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Biomedical subjects

R Kaufmann

Publications and source records attributed to R Kaufmann.

At least 307 records · Page 17Linked to original sources
PubMed1978

[Visual discrimination conditions in infants with increased risk for cerebral damage].

Infants judged at birth to be at risk for cerebral damage show at 2 to 4 months of age significant differences compared to normal controls with respect to visual behavior at presentation of geometric patterns: Children of the risk group discriminated less consistently between a striped pattern and a homogenous gray surface. Their average time of fixation is significantly longer, and they show increased variance within the test parameters. It was therefore concluded that parameters of visual fixation and discrimination could probably allow for more reliable prognoses for future cognitive development in an infant. A longitudinal study to test this hypothesis is already in execution.

Brain Damage, Chronic↗
PubMed1977

The effects of diphenylhydantoin on mechanical and electrical properties of isolated cat myocardium.

The effects of diphenylhydantoin (DPH) (4 X 10(-5) to 2 X 10(-4) M) on contractile activity and electrical properties were studied in isotonically shortening cat papillary muscles exposed to DPH. 1. DPH reduces amplitudes of contraction especially at low stimulation rates (6 to 12/min). At higher, more physiological rates the negative inotropic effect is comparatively small. 2. DPH accentuates the mechanical transients usually following step changes of frequency. 3. DPH reduces the maximum rate of depolarisation (MRD) of the normal action potential (AP) and slows conduction especially at high stimulation rates. AP duration is shortened especially at low stimulation rates. 4. In Ca-mediated "slow responses" DPH reduces MRD, overshoot and AP duration and abolishes the frequency-dependent alterations of these parameters. 5. The results suggest that the antiarrhythmic potency of DPH is due to a cooperative action on both the fast and the slow membrane channels. 6. It is speculated that DPH leads to an accumulation of Ca2+ within a "limited subsarcolemmal space" thereby decreasing the driving force for the slow inward current.

Action Potentials↗
PubMed1977

Development of visual discrimination (pattern preference) in normal infants.

Visual discrimination for vertical stripes versus an unpatterned visual stimulus (plain grey) was studied longitudinally in 75 "normal" infants born at term, at monthly intervals from 1 to 6 months of age. Total fixation time was found to progressively decrease with increasing age, with a very sharp jump between the values of 2 and 3 months. Correspondingly, the mean duration of a single fixation decreased. The number of single fixations increased by age, doubling at 6 months in comparison to 1 month. A preferential fixation for stripes was already evident at the age of 1 month. A probabilistic method for assessing discrimination in individuals is proposed. The values will be correlated with follow-up results of cognitive development until school-age.

Age Factors↗
PubMed1976

Metabolism of 14 C-vinyl chloride in vitro and in vivo.

Rat liver microsomes metabolise 14 C-vinyl chloride to intermediates which irreversibly bind to the microsomal protein and to soluble proteins and RNA, when these compounds are added to the incubation. A superoxide (O2) generating system comprised of phenazine methosulfate and NADH also converts 14 C-vinyl chloride to metabolites which irreversibly bind to albumin. These data are consistent with the assumption of chloroethylene oxide being the primary reactive metabolite of vinyl chloride. If rats are exposed to 14 C-vinyl chloride, about half of the radioactive metabolites in the liver microsomal fraction is bound irreversibly to microsomal protein, when assessed immediately after exposure. Large amounts of polar, extractable, metabolites are present in the cytosol fraction. The amount of radioactivity in tissues of the rats, irreversibly bound immediately after exposure, comprises 10 - 40% of the total radioactivity in tissues. This percentage rises up to 70% after 48 hrs. Som radioactivity derived from 14 C-vinyl chloride is also incorporated into DNA and RNA of liver. Whereas the peak of incorporation of 14 C into DNA is already reached immediately after exposure to 14 C-vinyl chloride, specific labelling of RNA increases after exposure until its maximum after 24 hours.

Albumins↗
PubMed1976

[Experimental studies on the mechanism of action of carbocromen on the isolated cat papillary muscle (author's transl)].

1. In isotonically shortening cat papillary muscle 3-(2-di-ethylaminoethyl)-4-methyl-7-(carbethoxy-methoxy)-2-oxo-1,2-chromene-hydrochloride (carbocromen; Intensain¿) (1-30 mug/ml) slightly increases contraction amplitude. 2. At low stimulation rates (6-12/min) the positive inotropic effect is more pronounced. 3. The maximal velocity of depolarization of the monophasic action potential is slightly reduced. 4. At all stimulation frequencies investigated (15-90/min) the total duration of the action potential -- especially at late repolarization level -- is strongly increased. Hence, functional refractory period is prolonged and maximal follow frequency reduced.

Action Potentials↗
PubMed1975

Inotropic and electrophysiological actions of verapamil and D 600 in mammalian myocardium. I. Pattern of inotropic effects of the racemic compounds.

A pattern analysis of inotropic actions was carried out on isotonically chortening cat papillary muscles exposed to (+/-)-verapamil and (+/-)-D 600 and compared to other Ca-antagonistic interventions. 1. (+/-)-Verapamil (1--5mug/ml) leaves contraction amplitudes nearly unchanged at 6/min, whereas at 60/min more than 90% depression (5 mug/ml) occurs. (+/-)-D 600 is about twice as effective as (+/-)-berapamil. 2. An increase of [Ca2+]O in the presence of (+/-)-verapamil or (+/-)-D 600 does not restitute the normal amplitude-frequency relationship. There is only a shift toward higher contraction amplitudes. 3. (+/-)-Verapamil and (+/-)-D 600 lead to typical biphasic inotropic transients after step changes of the friving rhythm. First a fast and (at higher frequencies) very pronounced negative staircase occurs, followed by a rather slowly developing positive staircase. 4. These drug effects contrast to the effects of lowering [Ca2+]O or of adding Ni2+ or La3+, which all produce a rather uniform depression of contraction amplitudes at all frequencies and do not elicit staircase phenomena such as seen under the influence of (+/-)-verapamil or (+/-)-D 600. 5. In contrast to the action of Ni2+, La3+ or low [Ca2+]O, (+/-)-verapamil slows down the restitution kinetics of Ca-reavailability from internal stores as determined by the amplitude of test contractions elicited after various periods of rest. 6. Drug-induced changes in the time course of the transmembrane action potential as depending on frequency may partially but not fully explain the contractile phenomena. 7. Possible interpretations as to the sites where (+/-)-verapamil or (+/-)-D 600 interferes with cardiac excitation-contraction coupling are given by the aid of a multicompartment model. This model describes excitation-contraction coupling in terms of transmembrane and intracellular Ca-movements.

Action Potentials↗
PubMed1975

Inotropic and electrophysiological actions of verapamil and D 600 in mammalian myocardium. II. Pattern of inotropic effects of the optical isomers.

On isotonically contracting cat papillary muscles analysis, a comparison of the effects of the optical isomers of verapamil and D 600 and the racemic drugs was performed. 1. (-)-verapamil (0.2-3.0 mug/mo) and (-)-D-600 (0.1 mug/ml-3.0 mug/ml) leave the steady state contraction amplitudes nearly unchanged at 6/min, but produce a strong depression at 60/min. (-)-D 600 is about 8 times as effective as (-)-verapamil. The (+)-isomers exert only a moderate negative inotropic effect (particularly at low frequencies). 2. Increase of [Ca2+]O does not restitute the normal amplitude-frequency relationship during exposure to either the (-)-isomers or the (+)-isomers. 3. The (-)-isomers lead to typical biphasic staircases after step changes of frequency. A fast negative staircase occurs first followed by a rather slowly developing positive staircase. In contrast, the (+)-isomers have little influence on the usual staircase pattern. 4. The strength-interval relationship for single test contractions elicited after frequent conditioning stimulation indicated that the (-)-isomers probably slow the restitution of intracellular Ca-reavailability. The (+)-isomers have no such effects. 5. The effects produced by the (+/-)-compounds correspond qualitatively to those of the (-)-isomers. 6. The very different patterns of inotropic actions observed indicate that the (-)- and (+)-isomers of verapamil and D 600 probably interfere with cardiac excitation-contraction coupling at different sites.

Animals↗
PubMed1975

Calcium movements controlling mammalian myocardial contractility: analog computation of contractile behavior assuming a multicompartmented model.

We present a model to be displayed on a medium scale analog computer, which describes excitation-contraction (E-C) coupling of the mammalian myocardium in terms of calcium movements occurring, on a sarcomere level, in a multicompartment system, Despite the fact that its mathematical formulations are oversimplifications of the mechanism involved, because the number of differential equations had to be limited, the model predicts with fair accuracy a large variety of inotropic phenomena thought to be the result of factors influencing cardiac E-C coupling in one way or another. Therefore, in its basic assumption, the overall concept might be correct, and if so, it should be possible to use the model in order to make predictions which can be tested experimentally and can help in understanding results which are otherwise difficult to interpret.

Action Potentials↗