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Biomedical subjects

R P Webb

Publications and source records attributed to R P Webb.

5 recordsLinked to original sources
PubMed1997

Use of transgenic plants to study antioxidant defenses.

The abundance of O2 and the highly energetic electron transfer reactions associated with thylakoid membranes make chloroplasts a major source of reactive oxygen intermediates (ROI) in photosynthetic tissues of plants. Attempts to reduce oxidative damage in chloroplasts have included the manipulation of ROI-scavenging enzymes by gene transfer technology. Much of this work has focused on chloroplast-localized superoxide dismutase (SOD), both chloroplast-targeted and cytosolic ascorbate peroxidase (APX) and glutathione reductase (GR). Increased activity of SOD in chloroplasts of transgenic tobacco plants generally leads to increased protection from membrane damage caused by exposure to methyl viologen (MV). In addition, overexpression of chloroplastic Cu/Zn SOD can lead to increased protection from photooxidative damage caused by high light intensity and low temperatures. Transgenic tobacco plants that overexpress APX either in the cytosol or chloroplastic compartments also show reduced damage following either MV exposure or photooxidative treatment and transgenic plants that express increased levels of GR have elevated pools of ascorbate and GSH. Though still preliminary, these results clearly indicate that alterations in the expression of enzymes involved in ROI-scavenging can have significant metabolic effects and provide the hope that this strategy can be used to develop crop plants with increased stress tolerance.

Antioxidants↗
PubMed1995

Postoperative management of cerebral air embolism: gas physiology for surgeons.

Cerebral gaseous microemboli are present in most, if not all, cardiopulmonary bypass-assisted operations. Fortunately, the great majority are subclinical. Clinically significant cases of cerebral air embolism are largely underdiagnosed, undertreated, and underreported. The management of cerebral air embolism has been challenged due to the lack of prospective, randomized studies. Preventive measures that have been implemented throughout the years, resulting from empirically acquired knowledge, have avoided frequent major mishaps. Perfusion accidents, in which massive amounts of gas are pumped into patients, are managed intraoperatively by common-sense heroic measures which, at best, remove 50% of the embolized gas. Postoperative confirmation of a neurologic insult after a cardiopulmonary bypass-assisted operation, in which a cerebral air embolism is likely the source, is one of the most distressing situations a surgical team has to confront, due in part to the lack of pathognomonic diagnostic tools and to the absence of a "scientifically proven" (supported by prospective, randomized studies) therapeutic regimen. In lieu of the latter, we present the physical and physiologic bases that will justify the use of several therapeutic tools when facing a suspected CAE. These tools, when applied rationally, will represent some of the most innocuous modalities in the medical armamentarium.

Aortic Valve↗
PubMed1993

Optoelectronic implementation of neural networks.

The performance of electronic neural networks will eventually be limited by the capacity of their interconnections as operating speeds are increased. The use of optical connections to link electronic elements offers a way to overcome this problem. In particular, spatial optic techniques are especially suited to neural systems because of their parallel structure. Three experimental optoelectronic networks are described that employ holographic components and arrays of high-speed optical modulators. These of a network to 64 x 8 connections with optical fan-out. A hybrid networks have been used to demonstrate operation at 50 MHz, novel training algorithms and the expansion technique for integrating optoelectronic systems is also being developed.

Algorithms↗