PubMed Health⌕ Search

Biomedical subjects

E Dick

Publications and source records attributed to E Dick.

At least 19 recordsLinked to original sources
PubMed2000

Computer simulation of intraventricular flow and pressure gradients during diastole.

A two-dimensional axisymmetric computer model is developed for the simulation of the filling flow in the left ventricle (LV). The computed results show that vortices are formed during the acceleration phases of the filling waves. During the deceleration phases these are amplified and convected into the ventricle. The ratio of the maximal blood velocity at the mitral valve (peak E velocity) to the flow wave propagation velocity (WPV) of the filling wave is larger than 1. This hemodynamic behavior is also observed in experiments in vitro (Steen and Steen, 1994, Cardiovasc. Res., 28, pp. 1821-1827) and in measurements in vivo with color M-mode Doppler echocardiography (Stugaard et al., 1994, J. Am. Coll. Cardiol., 24, 663-670). Computed intraventricular pressure profiles are similar to observed profiles in a dog heart (Courtois et al., 1988, Circulation, 78, pp. 661-671). The long-term goal of the computer model is to study the predictive value of noninvasive parameters (e.g., velocities measured with Doppler echocardiography) on invasive parameters (e.g., pressures, stiffness of cardiac wall, time constant of relaxation). Here, we show that higher LV stiffness results in a smaller WPV for a given peak E velocity. This result may indicate an inverse relationship between WPV and LV stiffness, suggesting that WPV may be an important noninvasive index to assess LV diastolic stiffness, LV diastolic pressure and thus atrial pressure (preload).

Blood Flow Velocity↗
PubMed1999

Left-ventricular pressure gradients: a computer-model simulation.

Both invasive left-ventricular pressure measurements and non-invasive colour M-mode echographic measurements have shown the existence of intraventricular pressure gradients (IVPGs) during early filling. The mechanisms responsible for these IVPG cannot be completely explained by the experiments. Therefore a one-dimensional numerical model is developed and validated. The model describes filling (both velocities and pressures) along a left ventricular (LV) base-apex axis. Blood-wall interaction in the left ventricle with moving boundaries is taken into account. The computational results for a canine heart indicate that the observed IVPGs during filling are the consequence of a complex interaction between, on the one hand, pressure waves travelling in the LV and, on the other hand, LV geometry, relaxation and compliance. The computational results indicate the pressure dependency of wavespeed (0.77-1.90 m-1 s) for different mean intraventricular pressures (0.88-5.00 mmHg) and IVPGs up to 2 mmHg, independent of the ratio of end systolic volume and equilibrium volume. Increasing relaxation rate not only decreases minimum basal pressure (2.8 instead of 3.6 mmHg) but also has a strong influence on the time delay between the minimum basal and apical pressures (14 ms instead of 49 ms). The results sustain the hypothesis that pressure-wave propagation determines IVPGs and that IVPGs are no proof of elastic recoil.

Blood Pressure↗
PubMed1999

A three-dimensional analysis of flow in the pivot regions of an ATS bileaflet valve.

Bileaflet heart valves are currently the most commonly implanted type of mechanical prosthetic valve, because of their low transvalvular pressure drop, centralised flow and durability. However, in common with all mechanical heart valves, implanted bileaflet valves show an inherent tendency for blood clot formation at the valve site. Fluid dynamical phenomena associated with blood clotting are elevated blood shear stresses and regions of persistent blood recirculation, particularly when both occur together. Using three-dimensional CFD modelling, combined with enlarged scale experimental modelling, we investigated the blood flow through the ATS bileaflet valve during forward flow, with particular attention to the leaflet pivot regions. Recirculating regions were found both within and downstream of the valve housing ring. Qualitative assessment of the entire cardiac cycle suggested that recirculating blood within the housing ring will be washed away whilst the valve is closed, but as with all bileaflet valve designs recirculating blood downstream of the valve may have a residence time much longer than one cardiac cycle.

Blood Flow Velocity↗
PubMed1989

Use of the mouse for the isolation and investigation of stomach-associated, spiral-helical shaped bacteria from man and other animals.

Spiral-helical shaped bacteria other than Campylobacter pylori have been shown to infect the human stomach. The characteristic helical morphology of these bacteria appears to be similar to that of bacteria found in the stomachs of many other animal species. Early reports on gastric bacteria suggested that rodents may be useful for investigation and isolation of stomach-associated bacteria. Therefore, anaesthetised mice were given, through a stomach tube, a heavy suspension of a spiral-helical bacterium from a cat, scrapings of gastric mucus from primates, or a homogenised whole-antral biopsy from a human patient. At intervals after inoculation, gastric biopsies were examined by lightmicroscopy and electronmicroscopy for the presence of spiral-helical bacteria. Significant colonisation was observed in 40% of mice 1 week, and in 80% of mice 11 weeks, after inoculation with suspensions of the cat isolate. Mice were also successfully colonised by spiral bacteria present in homogenised human biopsy material and by other spiral bacteria from a monkey. These observations suggest that mice may prove to be useful animals for the study of gastric bacteria that are, as yet, non-cultivable and for analysis of some of the attributes commonly thought to be involved in colonisation.

Animals↗
PubMed1989

Non Campylobacter pylori spiral organisms in the gastric antrum.

Colonisation of the human gastric antrum with non Campylobacter pylori spiral organisms is described. A moderately severe histological gastritis was present despite the fact that these organisms, in contrast to C. pylori, were not closely associated with the epithelial cell surface. Although in vitro culture of the organisms was unsuccessful, in vivo culture was achieved in the mouse stomach. Further study of these spiral organisms should provide important clues to the role of bacteria in upper gastrointestinal disease.

Adult↗
PubMed1989

The effect of parainfluenza 3 infection on guinea pig basophil and lung mast cell histamine release.

The guinea pig infected with parainfluenza 3 (P-3) has provided an animal model to study mechanisms of virus-induced asthma and airway hyperreactivity. Evidence to identify the mechanisms by which P-3 infection enhances airway hyperreactivity, however, has not been established. The present study evaluated the effect of P-3 infection on histamine release (HR) from isolated peripheral blood guinea pig basophils and lung mast cells. Basophil HR was determined in animals made basophilic with 13 daily intraperitoneal injections of sheep blood. On Day 10 of the sensitization, blood was obtained from all animals, and leukocyte HR was determined to sheep gammaglobulin (SG), which served as the secretagogue. After these baseline studies, the animals were separated into two groups; one was insufflated with P-3 virus and the other with growth medium that did not contain virus. Four days later, animals were killed, basophils and lung mast cells were isolated, HR was determined, and lung tissue was cultured for the presence of virus. In basophils isolated from animals proven to be infected with P-3 virus, we found significantly more histamine released in response to the lower doses of SG and a significant shift in the -log EC50 dose of this antigen causing HR in these cells. Experiments conducted with the calcium ionophore A23187 as the basophil secretagogue in the same experimental design did not demonstrate similar HR findings. Furthermore, a defect in calcium disposition did not account for the enhanced HR from basophils isolated from infected animals. HR from pulmonary mast cells was similar in cells isolated from P-3-infected and control insufflated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Extracellular K+ activity changes related to electroretinogram components. I. Amphibian (I-type) retinas.

Electroretinographic (ERG) and extracellular potassium activity measurements were carried out in superfused eyecup preparations of several amphibians. Light-evoked changes in extracellular K+ activity were characterized on the bases of depth profile analysis and latency measurements and through the application of pharmacological agents that have selective actions on the retinal network. Three different extracellular potassium modulations evoked at light onset were identified and characterized according to their phenomenological and pharmacological properties. These modulations include two separable sources of light-evoked increases in extracellular K+: (a) a proximal source that is largely post-bipolar in origin, and (b) a distal source that is primarily or exclusively of depolarizing bipolar cell origin. The pharmacological properties of the distal extracellular potassium increase closely parallel those of the b-wave. A distal light-evoked decrease in extracellular potassium appears to be associated with the slow PIII potential, based on a combination of simultaneous intracellular Müller cell recordings and extracellular ERG and potassium activity measurements before and during pharmacological isolation of the photoreceptor responses. The extracellular potassium activity increases are discussed with respect to the Müller cell theory of b-wave generation.

Ambystoma↗
PubMed1985

Extracellular K+ activity changes related to electroretinogram components. II. Rabbit (E-type) retinas.

Electroretinogram (ERG) and extracellular potassium activity (K+o) measurements were carried out in isolated superfused rabbit eyecup preparations under control conditions and during the application of pharmacological agents that selectively modify the light-responsive retinal network. Light-evoked K+o changes in the rabbit (E-type) retina resemble those previously described in amphibian (I-type) retinas. Different components of the light-evoked K+o changes can be distinguished on the bases of retinal depth, V vs. log I properties, and their responses to pharmacological agents. We find two separable sources of light-evoked increases in extracellular K+: a proximal source and a distal source. The properties of the distal light-evoked K+o increase are consistent with the hypothesis that it initiates a K+-mediated current through Müller cells that is detected as the primary voltage of the electroretinographic b-wave. These experiments also support previous studies indicating that both the corneal-positive component of c-wave and the corneal-negative slow PIII potential result from K+-mediated influences on, respectively, the retinal pigment epithelium and Müller cells.

Acetylcholine↗
PubMed1985

Distribution of glucose-1,6-bisphosphate and IMP-activated glucose bisphosphatase in brain and retina.

The activity of glucose-1,6-bisphosphatase and the level of its substrate were measured in 16 gray areas and four fiber areas of mouse brain and 10 layers or sublayers of monkey retina. Because of the low activity of the enzyme and the small sample sizes, it was necessary to develop a method with two different amplification steps (overall amplification about 10(6]. The enzyme ranged in activity 100-fold from a low in monkey retina photoreceptor cells to a high in the pyramidal layer of the hippocampus. However, in gray areas of the brain proper the range was only about fourfold. This, together with its requirement for IMP, suggests that the enzyme has a widespread metabolic function related to states of increased neuronal activity. Glucose-1,6-bisphosphate levels varied from 80 to 960 mu mol/kg dry weight in different areas of mouse brain and from 44 to 200 mu mol/kg dry weight in different layers of monkey retina. In general, the glucose bisphosphate levels correlated positively with the bisphosphatase activities; however, the three areas with the highest enzyme concentrations did not fit this pattern.

Animals↗
PubMed1984

Distribution of glycine, gamma-aminobutyric acid, glutamate decarboxylase, and gamma-aminobutyric acid transaminase in rabbit and mudpuppy retinas.

The distributions of glycine, gamma-aminobutyric acid (GABA), glutamate decarboxylase (EC 4.1.1.15), and GABA transaminase (EC 2.6.1.19) were determined in rabbit and mudpuppy retinas. In both species, peak levels of the amino acids and the enzymes occurred in the inner plexiform layer. Glutamate decarboxylase was almost entirely confined to the inner plexiform layer. Determinations were also made of the GABA content of 107 individual putative amacrine cell somas from mudpuppy retina. About 30% of those somas were found to have high endogenous GABA levels.

4-Aminobutyrate Transaminase↗
PubMed1984

Enzymes of energy metabolism in the mudpuppy retina.

The distributions of glycogen phosphorylase, hexokinase, phosphofructokinase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase, citrate synthase, malate dehydrogenase, beta-hydroxyacyl CoA dehydrogenase, and adenylokinase were determined in the mudpuppy retina. Distinct differences were found in regard to the glycolytic and oxidative capacities of the various layers. In the outer retina, citric acid cycle enzymes were high while glycolytic enzymes were low. Synaptic zones were distinctly enriched in all energy-producing enzymes. Mudpuppy photoreceptors were found to be rich in phosphorylase but poor in glucose-6-phosphate dehydrogenase, suggestive of some evolutionary divergence from mammals in the metabolic machinery which is used to support the visual process.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1983

Clinical implications of research on the mechanism of action of lithium.

Lithium is a unique drug in its clinical profile in psychiatry. Lithium has numerous biochemical effects, but none has yet been proven to be its mode of therapeutic action. Inhibition of noradrenaline-sensitive adenylate cyclase is reviewed as the only biochemical effect of lithium shown to occur in both animals and man at therapeutic lithium concentrations. A tetracycline antibiotic, demeclocycline, also blocks noradrenaline-sensitive adenylate cyclase. A clinical trial of demeclocycline in mania would provide a test of the adenylate cyclase theory of lithium action.

Adenylyl Cyclase Inhibitors↗
PubMed1981

Peptides influence retinal ganglion cells.

Neurotensin, substance P and (D-Ala2, Met5)-enkephalinamide were iontophoresed onto ganglion cells of the amphibian retina. Substance P and neurotensin were found to be excitatory while (D-Ala2, Met5)-enkephalinamide suppressed all types of ganglion cells. These findings are consistent with a functional role for peptides in the vertebrate retina.

Amphibians↗
PubMed1977

[The hypnotic effect of fentanyl and sulfentanil. An electro-encephalographic comparison (author's transl)].

1. Electroencephalographic activity was registered in healthy subjects before, during and 90 minutes after intravenous injections of sufentanil and fentanyl. 2. With a dosage of ratio of 1:10, i.e., 0.025 mg/70 kg body weight sufentanil: 0.25 mg/70 kg body weight fentanyl as well as 0.015 mg/70 kg body weight sufentanil: 0.15 mg/70 kg body weight fentanyl, sufentanil was hypnotically more potent from fentanyl. 3. Sufentanil acts more powerfully on the respiratory regulation than does fentanyl. Periods of apnoea occur more frequently but can be interrupted by external psychophysiological stimulation. 4. The evaluation of indices of certain EEG-waves, characterizing well defined electroencephalographic stages corresponding to the waking-sleeping-behaviour confirmed the visual over-all analysis of the EEG-stages. 5. Physiological observations on heartrate, systemic blood pressure, rapid eye movements during wakefulness, and slow eye movements during sleepiness showed no reliable differences between sufentanil and fentanil. The systematically documented symptoms and vegetative signs of subjects also showed neither differences nor side-effects.

Adult↗