Impact of external factors on the stability of human electrogastrograms.
Explore the source record for details and available documents.
Adult↗
Biomedical subjects
K L Bowes
Publications and source records attributed to K L Bowes.
Conoidal dipole model of electrical field produced by the human stomach.
Spontaneous depolarisation and repolarisation due to ionic exchange are the main properties of smooth muscle cells in the human stomach. This change in the distribution of electrical charge results in the creation of an electric field. The field manifests itself as a potential difference (biovoltage), recorded both in vitro and in vivo and known as gastric electrical activity (GEA). The aim of the paper is to describe a computer model of this electric phenomenon, considering all anatomical and electrophysiological particularities of the stomach, and to simulate real in vivo experiments with a computer. In the proposed model, the depolarised smooth muscle cells are represented as organised electrical dipoles distributed with known density in an annular band that moves distally with increasing velocity. Computer simulations of in vivo experiments using this model not only give the waveform, duration, amplitude and frequency of GEA, but they also represent the phase lag between different channels, the difference in propagation velocity along greater and lesser curvatures, and the electric coupling between different parts of the stomach. The effects of changed electrode configuration, surface area and distance from the stomach are described. Mathematical modelling is done in spherical co-ordinates, and the simulations are performed in a specially designed user-friendly IBM PC environment. Some of the unsolved problems in cutaneous electrogastrography are also discussed.
Electrophysiology↗
A model of gastric electrical activity in health and disease.
The idea of diagnosing gastric dysfunction from noninvasive measurements of gastric electrical activity (GEA) is intuitively appealing, but the predictive accuracy of the cutaneous signal, especially that of its amplitude, is still in question. Mathematical modeling provides a means of investigating, analyzing, and predicting GEA measured percutaneously. In this study, a model of GEA applicable both in health and disease was developed and simulated for a cylindrical body surface. Body-surface maps of the simulated electrogastrogram (EGG) were generated at a 20 by 20 array of sites on the model's surface, and the accuracy of the percutaneous method in detecting simulated gastric electrical abnormalities was determined. The relationship between the amplitude of the simulated surface EGG and the velocity of propagation of the myogenic activity was also investigated. This was compared to a similar investigation of the fluctuations in the amplitude of the surface EGG with the velocity of propagation of the serosal activity measured in humans. The diagnostic accuracy of the measured cutaneous EGG in humans was also determined. The results obtained from the mathematical model show that the amplitude of the electrogastrogram increases with the propagation velocity of GEA. Similar results were obtained from the experimental measurements. The amplitude of the simulated and measured cutaneous signal correlated well (p < 0.05) with the phase shift of the simulated and measured activities, (-0.85, -0.54), respectively. Serosal normal activity, tachygastria, and uncoupling were detected 67%, 90%, and 0% of the time, respectively, at the cutaneous electrode in humans. In simulations, normal activity and tachygastria were accurately detected at all 400 sites on the surface. Uncoupling simulated with 50% of the myogenic sources "diseased" was detected at only 20 of the 400 sites. The results confirm that the amplitude of the cutaneous signal is a function of the velocity of propagation of the myogenic signal. It also confirms that while GEA in health may be accurately predicted from percutaneous recordings, frequency and phase/coupling abnormalities are poorly detected from single-channel electrogastrograms. This suggests the use of multiple-channel surface recordings in clinical electrogastrography.
Body Surface Potential Mapping↗
Accuracy of cutaneous recordings of gastric electrical activity.
BACKGROUND: This study was undertaken to determine the accuracy of cutaneous electrogastrography (EGG). METHODS: The ability of EGG to assess gastric contractions and electrical frequency, phase lag, and waveform was studied in 4 healthy volunteers with cutaneous electrodes before and after eating, 4 healthy fasting volunteers with intraluminal pressure recording tubes and cutaneous electrodes, 1 patient with surgically implanted gastric serosal electrodes, and 4 anesthetized dogs with serosal force transducers and implanted and cutaneous electrodes. In 2 of the dogs, an intragastric distending balloon was introduced. RESULTS: The use of long-distance serosal electrodes allowed direct comparison of internal and cutaneous signals. Cutaneous electrodes recognized 80%-85% of changes in frequency with spectral analysis. Only 30%-40% of increases in EGG amplitudes were associated with gastric contractions. Gradual distention of the canine stomach after blocking contractions with atropine and glucagon increased the EGG amplitudes. No appreciable phase lag could be discerned with EGG. The descending portion of the EGG waveform was predominant. CONCLUSIONS: Frequency dynamics is currently the only reliable cutaneous EGG parameter.
Adult↗
An active feedback system for isotonic studies of smooth muscle.
A feedback system used to perform isotonic studies of smooth muscle is presented. This system is capable of applying a constant force to muscle samples regardless of their contractile activities. The force applied to the tissue is controlled using a proportional integral control system that drives a linear motor. The device is integrated into a sucrose gap tissue bath apparatus where measurements of displacement and electrical activity are also possible. The frequency of canine colonic smooth-muscle electrical oscillations is positively related to applied force.
Animals↗
Can transcutaneous recordings detect gastric electrical abnormalities?
The ability of transcutaneous recordings of gastric electrical activity to detect gastric electrical abnormalities was determined by simultaneous measurements of gastric electrical activity with surgically implanted serosal electrodes and cutaneous electrodes in six patients undergoing abdominal operations. Transient abnormalities in gastric electrical activity were seen in five of the six patients during the postoperative period. Recognition of normal gastric electrical activity by visual analysis was possible 67% of the time and with computer analysis 95% of the time. Ninety four per cent of abnormalities in frequency were detected by visual analysis and 93.7% by computer analysis. Abnormalities involving a loss of coupling, however, were not recognised by transcutaneous recordings. Transcutaneous recordings of gastric electrical activity assessed by computer analysis can usually recognise normal gastric electrical activity and tachygastria. Current techniques, however, are unable to detect abnormalities in electrical coupling.
Diagnosis, Computer-Assisted↗
Simultaneous measurement of electrical activity from two colonic smooth muscle layers using a dual sucrose gap apparatus.
An apparatus using the sucrose gap technique is presented. With this apparatus simultaneous measurements of contractile and intracellular electrical activity from the two smooth muscle layers of the colon are made. An "L-shaped" muscle preparation consisting of a leg from the circular muscle layer and a leg from the longitudinal muscle layer is used. A theoretical discussion of the device's operation is presented. Finally, experimental results that validate the theory are included.
Animals↗
Electrical and mechanical interactions between the muscle layers of canine proximal colon.
Electrical and mechanical interactions between the two smooth muscle layers of canine colon have been studied using a dual sucrose gap apparatus. Muscle samples were dissected into an L-shape, with one leg cut in the circular direction and the other cut in the longitudinal direction. Longitudinal muscle was removed from the circular leg and circular muscle was removed from the longitudinal leg. The bend of the L contained both layers. The activity of the two layers was studied simultaneously under basal conditions, after stimulation by neostigmine and carbachol, and in the presence of tetrodotoxin. Interactions were more common after stimulation and were marked by modification of one layer's mechanical and electrical activity during increased activity in the other layer. Two patterns were commonly observed. First, during a burst of membrane potential oscillations and spike potentials in the longitudinal layer, slow waves in the circular layer developed spike potentials and some slow waves were also prolonged. Second, during a slow-wave cycle in the circular layer, the amplitude of membrane potential oscillations in the longitudinal layer was increased with an associated increase in the incidence of spike potentials. These interactions were associated with contractions of increased strength, which were similar in both layers. All interactions continued after nerve-conduction blockade by tetrodotoxin.
Animals↗
Pressure response of human colon to intraluminal distension.
Pressure response to intraluminal distension was recorded in the ascending and descending colon of six subjects awaiting closure of transverse colostomies to assess and compare compliance in different regions of the human colon. Resistance to distension was significantly greater in the descending colon at intraluminal volumes of 30 ml or greater (P less than 0.01). An equal number of postmortem studies, representing passive connective tissue resistance, demonstrated a similar but more pronounced difference (P less than 0.001), which was maintained after correction for initial intraluminal diameter differences (P less than 0.001). The differences between in vivo and postmortem results indicated an active muscular component in the response of the ascending colon to distension compared with a totally passive distal response. These results support the concept of a functional division in the human colon.
Colon↗
Colonic and anorectal motility in young women with severe idiopathic constipation.
Forty-four severely constipated women and 16 (8 female, 8 male) asymptomatic volunteers underwent assessment of colon function by (a) clinical examination, (b) rectosigmoid intraluminal pressure recording, (c) colonic transit utilizing radiopaque markers, (d) anorectal manometry, and (e) rectosigmoid electrical activity. Constipated patients were characterized by (a) a greater volume and pressure of rectal distention required for both sensation and sphincter relaxation, (b) diminished basal and postmorphine motility indices only in the distal rectum, (c) delayed transit, and (d) an empty rectum when severely constipated. A neural abnormality affecting afferent nerves may be present in the rectum of female patients with severe idiopathic constipation. Delivery of stool to the rectum is impaired in these patients.
Adult↗
Study of transcutaneous and intraluminal measurement of gastric electrical activity in humans.
Explore the source record for details and available documents.
Electrodes↗
Noninvasive assessment of human gastric motor function.
Explore the source record for details and available documents.
Biomechanical Phenomena↗
Effect of the menstrual cycle on gastric emptying.
Gastric emptying of both solid- and liquid-phase markers was assessed in 7 normally-menstruating women who had undergone bilateral Fallopian tube ligations. The women were studied once during the follicular phase of their menstrual cycle and again during the luteal phase. Emptying of the liquid-phase marker was not significantly different during the two phases of the menstrual cycle. However, emptying of the solid-phase marker was significantly slower during the luteal phase of the cycle as compared to the follicular phase. This impairment of gastric emptying of solid was correlated with elevated serum levels of progesterone. This study demonstrates that the rate of gastric emptying of solids may vary with the phases of the menstrual cycle.
Adult↗
Esophageal motor abnormalities in gastroesophageal reflux and the effects of fundoplication.
Recordings of esophageal manometry obtained from 18 healthy control subjects and 32 patients with gastroesophageal reflux disease both before and after fundoplication were assessed. Preoperatively, the patients had a mean lower esophageal sphincter pressure at rest that was significantly lower (p less than 0.001) than that observed in the control group. The amplitude of peristaltic contractions, elicited by wet swallows, varied along the length of the esophagus. In patients with gastroesophageal reflux disease, the mean amplitudes recorded from the upper, middle, and lower esophagus were significantly lower (p less than 0.001) than those recorded from control subjects. No significant differences were observed between those patients with (53%) and without preoperative endoscopic evidence of esophagitis. After antireflux surgery (modified Nissen fundoplication), the mean amplitude of peristaltic contractions increased significantly (p less than 0.001) at all levels of the esophagus and were not significantly different from control values. This study describes motor abnormalities in the body of the esophagus associated with gastroesophageal reflux disease. These may arise secondary to gastroesophageal reflux inasmuch as they disappear after fundoplication.
Adolescent↗
Human colonic smooth muscle: electrical and contractile activity in vitro.
Extracellular electrical and contractile activities were recorded in vitro from strips of human colonic smooth muscle obtained at the time of surgery. Serosal electrical activity of longitudinally oriented strips from the taenia and intertaenial region was characterised by continuous oscillation at a frequency of 28 +/- 1/min. Contractions were marked electrically by a series of oscillations upon which spikes were superimposed. The electrical activity recorded from the submucosal surface of circularly oriented strips exhibited oscillations at 24 +/- 4/min, a frequency significantly lower (p less than 0.001) than that recorded from the serosal surface of similar preparations. The contractile force and frequency was dependent upon the part of the colon from which the strip originated; the most powerful contractions were recorded from strips of sigmoid colon. The contractile frequency of circularly oriented strips from the right colon was 6.3 +/- 0.6/min, significantly higher (p less than 0.001) than that of strips from the left colon (3.4 +/- 0.3/min). Stretching these strips caused an increase in contractile frequency to that of the electrical oscillation.
Colon↗
Human colonic smooth muscle: spontaneous contractile activity and response to stretch.
The length dependence of the spontaneous contractile activity of human colonic muscle was assessed in vitro. Muscle obtained from the right colon was more distensible than that of the left colon. This was true for all muscle layers. Maximum spontaneous active stress was exerted by both circular and longitudinal muscle layers of the right colon at greater degrees of stretch (p less than 0.001) than those of the left colon. The contractile frequency of longitudinally oriented strips increased with length. The contractile frequency of intertaenial longitudinally oriented strips from the right colon was lower (p less than 0.001) than that of strips from the left colon. The contractile frequency of circularly-oriented strips from the right colon (6.25 +/- 0.38 min) was higher (p less than 0.001) than that of strips from the left colon (3.35 +/- 0.35 min). The human colon appears to consist of two distinct areas based on the mechanical behaviour of the smooth muscle during spontaneous contraction.
Colonic Neoplasms↗
Effect of progesterone on canine colonic smooth muscle.
This study was undertaken to ascertain the effect and mode of action of progesterone on canine colonic smooth muscle in vitro. Circularly orientated strips of smooth muscle exhibited low-amplitude contractions at the slow wave frequency. Longitudinally orientated strips exhibited larger-amplitude contractions that were associated, electrically, with a series of "spikes" superimposed on a high-frequency oscillation in membrane potential. Progesterone reduced the contractile force of both the circularly and longitudinally orientated strips and the contractile frequency of the longitudinally orientated strips in a dose-dependent manner; this inhibitory effect was observed in the presence of tetrodotoxin but not atropine. The stimulatory effects of a high-potassium superfusate were antagonized by progesterone and verapamil, the effect of progesterone being reversed by increasing the calcium concentration of the superfusate. We conclude that progesterone exerts an inhibitory effect on colonic smooth muscle and this may be mediated by changes in the cytoplasmic calcium concentration.
Animals↗
Intracellular electrical activity in circular muscle of canine colon.
In vivo and extracellular in vitro studies of colon muscle have led to a great deal of disagreement on the characteristics of slow wave activity. As intracellular recordings of electrical activity in single cells give clear records which are easier to analyse, we used this method to study the slow wave activity of the circular muscle of three different parts of the canine colon. Mucosa was removed from segments of proximal, mid and distal canine colon and specimens from each segment were mounted in an organ bath perfused with oxygenated Krebs' solution. Membrane potential, amplitude and frequency of slow waves were measured using intracellular electrodes. Slow wave activity was present at a single, continuous frequency of 4-6 cpm in the circular muscle at all the sites studied in canine colon. There was no significant frequency gradient along the colon: the membrane potential and amplitude of slow waves did not differ significantly in the three parts of the colon.
Animals↗