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Biomedical subjects

F Keller

Publications and source records attributed to F Keller.

At least 307 records · Page 17Linked to original sources
PubMed1984

Kinetics of the redistribution phenomenon after extracorporeal elimination.

Evaluation of the efficiency of extracorporeal elimination is rendered difficult by the rebound phenomenon which may occur in plasma concentrations after hemodialysis, hemoperfusion, or plasma exchange. The term clearance, derived from the extraction rate, has the drawback that it is often based on the incompatible terms plasma concentration and blood flow. To avoid these difficulties, clearance may be calculated from kinetics of plasma concentrations. But this approach will lead to an overestimation of the eliminative efficiency, because plasma concentrations may decline faster than tissue levels, which will be indicated by the rebound phenomenon. The rebound is due to a redistribution from tissue into plasma and follows 2-compartment kinetics. However, the amount removed by extracorporeal elimination reflects the redistribution phenomenon and, simultaneously, can be used to evaluate the absolute efficiency. The amount removed can be derived from 1-compartment kinetics if redistribution can be neglected, and from 2-compartment kinetics if a redistribution takes place. The amount removed can also be evaluated using model- independent approaches, which may be applied even if sustained absorption or proliferation must be assumed. According to these approaches, the removed amount is given by graphic extrapolation, and it can be calculated from extracorporeal clearance and from concentrations in the removed fluid, or it can be eluted from the extracorporeal device.

Extracorporeal Circulation↗
PubMed1984

Carpal tunnel syndrome: a major complication in long-term hemodialysis patients.

One hundred and forty-five patients on hemodialysis for periods of 1 month to 16 years were examined clinically for carpal tunnel syndrome (CTS). Typical symptoms and clinical manifestations of symptomatic CTS, either unilaterally or in both hands, were detected in 21 of these patients (15%). In contrast to the classic form of CTS, hemodialysis CTS in our patients was frequently accompanied by Raynaud's phenomenon of those digits supplied by the median nerve. A highly significant correlation was established between the incidence of CTS and the duration of dialysis (p less than 0.001). The association of CTS with analgesic nephropathy was significantly higher (52%) than with other kidney diseases (p less than 0.034). Immediate relief of pain was achieved after carpal tunnel release (11 releases) in 8 of the 21 patients. Sensory and motor function was gradually, but often only partially, restored. Unoperated CTS progressed to loss of sensory and motor function within 1 to 4 years after the onset of symptoms. CTS should be considered a major late complication in patients on chronic hemodialysis.

Adult↗
PubMed1984

[Optical and histochemical polarization studies of the composition of the sialomucin coat at the trophoblast surface of the rabbit placenta depending on the stage of pregnancy].

Polarization microscopical and histochemical investigations were performed in 43 placentas of rabbits from the 10th to the 35th d of pregnancy at the maternal surface of the metabolic barrier of the placenta. The carboxyl groups of sialic acid and of proteins, sulphur containing amino acids of proteins and neutral carbohydrates were detected quantitatively and qualitatively by polarization optical and histochemical investigations. It is possible, that the increase of proteins in case of placenta insufficiency has diagnostic importancy.

Amino Acids, Sulfur↗
PubMed1984

[Biocompatibility of implants with and without fluorohydrocarbon glow-discharge polymer coating. 1. Histologic and semiquantitative estimation of subcutaneous reactions in guinea pigs].

The reaction of the subcutaneous tissue in guinea-pigs at implants of titanium, titanium/glow discharge polymer, Gisadent KCM (chromium cobalt molybdenum alloy), and Gisadent/glow discharge polymer was investigated by a semiquantitative method of informing character. The 4 tested materials were well-tolerated at which titanium caused the smallest reaction.

Animals↗
PubMed1984

[Biocompatibility of implants with and without fluorohydrocarbon glow-discharge polymer coating. 2. Automated equidensitometric recording of tissue reactions].

A conclusion on the biocompatibility, the solubility, and the chronic toxicity of different implant materials showed the equidensitometric measurement of the capsular thickness in the environs of the implants by means of the electronic image interpretation equipment Densitron. The method, the results, and the advantages of the technique are described.

Animals↗
PubMed1984

[Biocompatibility of implants with and without fluorohydrocarbon glow-discharge polymer coating. 3. Mathematical models of the subsiding processes of the tissue reaction].

The subsidence process of the tissue reaction was estimated by the thickness of the fibrous capsule as well as different histologic characteristics in dependence on the period after the implantation of 4 several implant materials. This subsidence process was fitted mathematically by an exponential function respectively a power function by means of the regression analysis. The power function described best the experimentally found curve. The correspondence, on principle, of the subsidence process of the fibrous capsula thickness on the one hand and the 9 histologic characteristics on the other hand could be proved. A standard valuation for subcutaneous tests is demanded which include the designation of the thickness of the fibrous capsula as well as characteristic cell type frequencies as histologic characteristics.

Animals↗
PubMed1984

Effect of repeated plasma exchange on steady state kinetics of digoxin and digitoxin.

The effect of repeated plasma exchanges on the steady state kinetics of digoxin (3 patients) and digitoxin (4 patients) was investigated in 7 patients. Plasma exchange was performed 3 times a week for 4 weeks up to 12 exchanges using a hollow fiber membrane. In each exchange, 4000 ml plasma were filtered within 1 to 2 h and replaced by an albumin containing (20 g/l) physiological electrolyte solution. Digoxin and digitoxin concentrations in blood and filtered plasma were measured by radioimmunoassay. The effects due to the amount eliminated by plasma exchange were distinguished from the effects due to hypoalbuminemia. The eliminative effect was confined to the plasma compartment. It resulted in a marginal decrease in the elimination half-life from 1.6 to 1.59 days for digoxin and 4.3 to 4.2 days for digitoxin. Theoretically, it can be calculated that the hypoalbuminemia caused an increase in the volume of distribution from 451 to 497 l (digoxin) and 35 to 50 l (digitoxin) and a further decrease in the elimination half-life from 4.2 to 4.1 days in the case of digitoxin (not digoxin). If given within 2 h prior to plasma exchange, 13 to 50% of the digitoxin dose (not digoxin) was eliminated. Alteration of digoxin and digitoxin dosage during repeated plasma exchanges is not recommended, but drugs should be given after, not before plasma exchange.

Adult↗
PubMed1984

Brain pharmacokinetics of centrally acting drugs, a quantitative autoradiographic study.

The concentration kinetics of 14C labeled diazepam, chlorpromazine and iodoantipyrine were studied in several regions of rat brain shortly after intravenous (i.v.) administration by a quantitative autoradiographic method. A highly significant linear relationship was found between regional diazepam resp. chlorpromazine concentration, and regional cerebral blood flow (rCBF) 1 min after injection. Moreover, a linear relationship was found between rCBF and, on the other hand, firstly diazepam concentration decrease between 1 and 2 min, secondly increase in chlorpromazine concentration between 1 and 5 min, and finally decrease of chlorpromazine concentration between 5 and 30 min. The regional kinetics of diazepam were compared with those of iodoantipyrine, a tracer assumed to be freely diffusible through the blood-brain barrier.

Animals↗
PubMed1984

Exponential function of chymotrypsin action.

Enzyme kinetics are usually described by the hyperbolic Michaelis-Menten equation, but they can also be described by the following exponential function: -dS/dt = Vm [1 - exp (-S/Km)]. The time-dependent decrease of the substrate (-dS/dt) is an exponential function of maximal velocity (Vm), the Michaelis constant (Km) and the actual substrate value (S). This exponential function is based on the assumption that the association of the substrate-enzyme complex is a concentration-dependent process, whereas the transformation of the substrate-enzyme complex is time-dependent. It can be shown that this exponential function is a more general solution of which the hyperbolic Michaelis-Menten equation is a special derivative under the conditions of low substrate (S) and high constant (Km) values. If the association process is time-dependent, the decline in substrate values will show a more concave curve. However, exponential functions in general are more concave than hyperbolic functions. Probably, therefore, the enzyme action of chymotrypsin could be described more appropriately by the present exponential function than by the conventional hyperbolic function.

Chymotrypsin↗
PubMed1983

Ecto-adenosine triphosphatase activity at the cholinergic nerve endings of the Torpedo electric organ.

Synaptosomes isolated from the electric organ of Torpedo marmorata contain activity of an ATPase which is located at the extracellular face of the plasma membrane. Ecto-ATPase activity can be stimulated independently and to a similar extent by either Ca-2+ or Mg-2+. Apparent Km-values for ATP are 79 microM and 53 microM for Ca-2+ and Mg-2+ respectively. Apparent Km-values for Ca-2+ and Mg-2+ at 1 mM ATP are 0.71 mM and 0.61 mM respectively. The enzyme is also activated by Mn-2+ and GTP can replace ATP as a substrate. Presence of 5'- nucleotidase activity suggests that adenosine is the final hydrolysis product. Thus hydrolysis of nucleotides released during exocytosis of synaptic vesicle contents and purine salvage must be a major role of this ecto-enzyme. We furthermore suggest that the ecto-ATPase may provide the key to understanding the storage of the high energy compound ATP in cholinergic synaptic vesicles. On depolarization of the nerve terminal and exocytosis, ATP represents the signal for activating the ATPase whereby concentrations of Ca-2+ and Mg-2+ are already saturating. Following depolarization induced Ca-2+ influx, a possible function of the ATPase may be the outward transport of Ca-2+ from the nerve terminal.

Adenosine Monophosphate↗
PubMed1983

Choline acetyltransferase in organotypic cultures of rat septum and hippocampus.

Choline acetyltransferase (CAT) activity in the hippocampus originates almost exclusively in axons from neurons located in the medial septum. In the rat, the development of CAT in the hippocampus takes place during the first 3 weeks after birth. The development of CAT was studied in organotypic cultures of fetal rat septum and early postnatal rat hippocampus. In some septal explants, enzyme activity increased up to 10-fold during the first 3-4 weeks in vitro. Acetylcholinesterase (AChE) histochemistry showed the presence of AChE-positive cells and fibers in many explants. Thus it appears that septal cholinergic neurons develop CAT and AChE activity even without making contact with their target cells. However, the development of CAT was accelerated by the presence of hippocampal tissue. No CAT activity was found in the hippocampal cultures, confirming that there are few, if any, intrinsic cholinergic cell bodies in the hippocampus.

Animals↗
PubMed1983

Elimination kinetics of plasma exchange.

Interest in the therapeutic use of plasma exchange for various diseases is growing. The two different effects of plasma exchange are elimination and activation. The kinetics are linear for elimination by plasma exchange, but not for activation. Plasma exchange is performed intermittently and can be described by intermittent kinetics. According to intermittent kinetics, plasma exchange removes 50% to 75% of a substance in plasma within 1-2 h, corresponding to an elimination half-life of 30-40 min. Hybrid kinetics, a mixture of actually intermittent but theoretically continuous elimination by plasma exchange, can however also be applied. Hybrid kinetics are more convenient and more reliable than intermittent kinetics. This is because hybrid kinetics are based solely on the concentrations before each plasma exchange; hybrid kinetics also reflect removal from the entire body and not just from the plasma compartment. According to hybrid kinetics, the amount of a substance in the body removed within 3-4 days is 50% of the difference between the initial and the final plasma concentration, depending on the intensity of plasma exchange. The intensity may well contribute at least in part to the beneficial effect of plasma exchange in various diseases.

Antibodies↗
PubMed1983

Effect of primary renal disease and risk factors on kidney graft survival.

The important role of immunological factors, HLA typing and pretransplant blood transfusion on improved kidney graft survival is well established. Additionally, graft survival depends on risk factors such as diabetes and age of the recipient. The effect of other clinical risk factors on graft survival was evaluated in 187 patients who received kidney transplants at our centre between 1970 and 1981. Graft survival according to the life table method and statistical analysis according to the logrank test revealed 4 main risk factors. Graft survival is significantly lower in type I diabetics and analgesic nephropathy, whereas it is better in hereditary and other renal diseases. Additional risk factors are coronary heart disease and repeated grafting. Time of dialysis before transplantation and age of the recipient showed no detrimental effect on graft survival.

Adult↗
PubMed1983

[Isolation of 503 strains of virus in meningeal syndromes. Virologic and epidemiologic study].

An epidemiological and virological study on meningitis in Alsace during the 13-year period 1968-1981 is reported. 503 viruses isolated were associated with the diagnosis of meningitis. The Echovirus type 30 accounted for 48 p. 100 of the cases, the mumps virus of 12 p. 100. The remarkable high incidence of Echo 30 virus-associated cases is related to three outbreaks which occurred in Alsace during the summers of 1968, 1975 and 1980. Children below 12 years of age are the most sensitive population and particularly boys who made up 2/3 of the number of cases.

Adolescent↗