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Biomedical subjects

H Richter

Publications and source records attributed to H Richter.

At least 91 records · Page 5Linked to original sources
PubMed1994

Quantitative judgements and matching of subjective speed of apparent laser speckle flow induced by refractive defocus.

The speed of laser speckles induced by refractive defocus was determined by means of the direct method of free magnitude estimation in combination with sensory verbal descriptors. Physical measures of angular velocities were obtained by matching a similar pattern under the viewer's control to the laser speckles for equal subjective velocity. Theoretical speckle speed was calculated from geometrical formulae proposed by Charman [7]. The velocity percept of apparent speckle motion was a monotonic function of the refractive power of the positive lenses added to the observer's eye, although it exhibited a tendency of levelling off at the greatest strength. The magnitude estimates of this motion percept were highly correlated with corresponding subjective judgements of the angular velocity of the real motion of the matched pattern. Theoretical velocity plotted against empirically obtained values of velocity through matching yielded a product moment correlation coefficient of 0.98 and a regression coefficient of 0.94 indicating a high internal and external validity of these measurements as well as the usefulness of speckle speed as a cue for voluntary changes of the crystalline lens of the eye.

Acceleration↗
PubMed1994

Velocity percepts of apparent laser speckle motion modulated by voluntary changes of visual accommodation: real-time, in-vivo measurements of the accommodative response.

This study examined negative volitional accommodation under open-loop viewing conditions by means of a coherent laser light pattern (633 nm) whose direction and velocity of motion is determined by the refractive state of the eye. Using the direct scaling procedure of free magnitude estimation, the subjects were required to quantitatively judge velocities of speckles when the retinal image of the subjects' eye was minimally influenced and when the subject was instructed to exert voluntary negative accommodation. Real-time, in-vivo measures of accommodation indicated that the dioptric strength of the crystalline eye lens was reduced under the condition of mental effort, and that the volitional accommodation values ranged between -0.26 and -1.90 D. The amplitude of these responses were noticeably correlated with individual measures of dark focus, so that larger dark focus values were associated with higher amplitudes of the voluntary negative response, and vice versa. By converting the dioptric strength of added optical lenses and the in-vivo measures of the eye lens curvature into angular velocities of laser speckles whose speed changes with focus relative the plane of stationarity, a specification of the proximal stimulus flow was obtained. The psychophysical functions describing the relationship between subjective speed and angular velocity generated either by placing lenses in front of the eye or by voluntary changes in accommodation had approximately the same appearance suggesting that the percepts reported by the subjects were valid and veridical estimates of the velocity of speckle movement.

Acceleration↗
PubMed1994

Monoclonal antibodies and idiotypic network activation for ovarian carcinoma.

Antibodies can be processed by the B- and T-cell systems and may lead to a selective activation of the immune system. The network structure of the immune system implicates the possibility of a selective immunization by the activation of idiotypic cascades. In a retrospective analysis, patients with advanced ovarian carcinoma, who had received MAb, against the cancer-associated antigen CA125 for diagnostic purposes, were analyzed for the production of anti-idiotypic antibodies, survival rate, and immunological effects. Furthermore, we started a prospective and randomized study for ovarian cancer patients, using a different antigen, TAG72, for the induction of idiotypic cascades. Our first results on 58 patients with advanced ovarian carcinomas showed that the induction of anti-idiotypic-antibodies against OC125 mimicking the TAA Class III CA125 leads to a prolongation of the survival rate, and, in extended stages, to an induction of antitumoral immunity, and that the induction of idiotypic cascades is also possible for different antigens like TAG72. Summarizing the activation of idiotypic network cascades seems to be a very effective way of intervention in the immune system of patients with advanced stages of ovarian carcinoma. A prospective study of the adjuvant approach seems to be necessary.

Antibodies, Anti-Idiotypic↗
PubMed1994

Idiotypic cascades after injection of the monoclonal antibody OC125. A study in a mouse model.

In an animal model, we evaluated the possibility to induce antibodies directed against the tumor-associated antigen CA125 by immunization with the anti-CA125 antibody OC125 via activation of the idiotypic network. Our results show that Balb/c mice, immunized by repeated administrations of F(ab')2-fragments of the OC125 antibody (Ab1), produced anti-idiotypic antibodies (Ab2). The binding of these antibodies to the OC125 could be completely inhibited by the antigen CA125, suggesting that the anti-idiotypic antibodies imitate the original target antigen of the OC125. After induction of these paratope-binding anti-idiotypic antibodies (Ab2 beta), a murine IgG-anti-CA125 (Ab3) response arose in the same mice. The induction of idiotypic cascades offers the possibility of immunization against tumor-associated antigens without using the original antigen and breaking antitumor tolerance.

Animals↗
PubMed1994

[Effect of hardness and surface quality of metal cones on fracture load of ceramic ball heads of hip endoprostheses].

The safety of ceramic ball heads attached to hip endoprostheses by means of a conical fitting requires that the connection be designed with the ceramic material in mind. The ISO 7206-5 standard describes a static testing protocol to measure the maximal loading limit of the conical connection. In order to achieve high fracture loads in this test, it is necessary to optimize the load-bearing parts of the connection to prevent stress concentrations, to which the ceramic ball is sensitive. For this reason, manufacturers of ceramic balls give their customers specifications for the design of the metal taper, specifying tolerances for angle, roughness, roundness and straightness. In order to investigate which parameters of the metal taper have an influence on the fracture load achievable according to ISO 7206-5, fracture load tests were conducted with zircon oxide (ZIOLOX) heads in combination with test tapers from various manufacturers. The test tapers were made of Ti- or CoCr-based alloys. Before the tests the tapers were completely measured and characterized according to geometric parameters of roughness, roundness, straightness, profile and angle, and physical parameters such as hardness and elastic modulus. Subsequent measurements after the fracture tests characterized changes that occurred in the metal tapers. The fracture loads achieved depended on the potential for deformation of the taper surface. This potential can be described by a factor computed as hardness/roughness. A dependence of the fracture load on elastic modulus, form deviations or taper angle could not be established within the Cerasiv specifications.

Ceramics↗
PubMed1993

[Gender-specific differences of risk factors of atherosclerosis. A study of 3,850 Vienna employees].

Atherosclerosis is the most frequent cause of death in Austria as well as in the other western industrialized countries. Sex specific differences in the various age groups concerning relative myocardial infarction-mortality stimulated us to investigate the risk factors for atherosclerosis in 3850 employees. An extensive lipid status, liver and kidney function parameters were determined, the blood-pressure was measured, and a cardiovascular centered case history was examined. The mean cholesterol level and the LDL-cholesterol level in males were significantly higher than in females (cholesterol: males 223.8 +/- 56.8 mg/dl, females 208.2 +/- 43.3 mg/dl, LDL-cholesterol: male 151.9 +/- 55.1 mg/dl, female 132.2 +/- 40.1 mg/dl, p < 0.001). The mean HDL-cholesterol level in males were significantly lower than in females (males: 45.0 +/- 11.6 mg/dl, females 56.2 +/- 13.3 mg/dl, p < 0.001). No significant difference concerning smoking-behaviour could be determined between female and male participants in this cohort (33.0% of the males resp. 33.6% of the females stated that they smoked cigarettes). Hypercholesterolaemia and cigarette-smoking are the main risk factors for both sexes, however the situation of women-except for the 6th decade-is much better than that of men. Remarkable is the increasing number of female-smokers, especially at younger age.

Adult↗
PubMed1992

Financing health services in Sub-Saharan Africa: options for decision makers during adjustment.

The financing of health services has become an increasingly critical and urgent issue in many developing countries particularly in Sub-Saharan Africa. This paper analyses options available to policy makers. The possible effects and side effects of strategies are described based on the experience from different countries. The dangers of simplistic solutions are discussed. A cautious approach is recommended taking into consideration the lessons learned in other regions accompanied by a careful ongoing evaluation especially regarding the ability to pay of the poorer sections of the population. Providing for equity in health care should be an important guiding principle. It therefore appears to be necessary to find an appropriate mix of public and private sector interventions with elements of cost-sharing for services and drugs, insurance schemes and more efficient use of available resources.

Africa↗
PubMed1992

Maintenance of left ventricular function (90%) after twenty-four-hour heart preservation with deferoxamine.

During 24-h in vitro heart preservation and reperfusion, irreversible tissue damage occurs caused by reactive oxygen intermediates, such as superoxide radicals, singlet oxygen, hydrogen peroxide, hydroperoxyl, hydroxyl radicals, as well as the peroxynitrite radical. Reduction of the related oxidative damage of reperfused ischemic tissue by free radical scavengers and metal chelators is of primary importance in maintaining heart function. We assessed whether deferoxamine (DFR) added to a cardioplegia solution decreased free radical formation during 24-h cold (5 degrees C) heart preservation and normothermic reperfusion (37 degrees C) in the Langendorff isolated perfused rat heart. The deferoxamine treated hearts were significantly (p less than .001) better preserved than the control hearts after 24 h of preservation with regard to recovery of left ventricular diastolic pressure, contractility (+dP/dt), relaxation (-dP/dt), creatine kinase release, and lipid peroxidation. DFR preserved cell membrane integrity and maintained 93% of left ventricular contractility. The evidence suggests that DFR reduces lipid peroxidation damage by reducing free radical formation and thereby maintaining normal coronary perfusion flow and myocardial function.

Animals↗
PubMed1992

[Risk factors of atherosclerosis--primary examination of Vienna employees].

In the course of an atherosclerosis intervention study, a basic medical check-up of 2105 out of 4800 employees of a Viennese banking house was carried out (37.1 +/- 11.0 years, 54.6% females). Apart from liver and kidney function parameters, an extensive lipid status was determined, the blood pressure was measured, and a cardiovascular-centered case history ascertained. The mean cholesterol level in females was 208.3 +/- 54 mg/dl and that in males was 226.8 +/- 61.1 mg/dl. The HDL-cholesterol level in males was 43.8 +/- 11.9 mg/dl; that in females (54.9 +/- 13.4 mg/dl) was significantly higher. The mean value of LDL-cholesterol in the entire group was 141.6 +/- 51.4 mg/dl and it was significantly higher in males, as well as in participants with known hypertension. 33.4% of the persons stated that they smoked. The obtained data will serve not only to discover potential interrelations between the individual risk factors of atherosclerosis in Austria, but also in particular as a basis for interventional strategies on the part of the company's medical services.

Adolescent↗
PubMed1991

Immobilization of soluble fibrin on factor XIIIa-coated polystyrene beads mediated by N-terminal fibronectin fragments. II. Demonstration of covalent adducts of fibrin peptide chains and fibronectin fragments.

Previous experiments had shown that the free N-terminal fibronectin 30-kDa-domain mediates binding of soluble 125I-fibrin to transamidase-coated polystyrene beads (Hörmann et al., Biol. Chem. Hoppe-Seyler 368, 669-674, 1987). Now, the formation of covalent adducts of the N-terminal fragment with fibrin peptide chains is demonstrated. Binding of soluble 125I-fibrin was performed in presence of N-terminal fibronectin 30-kDa or 70-kDa fragments. The material adsorbed was removed from the beads under reducing conditions and analysed by dodecylsulfate gel electrophoresis followed by autoradiography. The 30-kDa fragment gave rise to bands of 80 kDa and 180-200 kDa which were lacking in the products of the 70-kDa compound. Instead, they showed bands at 120 kDa and ca. 280 kDa. Evidently, those bands represented covalent adducts of fibrin peptide chains or their dimers with the 30-kDa or the 70-kDa fragment, respectively. In addition, dimeric gamma-chains and alpha-chain polymers of fibrin were present indicating partial polymerization of bead-attached fibrin.

Electrophoresis, Polyacrylamide Gel↗