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M Hawley

Publications and source records attributed to M Hawley.

3 recordsLinked to original sources
PubMed1992

Experimental assessment of electrical impedance imaging for hyperthermia monitoring.

Two experimental studies are presented that attempt to assess the use of electrical impedance tomography (EIT) to map thermal changes deep in the body. The first was a joint study between our group in Sheffield and the Daniel den Hoed Cancer Center in Rotterdam, funded by the COMAC-BME Hyperthermia project. Phantom and in vivo experiments were conducted with a deep heating ring-capacitive hyperthermia device; the results highlighted some of the inherent problems (electromagnetic interference, nonuniform sensitivity) that remain to be solved for this application. The second experimental study involved heating the stomachs of volunteers by pumping known quantities of liquid (a salt/glucose solution, conductivity 5 mS) at controlled temperatures (25, 37 and 47 degrees C) in and out of the stomach via a nasogastric tube. Results indicated that the level of thermal change induced by these liquids could be reproducibly measured by impedance imaging. Both studies were a further step in assessing the capabilities of EIT for noninvasive monitoring of deep body hyperthermia. The results are encouraging and indicate the value of continued development of EIT for non-invasive thermometry.

Electric Conductivity↗
PubMed1985

Onset and progression of experimental bioprosthetic heart valve calcification.

Calcification, the major cause of bioprosthetic heart valve failures, is a serious clinical problem with uncertain pathogenesis. The objectives of the present study were to define the progressive chemical and morphologic sequence of mineralization in glutaraldehyde-treated porcine aortic valve cusps implanted subcutaneously in rats and to compare the pathology and pathophysiology of calcification in subcutaneous implants with that of orthotopic valve replacements in calves. Cusps were implanted subcutaneously in 3-week-old rats for 24 hours to 18 weeks. Cuspal calcium was 114 +/- 18 micrograms/mg of dry weight (mean +/- SEM) at day 21 and 218 +/- 6 at day 56 of implantation and unchanged thereafter. The earliest mineral deposits, noted at 48 hours, were associated with devitalized porcine connective tissue cells, but by 7 days, mineral deposits also involved collagen bundles. Scanning electron microscopy with energy-dispersive x-ray analysis demonstrated predominant accumulation in the spongiosa with a spongiosa to fibrosa energy-dispersive x-ray analysis count ratio of calcium of 15 at 21 days. In stent-mounted glutaraldehyde-preserved porcine valves implanted in five calves as mitral replacements for 69 to 142 days, cuspal calcium was 86 micrograms/mg (mean) (range 47 to 128). Calf implants also had cell oriented and collagen calcification predominating in the valvar spongiosa. In both rat subcutaneous and calf mitral valve models, early diffuse calcific microcrystals evolved into confluent nodules that disrupted tissue architecture. It is concluded that calcification of glutaraldehyde-preserved porcine aortic valves implanted subcutaneously in rats begins within 48 hours, earliest deposits are localized to residual porcine connective tissue cells, but latter deposits also involve collagen fibrils, mineralization is most prominent in the spongiosa, the pathology of calcification in rat subcutaneous implants and calf mitral replacements is comparable, suggesting a common pathophysiology, and calcific nodule formation most likely initiates clinical features.

Animals↗