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Biomedical subjects

O Richter

Publications and source records attributed to O Richter.

At least 19 recordsLinked to original sources
PubMed1999

Simulation of herbicide degradation in different soils by use of Pedo-transfer functions (PTF) and non-linear kinetics.

The degradation behaviour of bentazone in 14 different soils was examined at constant temperature and moisture conditions. Two soils were examined at different temperatures. On the basis of these data the influence of soil properties and temperature on degradation was assessed and modelled. Pedo-transfer functions (PTF) in combination with a linear and a non-linear model were found suitable to describe the bentazone degradation in the laboratory as related to soil properties. The linear PTF can be combined with a rate related to the temperature to account for both soil property and temperature influence at the same time.

Algorithms↗
PubMed1998

[Laparoscopic implantation of catheters for continuous ambulatory peritoneal dialysis].

Continuous ambulatory peritoneal dialysis (CAPD) has become an established procedure and is an equal alternative to haemodialysis (HD) in the management of terminal renal failure. Nevertheless CAPD still plays a minor role compared with HD (10% of all dialyses). CAPD offers advantages in quality of live but is still associated with a significant number of complications. The improvement of surgical technique and development of new peritoneal dialysis catheters (PDK) improved the results of peritoneal dialysis. 3 methods for implantation of PDK are used: the open surgical technique, the blind percutaneous procedure and the laparoscopic method. The latter technique is currently an accepted practice. 10 patients were treated by the laparoscopic method. Additionally to the PDK-tunnel of the abdominal wall we used 2 trocars (1 x 5 mm, 1 x 12 mm). Advantages of this technique are avoiding of perforating lesions, possibility for further operations and a safe implantation of the PDK. Peritoneal dialysis was started 7 days after operation with initially low dialysate volumes. The observed incidence of complications and removed catheters are comparable to the reports in the literature.

Catheters, Indwelling↗
PubMed1998

[TNF-alpha secretion by peritoneal macrophages in endometriosis].

Beside of other cytokines and growth-factors Tumor Necrosis Factor Alpha (TNF-alpha) exerts as a macrophage-derived cytotoxic product a variety of immunologic effects in the human organism. It is also an important angiogenetic factor and regarding its cytotoxicity toward gametes TNF-alpha plays an essential role as pelvine mediator of sterility. The purpose of our study was to evaluate the TNF-alpha-synthesis of Peritoneal-Macrophages (PM) in patients with and without endometriosis and to determine if a correlation exists between TNF-alpha-synthesis and various degrees of the activity of endometriosis. For reasons of sterility 40 women underwent diagnostic laparoscopy and were staged according to the rAFS-classification as well as the macroscopic aspect of activity into a control group with endometriosis-free pelvic situs (n = 14) and three subgroups characterized by the increasing stage of the disease (n = 26). The TNF-alpha-concentrations (median) in the control group were 3.3 pg/ml, in group 2 with stage I/II rAFS and only low active endometriosis 60.2 pg/ml, in group 3 with stage I/II rAFS but high active endometriosis 83.2 pg/ml and in group 3 with stage III/IV rAFS 168 pg/ml. These data were statistically high significant and showed good conformity with the histological findings. We found significant higher TNF-alpha-concentrations in the peritoneal fluid of patients with endometriosis than in the peritoneal fluid of healthy women. There is a correlation between TNF-alpha-concentrations and the degree of disease.

Adult↗
PubMed1997

[Modification of transplacental digoxin transfer in the isolated placental lobule].

Digoxin is widely used in the transplacental therapy of fetal tachyarrhythmia. Unfortunately, in cases with severe cardiac insufficiency and hydrops fetalis, transplacental passage of digoxin is often hampered and therapy therefore ineffective. The present study was designed to establish the isolated placental lobule to quantify transplacental digoxin passage under different experimental conditions. Ten human placentas were obtained immediately after delivery, and a lobule was dually perfused after cannulating a small artery and vein of the chorionic plate and piercing four catheters through the corresponding basal plate. Flow rates were 12 ml/min in the maternal circuit and 6 (I) respectively 3 ml/min (II) in the fetal circuit. The maternal circuit was spiked with digoxin to 6.18 +/- 0.40 ng/ml, and transplacental passage was calculated from repeated fetal and maternal perfusate samples (Fluorescence-Polarization-Immunoassay; TDx, Abbott Laboratories). Within three hours of recirculating perfusion with a fetal flow rate of 6 ml/min (I), digoxin concentrations in the maternal circuit (400 ml) declined to 3.56 +/- 0.09 ng/ml, whereas digoxin levels in the fetal compartment (200 ml) increased to 2.58 +/- 0.37 ng/ml. With a fetal perfusion rate of 3 ml/min (II), the efflux of digoxin out of the maternal circuit was lower (p < 0.05) and the influx in the total compartment was reduced (fetal digoxin concentrations reached only 26.9 +/- 10.6% vs. 39.1 +/- 5.5% of the initial maternal digoxin concentrations). These data suggest that severe fetal cardiac insufficiency with reduced placental perfusion may be in part responsible for the decrease of transplacental digoxin passage in fetuses with hydrops.

Anti-Arrhythmia Agents↗
PubMed1994

Partitioning of chemically modified low-density lipoprotein in aqueous polymer two-phase systems.

Aqueous polyethylene glycol (PEG)-dextran two-phase systems containing 10 mM Tris.HCl (pH 7.4) were used for the partitioning of chemically modified low-density lipoprotein (LDL). Anionic modification connected with an increase in the negative surface charge of lipoproteins favours the accumulation of modified LDL in the top phase. The partition coefficient increases depending on the extent of modification. Cationic modification yields lower values for the partition coefficient. Positively charged LDL favours a bottom-phase accumulation. With weakly charged and nearly neutral particles, the Van der Waals interaction between polymer and particle preponderates over electrostatic interactions, leading to a favoured accumulation of LDL in the PEG-rich top phase. Results of measurements of the relative electrophoretic mobility and the determination of free amino groups are in agreement with the calculated values of the partition coefficient. Because the partitioning of LDL is accompanied by aggregation at the interface, experimental techniques have to be carefully standardized. Subtle differences in the surface properties of modified LDL can be detected.

Acetylation↗
PubMed1991

Partition of serum lipoproteins in a polyethylene glycol/dextran two-phase system.

Aqueous two-phase systems containing polyethylene glycol (PEG) and dextran as phase forming polymers were used for the partition of unmodified and hypochlorite modified lipoproteins. Low density lipoprotein (LDL) was separated from high density lipoprotein (HDL) by sequential ultracentrifugation from human plasma. In agreement with the higher electrophoretic mobility, high density lipoprotein shows a higher value of the partition coefficient in contrast to low density lipoprotein. An increase in the concentration of chloride ions reduces the enrichment of lipoprotein in the top phase and favours the accumulation of aggregated material at the interface. The partition coefficient strongly depends on the age of the lipoprotein sample. Differences in the value of the partition coefficient could be obtained for the lipoprotein fractions HDL-2 and HDL-3. Hypochlorite modified LDL shows higher values of the partition coefficient due to the higher negative charge of the modified lipoprotein particle.

Chemical Phenomena↗
PubMed1991

Modification of low density lipoproteins by sodium hypochlorite.

Human low density lipoproteins (LDL) were incubated with increasing amounts of sodium hypochlorite. A decrease of the number of free amino groups on the LDL surface starts only upon addition of 30-40 moles NaOCl per mole apoB, whereas all detectable SH groups are oxidized after addition of nearly 17-20 moles NaOCl. All hypochlorite-modified LDL samples have a higher electronegative surface charge compared with native LDL as revealed by agarose gel electrophoresis and partition of LDL in an aqueous polyethylene glycol/dextran two-phase system. The more NaOCl is used to alter LDL, the higher is the electrical surface charge. Changes in surface charge are found already at low NaOCl concentrations where no decrease of amino groups is detected. It is assumed that changes in surface charge are caused by the formation of monochloramines and especially at low degrees of modification by a further unknown contribution. An effect on the primary structure of apoB or peroxidation-like changes in NaOCl-altered LDL could not be found under our experimental conditions. The results are discussed with respect to such modifications under in vivo conditions by hypochlorous acid generated in stimulated phagocytosing cells.

Dextrans↗
PubMed1988

[Residues of active substances after consumption of contaminated food: status report on the evaluation of residues with examples of two drugs].

Pharmacokinetic models are presented for the computation of time courses of blood levels of drugs in man following the consumption of contaminated food. Mathematically, two linear systems of differential equations are set up for the donor organism (e.g., trout) and for the recipient, (e.g., man), where the first system generates the initial conditions for the second. Models of this kind are applied to the transfer of chloramphenicol to man via carp and trout (which had previously been administered this drug) and to the transfer of theophylline to infants via breast milk. Limiting concentration profiles are computed by constructing the most favourable and most adverse combinations of parameters with respect to drug elimination in both the donor and recipient organism.

Animals↗
PubMed1986

[Analysis of decay curves with biphasic kinetics].

Medication of trout and carps with chloramphenicol and sulfadimidine results in tissue residues which best fit by a biexponential decay curve. The analysis of residues does not reveal any systematic deviations of the data from the model. On the basis of this model half lives for the fast and slow drug elimination phases can be estimated. For the assessment of withdrawal times it is necessary to compute confidence limits for the decay curves. A withdrawal time may be defined by the intersection of recommended maximal concentrations with the upper confidence limit. This analysis does not include any metabolites. This model is also suited for monitoring purposes. It is recommended to apply the procedure to all chemicals exhibiting biexponential decay kinetics.

Animals↗
PubMed1985

Pharmacokinetic data analysis of alfentanil after multiple injections and etomidate-infusion in patients undergoing orthopedic surgery.

The pharmacokinetics of Alfentanil, a new short acting analgesic, and Etomidate, a very short acting hypnotic compound, were studied in patients undergoing orthopedic surgery. Anesthesia was induced by bolus i.v. injection of Alfentanil and Etomidate, whereas the maintenance was performed by continuous infusion of Etomidate and repetitive i.v. injections of Alfentanil. The kinetics of the analgesic can be described by a two-compartment model; the elimination half-life has a mean value of 64.8 +/- 38.5 min. No cumulation of the drug was seen in spite of multiple injections. Concerning Etomidate it is not clear whether one or two compartments are needed. The mean elimination half-life is 29.4 +/- 6.2 min. The results suggest a possible shortening of the half-life of Etomidate in the presence of Alfentanil.

Adult↗
PubMed1985

[Pharmacokinetics and pharmacodynamics of proxyphylline in asthmatic children].

In 15 asthmatic children and 3 healthy adult volunteers the pharmacokinetics and pharmacodynamics of proxyphylline under oral treatment, and the pharmacokinetics after intravenous administration were determined. The concentration-time-courses after intravenous application could best be fitted to an open 2-compartment model whereas the pharmacokinetics after oral treatment followed an open 1-compartment model. Under oral administration great inter- and intraindividual variances of the serum levels occurred. These differences which showed no age-dependency were suggested to be due to variations of the absorption velocity and the elimination half-lifes. In order to evaluate the curative efficacy of proxyphylline on lung function parameters all children had to undergo a whole body-plethysmography. No significant antiobstructive effects on the relevant baseline ventilation parameters could be observed. The protective efficacy of proxyphylline was determined in asthmatic children who developed an exercise induced asthma after a 7 minutes run. Only in 3 of 11 children a significant reduction of the enhanced airway resistance occurred. No correlation between serum levels and the protective effects was found. The present results show that there is no positive association between pharmacokinetics and pharmacodynamics of proxyphylline in asthmatic children. A safe antiobstructive therapy appears to be impossible within the dose range recommended so far.

Administration, Oral↗
PubMed1984

The relationship between pharmacodynamics and pharmacokinetics in asthmatic children receiving a sustained-release formulation of theophylline.

Pharmacodynamic response as well as serum and saliva concentrations of theophylline were monitored in 15 children under a long term theophylline treatment. Respiratory parameters, such as vital capacity and total bronchial resistance all related to bronchodilatation, were measured by use of a bodyplethysmograph. Measurements were performed before treatment and during the steady state with respect to serum levels. Due to small differences between peak and trough concentrations, no correlations between serum concentrations and respiratory parameters were found during the steady state. However, some important respiratory parameters exhibit considerable differences with respect to pretreatment values. In conclusion, one can state that during the steady state, theophylline exerts a constant influence on bronchodilatation which depends only slightly on the concentration range achieved.

Adolescent↗