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D C Barber

Publications and source records attributed to D C Barber.

At least 73 records · Page 4Linked to original sources
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

The effect of methodology and tracer identity on a non-invasive index of liver blood flow.

There are a number of clinical conditions in which quantification of the relative flow in the arterial and portal vessels supplying the liver may be of diagnostic use. The hepatic perfusion index has been proposed as a non-invasive indicator of relative blood flows. The technique involves analysis of first-pass time-activity curves over the liver and kidney with the calculations of an index which is derived from the slopes of the hepatic curve before and after the renal peak. In previously published studies, the methodology adopted has been variable, both in the analysis and in tracer identity. This study examines the effect of both physical and physiological variables on the index. The results indicate that in addition to relative arterial and portal flows, the index is dependent on bolus quality, the length of time over which the slopes are averaged, transit times through the liver and splenic and mesenteric circulations, and the degree of tracer extraction. Furthermore, the data suggest that values in the currently considered abnormal range may be poor indicators of relative arterial and portal venous flows.

Humans↗
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↗
PubMed1986

Factor analysis of dynamic function studies using a priori physiological information.

The computation of physiological factors and factor images by factor analysis in dynamic structures using the constraints of positive factors and spatial distribution of these factors (FADS), currently used by a number of research workers, is investigated. While the positivity constraints used may be quite acceptable physically, they cannot be strictly said to have direct correlations with the underlying physiological mechanisms in a dynamic study. In principle, FADS estimates the underlying model in the absence of a priori physiological information, and therefore, it is possible that in some situations an incorrect model is extracted. A procedure called IBFADS (information-based factor analysis in dynamic structures) is described which incorporates the IM (intersection method) technique previously developed into FADS, in order to reduce the error in the estimation of the correct model. IM uses a constraint based on physiology of one of the dynamic structures in the model. A computer simulated dynamic phantom study is used to demonstrate IBFADS.

Computer Simulation↗
PubMed1986

A completely automatic method of processing 131I-labelled Rose Bengal dynamic liver studies.

A completely automatic method of measuring Rose Bengal uptake by the liver, expressed in terms of the half-time T1/2, is described. There is no requirement to construct time-activity curves with blood background activity correction as in the conventional regions-of-interest method. All the dixels in the image of a study are used in the actual data analysis. The method is therefore independent of operator influence. The intersection method is offered as an alternative to the manual method. The intersection method uses principal components analysis as a first step in the computation of the intersection of a theory space and a study space. A simple exponential function is used to generate the liver theory space. Sixty 131I Rose Bengal liver function studies were processed by the intersection method. The first forty minutes of patient data were used in the analysis. To validate the new method, computed T1/2 values were compared with those obtained by the manual method. A standard statistical test showed no significant difference between the two methods. Regression analysis gave a value for the coefficient of correlation of 0.89. The intersection method is currently in routine use for the automatic analysis of Rose Bengal liver studies and is faster than the manual method.

Autoanalysis↗
PubMed1986

Carotid artery blood flow: single factor classification of Doppler waveforms.

The usefulness of principal components factor analysis as a way of classifying Doppler waveforms from the carotid artery has been established. The waveform is first reduced to a small set of coefficients which capture, via their associated principal components, the essential shape of the waveform. The vector of these coefficients can be used to classify the waveform by finding the position of this vector in a classification space relative to one or more classifying surfaces. This short communication will show how these two steps may be combined to produce a single factor for classification.

Carotid Arteries↗
PubMed1986

Simultaneous measurement of gastric emptying, small bowel residence and colonic filling of a solid meal by the use of the gamma camera.

A method for determining the profiles of gastric emptying, small intestinal residence, and colonic filling of a solid test meal, labelled with 250 microCi 99mTechnetium sulphur colloid has been evaluated in nine healthy volunteers and six patients with a disturbance in bowel habit. Mean small bowel transit time was determined by deconvolving the rate of colonic filling with the rate of gastric emptying. In normal subjects, the stomach appeared to empty exponentially with a half time of 1.2 +/- 0.3 hours (mean +/- SD). Food reached the colon by 2.8 +/- 1.5 hours. The mean small bowel transit time was 4.0 +/- 1.4 hours. In most normal subjects, the colon appeared to fill in a linear fashion with approximately 16% food residues entering every hour, and the profile of colonic filling in normal subjects was similar to the profile of ileal emptying observed after feeding a similar radiolabelled solid meal to 14 patients equipped with terminal ileostomies. There was a highly significant correlation between the onset of breath hydrogen excretion and the appearance of radioactivity over the caecum (r = 0.88, p less than 0.01), though in one third of subjects the increase in caecal radioactivity preceded the rise in breath hydrogen concentration by more than 20 minutes. There was also a highly significant correlation between the mean transit time and values for colonic filling but not values for gastric emptying. Patients with irritable bowel syndrome who had diarrhoea tended towards short small bowel transit and early colonic filling, whereas patients who have constipation tended towards long small bowel transit and delayed colonic filling. This method offers a novel means of assessing small bowel transit time, small bowel residence and the profile of colonic filling in man.

Adult↗
PubMed1985

Towards automatic analysis of dynamic radionuclide studies using principal-components factor analysis.

A method is proposed for automatic analysis of dynamic radionuclide studies using the mathematical technique of principal-components factor analysis. This method is considered as a possible alternative to the conventional manual regions-of-interest method widely used. The method emphasises the importance of introducing a priori information into the analysis about the physiology of at least one of the functional structures in a study. Information is added by using suitable mathematical models to describe the underlying physiological processes. A single physiological factor is extracted representing the particular dynamic structure of interest. Two spaces "study space, S' and "theory space, T' are defined in the formation of the concept of intersection of spaces. A one-dimensional intersection space is computed. An example from a dynamic 99Tcm DTPA kidney study is used to demonstrate the principle inherent in the method proposed. The method requires no correction for the blood background activity, necessary when processing by the manual method. The careful isolation of the kidney by means of region of interest is not required. The method is therefore less prone to operator influence and can be automated.

Humans↗
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↗
PubMed1985

Analysis of the heart rate and breathing patterns of infants destined to suffer sudden infant death syndrome: probability density function analysis.

From a prospective study into the sudden infant death syndrome in which 24-h recordings of the ECG and respiratory waveform (abdominal wall movement) were made on a population of full-term infants, 22 recordings were obtained on 16 infants who subsequently suffered sudden infant death syndrome. The probability density function for the instantaneous heart rate and the breath to breath intervals and their randomly variabilities were calculated for these 22 recordings and for a control group of 324 infants randomly selected from the remainder of the population. A principal components analysis was then performed to classify the data and to make comparisons between infants. The infants in the analysis were divided into three postnatal age groups. No differences were found between the sudden infant death syndrome cases and the control group for the breath to breath intervals and its variability or for the instantaneous heart rate. Three sudden infant death syndrome cases lay outside the range of values for the heart rate variability at 6 wk of age.

Age Factors↗
PubMed1984

Relationship between postprandial motor activity in the human small intestine and the gastrointestinal transit of food.

Profiles for gastric emptying and colonic filling were determined in 20 normal volunteers by means of a gamma camera and dedicated minicomputer after ingestion of a radiolabeled solid meal. These were compared with intraluminal pressure activity, recorded simultaneously from three sites (each separated by 50 cm) in the small intestine by infusion manometry. Recordings were continued for at least 8 h or until all the radioactivity appeared in the colon. Colonic filling was approximately linear, occurring at an average rate of 16% of the meal residues per hour. There were significant inverse correlations (p less than 0.01) between the pressure activity in the proximal jejunum during the first 3 h after ingestion and the times taken for 50% and 80% of the meal residues to enter the colon, and direct correlations between total small intestinal pressure activity and the half-time for gastric emptying. Phase III of the interdigestive migrating motor complex appeared between 3 and 9 h after ingestion (when between 15% and 80% of the meal remained in the small intestine), but did not necessarily migrate to the next recording site until much later. The time of appearance of phase III in the proximal jejunum was directly correlated with the half-time for gastric emptying (p less than 0.05) and with the intraluminal pressure activity recorded at that site during the first 3 h after food ingestion (p less than 0.01). The time at which 80% of the meal residues had entered the colon was significantly shorter in 6 subjects, in whom a postprandial activity front appeared to migrate throughout the small bowel, compared with 13 subjects, in whom this did not occur (5.0 +/- 0.5 h vs. 7.0 +/- 0.4 h, p less than 0.01). These studies have shown that gastrointestinal transit of a solid meal is related to both fed and fasted intraluminal pressure activity in the small intestine.

Adult↗
PubMed1983

Comparison of jejunal and ileal absorptive functions for glucose and valine in vivo--a technique for estimating real Km and Jmax in the domestic fowl.

1. A technique is described that enables the kinetic characterisation of the saturable absorption mechanisms in the chicken jejunum and ileum for glucose and valine in vivo (after correction for non-saturating components and unstirred layers) by estimation of real Km and Jmax. 2. In the ileum both nutrients have lower real Km and higher Jmax values than in the jejunum indicating, at least for hexose and amino acids, that the ileal enterocytes are functionally equipped and anatomically well-sited to fulfil the role of scavengers of the small intestine.

Animals↗
PubMed1983

Reticuloendothelial function in coeliac disease and ulcerative colitis.

Patients with ulcerative colitis and coeliac disease who had been shown by impaired clearance of heat damaged red cells to have diminished splenic phagocytosis, were examined for evidence of more generalised reticuloendothelial malfunction by measuring their circulatory clearance of micro-aggregated albumin. Although in animals micro-aggregated albumin is largely removed by Kupffer cells, we found impaired clearance in otherwise normal subjects who had previously had surgical splenectomy. In patients with hyposplenism because of bowel disease there was no additional impairment of micro-aggregated albumin clearance, indicating that their hyposplenism is an isolated phenomenon and not part of a generalised reticuloendothelial atrophy. Patients with coeliac disease and normal splenic function had increased reticuloendothelial catabolic activity; this was not present in patients with coeliac disease and abnormal splenic function.

Adolescent↗