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Biomedical subjects

A W Preece

Publications and source records attributed to A W Preece.

At least 37 records · Page 2Linked to original sources
PubMed1991

New materials for dielectric simulation of tissues.

Two novel materials have been developed to simulate the dielectric properties of human muscle and fat at 1000 MHz. These materials, which are based on ethanediol set with gelatine, are easily made and have good mechanical properties. The complex permittivity, epsilon *, of each material was measured with an open-ended coaxial sensor in conjunction with an automatic network analyser. Values of epsilon * at 1000 MHz and room temperature (49.4-24.4j for the muscle-equivalent material, 8.2-3.6j for the fat-equivalent) compared well with literature values for tissue at body temperature. Thermal properties were also considered. Specific heat capacities of the materials at room temperature were measured by differential scanning calorimetry and found to be very close to values predicted by theory. Densities were also measured and the thermal conductivities estimated. For comparison, new measurements were made of the specific heat and density of human muscle and fat at body temperature.

Adipose Tissue↗
PubMed1990

Theoretical and experimental comparison of three types of electromagnetic hyperthermia applicator.

There is evidence that heating of malignant tissue in the treatment of cancer may be beneficial and so the performance of different applicator designs needs to be established. A theoretical model of the dielectric loaded waveguide applicator is compared with models of two other applicators which depend on energy radiated from conductors carrying high frequency current. The latter are exemplified by the compact resonant patch applicator and the lightweight inductive current sheet applicator. It is shown that heating profiles and field penetration of each applicator are similar for equal radiating areas, and these results have been substantiated experimentally. Impedance match as a function of frequency and load is also compared for the three types of applicator.

Electromagnetic Phenomena↗
PubMed1987

Changes in helper and suppressor T lymphocytes following radiotherapy for breast cancer.

Changes in total lymphocyte, T lymphocyte, T helper and T suppressor lymphocyte numbers were studied in 22 patients with breast cancer before and after radiotherapy. T lymphocyte subsets were measured using monoclonal antibodies and fluorescence microscopy. After treatment the total lymphocyte count fell significantly and was still reduced 9 months later, but the proportion of cells labelled as T lymphocytes was unchanged during this period. The helper-suppressor ratio, which was within the normal range before radiotherapy, was significantly reduced at 3 months and 9 months after. Following treatment both T helper and T suppressor cell numbers were significantly reduced. T helper cell numbers remained reduced throughout the study period but T suppressor cell numbers showed a recovery to normal values 9 months after radiotherapy.

Breast Neoplasms↗
PubMed1987

A carbon chamber for vital microscopy of bone healing.

We describe a carbon chamber implanted in the ulna of fowl. A window permitted daily microscopy of bone formation including observations of tetracyline labelling. The chamber could be heated to 5 degrees above body temperature by 600 kHz radio frequency.

Animals↗
PubMed1984

The cytotoxicity of kaolin towards macrophages in vitro.

The inhalation of china clay dust by man can cause pneumoconiosis. In an attempt to identify the factors responsible the cytotoxicity in vitro of china clay dust towards mouse peritoneal macrophages was examined. Respirable dusts collected at china clay drying plants were cytotoxic towards the cells. This activity was caused by kaolinite (the major mineral in china clay) and was not due to the presence of ancillary minerals. The cytotoxicity of kaolinite was not due to particle morphology and the positively charged edges of the mineral contributed only slightly to cytotoxicity. An electron microscope study showed that macrophages phagocytosed PVPNO-coated kaolinite particles indicating that the low cytotoxicity of these particles was not due to poor phagocytosis. Residence of china clay in rat lungs appeared to reduce its cytotoxicity. It was concluded that the cytotoxicity of kaolinite was probably related to the proposed amorphous silica-rich gel coating on the particles. The relevance of the findings in vitro to the effects in vivo of china clay is discussed.

Animals↗
PubMed1983

The analysis of the red cell unsaturated fatty acid test for multiple sclerosis using laser cytopherometry.

Using a laser cytopherometer, the electrophoretic mobility of glutaraldehyde-fixed erythrocytes from patients with multiple sclerosis (MS) has been compared with that of cells from control subjects. The effect of incubating cells with different concentrations of linoleic acid (LA) has been tested. At a concentration of 20 micrograms LA per 2 x 10(7) cells, slower mobilities were observed, on average, than those of control subjects, but there was overlap between control and patient groups. At a higher concentration of LA (160 micrograms per 2 x 10(7) cells), many of the MS samples showed a slower mobility than the control samples, although overlap was still evident. The value of the application of laser cytopherometry compared with conventional cytopherometry to this type of test is discussed.

Adult↗
PubMed1983

The electrophoretic mobilities of minerals determined by laser Doppler velocimetry and their relationship with the biological effects of dusts towards macrophages.

The role of surface charge in the pathogenicity of mineral dusts has been little studied, partly due to the time consuming nature of such determinations using conventional microelectrophoresis apparatus. In this work the use of laser Doppler velocimetry proved to be a rapid method of determining the electrophoretic mobility of mineral dusts. Ceramic ball milling of fibrous minerals, whilst dramatically reducing the cytotoxicity of the dusts towards macrophages, had only a small effect on electrophoretic mobility. It is concluded that some other factor, possibly fibre morphology, is important for observed biological effects. The coating of quartz and kaolinite with poly-2-vinyl pyridine-N-oxide dramatically lowered their cytotoxicity towards macrophages. The dusts' electrophoretic mobilities were also lowered. The significance of these findings is discussed.

Animals↗
PubMed1983

Factors involved in the cytotoxicity of UICC amosite towards macrophages.

The cytotoxicity of various ball-milled UICC amosite samples toward mouse peritoneal macrophages in vitro was examined. On increased ball milling, the cytotoxicity of the amosite samples fell. This decreased biological activity seemed to correlate best with number of fibers longer than 4 micron/micrograms dust, rather than total number of fibers or the electrophoretic mobility of the amosite samples.

Animals↗
PubMed1981

A laser Doppler cytopherometer for measurement of electrophoretic mobility of bioparticles.

A wide-angle laser Doppler spectrometer has been combined with a number of high-field-strength cytopherometer designs for the purpose of studying the electrophoretic mobility (EPM) of biological particle and cells in non-physiological and physiological media. This produces a typical Doppler shift of 100 Hz for an EPM of 1.0 micrometers s-1 V-1 cm, and a shift-to-width ratio of greater than 10 for human erythrocytes in physiological saline. The unit uses two equal-intensity beams of identical pathlength, crossing in the measuring volume at an angle of 40--90 degrees in air and can function in either a fringe or coherent mode. The resolution for human cells and bioparticles is comparable with conventional cytopherometry but the data collection rate is many times higher.

Animals↗
PubMed1980

Response of human lymphocytes to PHA and tumour-associated antigens as detected by fluorescence polarization.

Fluorescence polarization measurement during the progress of fluorochromasia has been used to study the response of human lymphocytes to phytohaemagglutinin (PHA) and to tumour-associated antigens, as a basis for the detection of malignant disease. Polarization (P) values of both stimulated and unstimulated lymphocytes decreased with increasing intracellular fluorescence intensity, and with the duration of the fluorochromatic reaction. When these effects were taken into account, there was no significant difference in the change of P following stimulation of lymphocytes from 50 cancer patients or healthy subjects; the magnitude of the response was related more to the age of the donor and to the extent of granulocyte contamination of the lymphocyte preparation than to the presence of cancer. There were, however, significant differences in the change in leakage of fluorescein out of the lymphocytes and in the change in hydrolysis rate after PHA stimulation between lymphocytes from healthy individuals and from patients with cancer.

Adult↗
PubMed1975

Studies with the macrophage migration inhibition (MMI) test in patients with malignant disease.

Macrophage migration inhibition (MMI) tests have been carried out using lymphocytes from twenty-six patients with malignant disease and from twenty-two other subjects. The antigens used were the same as those employed in the macrophage electrophoretic mobility (MEM) test. The results indicate that the inforation obtained using the MMI test is similar to that found with the MEM test.

Adult↗