference, indicating that the sensation during antral distension depends on deformation rather than on tension.

Determinants of transpyloric fluid transport: a study using combined real-time ultrasound, manometry, and impedance recording

Intraluminal impedance recording has made it possible to record fluid transport across the pylorus during the interdigestive state without filling the stomach. During antral phase II, fluid transport occurs with and without manometrically detectable antral contraction. Our aim was to investigate the relationships between ultrasonographic patterns of antral contraction, manometric pressure waves, and transpyloric fluid transport during antral phase II. Antral wall movements were recorded by real-time ultrasound (US) in eight healthy volunteers (mean age 24 +/- 7 yr) during 17 +/- 5 min of antral phase II. Concomitantly, a catheter positioned across the pylorus, monitored by transmucosal potential difference measurement, recorded five impedance signals (1 antral, 1 pyloric, and 3 duodenal) and six manometric signals (2 antral, 1 pyloric, and 3 duodenal). Antral contractions detected by US at the level of the two antral impedance electrodes were classified according to their association with a pyloric opening or a duodenal contraction. Transpyloric liquid transport events (impedance drop of >40% of the baseline with an antegrade or retrograde propagation) and manometric pressure waves (amplitude and duration) were identified during the whole study and especially during each period of US antral contraction. A total of 110 antral contractions was detected by US. Of these, 79 were also recorded by manometry. Fluid transport across the pylorus was observed in 70.9% of the US-detected antral contractions. Pyloric opening was observed in 98.6% of the contractions associated with fluid transport compared with 50% in the absence of fluid transport (P < 0.05). Antral contractions associated with fluid transport were significantly (P < 0.05) more often propagated to the duodenum (92%) than those without fluid transport (53%). Pressure waves associated with fluid transport were of higher amplitude (208 mmHg, range 22-493) and longer duration (7 s, range 2.5-13.5 s) than those not associated with fluid transport (102 mmHg, range 18-329 mmHg, and 4.1 s, range 2-8.5 s; P < 0.05). The propagation of the antral contractions in the duodenum in US was always associated with a pyloric opening, whereas only 8 of the 25 contractions without duodenal propagation were associated with a pyloric opening (P < 0.05). The presence of duodenal contractile activity before the onset of an antral contraction in US was always accompanied by pyloric opening and with fluid transport in 93.3%, compared with 56.8% in its absence (P < 0.05). In antral phase II, US is the most sensitive technique to detect antral contractions. Transpyloric fluid transport observed in relation to antral contractions occurs mainly in association with contractions of high amplitude and long duration and is associated with pyloric opening and/or duodenal propagation.

Interdigestive transpyloric fluid transport assessed by intraluminal impedance recording

Our aim was to explore the use of intraluminal impedance recording for assessment of interdigestive transpyloric fluid movements. Twenty healthy volunteers were studied with a catheter allowing the recording of five antropyloroduodenal impedance signals simultaneously with six pressure signals. Patterns induced by air were verified by standard ultrasound. Transpyloric Doppler ultrasound was used to validate impedance patterns associated with transpyloric fluid transports. Impedance changes caused by air (short-lived increases) occupied 14 +/- 12% of the time in the antrum and 0.8 +/- 0.5% in the duodenum (P < 0.005). All fluid transport events lasting >4 s were recorded by both Doppler and impedance techniques. Transpyloric fluid transport was observed in all three phases of the antral migrating motor complex. The total number of transport events was significantly higher (P < 0.05) in phase II (18 +/- 7) than in phases I (2.6 +/- 2) and III (6.1 +/- 3). Retrograde transport was observed mainly in antral phase I (54% of fluid movements, compared with 2.5% in phase II and 18.5% in phase III, P < 0.05). During phase II, 80 +/- 13% of the impedance changes were associated with manometric events and 72 +/- 9% of the antral contractions were associated with transpyloric fluid transport. Prolonged assessment of interdigestive transpyloric fluid transport events using intraluminal measurement of impedance is possible. Manometrically detectable contractions are the most frequent, but not the only, driving forces of these events.