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Biomedical subjects

R Heinrich

Publications and source records attributed to R Heinrich.

At least 127 records · Page 7Linked to original sources
PubMed1985

Exposure to fluorotrichloromethane (R-11).

Three volunteers were exposed to fluorotrichloromethane (R-11) under experimental conditions. Solvent levels in ambient and alveolar air, in blood and urine were measured. The mean concentration of R-11 in ambient air was 657 ml/m3. The average values of pulmonary retention and solvent levels in alveolar air and blood were 18.2%; 537 ml/m3 and 2.8 mg/l. Inter-individual variations of these parameters are negligible. R-11 concentrations in urine--in contrast to blood or alveolar air--depend on the dose taken up. After termination of exposure, R-11 concentrations in alveolar air and in blood are excreted with biological half-lives of seven and eleven minutes respectively during the first phase of elimination and with 1.8 and 1.0 h respectively during the second phase of elimination. Though ambient monitoring should, in most cases, be sufficient for the prevention of occupational diseases, the R-11 concentration in alveolar air seems to be the best parameter if biological monitoring seems to be necessary.

Adult↗
PubMed1985

Mathematical models of metabolic systems: general principles and control of glycolysis and membrane transport in erythrocytes.

General methods for the mathematical modeling of metabolic systems are discussed. Attention is paid to the simulation of steady states as well as time dependent behaviour of biochemical reaction networks. Control coefficients are used for the quantitative evaluation of the parameter dependence of model variables. The methods are applied to the mathematical analysis of the energy metabolism of erythrocytes. New results are presented concerning the interaction of glycolysis and osmotic behaviour of the red cell (metabolic-osmotic model). A general method for the calculation of control coefficients is developed which gives the basis also for the interpretation of control coefficients using chains of causal actions.

Adenine Nucleotides↗
PubMed1985

A kinetic model for the interaction of energy metabolism and osmotic states of human erythrocytes. Analysis of the stationary "in vivo" state and of time dependent variations under blood preservation conditions.

A model is presented which considers in a coherent way the energy metabolism, the membrane transport as well as the osmotic and electrostatic conditions of human erythrocytes. Particular attention is paid to the simulation of the system behaviour under blood preservation conditions as well as after transfusion of erythrocytes. The model considers the main glycolytic reactions, the active and passive transport of ions and the charges and osmotic actions of permeable and nonpermeable compounds. The glycolytic enzymes are characterized by realistic kinetic equations. Various non-stoichiometric regulatory couplings are taken into account. The passive transport of anions and cations is described by the Goldman-flux-equation. Mathematically, the system is described by 8 nonlinear differential equations for the concentrations of the glycolytic intermediates and ions, for the cell volume and the transmembrane potential. Further, various algebraic equations are taken into account which consider conservation conditions and equilibrium relations. The mathematical description is simplified by application of the quasi-steady state approximation. The model equations are solved for the stationary "in vivo" state and for the time dependent states observed during blood preservation and after transfusion. The theoretical results obtained by numerical integration are compared with experimental data. Conclusions are drawn with respect to the characterization of the recovery process of the energy metabolism and of the ionic states of erythrocytes after blood preservation and transfusion.

Adenine Nucleotides↗
PubMed1985

Efficiency and design of simple metabolic systems.

A theoretical approach to the explanation of the structural design of metabolic pathways is presented. It is based on the hypothesis that due to natural selection during evolution the cellular metabolism of present-day organisms may be characterized by optimal properties. Two cardinal terms enter the theory: 1) the efficiency of metabolic pathways and 2) the evolutionary effort for the change of the kinetic parameters of the involved enzymes by mutations of the corresponding genes. For both quantities simple mathematical expressions are proposed. By maximizing the efficiency under the constraint of a constant evolutionary effort the theory allows the calculation of the optimal parameter distribution. The theoretical concept is applied to simple metabolic systems consisting of monomolecular reactions only. It is shown that in the optimal state of the linear enzymatic chain the evolutionary effort is mainly spent on the enzymes located at the beginning of the chain. This tendency is more pronounced if the kinetic equations of the enzymes are first-order rate laws. With respect to Michaelis-Menten enzymes the optimal state is characterized by a decrease of the maximal activities and an increase of the fractional saturation of the enzymes towards the end of the chain.

Animals↗
PubMed1984

[Swallowed coin].

Explore the source record for details and available documents.

Digestive System↗
PubMed1984

Measurements of local PO2 in the resting skeletal muscles of rats with portocaval anastomosis (PCA) under normoxic conditions.

Direct measurements of local oxygen pressure by means of platinum multiwire electrode were performed in rats to investigate the effect of an end-to-side portocaval shunt procedure on muscle tissue oxygenation. Compared with intact rats and/or sham operated animals, rats with portocaval anastomosis showed a significant increase of muscle tissue oxygenation with nearly bellshaped pO2 histograms. This considerable increase in tissue oxygenation might appear to be due to the well known PCA induced hyperdynamic cardiovascular state.

Animals↗
PubMed1984

A theoretical approach to cluster formation in biological membranes.

A theoretical analysis of cluster formation within the lipid matrix of biological membranes is presented. Various models are analysed: (a) one-dimensional monolayer, (b) two-dimensional monolayer and (c) one dimensional bilayer. Furthermore, lipid-protein interactions are considered. The model is based on differential equations for the probabilities ai and bi which characterize the occupation of the lattice site i by the lipids A and B, respectively. These differential equations are an approximation of the Master-equation. Steady states as well as time-dependent variations are analysed. Depending on the interaction energies of the two lipids, different stationary lipid distributions are obtained, including clusters of lipids A or B and alternating structures. The distributions may be dynamically stable or unstable. It is shown that phase transitions within the lipid matrix may be induced by alteration of the composition of the membrane, by changing the interaction energies of the lipids, by variation of the temperature or by lipid-protein interactions. The transitions between different stationary distributions are studied by use of bifurcation diagrams. The analysis of time-dependent states reveals that unstable structures of the membrane may be important for certain time periods. Consideration of the lipid bilayer leads to a great number of possible distributions, which may be symmetric or asymmetric with respect to the outer and inner leaflets of the membrane.

Membrane Lipids↗
PubMed1984

A metabolic osmotic model of human erythrocytes.

A metabolic osmotic model of red blood cells is presented which takes into account the main reaction steps of glycolysis and the passive and active fluxes of ions across the cell membrane. Cellular energy metabolism and osmotic behaviour are linked by the ATP consumption for the active transport of cations as well as by the osmotic action of the glycolytic intermediate 2,3-diphosphoglycerate (2,3-DPG). The model is based on a system of differential equations describing the metabolic reactions and transport processes. Further, two algebraic conditions for the osmotic equilibrium and the electroneutrality of the cell are considered. Using realistic system parameters the model allows the calculation of a great number of dependent variables, among them the cell volume, the concentrations of metabolites and ions and the transmembrane potential. Only stationary states are considered. The parameter dependence of important model variables is characterized by control coefficients. The main results are: (a) The volume of erythrocytes is mainly determined by the permeabilities of the leak fluxes of cations, the content of hemoglobin and the activity of the hexokinase-phosphofructokinase system of glycolysis; (b) Changes of volume affect the glycolytic rate mainly by changing the concentration of ATP which is a regulator of glycolysis; (c) A change in the membrane area may affect the other cell properties only if it is connected with variations of the number of active and leak sites of the membrane.

2,3-Diphosphoglycerate↗
PubMed1984

Determination of cobalt in biological materials by voltammetry and electrothermal atomic absorption spectrometry.

For industrial purposes cobalt is used to a large extent. About 2,300 persons are occupationally exposed to this carcinogenic metal in Western Germany. As reliable analytic methods for biological monitoring are not available we developed procedures for analyzing cobalt in whole blood and urine by using two independent methods, voltammetry and ETAAS. For ETAAS-analysis of urine the cobalt content is chelatized and extracted in an organic solvent. This clean-up step enables us to calibrate with aqueous standards.--Samples of whole blood are directly injected into the graphite tube after being diluted with a homogeniziser. For their gentle thermal decomposition we use a temperature/time programme containing six steps. Both kinds of sample treatments are uncomplicated and permit routine applications. For voltammetric determination of cobalt in urine and blood the biological material must be completely mineralized. The dry residue is dissolved in a NH4Cl/NH3 solution. Cobalt is chelatized with 2,3-butanedione-dioxime and preconcentrated by adsorption at the hanging mercury electrode. By scanning the potential into negative direction the cobalt complex is reduced. The resulting signal can be used for the quantitative determination. For comparison of both methods we have analyzed blood and urine samples of occupationally exposed persons. We found very good correlations with a statistical significance at the level of 0.01%.

Cobalt↗