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Biomedical subjects

D Harder

Publications and source records attributed to D Harder.

At least 55 records · Page 3Linked to original sources
PubMed1992

Non-invasive determination of systolic blood pressure by heart sound pattern analysis.

A new concept of non-invasive blood pressure measurement by heart sound pattern analysis is described. The known diagnostic criterion of the 'accentuated' second heart sound of a hypertensive patient is here converted into a computer-aided pattern-recognition process for the second heart sound, applicable over the entire scale of blood pressure. After a 'learning phase', during which the second heart sound is recorded, analysed and correlated with a set of systolic blood pressure values of the individual patient, the computer is able to determine systolic blood pressure of the same patient from the acoustic spectrum of the second heart sound with sufficient precision. The method is in principle suited for automatically repeated blood pressure measurements, but further development is still needed for conversion into a widely practicable procedure.

Blood Pressure↗
PubMed1991

Dosimetry and physical treatment planning for iodine eye plaque therapy.

The dosimetry of eye plaques loaded with iodine-125 seeds (type 6702) was performed by means of computer calculations and measurements with thermoluminescent dosimeters (TLD). Measurements of the depth dose distribution (2-25.5 mm) along the transverse axis of a single seed were performed in water equivalent phantom material. The transverse axis attenuation and geometry factor F(r) was obtained by applying a least squares fit to the measured data. Based on the resulting radial dose function, a computer program was developed which calculates dose distributions within the eye for arbitrary loading and placement of the eye plaque. The computational results were verified by TLD measurements in an eye phantom.

Brachytherapy↗
PubMed1990

Algorithms for the evaluation of radiation induced chromosome aberration yields per cell from flow karyotypes.

CHO-K1 cells were irradiated in G0/G1-phase with 150 kV X-rays. Single chromosomes isolated from metaphase cells and stained with DNA intercalating dye DAPI were analyzed in the ICP 22 with a modified flow chamber. In order to study dose-dependent changes in the flow karyotypes, they were split into peak- and background-portions by an iterative fit algorithm. As in a first approach, estimates of the frequencies of chromosome lesions were derived from an evaluation of the dose-dependent reduction in peak contents. The number of radiation-induced lesions per chromosome was found to be proportional to its length. As a second approach, the number of fluorescence events in the histogram background was corrected for non-chromosomal debris and evaluated interms of chromosome aberration frequency per cell, which was consistent with the yields of dicentric chromosomes and acentric fragments observed in microscopic investigations. As a third approach, lesion frequencies were calculated from the corrected background light sum in the karyotypes, utilizing a Monte Carlo model to simulate the effect of aberration formation on the flow histogram. The results indicate that the number of chromosome lesions observed by flow cytometry can be quantitatively related to the yield of structural chromosome aberrations detected by microscopic analysis. Dose-effect relations and split-dose kinetics are given as examples demonstrating the usefulness of this technique in radiobiology. Time saving compared to microscopic analysis was of the order of 90%.

Algorithms↗
PubMed1990

[Development and dosimetry of a 125 iodine applicator for brachytherapy of intraocular tumors].

Due to the low gamma energy (27-35 ke V), iodine 125 is especially suitable for brachytherapy of intraocular tumors. 125I is available as encapsulated seeds. Applicators can be individually loaded with these seeds to accommodate the shape of the tumor as much as possible. To measure the depth-dose distribution LiF thermoluminence detectors (TLDs, 1 mm3) are embedded in an RW-1 eye phantom at various distances and directions from the high active plaque positioned at the top of the phantom. To obtain the three-dimensional dose distribution, the TLDs are read after exposure for the appropriate time period. Based on experimental measurements of the 125I plaque, a computer program is developed to calculate the dose distribution within the eye and the radiation time for intraocular tumors. These results are very similar to those obtained when using mathematical equations published in the literature. In summary, three-dimensional dose distribution at various distances from an 125I eye plaque has been experimentally determined using a new method. This is an important prerequisite for introducing 125I plaques into the treatment of intraocular tumors.

Brachytherapy↗
PubMed1989

[Lymphomatoid papulosis resembling ecthyma. A case report].

A 54-year-old female patient recurrently developed disseminated papules, red-brown in color and partly ulcerous, which spontaneously disappeared after 3-6 weeks. Histological examination revealed dense infiltration of atypical lymphocytes with epidermotropism. Immunohistological analysis showed predominantly helper T-cells (CD 4). Accordingly, we established the diagnosis of lymphomatoid papulosis. There was no evidence of malignant lymphoma.

Biopsy↗
PubMed1989

[Dosimetry of ruthenium applicators with an eye phantom and small volume thermoluminescence detectors].

Even though 106Ru/106Rh applicators have been in clinical use over more than two decades for the radiotherapy of malignant uveal melanomas, the dosimetry of emitted beta radiation is still a physical problem. The dose rate at the applicator surface and the depth dose in tissue equivalent material can be determined only within +/- 30% error. Using new cubic-shaped thermoluminescence detectors (TLD) with small volume the dose distribution is examined in water equivalent material (RW-1). The spatial resolution is 14 times better compared to the previous technique. From dose measurements in an eye phantom the homogeneity of nuclide deposition and the depth dose distribution of a 106Ru/106Rh applicator are determined.

Brachytherapy↗
PubMed1986

Kinetics of the effect of ara C on chromosome aberration yield in irradiated human lymphocytes.

In unstimulated lymphocytes the enhancing effect of ara C on the yield of X-ray-induced dicentric aberrations was maximal if ara C was added immediately or up to 2 h after irradiation. When ara C was added later the enhancing effect decreased and practically vanished by 5 h. In stimulated lymphocytes the ara C effect declined faster and practically vanished by 3 h. If ara C was added for 1 h immediately after irradiation, then the aberration yield observed in G0, early G1 and late G1 cells was similar whereas it increased significantly from G0 to late G1 cells without ara C post-treatment. The results are discussed in relation to the classical model of aberration formation.

Chromosome Aberrations↗
PubMed1986

Temperature and the formation of radiation-induced chromosome aberrations. I. The effect of irradiation temperature.

Irradiation temperature, changed from 37 degrees C to 4 degrees C, acts as a dose-modifying factor with regard to the dose-yield relationship for dicentric chromosome aberrations in human lymphocytes irradiated with 150 kV X-rays. The temperature dependence of the aberration yield observed at constant dose is S-shaped, with a sharp rise near 15 degrees C from a lower plateau below 12 degrees C to a higher plateau beyond 17 degrees C. The aberration yield is determined by the irradiation temperature, irrespective of fast temperature changes from 4 degrees C to 37 degrees C or from 37 degrees C to 4 degrees C, applied at various delay times before and after irradiation. It is concluded that irradiation temperature influences the formation of chromatin lesions rather than their interaction.

Chromosome Aberrations↗
PubMed1986

Temperature and the formation of radiation-induced chromosome aberrations. II. The temperature dependence of lesion repair and lesion interaction.

Dicentric chromosome aberration yields have been measured after single-exposure and split-dose irradiations of human lymphocytes with 150 kV X-rays. Various temperature programmes between 4 and 37 degrees C were applied before, during and after irradiations and in the radiation-free interval. It was found that chromatin lesion repair was completely suppressed at 21 degrees C and below, whereas lesion formation is reduced only below 17 degrees C. The interaction between repairable lesions which leads to exchange-type aberrations is also suppressed by low temperatures. Hypothermic suppression of chromatin lesion repair and interaction is fully reversible at least up to 12 h of maintenance of the 'stored' state of these lesions.

Chromosome Aberrations↗
PubMed1986

Membrane ATPase mechanism of K+-return relaxation in arterial muscles of stroke-prone SHR and WKY.

These studies compared the importance of electrogenic Na+-K+ active (ATP driven) transport, changes in K+ conductance, and passive Ca2+-Na+ countertransport in the large relaxation that occurs in the rat caudal and basilar artery on return to K+ from K+-free solutions. Furthermore, we compared the importance of these three membrane electrical mechanisms in stroke-prone spontaneously hypertensive rats (SP-SHR) versus their normotensive Wistar-Kyoto control rats (WKY) in basilar (cerebral) and caudal arteries. We found that in both basilar and caudal arteries the hyperpolarization and relaxation that occurred on return to K+ after exposure to a 0 K+ (extracellular) solution was consistently greater in SP-SHR than in WKY. The change in membrane potential occurring on transition to 0 K+ in arteries maintained at low temperature (16 degrees C), used as an estimate of the change in K+ conductance during the K+ transition, was not different in either basilar or caudal arteries between SP-SHR and WKY. Thus the hyperpolarization on return to K+ at body temperature would depend primarily on the level of activity of the membrane ATPase, referred to as the Na+ pump. We also sought to compare the passive (but electrogenic) Ca2+-Na+ countertransport mechanism between strains for both arteries, but we were unable to detect any evidence of the predicted hyperpolarization-contraction on transition from 145 to 10 mM extracellular Na+. Furthermore, the return to extracellular Na+ solution failed to show the depolarization-relaxation predicted by the Ca2+-Na+ countertransport mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗
PubMed1985

[Cervix priming in induced abortion in the 1st trimester using intracervical administration of sulprostone gel].

In a prospective, randomised study 40 primigravidae were treated intracervically with 0.05 mg or 0.1 mg Sulprostone-Tylose gel in order to soften the cervix prior to first trimester termination of pregnancy. Curettage was performed on the average 7.5 hours after prostaglandin administration. For objective demonstration of the priming effect, the force required for dilatation of the cervical canal was measured in Newtons by a special tonometer before prostaglandin application and before operation. The maximal dilatability with a force of 10 N, the increase in dilatability after local PG application, and the patency of the cervix were measured. The occurrence of PG-induced lower abdominal pain associated with contractions was analysed with regard to the number of episodes at pain, their timing and the required amount of analgesics. A modified visual analogue scale was used to evaluate the subjective pain experience. The abortive effect of 0.1 mg Sulprostone was found to be more efficient than the 0.05 mg dose. There was no statistical significant difference between the two doses, however, for the priming effect detectable with the tonometer. The subjective experience of pain, use of analgesics and the frequency of gastrointestinal side effects were significantly higher with 0.1 mg than with 0.05 mg Sulprostone. The visual analogue scale allows the patient to quantify, at least to some extent, her experience of pain, and enables a differentiated analgetic therapy. Because of its effectiveness and low rate of side effects, the intracervical application of 0.05 mg Sulprostone gel promises to be an advantageous alternative to other methods of cervical priming.

Abortifacient Agents↗
PubMed1985

Polyethylene-based water-equivalent phantom material for x-ray dosimetry at tube voltages from 10 to 100 kV.

A water-equivalent plastic material RW-1, in the form of thin foils as well as of thicker sheets, has been produced by melting powdered polyethylene together with CaCO3 and MgO. The mixture has been developed in a three-step procedure, starting with provisional mixtures and using data from their measured attenuation curves to determine the final composition. The attenuation curves of RW-1 and of water, as well as their backscatter factors, are in excellent agreement for x-ray tube voltages from 10 to 100 kV.

Humans↗
PubMed1985

[Introduction to a new definition of the standard of dose exposures and dose units by the German Industrial Norm DIN 6814, Part 3].

The recent draft of the DIN standard on dose quantities and dose units is presented in original version and explained by the chairman of the Working Committee Dosimetry. There are important modifications by the introduction of SI units, the new definitions of site dose and individual dose, characteristic dose rate and dose rate constant, as well as by corrections of the notions "secondary electron equilibrium and "free in air".

Germany, West↗