Gene/Protein Disease Symptom Drug Enzyme Compound
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 4,089 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A numerical model of the cardiovascular system was used to quantify the influences on cardiac function of intrathoracic pressure and intravascular and intraventricular hydrostatic pressure, which are fundamental biomechanical stimuli for orthostatic response. The model included a detailed arterial circulation with lumped parameter models of the atria, ventricles, pulmonary circulation, and venous circulation. The venous circulation was divided into cranial, central, and caudal regions with nonlinear compliance. Changes in intrathoracic pressure and the effects of hydrostatic pressure were simulated in supine, launch, sitting, and standing postures for 0, 1, and 1.8 G. Increasing intrathoracic pressure experienced with increasing gravity caused 12% and 14% decreases in cardiac output for 1 and 1.8 G supine, respectively, compared to 0 G. Similar results were obtained for launch posture, in which the effects of changing intrathoracic pressure dominated those of hydrostatic pressure. Compared to 0 G, cardiac output decreased 0.9% for 1 G launch and 15% for 1.8 G launch. In sitting and standing, the position of the heart above the hydrostatic indifference level caused the effects of changing hydrostatic pressure to dominate those of intrathoracic pressure. Compared to 0 G, cardiac output decreased 13% for 1 G sitting and 23% for 1.8 G sitting, and decreased 17% for 1 G standing and 31% for 1.8 G standing. For a posture change from supine to standing in 1 G, cardiac output decreased, consistent with the trend necessary to explain orthostatic intolerance in some astronauts during postflight stand tests. Simulated lower body negative pressure (LBNP) in 0 G reduced cardiac output and mean aortic pressure similar to I G standing, suggesting that LBNP provides at least some cardiovascular stimuli that may be useful in preventing postflight orthostatic intolerance. A unifying concept, consistent with the Frank-Starling mechanism of the heart, was that cardiac output was proportional to cardiac diastolic transmural pressure for all postures and gravitational accelerations.
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PMID:Numerical simulation of the influence of gravity and posture on cardiac performance. 1196 76

In parallel with the experience in most countries, early clinical experiments with dialysis in Britain did not lead to general adoption of the treatment. After a decade, dialysis for acute kidney failure was re-established at Leeds General Infirmary under the direction of Dr Frank Parsons, who had been inspired by Dr John Merrill in Boston. The intervening period was not characterized by indifference to kidney failure, but was devoted to defining acute kidney failure and successfully applying "conservative" measures, such as dietary regimens based on the scientific understanding and teaching of the time. The circumstances influencing the start of dialysis therapy at Leeds in 1956 and subsequent events up to the early 1960s are discussed in relation to the national medical scene.
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PMID:Early dialysis in Britain: Leeds and beyond. 2123 95