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Biomedical subjects

J Maier

Publications and source records attributed to J Maier.

At least 19 recordsLinked to original sources
PubMed1992

Endothelin-1 in patients with complicated and uncomplicated myocardial infarction.

Endothelin-1 concentrations were measured in peripheral venous blood samples from 42 patients with acute myocardial infarction. In patients with ischemic or hemodynamic complications (n = 11), endothelin-1 concentrations were significantly higher already on admission (P = 0.008) and remained significantly higher until day 6 after admission compared to patients with uncomplicated infarctions (n = 31; P = 0.035). There were no close correlations between peak concentrations of endothelin-1 and creatine kinase or creatine kinase isoenzyme MB mass in either group. Only in complicated patients did left ventricular ejection fraction correlate closely and inversely with peak endothelin-1 concentrations (r = -0.71; P = 0.03). Therefore, plasma endothelin-1 concentrations in patients with acute myocardial infarction patients may reflect states of markedly depressed cardiac performance and recurrent myocardial ischemia.

Adult↗
PubMed1992

Control of cell-cycle-associated tetrahydrobiopterin synthesis in rat thymocytes.

The cell-cycle progression of rat thymocytes from G0 through G1 to DNA synthesis is associated with a transient synthesis of H4biopterin, the concentration of which reaches a maximum at the time of S-phase entry and then decreases. This synthesis of H4biopterin is controlled by the specific activity of GTP cyclohydrolase I, which peaks in G1/S cells. In contrast, the catalytic activity of sepiapterin reductase remains constant throughout the cell-cycle. At G0 the steady state mRNA levels specific for GTP cyclohydrolase I and sepiapterin reductase, respectively, are below the limits of detection. Both accumulate as the thymocytes progress through the cell-cycle but lack cyclic down regulation. The data indicate that the variations in H4biopterin synthesis during the cell-cycle are caused by growth regulated increase in GTP cyclohydrolase I mRNA expression, with subsequent post-translational inactivation. This latter is likely due to the degree of enzyme phosphorylation.

Alcohol Oxidoreductases↗
PubMed1990

[Radiotelemetric studies of the body temperature of white-tufted monkeys (Callithrix jacchus)].

A newly developed telemetry system was used to study deep body temperature (BT) of two adult male common marmosets (Callithrix jacchus). The BT-curves of both monkeys showed a similar clear circadian rhythm with a range up to 3.5 degrees C. At environmental temperature of 28 degrees C (ET) the BT of the monkeys varied in the daytime dependent on their spontaneous activity, with little individual differences between 37.5 degrees C and 39.3 degrees C; at night the BT of the remarkably deeply-sleeping animals decreased to an average at 35.8 degrees C. Elevating ET up to 30 degrees C effected an increase of BT by 0.6 degrees C, both during day and night. On the contrary, reducing ET to 24 degrees C the BT increased only at night, by 0.2 degrees C at ad libitum food intake and 1.0 degrees C at fasting. Measurements of BT by inserted rectal thermometer caused, compared with telemetry, an average at 0.4 degrees C higher values.

Animals↗
PubMed1990

Echo-planar imaging of intravoxel incoherent motion.

The recently established single-shot technique of echo-planar imaging of intravoxel incoherent motion (IVIM) for determining and imaging the variations of microscopic motions of water has been applied to studies of water perfusion in phantoms and to in vivo studies of diffusion and perfusion in cat and human brains. The phantom results demonstrate that perfusion levels comparable with those found in vivo have easily observable and reproducible effects on signal amplitude that are consistent with previous IVIM theory. Reliable measurements of the diffusion coefficient in various types of brain tissue have been obtained. The results for white matter are consistent with the existence of anisotropic diffusion in oriented bundles of myelinated nerve fibers. The results for gray matter can be fitted to the IVIM theory and suggest a value of up to 14% for the fraction of the signal contributed by randomly perfusing fluid in normal cerebral cortex.

Animals↗
PubMed1990

[Laser-induced occlusion of corneal blood vessels with variable emission and absorption].

Laser light has repeatedly been proposed for the occlusion of corneal neovascularizations. Priority has to be given to minimize laser energy in order to limit side effects such as corneal burns. We investigate the influence of variable emission wavelength using a dye laser or dye-enhanced absorption with intravenous sodium fluorescein. Laser energy can be reduced using intravenous dyes at vessel diameters less than 50 microns. Permanent occlusion is achieved in 43% instead of 28% without dye-enhanced absorption. Vessels measuring greater than 50 microns in diameter can be occluded best at lowest laser energy levels when 575 nm laser light is used, which approximates the absorption maximum of hemoglobin.

Absorption↗
PubMed1987

Visual acuity of human infants at scotopic, mesopic and photopic luminances.

Visual acuity of 2-month-old infants and adults was measured between -2.6 and +2.7 log10 cd/m2 using standard psychophysical techniques. The acuity-vs-luminance curve was similar for infants and adults: acuity improved with increasing luminance until 0.0 log cd/m2, and was constant above that luminance. However, the infant curve was slightly shallower than the adult curve, and infant acuity was over 3.5 octaves poorer than adult acuity at all luminances. The infant acuity-vs-luminance curve was compared with adult curves measured 21 degrees and 51 degrees from fixation, and at 21 degrees with +8, +/- 3.25 and 0.0 D of experimental refractive error. The results indicated that infants' poor acuity cannot be fully explained by: refractive error, foveal immaturity, scotopic detection of stimuli, functional similarity between infant vision and adult vision in the periphery, or by an overall reduction in visual sensitivity.

Adult↗
PubMed1987

Principal components analysis for source localization of VEPs in man.

This study defines and compares the topologies of the visual evoked potentials to various stimuli such as pattern onset/offset, pattern reversal, pattern motion and high frequency luminance flicker. The responses recorded from 24 occipital derivations were examined using a three sphere conductance model to represent the head, with the assumption that activity from an underlying cortical source is equivalent to a single dipole. Principal components analysis was used to find the dimensionality of the data space. From this analysis could be concluded that all stimuli evoked responses in the primary visual cortex. Only pattern onset, and to a lesser degree pattern offset and pattern reversal, yielded activity in higher visual areas. In particular it has been shown that the CI, CII interval of the pattern onset response has its origins in two different cortical regions. A fast positive (CI)-negative (part of the CII) component arises from area 18 (or 19), a slower negative (initial part of CII) component comes from area 17.

Evoked Potentials, Visual↗
PubMed1986

Pattern reversal stimuli: motion or contrast?

Pattern reversal stimuli are widely used for electrophysiological examination of the visual system. To investigate the mechanisms contributing to the pattern reversal EP (PREP) we performed experiments with a trained alert macaque monkey, using both contrast and motion stimuli. It was found that, as in man, for parafoveal and peripheral stimulation the PREP can be constructed from the EPs to the onset and offset of pattern motion. On the other hand foveal stimulation activates the contrast mechanism only. Our conclusion is that pattern reversal data should be considered with caution since pattern reversal can activate motion as well as contrast mechanisms. This ambiguity is not present in the pattern appearance-disappearance stimulus.

Animals↗
PubMed1985

Flicker and movement constituents of the pattern reversal response.

A counterphase-modulated (i.e. contrast reversing) pattern will affect hypothetical neural elements sensitive to motion as well as hypothetical elements sensitive to changes in contrast and other elements sensitive to local luminance. Attempts to describe visual evoked potentials (VEPs) to contrast reversal entirely in terms of luminance change or entirely in terms of contrast change have been unsuccessful; strong interactions between responses to contrast decrease and increase had to be postulated ad hoc in order to account for the contrast reversal VEP, and no explanation for these interactions has been proposed. Rather than attempting to separate the reversal VEP into responses to contrast decrease and increase, we attempt here to analyze the reversal VEP into responses to motion onset and offset. We find that VEPs to an abrupt displacement of less than one square's width of a checkerboard pattern are qualitatively similar to the contrast reversal VEP, and that the displacement VEP can be seen as the limiting case of a motion onset response shortly followed by a motion offset response. When displacement occurs during steady motion, the displacement and motion responses interact. We conclude that the contrast reversal VEP is better described in terms of motion onset and offset response than in terms of contrast onset and offset responses.

Adaptation, Ocular↗
PubMed1985

Precipitation methods for the determination of LDL-cholesterol.

The selective precipitation of low-density lipoproteins (LDL) with polyvinyl sulfate (PVS), and the immunoprecipitation of high-density lipoproteins (HDL) and very-low-density lipoproteins (VLDL) with an anti-HDL antibody, can both be used to establish simple methods for the determination of LDL cholesterol. Whereas the PVS method requires the calculation of LDL cholesterol as the difference of total and supernatant cholesterol, the immunoprecipitation method allows the direct measurement of LDL cholesterol in the supernatant. As a first step, both methods were optimized to yield accurate values for normolipemic and slightly hyperlipemic serum samples. Moreover, the determination of LDL-cholesterol in lipemic sera can be achieved by a combination of immunoprecipitation and polyanion precipitation.

Chemical Precipitation↗
PubMed1984

Technique-related variation in results of FANA tests.

We compared the reliability and reproducibility of three tests for fluorescent antinuclear antibodies (FANA) that are routinely performed in our laboratory. Sera from 72 patients, selected according to diagnosis (SLE in 28, RA in 12, and other connective-tissue diseases in 33), and from 32 healthy controls were tested with all three assays. There were wide variations between the results obtained with these tests. The variations did not reflect sensitivity or degree of standardisation (reproducibility on retesting was greater than 95%) and appeared to be inherent in the techniques. Clinicians should be aware of the technique-related differences in FANA assays.

Antibodies, Antinuclear↗
PubMed1982

Rapid separation of immunoglobulin M by immunoaffinity chromatography for detection of specific antibodies to rubella and Treponema pallidum.

A rapid and easy method for isolating IgM from serum specimens in order to detect specific antibodies against Treponema pallidum and rubella virus by routine serologic procedures is described. Serum IgM was isolated by immunoaffinity chromatography using anti-human IgM antibodies covalently bound to controlled-pore glass beads in a microcolumn. The final concentration of the IgM in the samples tested amounted to at least 16% (average 32%) of the original concentration (corresponding to a serum dilution of 1 : less than 8). IgG contamination did not exceed 0.38% of the original serum concentration. The capacity of the column was stable for at least 50 absorption/elution cycles. The new technique enables rapid and reliable detection of specific IgM by the rubella hemagglutination inhibition and Treponema pallidum hemagglutination tests.

Animals↗
PubMed1979

[Diagnosis and therapy of pancreatic carcinoma (author's transl)].

Report of 143 cases of pancreatic carcinoma and the operations carried out. In 14 cases (operability rate 10%) a pancreaticoduodenectomy was performed. The operative lethality rate came to 14,3%. The longest survival time was 7 1/4 years, the shortest 11 months. Early diagnosis, early laparotomy and operation as radical as possible are emphasized.

Adult↗