Biomedical subjects

A Shelton

Publications and source records attributed to A Shelton.

4 recordsLinked to original sources

PubMed1995

Elastomeric valves, a new design.

The convex bileaflet valve replaces the flat biflap inflow valve designed by Long Sheng Yu and the tricusp semilunair outflow valve. One reason is easier manufacturing. Convex bileaflet valves are developed for the 11, 20, 40, 70 and 140cc ventricles. Testing included curves (Cardiac Output versus Venous Pressure, Cardiac Output versus Heart rate), flow visualization studies, paint and bloodbag studies. The curves and flow visualization were done by connecting ventricles to one of our standard mock circulations. Paint and bloodbag studies were done by connecting the hearts to a bloodbag, but the bag was filled with water for the paint studies. The curves show high cardiac output, even with pumping at high heart rates (150 BPM+). The flow visualization shows a good stream through the sinus Valsalvae. No stagnating flow is visible. The bloodbag studies which provoke thrombosis show it on the edges of the heart valves, and little in the groove between the valve and the sinus Valsalvae. Heparninzation prevents the thrombosis. Results of our tests were good. The convex bileaflet valve seems to have good future.

Biocompatible Materials↗

PubMed1987

The response of Escherichia coli to ciprofloxacin and norfloxacin.

The action of ciprofloxacin and norfloxacin on two strains of Escherichia coli was studied by diverse methods including electronmicroscopy, viable counting and continuous turbidimetric monitoring. During the first few hours of exposure to inhibitory concentrations of the drugs, the opacity of bacterial cultures continued to increase for a period that was inversely proportional to the drug concentration. This change corresponded to the appearance of filamentous bacteria, swollen forms and some lysis. There was subsequently a gradual drop in opacity during which extensive lysis occurred. As judged by viable counts of bacteria washed free of drug, cell death occurred within 30 min of first exposure to the drugs and continued over a 3-h period. Ultrastructure studies demonstrated that lysis was preceded by the formation of vacuoles, predominantly at the poles of the cells. At these sites, breaks in the cell walls eventually occurred, resulting in extrusion of the cytoplasmic contents.

Cell Wall↗

PubMedDate not supplied

Increased urine histamine and contrast media reactions.

Urine samples were collected from 200 subjects undergoing intravenous pyelography. The urine histamine levels were compared with those of 132 normal control subjects, 11 subjects with systemic mastocytosis, six subjects with idiopathic anaphylaxis, and ten subjects experiencing mild anaphylactic reactions during allergy immunotherapy. Compared with normal controls, as a group, all subjects receiving intravenous contrast media had increased urine histamine (P less than 0.05 by Student's t-test) while those subjects experiencing adverse reactions had considerably larger increases. The urine histamine levels in the subjects experiencing systemic reactions were in the same range as those observed in patients having mild anaphylactic reactions to immunotherapy and somewhat lower than those found in idiopathic anaphylaxis or systemic mastocytosis. These data suggest that some histamine release accompanies infusions of contrast media in all subjects and that larger amounts of histamine release are associated with adverse reactions.

Adolescent↗

PubMedDate not supplied

The development of a valveless cardiac assist device attached to the ventricular apex.

Konstantinov et al, in October, 1991, published a novel way to bridge a patient for heart transplantation. They proposed to cut off both ventricles high under the atrioventricular groove, leaving the atria, aorta, and pulmonary artery and their valves intact and to attach pneumatically driven, valveless pulsating pouches to assist the heart until a donor could be found. The removal of the ventricles just below the atrioventricular groove is called the "high cut"; it, however, destroys the chordae tendineae rendering the mitral and tricuspid valves insufficient. These have to be replaced by tissue inflow valves. We chose to cut off the ventricles at a lower level (the "low cut") to leave the papillary muscles on both sides intact, thereby saving the integrity of the mitral and tricuspid valves. Pulsating pouches were made to fit the heart at this lower level. They can be easily connected to the remaining heart after a specially disigned cuff has been sutured over the ventricular stumps. The pouches were pumped during the systole of the natural heart, but the myocardium may have to be electrically stimulated during systole to prevent undue distension. If the turgor is too weak to prevent distension, a sleeve over the ventricles is provided. To find the best location for these pouches, human cadaver implantations were done and the pre peritoneal cavity was found to be the most suitable. In vitro testing to determine how much flow could be pumped was done by attaching the pouches to fresh pig hearts and connecting them to a double sided mock circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Output↗