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Biomedical subjects

S G Kovacs

Publications and source records attributed to S G Kovacs.

6 recordsLinked to original sources
PubMedDate not supplied

The role of polymeric surface smoothness of biliary stents in bacterial adherence, biofilm deposition, and stent occlusion.

Bacterial adherence and biofilm deposition onto the surface of polymers used for biliary stents are the initial events that ultimately lead to stent occlusion. Vivathane is a new polymer with an ultrasmooth surface. In this study, stents made from Vivathane were compared to standard plastic stents in an in vitro model. Polyethylene, C-flex, and Vivathane stents were connected in parallel and perfused with infected bile. The surfaces of the polyethylene and C-flex stents developed exuberant bacterial growth and biliary sludge deposition. Vivathane stents were nearly free of bacteria and demonstrated no propensity for biliary sludge deposition. These results indicate that polymeric surface irregularities promote bacterial adherence, biofilm deposition, and accumulation of biliary sludge. The ultrasmooth surface of Vivathane does not allow bacterial adherence and biofilm deposition. Vivathane holds promise as a new polymer for use in biliary stents in long-term applications.

Bacterial Adhesion↗
PubMedDate not supplied

A magnetically actuated left ventricular assist device.

Over the past 6 years, research has led to development of a small, lightweight, power-efficient, uniquely simple ventricular assist device driven by a magnetic actuator. Magnetic actuation permits total elimination of all mechanical motion converter components used for pusher plate displacement, resulting in a significant reduction in complexity and resultant increase in reliability. Extensive in vitro mock loop development has resulted in a left ventricular assist device (LVAD), the primary design parameters of which for the clinical prototype actuator and pump are 1) an actuator weight of 312 g, 2) actuator size of 32.5 cm3, 3) power requirements of 7.8 to 11.4 watts (60-100 beats per minute [BPM]), and 4) system efficiency of 24% to 34% and average dynamic stroke volume of 65 ml. Initial in vivo tests assessed this LVAD's performance in four sheep under three acute conditions of ventricular dysfunction. The results demonstrate that, at a pump-rate of 100 BPM, mean aortic pressure increased by 45-50 mmHg during 1) beta blockade, 2) coronary ligation, and 3) ventricular fibrillation. Pump flow ranged from 2.71 L/min to a maximum of 4.6 L/min. Acute test periods were arbitrarily set for 6 hours duration. Of the four sheep, two survived, one lived 5 hours, and the fourth lived 4.5 hours. Global fibrillation was the primary cause of failure. This initial in vivo data demonstrates the pump's ability to maintain satisfactory hemodynamic parameters of flow and pressure under three acute conditions of extreme left ventricular dysfunction in an animal model. These initial LVAD performances were encouraging. Further tests will use calves with a greatly expanded performance evaluation protocol.

Adrenergic beta-Antagonists↗
PubMedDate not supplied

Prosthetic valve selection for a pulsatile LVAD.

During the final development of a unique Magnetically Actuated Left Ventricle Assist Device (MALVAD), three of the most widely used clinical prosthetic valves were evaluated to determine their suitability for the stringent requirements for LVAD use, in both the inflow and outflow positions. The three valves (St. Jude Medical-SJM; Medtronic Hall-MH; Bjork-Shiley Convex-Concave-BSCC), with lumen size of 25 mm, were tested in the same appropriate mock loop to the following set of hydraulic parameters: 1) after-load systemic pressure = constant 100 mmHg; 2) preload pressure ranged from 3 mm to 18 mmHg; 3) beat rate ranged from 60 bpm to 80 bpm. Pump actuator power was held constant, correspondent with specific bpm rate, for all valves tested. Results from a series of 10 bench tests per valve showed that the SJM was significantly better, on a statistical basis, than both the MH and BSCC valves, at fill pressures of 5 mmHg. At 10-mm fill pressure, however, the statistical flow rates for both the SJM and the MH valves were significantly superior to the BSCC valve, so that the BSCC valve was classified as a marginal candidate for LVAD use. The SJM and MH valves had bench test flow-rate values whose numerical difference was too small to serve conclusively as an arbitrary basis for valve choice. Because of this, the two valves were further evaluated in terms of two widely recognized, mandatory LVAD valve design criteria: (1) comparative mechanical ruggedness, and (2) relative ease and simplicity of LVAD design inclusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗