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Biomedical subjects

W Clay

Publications and source records attributed to W Clay.

12 recordsLinked to original sources
PubMed1991

Hemodynamic evaluation of a chronically implanted, electrically powered left ventricular assist system: responses to acute circulatory stress.

Hemodynamic stress testing was performed in four calves with a chronically implanted left ventricular assist device consisting of a double-valved pump interposed between the left ventricular apex and the descending thoracic aorta. The device was powered either pneumatically (n = 1) or with a transcutaneous energy transmission system (n = 3). Hemodynamic evaluation (cardiac output and right and left ventricular and pulmonary and carotid artery pressures) was carried out at baseline and during all hemodynamically stressed states. Atrial pacing and ventricular pacing to a heart rate of 140 beats/min resulted in no significant change in right or left heart filling pressures or cardiac output. Preload reduction with nitroprusside or transient inferior vena cava balloon occlusion resulted in a marked decrease in left ventricular pressure with preservation of mean arterial pressure. Phenylephrine administration resulted in a marked rise in mean arterial pressure with no change in cardiac output or filling pressure. Induction of ventricular fibrillation resulted in a decrease of mean left ventricular pressure to 11 +/- 8 mm Hg, but mean arterial pressure was maintained at greater than or equal to 50 mm Hg. It is concluded that a multicomponent, implantable, electrically powered assist system is capable of maintaining a normal cardiac output under a wide range of loading conditions and chronotropic states. Although this device is clearly preload dependent, it is capable of maintaining normal systemic pressures during conditions of severe left ventricular dysfunction and circulatory collapse.

Animals↗
PubMed1988

Factors affecting oviposition site preference by Toxorhynchites splendens in the laboratory.

In a series of laboratory oviposition assays, gravid Toxorhynchites splendens exhibited a preference for cups containing Aedes aegypti larval rearing water, but not for cups containing liquid cultures of bacteria, live Ae. aegypti in distilled water, Ae. aegypti larval holding water with reduced bacterial contamination, or methyl propionate at 0.1, 0.2 and 0.3% in distilled water. Preoviposition flight behavior was elicited by dark-colored containers, but few eggs were deposited if they contained no water. An invisible source of humidity placed in cups enhanced oviposition, but a reflective surface placed in dry cups did not. It is concluded that this species is strongly influenced by humidity and visual stimuli in the acceptance of a site for oviposition.

Aedes↗
PubMed1987

Injury and disability effects of motor car accidents.

The results of a field experiment into the relations between injuries and disability are presented. In this study the effect of the variables age, sex, injury severity, and injury location on the disability rate was investigated. Injury location appears to have the greatest effect on the chance of disability. Injuries located in the locomotive system cause much disability and injuries of the internal organs cause little disability. The variables age (greater than or equal to 15 years), sex, and injury severity--MAIS greater than or equal to 2--have little influence on disability occurring. It is therefore clear that MAIS is not a good predictor of disability. Among children, injuries cause much less disability, approximately 50% of that among the adults.

Accidents, Traffic↗
PubMed1986

Thermedics' approach to ventricular support systems.

Temporary and permanent ventricular assist systems, developed by Thermedics, Inc., are described, including rationale, design, operation and surgical applications. Clinical data are presented for pneumatically driven temporary left ventricular assist devices (LVAD). Usefulness of this device rests on the assumption that tissue of a weakened heart can recover if relieved for a time by an LVAD. The surgical implantation of an LVAD is reported in a case where the patient later received a heart transplant. The concept and technology of the subsystems of a permanent ventricular assist system (VAS), now ready for preclinical trials, are discussed. Design of a low-speed, torque-motor driven blood pump is described. Details are presented on transcutaneous energy transmission by means of a transformer, one of whose coils is embedded under the skin. Though less efficient than percutaneous transmission, the method eliminates infection risk. Special types of polyurethanes are analyzed in respect to their biocompatibility. It is concluded that flocking of the polyurethane surface allows the growth of a biological lining which is highly antithrombogenic. Sintered metal powders are found to be most efficient for fabrication of rigid pump components. A lenticular pump design is proposed to solve the problem of pressure differentials in the sealed device. Cardiac endocrine functions are cited in support of using assist devices that leave the heart in place.

Assisted Circulation↗
PubMed1981

Energy transmission across intact skin for powering artificial internal organs.

The prototype for a transcutaneous energy transmission system (TETS) meets the engineering goals of high efficiency, limited heating of surrounding tissues due to losses in implanted components, and excellent resistance to misalignment and uncoupling of the coils. Higher efficiencies, reduced thermal generation, and lighter implanted components are the goals of future designs. Improvements will be made based on the findings of a complete in vitro electrical characterization of the present system, varying operating frequency, the number of turns in the 2 coils, and the voltages and currents in the 2 coils. The results of short-term in vivo studies indicate that the temperature rise in tissues surrounding the implanted components is not excessive, that the layer of cutaneous tissue covering the secondary coil is viable and that the thickness of the tissue separating the 2 coils stabilizes after about 2 wks. Definitive statements await the results of in vivo studies lasting longer than 6 mos. Similarly, an evaluation of the effectiveness of butyl as a moisture barrier awaits the results of long-term in vivo, and in vitro immersion test.

Animals↗