Kenneth L. Bowes

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.

Microprocessor controlled movement of solid colonic content using sequential neural electrical stimulation

BACKGROUND AND AIMS Invoked peristaltic contractions and movement of solid content have not been attempted in normal canine colon. The purpose of this study was to determine if movement of solid content through the colon could be produced by microprocessor controlled sequential stimulation. METHODS The study was performed on six anaesthetised dogs. At laparotomy, a 15 cm segment of descending colon was selected, the proximal end closed with a purse string suture, and the distal end opened into a collecting container. Four sets of subserosal stimulating electrodes were implanted at 3 cm intervals. The segment of bowel was filled with a mixture of dog food and 50 plastic pellets before each of 2-5 random sessions of non-stimulated or stimulated emptying. Propagated contractions were generated using microprocessor controlled bipolar trains of 50 Hz rectangular voltage having 20 V (peak to peak) amplitude, 18 second stimulus duration, and a nine second phase lag between stimulation trains in sequential electrode sets. RESULTS Electrical stimulation using the above mentioned parameters resulted in powerful phasic contractions that closed the lumen. By phase locking the stimulation voltage between adjacent sets of electrodes, propagated contractions could be produced in an aboral or orad direction. The number of evacuated pellets during the stimulation sessions was significantly higher than during the non-stimulated sessions (p<0.01). CONCLUSIONS Microprocessor controlled electrical stimulation accelerated movement of colonic content suggesting the possibility of future implantable colonic stimulators.

The Normal Human Esophageal Mucosa: A Histological Reappraisal

In 19 asymptomatic subjects, a total of 95 mucosal suction biopsies were taken from multiple sites in the distal 10 cm of esophagus. The biopsies were examined for evidence of basal cell hyperplasia and elongated dermal papillae, features considered to be histological consequences of gastroesophageal reflux. Fifty-seven per cent of the biopsies in the distal 2.5 cm of the esophagus and 19% of the biopsies above 2.5 cm exhibited these histological features.

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.

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.

Origin of Slow Waves in the Canine Colon

The objectives of this work were to determine the origin of slow wave activity in the canine colon, to examine the slow wave characteristics in the circular and longitudinal muscle layers, and to examine the roles played by each of these layers in the generation of this activity. Extracellular electrical activity was recorded in vitro from strips of intact muscle wall and from isolated circular and longitudinal muscle using either multiple electrodes applied to one side of the specimen or two electrodes applied simultaneously to opposite sides of the tissue. Intracellular electrical activity was also studied in intact muscle, in isolated circular muscle, and in isolated longitudinal muscle. Slow waves were recorded extracellularly from circular and longitudinal muscle when the two layers formed the intact muscle wall; they were also recorded from isolated circular muscle, but not from isolated longitudinal muscle. Removal of the submucosa from the circular muscle surface abolished slow waves recorded from both isolated circular muscle and the intact specimen. Exposure of the mucosal surface of isolated circular muscle to a hypertonic solution of KCl abolished slow waves, while exposure of the serosal surface to the same concentrations had no effect. Slow waves are not generated in longitudinal muscle. Slow waves in circular muscle are dependent on the integrity of the junction between the submucosa and the innermost circular layer.

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.

Computer model of gastric electrical stimulation

The aim of the study was to simulate gastric electrical stimulation using a computer model of gastric electrical activity and suggest a possible avenue toward reliable gastric pacing. Modeling was based on the conoidal dipole model of gastric electrical activity described earlier. It was assumed that local, nonpropagated contractions can be produced circumferentially using 4 rings of stimulating electrodes supplied with 2-sec phase-locked bipolar trains of 50 Hz, 15 V (peak to peak) rectangular voltage. Temporal and propagation organizations of gastric electrical activity described in the conoidal dipole model were used to derive the geometry of the stimulating electrodes and the time shifts for phase-locking of the electrical stimuli applied to the different circumferential electrode sets. The major assumptions and findings of the model were tested on two unconscious dogs. The model produced completely controllable simulated gastric contractions that could be propagated distally by phase-locking the stimulating voltage. The values of interelectrode distances in different rings, as well as the distances between the successive rings, were also derived. The concept of invoked circumferential contractions that are artifically propagated by phase-locking the stimulating voltage could be an avenue toward reliable gastric pacing of gastroparetic patients.

Noninvasive Assessment of Human Gastric Motor Function

A noninvasive technique to monitor gastric electrical activity (GEA) and mechanical activity as an aid in assessing gastric motor function is presented. The GEA is measured with ordinary ECG electrodes located on the torso in the region above the stomach. The mechanical activity is recorded through an electrical impedance monitoring device. A study of a mathematical model of the electrically active antral part of the stomach in the body revealed that the waveform of the extracorporeally measured signals can be related to the direction of propagation of the GEA. This feature was confirmed experimentally.

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.