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Biomedical subjects

F Keller

Publications and source records attributed to F Keller.

At least 73 records · Page 4Linked to original sources
PubMed1999

Analysis of the nu8 + nu9 Band of HNO3, Line Positions and Intensities, and Resonances Involving the v6 = v7 = 1 Dark State.

Using a high-resolution (R = 0.0025 cm-1) Fourier transform spectrum of nitric acid recorded at room temperature in the 1100-1240 cm-1 region, it has been possible to perform a more extended analysis of the nu8 + nu9 band of HNO3 centered at 1205.7075 cm-1. As in a recent analysis of this band [W. F. Wang, P. P. Ong, T. L. Tan, E. C. Looi, and H. H. Teo, J. Mol. Spectrosc. 183, 407-413 (1997)], the Hamiltonian used for the line positions calculation takes into account, for the upper state, the DeltaK = +/-2 anharmonic resonance linking the rotational levels of the v8 = v9 = 1 "bright" vibrational state and those of the "dark" v6 = v7 = 1 vibrational state. More than 4800 lines were assigned in the nu8 + nu9 band, which involve significantly higher rotational quantum numbers than in previous works. On the other hand, and surprisingly as compared to previous studies, the nu8 + nu9 band appears to be a hybrid band. In fact, nonnegligible B-type transitions could be clearly identified among the much stronger A-type lines. Accordingly, a set of individual line intensities were measured for lines of both types and were introduced in a least-squares fit to get the A- and B-type components of the transition moment operator. Finally, a synthetic spectrum of the 8.3-µm region of HNO3 has been generated, using for the line positions and line intensities the Hamiltonian constants and the expansion of the transition moment operator which were determined in this work. In this way, the B-type and the A-type components of the nu8 + nu9 band appear to contribute for about (1/4) and (3/4), respectively, to the total band intensity. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

[Histological biomorphosis of human heart valve. II. Morphometric studies].

Previous polarization-microscopical measurements combined with silver-staining methods at histological sections of the bicuspid valve and the tricuspid valve in the region of fibrosa showed (similar to that of the corresponding tendinous cords) for middle-aged persons a distinct difference in the collagen composition in comparison between high pressure vs. low pressure system. The aim of the current study was the morphometric investigation of the collagen composition, of the relative content of total collagen (measured as relative number of total collagen fibers per measuring area), and of the cell-collagen relation in dependence of age and possibly on sex in the high and low pressure system, respectively. Tissue samples of atrioventricular valves of 67 probands of both sexes were available. The probands were healthy with regard to heart and circulation and distributed in 3 age groups (1st to 2nd decade, 3rd to 5th decade, and 6th to 9th decade). After corresponding preliminary treatment, the histological sections of tissue samples were evaluated by a suitable combination of polarization-microscopical, immuno-histochemical, and morphometrical methodology. The thickness of the heart valves was measured by microscopic image analysis. A rise of the number of fibers per measuring area (ma) for both sexes and both valves was observed with increasing age. The slopes of the linear regression curves and the mean values of the numbers of collagenous fibers/ma (for each age group) were different between both sexes. They depend upon the valve considered. Analogous to these results, the differentiated statements were possible to the number of fibers/ma and to the percentages of the fiber species by the distinction between the collagen types I and III in the fibrosa of the heart valves. Whereas the relative numbers of fibers/ma rose with increasing age, the number of cell (fibroblasts, fibrocytes) nuclei for both valves and sexes slightly decreased. For the latter, there was no difference between high and low pressure system in contrast to the collagenous fibers. The opposite age-dependent behavior of the collagenous fibers and of their producing cells during the biomorphosis of the heart valves could be explained with the collagen turn-over.

Adolescent↗
PubMed1999

Clinical course after total parathyroidectomy without autotransplantation in patients with end-stage renal failure.

In patients with chronic renal failure, hyperparathyroidism is a common problem and surgical parathyroidectomy (PTX) is frequently required. The three different surgical approaches are subtotal PTX, total PTX with autotransplantation, and total PTX without autotransplantation. Recurrence of hyperparathyroidism varies from 5% to 80% in different studies for the first two surgical approaches. To minimize the risk for recurrence, and because we fear severe relapses with calciphylaxia, we perform total PTX without autotransplantation. From October 1993 to October 1997, 20 patients (9 men and 11 women) underwent total PTX without autotransplantation (median age, 52 years; range, 23 to 74 years; median dialysis time before PTX, 6.5 years; range, 1 to 22 years). All patients were supplemented with vitamin D analogues postoperatively. Patients were followed up for 1 to 48 months (median, 20 months). Bone pain, when present, disappeared within the first week after total PTX. Postoperatively, most patients had temporary hypocalcemia. In the long term, five patients had asymptomatic hypocalcemia. One patient, however, repeatedly had hypocalcemic seizures. Five patients developed asymptomatic hypercalcemia when supplemented with calcitriol. At the end of the individual's observation time, parathyroid hormone (PTH) levels were less than normal in six patients, normal in seven patients, and increased in seven patients despite total PTX. We conclude that total PTX should be reconsidered an option for the treatment of hyperparathyroidism secondary to renal failure. There was no evidence of clinical bone disease after total PTX. Apparently, remaining ectopic parathyroid tissue accounts for PTH levels after total PTX.

Adult↗
PubMed1999

Metabolism of D-glycero-D-manno-heptitol, volemitol, in polyanthus. Discovery Of a novel ketose reductase1

Volemitol (D-glycero-D-manno-heptitol, alpha-sedoheptitol) is an unusual seven-carbon sugar alcohol that fulfills several important physiological functions in certain species of the genus Primula. Using the horticultural hybrid polyanthus (Primula x polyantha) as our model plant, we found that volemitol is the major nonstructural carbohydrate in leaves of all stages of development, with concentrations of up to 50 mg/g fresh weight in source leaves (about 25% of the dry weight), followed by sedoheptulose (D-altro-2-heptulose, 36 mg/g fresh weight), and sucrose (4 mg/g fresh weight). Volemitol was shown by the ethylenediaminetetraacetate-exudation technique to be a prominent phloem-mobile carbohydrate. It accounted for about 24% (mol/mol) of the phloem sap carbohydrates, surpassed only by sucrose (63%). Preliminary 14CO2 pulse-chase radiolabeling experiments showed that volemitol was a major photosynthetic product, preceded by the structurally related ketose sedoheptulose. Finally, we present evidence for a novel NADPH-dependent ketose reductase, tentatively called sedoheptulose reductase, in volemitol-containing Primula species, and propose it as responsible for the biosynthesis of volemitol in planta. Using enzyme extracts from polyanthus leaves, we determined that sedoheptulose reductase has a pH optimum between 7.0 and 8.0, a very high substrate specificity, and displays saturable concentration dependence for both sedoheptulose (apparent Km = 21 mM) and NADPH (apparent Km = 0.4 mM). Our results suggest that volemitol is important in certain Primula species as a photosynthetic product, phloem translocate, and storage carbohydrate.

Journal Article↗
PubMed1999

A mixed approach and a distribution-free multiple imputation technique for the estimation of a multivariate probit model with missing values.

In the present paper a mixed generalized estimating/pseudo-score equations (GEPSE) approach together with a distribution-free multiple imputation technique is proposed for the estimation of regression and correlation structure parameters of multivariate probit models with missing values for an ordered categorical time-invariant variable. Furthermore, a generalization of the squared trace correlation (RT2) for multivariate probit models, denoted by pseudo-RT2, is proposed. A simulation study was conducted, simulating a probit model with an equicorrelation structure in the errors of an underlying regression model and using two different missing mechanisms. For a low 'true' correlation the difference between the GEPSE, a generalized estimating equations (GEE) and a maximum likelihood (ML) estimator were negligible. For a high 'true' correlation the GEPSE estimator turned out to be more efficient than the GEE and very efficient relative to the ML estimator. Furthermore, the pseudo-RT2 was close to RT2 of the underlying linear model. The mixed approach is illustrated using a psychiatric data set of depressive in-patients. The results of this analysis suggest that the depression score at discharge from a psychiatric hospital and the occurrence of stressful life events seem to increase the probability of having an episode of major depression within a one-year interval after discharge. Furthermore, the correlation structure points to short-time effects on having or not having a depressive episode, not accounted for in the systematic part of the regression model.

Depressive Disorder↗
PubMed1999

Tonsillectomy does not prevent a progressive course in IgA nephropathy.

BACKGROUND: IgA nephropathy, or Berger's disease, is a primary mesangioproliferative glomerulonephritis, usually with a favourable prognosis. PATIENTS AND METHODS: To investigate the effect of tonsillectomy we conducted a retrospective investigation on renal outcome in 55 patients with IgA nephropathy in an outpatient university clinic between 1968 and 1994. Established risk factors for progressive IgA nephropathy were equally distributed in 16 patients subjected to tonsillectomy and in 39 patients without tonsillectomy. Renal survival and impact of risk factors were estimated by Kaplan-Meier analysis and Cox regression model. RESULTS: Seen in terms of the bivariate Kaplan-Meier analysis the probability of renal survival 10 years after biopsy was 0.37 for the 16 patients with tonsillectomy and 0.63 for the 39 patients without tonsillectomy (log-rank test p = 0.49, not significant). In the multivariate Cox regression model with 6 independent clinical covariates, initially high serum creatinine concentration had the strongest impact on renal outcome (p = 0.002), with a hazard ratio of 8.9 (95% CI: 2.3-35.0). Tonsillectomy had no significant influence in the Cox model (p = 0.37), displaying a hazard ratio of 1.7 (95% CI: 0.5-5.7). CONCLUSION: In conclusion, tonsillectomy does not reduce the risk of developing renal failure or prevent a progressive course of IgA nephropathy.

Adult↗
PubMed1999

Hypercalcemia-induced renal insufficiency during therapy with dihydrotachysterol.

During vitamin-D therapy drug accumulation and intoxication should be considered. In the present study we report on five patients with renal insufficiency during therapy with dihydrotachysterol or calcitriol. Four patients received dihydrotachysterol for 29 (7-44) years and one patient received calcitriol for 4 years to treat hypoparathyroidism after thyroid surgery. As confirmed by renal biopsy impairment of renal function was due to calcifications as a consequence of prolonged hypercalcemia. The effective duration of dihydrotachysterol is ten days as compared with five days for calcitriol. Severe hypercalcemic episodes with dihydrotachysterol are longer-lasting than those with the shorter acting vitamin-D derivatives. Further, they occur with higher incidence as was shown by our own observations and previously published data by other workers. Hence, impairment of renal function during therapy with dihydrotachysterol should be considered as being due to hypercalcemia and hypercalciuria.

Aged↗
PubMed1999

Pharmacokinetic principles during continuous renal replacement therapy: drugs and dosage.

Some drugs are removed significantly by continuous renal replacement therapies (CRRTs), and a substitutional dose is required to prevent underdosing of the substance. This review outlines the basic pharmacokinetic principles that determine whether a dose adjustment is required. Only the free non-protein-bound fraction of a drug can pass through the dialyzer membrane. In postdilution hemofiltration the drug clearance equals the ultrafiltration rate, while in predilution hemofiltration, the dilution of the blood prior to filtration needs to be considered when calculating clearance. In continuous hemodialysis, drugs are eliminated by diffusion. Drugs with a higher molecular weight will diffuse more slowly and show a lower clearance than smaller drugs. The clinical relevance of a given drug clearance caused by CRRT will mainly depend on the competing drug clearance by other elimination pathways. Even a high clearance for a drug may be irrelevant for overall drug removal if nonrenal clearance pathways provide a much higher clearance rate. The ideal drug to be removed by CRRT that requires a dose adjustment has: a low protein binding, a low volume of distribution, and a low nonrenal clearance. Examples include aminoglycosides, vancomycin, fosfomycin, and flucytosine. Even if there are no studies available on the pharmacokinetics of a particular drug during CRRT, knowledge of the basic concepts of drug elimination by continuous hemodialysis allows a prediction of whether or not a dose adjustment will be required during CRRT.

Anuria↗
PubMed1999

Individualized drug dosage in patients treated with continuous hemofiltration.

BACKGROUND: Subtherapeutic drug dosing may be even more dangerous than overdosage, especially for intensive care patients requiring hemofiltration. PROPOSAL: According to Dettli's fundamental equation, body clearance of any drug (Cl) is a linear function of creatinine clearance (Cl = Cl anur + a x C(Cr)), with [a = (Cl norm - Cl anur)/C(Cr), norm]. We propose to individualize drug dosage during high-flux hemofiltration by basing it on Dettli's equation and on total C(Cr) (C(Cr) tot = C(Cr) ren + C(Cr) filt). Using this approach, drug clearance will eventually be overestimated for drugs with substantial tubular secretion and for high-efficiency hemofiltration (C(Cr) tot > 30 ml/min). CONCLUSION: In patients undergoing hemofiltration, the total C(Cr) approach might be a practical alternative to standardized dosing schemes for deriving an individualized dosage from published pharmacokinetic data and functions.

Creatine↗
PubMed1999

The "point of no return" and the rate of progression in the natural history of IgA nephritis.

BACKGROUND: Based on the observation of 7 patients with chronic IgA nephritis and on a course to end-stage renal failure after several years, D'Amico et al. [1993] reported on a "point of no return" at 2.5 to 3 mg/dl serum creatinine. After exceeding this limit all 7 patients exhibited an irreversible progressive renal failure. PATIENTS AND METHODS: Therefore, 115 patients with IgA nephritis from the "German Glomerulonephritis Therapy Study" were examined in order to look for the existence of such a "point of no return". RESULTS: Three different courses could be distinguished: a stable chronic course with constantly normal or only minor elevated serum creatinine lasting for years (91 patients), a progressive course with continuously increasing serum creatinine (22 patients), and a rare (only 2 patients) early acute course with a short-term increase of serum creatinine followed by a rapid return to the normal range. After exceeding 3 mg/dl serum creatinine no remissions were observed in the progressive cases. Sixteen patients showed a rapid, continuously progressive course until end-stage renal failure with exactly the same progression as the 7 patients of D'Amico et al. Six patients of the 22 progressors were not observed long enough. The serum creatinine level doubled on average from 3 to 6 mg/dl within 10 months. CONCLUSION: Our study confirmed the existence of a "point of no return" at 3 mg/dl (265 micromol/l) during the natural course of chronic IgA nephritis.

Adolescent↗
PubMed1998

Identification and characterization of a bovine neurite growth inhibitor (bNI-220).

The poor axonal regeneration that follows lesions of the central nervous system (CNS) is crucially influenced by the local CNS tissue environment through which neurites have to grow. In addition to an inhibitory role of the glial scar, inhibitory substrate effects of CNS myelin and oligodendrocytes have been demonstrated. Several proteins including NI-35/250, myelin-associated glycoprotein, tenascin-R, and NG-2 have been described to have neurite outgrowth inhibitory or repulsive properties in vitro. Antibodies raised against NI-35/250 (monoclonal antibody IN-1) were shown to partially neutralize the growth inhibitory effect of CNS myelin and oligodendrocytes, and to result in long distance fiber regeneration in the lesioned adult mammalian CNS in vivo. We report here the purification of a myelin protein to apparent homogeneity from bovine spinal cord which exerts a potent neurite outgrowth inhibitory effect on PC12 cells and chick dorsal root ganglion cells, induces collapse of growth cones of chick dorsal root ganglion cells, and also inhibits the spreading of 3T3 fibroblasts. These activities could be neutralized by the monoclonal antibody IN-1. The purification procedure includes detergent solubilization, anion exchange chromatography, gel filtration, and elution from high resolution SDS-polyacrylamide gel electrophoresis. The active protein has a molecular mass of 220 kDa and an isoelectric point between 5.9 and 6.2. Its inhibitory activity is sensitive to protease treatment and resists harsh treatments like 9 M urea or short heating. Glycosylation is, if present at all, not detectable. Microsequencing resulted in six peptides and strongly suggests that this proteins is novel.

3T3 Cells↗
PubMed1998

High-Resolution Analysis of the nu6, nu7, nu8, and nu9 Bands of H15N16O3 Measured by Fourier Transform Spectroscopy.

The analysis of the nu6, nu7, nu8, and nu9 bands of H15N16O3 located at 646.9641, 578.4719, 743.6166, and 458.2917 cm-1, respectively, has been carried out in the 400-800 cm-1 region using high-resolution Fourier transform spectra recorded at Ottawa. Using the ground state energy levels calculated from the v = 0 rotational constants of H15N16O3 [A. P. Cox, M. C. Ellis, C. J. Attfield, and A. C. Ferris, J. Mol. Struct. 320, 91-106 (1994)], it was possible to assign the A-type nu6 and nu7 bands and the C-type nu8 and nu9 bands of H15N16O3 up to high J and Ka rotational quantum numbers. The v6 = 1, v7 = 1, v8 = 1, and v9 = 1 experimental energy levels were then introduced in a least-squares fit calculation and precise upper state Hamiltonian constants (band centers and rotational constants) were determined allowing one to reproduce the infrared data to within the experimental uncertainty. Copyright 1998 Academic Press.

Journal Article↗
PubMed1998

[Inpatient treatment of depressed patents. Conceptual considerations and results of a pilot project for quality assurance in Baden-Württemberg].

Quality-assurance activities will become more important in psychiatry during the next few years. In relation to other medical disciplines, some special aspects concerning structure, process and outcome quality as well as practical realization and methodologic aspects must be considered. These specific issues were the focus of a study dealing with the treatment of depressed inpatients. The experiences and results as well as considerations concerning future quality-assurance projects are discussed.

Adult↗