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Biomedical subjects

B H Brown

Publications and source records attributed to B H Brown.

At least 91 records · Page 5Linked to original sources
PubMed1987

Applied potential tomography: a new non-invasive technique for assessing gastric function.

Applied potential tomography is a new, non-invasive technique that yields sequential images of the resistivity of gastric contents after subjects have ingested a liquid or semi-solid 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 APT 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 APT 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, APT 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. A preliminary study is also presented that assesses the technique as a means of measuring gastric acid secretion. Comparison of resistivity changes with measured acid secretion following the injection of pentagastrin shows good correlations. APT might offer a non-invasive alternative to the use of a nasogastric tube and acid collection.

Duodenal Ulcer↗
PubMed1987

Applications of applied potential tomography (APT) in respiratory medicine.

Impedance pneumography, electrical impedance measurements of the lung, is a technique which has been widely used to monitor respiration non-invasively and more recently, the onset of pulmonary oedema. Attempts have been made to try to localise the changes in impedance using electrode arrays and electrode guarding. These techniques allow localisation to a particular hemithorax, but the resolution of the majority of the systems remains poor. To assess the performance and possible clinical applications of APT, measurements have been made following increases in lung volume and pulmonary blood volume. During inspiration an increase in both the area and the magnitude of the impedance changes over the area of the lungs was observed. Numerical analysis of the impedance changes in normal subjects reveals a consistently high correlation between the volume of air inspired and the magnitude of the impedance changes. The resolution of the system is sufficient to monitor differences in ventilation in the right and left lung and to measure variations in these levels with posture. Preliminary clinical work suggests that APT may be used to detect ventilatory defects in certain types of lung disease. APT measurements show a decrease in resistivity over the area of the lungs when the pulmonary blood volume is increased by the intravenous infusion of 1.5 litres of isotonic saline. Similar changes in the volume of fluid in the lungs are known to occur in pulmonary oedema. APT measurements of lung impedance may detect the onset of pulmonary oedema in high risk patients.

Adult↗
PubMed1987

Localisation of cardiac related impedance changes in the thorax.

The existence of variations of normal human thoracic impedance, during the cardiac cycle to high frequency electrical current is well known. Since the impedance variations within the thorax are synchronous with the electrocardiogram (ECG), they are attributed to cardiac activity. They can arise from the change of either the rate of blood flow or the blood volume in the heart chambers, the great blood vessels and the lungs. However, their relative contribution is not known. Many investigators have worked on the non-invasive determination of some cardiac parameters using surface electrode impedance measurements on the thorax. Since the relationships between the measurement results and the pulsatile circulation of blood in various organs inside the chest are not well known, the information determined by surface impedance measurements is not as accurate as the results of invasive techniques. Recent advances in the clinical use of applied potential tomography (APT), or electrical impedance imaging, showed that the APT system gives a good soft-tissue contrast and has good sensitivity to resistivity changes. It is therefore concluded that the origin of thoracic impedance changes related to cardiac activity can be deduced from APT images. Our initial studies of ECG gated dynamic APT images of the thorax show that cardiac related thoracic impedance variations originating from different organs can be separated. Sequential APT images of the thorax during the cardiac cycle are presented. The movement of blood from the ventricles to the lungs and vascular system and back to the ventricles is observable in these images.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Electrical impedance tomography; the construction and application to physiological measurement of electrical impedance images.

Electrical impedance tomography enables images of tissue resistivity to be produced from measurements made via an array of surface electrodes. Using the technique of Applied Potential Tomography (APT) an array of 16 electrodes placed around the trunk has been used to image gastric, respiratory and cardiac related events. Some of the advantages and disadvantages of the technique are considered and the possibility of improvement discussed. Some cardiac gated images are presented which show the movement of blood on systole so allowing cardiac output and lung perfusion to be displayed.

Algorithms↗
PubMed1987

Applied potential tomography. A new noninvasive technique for measuring gastric emptying.

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.

Colloids↗
PubMed1985

Applied potential tomography: possible clinical applications.

Applied potential tomography (APT) or electrical impedance imaging has received considerable attention during the past few years and some in vivo images have been produced. This paper reviews the current situation in terms of what in vivo results have been and are likely to be obtained in the near future. Both static and dynamic imaging are possible and these two areas are dealt with separately. Features of the existing in vivo imaging system are good tissue contrast, high-speed data collection, good sensitivity to resistivity changes, low spatial resolution, low cost and no known hazard. It is concluded that the most promising way forward to clinical application in the short term is to use dynamic as opposed to static imaging. An example of lung imaging is shown and the application to measuring regional ventilation and pulmonary oedema is discussed. Use of APT for the detection of intraventricular bleeding in neonates is discussed as is the proven ability to study gastric physiology by imaging resistivity distribution changes following the ingestion of conducting or insulating fluids. Other areas of possible application which are considered are blood flow measurement, cell counting, measurement of lean-fat ratios and the detection of soft tissue lesions.

Cell Count↗
PubMed1983

Electrical stimulation at the wrist as an aid for the profoundly deaf.

The development and evaluation of a sensory electrical substitution aid for the profoundly deaf is described. The aid is a small wrist-worn device which converts sound into an electrical stimulus at the wrist. The initial aim was to give profoundly deaf people useful information from ambient sounds. Evaluation of the Mark 1 aid on 15 hearing and five profoundly deaf people indicated that such a device might be of use to some deaf people. Investigation of the sensitivity of the peripheral nervous system to electrical pulse stimulation showed that information could be transmitted in a more efficient manner so a Mark 2 aid was developed which incorporated circuitry to transmit pitch information, potentially useful in lipreading. The Mark 2 aid was shown to give improved results over the Mark 1 aid in transmitting voice intonation, but gave no help in an isolated word lipreading test. A portable Mark 2 aid was developed to enable clinical trials to be carried out on profoundly deaf people.

Adult↗
PubMed1981

Effect of diazepam on pancuronium-induced neuromuscular blockade maintained by a feedback system.

The possibility of an interaction between diazepam and pancuronium bromide was investigated in six patients undergoing general anaesthesia maintained with fentanyl, droperidol and nitrous oxide. Neuromuscular blockade was controlled using a feedback mechanism which automatically adjusted the rate of injection of pancuronium to maintain between 71.4 and 72.9% blockade. Diazepam 0.14 mg kg-1 i.v. produced blood concentrations within the therapeutic range, but did not produce consistent changes in the level of blockade, pancuronium concentration in the blood or pancuronium consumption measured over 20 min.

Adolescent↗
PubMed1980

Respiratory patterns and risk of sudden unexpected death in infancy.

The overnight respiratory patterns of 25 infants at high risk and 42 infants at low risk of sudden unexpected death were studied during the first 6 months of life. 'Risk' was determined using the birth scoring criteria of Carpenter and Emery. Recordings were made at home using a twin-channel radar chest movement detector which was designed to avoid the need for contact with the infant. The recordings were analysed for respiratory frequency, total duration of apnoea, periodic breathing, duration of regular breathing, and amount of body movement. The high risk group of infants showed respiratory frequencies that were significantly higher than those of the low risk group. None of the other parameters showed significant differences between the groups. These findings do not support the widespread use of home apnoea monitors for infants.

Humans↗
PubMed1979

Training for biomedical engineering in India.

There are biomedical engineers in India and a demand for their services, but there is an absence of trained technical staff to apply the subject within the hospitals. The current situation of the medical electronics aspect of biomedical engineering within Industry, the Hospitals and Educational Institutions is described and some of the problems identified. The particular problems of the growth of a complex technical subject within a developing country are also considered.

Biomedical Engineering↗
PubMed1977

Relationship between changes in intraluminal pressure and transmural potential difference in the human and canine jejunum in vivo.

Recordings of transmural potential difference (PD) across the jejunum of conscious man in situ are characterised by spontaneous fluctuations of up to 10 mV. In 25 of 31 subjects (comprising seven normal controls and 24 patients under investigation for malabsorption, six of whom had coeliac disease) we observed a clear association between these fluctuations and changes in intraluminal pressure recorded at the same site. The most frequent PD changes were associated with type III pressure waves. These consisted predominantly of large waver (3-1 +/- 0-1 mV; mean +/- SEM, n = 317) which reached maximal amplitude approximately 45 seconds after the pressure peak and had a duration of 120 +/- 3 s, but also included less frequent spikes (0-5 +/- 0-1 mV; n = 110) concurrent with the pressure wave with a duration of 5 +/- 1 s. Although by recording at two sites in the jejunum 10 cm apart we were able to demonstrate that type III pressure waves appeared to be propagated aborally at a median rate of 60 cm per minute, the apparent rates of propagation of the corresponding PD waves were much more variable. The largest PD changes (7-8 +/- 0-4 mV; n = 19), lasting several minutes, were found in association with runs of type I waves (basic rhythm) superimposed on a type III wave. Both pressure and PD activities were suppressed by intramuscular propantheline bromide. Intraluminal pilocarpine caused a transient rise in PD not always accompanied by a change in pressure. Distention of the jejunum by rapid injection of a bolus of isotonic sodium chloride produced a delayed rise in the PD which could be prevented by prior administration of propantheline bromide. Experiments using Thirty-Vella loops of proximal jejunum in conscious dogs confirmed the effect of jejunal distension on the PD and also demonstrated that spontaneous retching is preceded by an increase in the PD. Consideration of these results in conjunction with data from other workers suggests the hypothesis that the larger spontaneous fluctuations in transmural PD in the jejunum of conscious man are caused by changes in electrogenic secretion associated with intestinal motility and mediated by cholinergic mechanisms. The possible association of increased secretory activity with motility may have functions of lubrication as well as diluting and mixing the chyme for easier digestion and absorption.

Animals↗