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Investigations have been carried out using the Sheffield mark II real-time EIT system, to look at changes in conductivity associated with swallowing. A ring of 16 electrodes was placed around the neck of 10 subjects, who then performed swallows with four liquids of different conductivities, ranging from water (sigma = 0.03 mS cm-1) to salty soup (sigma = 35.8 mS cm-1). Results showed that the conductive and non-conductive liquids could be distinguished. Bolus transit times were calculated from region of interest curves, and the average transit time for the 10 subjects was found to be 320 +/- 100 ms.

The aim of this study was to investigate the feasibility of using applied potential tomography (APT), a noninvasive and nonradioactive method, to measure the rate of gastric emptying in preterm babies and infants < 3 months old. APT, a form of electrical impedance tomography, creates tomographic images of tissue resistivity to a small electrical current and has been used to study gastric emptying in adults. The rate of gastric emptying of 53 preterm infants and 29 term infants was measured. The test feed was either milk (formula milk or expressed breast milk) or Dioralyte (a commercial rehydration solution). When a nasogastric tube was present, the results obtained by APT were validated by comparing the volume of feed estimated to be present with the volume that could be aspirated. All infants completed the investigation without any problems. APT demonstrated a slower rate of emptying of milk feeds than Dioralyte and showed that milk and Dioralyte feeds in preterm babies emptied at a similar rate to feeds in term infants. In validation studies, gastric emptying has been observed in 44 of 47 studies, and this finding was confirmed by aspiration of the nasogastric tube. Applied potential tomography is a safe, noninvasive method for measuring gastric emptying in small infants.

A planar array of electrodes has been used to provide a longitudinal section of the stomach. Impedance changes at the gastric frequency of 0.05 Hz can be detected. The changes are mainly located around the periphery of the stomach image, suggesting that they are the result of movement of the stomach wall. The generation of a vector histogram of wall movement gives a noninvasive method which appears to quantify the peristaltic waves which produce transport in the stomach.

A planar array of electrodes has been used to provide a longitudinal section of the stomach. Impedance changes at the gastric frequency of 0.05 Hz can be detected. The changes are mainly located around the periphery of the stomach image, suggesting that they are the result of movement of the stomach wall. The generation of a vector histogram of wall movement gives a non-invasive method which appears to quantify the peristaltic waves which produce transport in the stomach.

Gastric emptying in a group of 49 vomiting infants with infantile hypertrophic pyloric stenosis (IHPS) was investigated using applied potential tomography. Fourteen asymptomatic infants were also studied as a control group. A Dioralyte test feed (25 ml/kg/feed) was used for all the studies. The infants with IHPS were investigated before and at two, four, and seven days after an operation; the other infants were investigated once. The results show that the infants with IHPS have no or little gastric emptying before the operation and gradually return to normal emptying by the seventh day after the operation. A significant difference in gastric emptying was noted between the control infants and the infants with IHPS before and at two and four days after the operation. The applied potential tomography method is suitable for studying gastric emptying in infants, with no morbidity nor complications. It also allows multiple studies to be performed without upset or discomfort.

Electrical Impedance Tomography (EIT) is assessed as a means of monitoring deep hyperthermia treatments in both phantom and in vivo studies. EIT measurements during heating of an inhomogeneous leg phantom show good correlation with internal temperatures measured with invasive probes. Measurements whilst altering the temperature of the stomach contents in volunteers demonstrate the capability of EIT for imaging temperature change at depth in the torso. Significant problems remain to be overcome before EIT can be used in the clinic; however, the technique may be an important additional control factor as a complement to invasive monitoring.

Two experimental studies are presented that attempt to assess the use of electrical impedance tomography (EIT) to map thermal changes deep in the body. The first was a joint study between our group in Sheffield and the Daniel den Hoed Cancer Center in Rotterdam, funded by the COMAC-BME Hyperthermia project. Phantom and in vivo experiments were conducted with a deep heating ring-capacitive hyperthermia device; the results highlighted some of the inherent problems (electromagnetic interference, nonuniform sensitivity) that remain to be solved for this application. The second experimental study involved heating the stomachs of volunteers by pumping known quantities of liquid (a salt/glucose solution, conductivity 5 mS) at controlled temperatures (25, 37 and 47 degrees C) in and out of the stomach via a nasogastric tube. Results indicated that the level of thermal change induced by these liquids could be reproducibly measured by impedance imaging. Both studies were a further step in assessing the capabilities of EIT for noninvasive monitoring of deep body hyperthermia. The results are encouraging and indicate the value of continued development of EIT for non-invasive thermometry.

Applied potential tomography (APT) is a new noninvasive, nonradioactive method of measuring gastric emptying, which generates profiles of emptying of liquids that are similar to those obtained simultaneously by scintigraphy and dye dilution. This study validates the ability of APT to measure emptying of a solid beefburger test meal from the stomach by comparing the results obtained with those obtained simultaneously by scintigraphy. When acid secretion was inhibited, there was a significant correlation between the two methods for the time taken for half the meal to empty from the stomach and the amount of meal emptied at different time intervals. Furthermore, the profiles of gastric emptying obtained by APT resembled those obtained by scintigraphy in most studies. If acid secretion was not inhibited, there was no correlation between values obtained by the two methods.

The commonly accepted model for gastric emptying suggests that the 'antral mill' is responsible for the triturition and subsequent emptying of solid food from the stomach. Little is known about the contribution to solid emptying made by other digestive mechanisms such as acid-pepsin secretion. We have investigated the effect of inhibiting gastic secretion on the rate at which a solid test meal emptied from the stomach. Using a radiolabelled beefburger, we performed paired gammacamera studies on consecutive days in 10 fasted, healthy volunteers to compare gastric emptying of the test meal with and without oral cimetidine (400 mg 1 hour before the test, 800 mg at the start of the meal). Inhibition of acid-pepsin secretion by cimetidine was associated with an appreciable delay in the rate of emptying of the burger from the stomach (T50 cimetidine 187 (16) min (mean (SEM); T50 no cimetidine 146 (15) min; p less than 0.01, paired t test). This delay was related to a change in the slope of the emptying profile and was not associated with a prolonged lag phase. These results may be explained by the relative achlorhydria and reduced pepsin activity induced by cimetidine impairing the breakdown of solid food into particles small enough to leave the stomach.

The relation between gastric emptying and the intragastric distribution of 300 ml radiolabelled beef consomme with and without 60 g margarine was investigated by performing randomised, paired gammacamera studies in seven healthy male volunteers (aged 20-22 years). The low calorie bland meal emptied rapidly from both the proximal and distal stomach after a short lag period (4-6 min), during which 24-50% of the liquid passed into the distal stomach. Addition of margarine to the liquid test meal increased the lag period (median 32 min, range 7-60 min; p less than 0.01) and decreased the slope of emptying (T1/2 lag period 88 min, 49-146 min v 15 min, 10-57 min; p less than 0.01). During the lag period there was an initial filling of the distal stomach, similar to that with the bland liquid, followed by a redistribution of between 19% and 61% (median 46%) of the distal stomach contents back into the proximal stomach. At the onset of emptying, the distal stomach filled (median 30%, range 16-34%) and during this time the proximal stomach emptied twice as fast as the whole stomach (p less than 0.05). Thereafter, the distal stomach capacity remained relatively constant while both the proximal and whole stomach emptied at similar rates. This study shows that the delay in gastric emptying of a liquid that has a high fat content is due in part to a redistribution of distal stomach contents back into the proximal stomach.

Applied potential tomography (APT) is a new, non-invasive technique that can yield sequential images of changes in the resistivity of gastric contents. Studies were performed to investigate the application of APT to measure gastric acid secretion. Experiments in 20 normal volunteers showed that changes in gastric resistivity were closely correlated with changes in the volume (r = 0.80), the acidity (r = 0.83) and the total conductivity of gastric contents (r = 0.87). Studies in 13 patients referred for a pentagastrin test showed that changes in gastric resistivity before pentagastrin were closely correlated with basal acid output measured on a separate occasion (r = 0.85, p less than 0.001), while changes in gastric resistivity after pentagastrin were correlated with maximal acid output (r = 0.58, p less than 0.05). Ingestion of alcohol by six normal subjects decreased gastric resistivity markedly, probably due to alcohol induced gastric acid secretion as it was prevented by cimetidine. Applied potential tomography is a safe non-invasive method of measuring gastric acid secretion. The equipment is simple to use, and the test is comfortable and acceptable to patients.

Applied potential tomography is a new, noninvasive technique that yields sequential images of the resistivity of gastric contents after subjects have ingested a liquid or semisolid meal. This study validates the technique as a means of measuring gastric emptying. Experiments in vitro showed an excellent correlation between measurements of resistivity and either the square of the radius of a glass rod or the volume of water in a spherical balloon when both were placed in an oval tank containing saline. Altering the lateral position of the rod in the tank did not alter the values obtained. Images of abdominal resistivity were also directly correlated with the volume of air in a gastric balloon. Profiles of gastric emptying of liquid meals obtained using applied potential tomography were very similar to those obtained using scintigraphy or dye dilution techniques, provided that acid secretion was inhibited by cimetidine. Profiles of emptying of a mashed potato meal using applied potential tomography were also very similar to those obtained by scintigraphy. Measurements of the emptying of a liquid meal from the stomach were reproducible if acid secretion was inhibited by cimetidine. Thus, applied potential tomography is an accurate and reproducible method of measuring gastric emptying of liquids and particulate food. It is inexpensive, well tolerated, easy to use, and ideally suited for multiple studies in patients, even those who are pregnant.

Two new non-invasive methods of measuring gastric emptying, impedance epigastrography (IE) and applied potential tomography (APT) have been compared. Measurements in vitro showed that there is a good correlation between the square of the radius of a glass rod placed in the centre of a tank and values obtained by IE or APT. However, if the rod is moved anteriorly in the tank IE values increase markedly, whereas APT values are unchanged. Both APT and IE can be used to follow gastric emptying of liquid meals; however, the results obtained using APT are more reproducible and have a better correlation with those obtained simultaneously by scintigraphy. Neither method was able accurately to follow gastric emptying unless gastric acid secretion was inhibited by cimetidine.