Biomedical subjects

J R Lloyd

Publications and source records attributed to J R Lloyd.

51 records · Page 3Linked to original sources

PubMed1988

Distinction of alpha- and beta-aspartyl and alpha- and gamma-glutamyl peptides by fast atom bombardment/tandem mass spectrometry.

A fast atom bombardment/collisional activation/linked-scan at constant B/E (tandem mass spectrometric) method is described which can distinguish between alpha- and beta-aspartyl and alpha- and gamma-glutamyl underivatized peptides. The method is based upon differences in loss of CO from aspartyl or glutamyl B-fragment ions (IB) in these isomers which are rationalized from the stability of the resultant A-fragment ions (IA). It was observed that the ratio of IB:IA which was used in this determination was dependent upon the collision cell pressure. The higher the collision cell pressure, the larger the difference between the IB:IA ratios for these linkages.

Aspartic Acid↗

PubMed1988

In situ evidence for the involvement of superoxide anions in cutaneous porphyrin photosensitization.

Dihematoporphyrin ether, also known as Photofrin-II (Pf-II) is currently used in the diagnosis and management of a variety of epithelial neoplasms, in a modality known as photodynamic therapy (PDT). A major drawback of these porphyrins for PDT is their ability to evoke prolonged cutaneous photosensitization. The mechanism of tumor ablation and cutaneous photosensitization by these photosensitizers is thought to relate to the generation of one or more reactive oxygen species such as superoxide anion, singlet oxygen and hydroxyl radical. However, the role of these oxygen species has not been established unequivocally. In this study, the mechanism of Pf-II-mediated cutaneous photosensitization was examined using murine ear swelling as a marker. The mice treated with Pf-II and light demonstrated two-fold enhancement of ear swelling whereas animals treated with the SOD mimic, beta-carotene and dimethyl sulfoxide (DMSO) had considerably less ear swelling (p less than 0.01). The observed protective effect was dependent on the dose of each quencher and followed the pattern SOD mimic DMSO beta-carotene. The histopathologic alterations caused by Pf-II photosensitization were significantly alleviated by pretreatment with SOD mimic whereas beta-carotene and (DMSO) were less effective. Inhibitors of superoxide dismutase (sodium diethyldithiocarbamate) and catalase (hydroxyl amine and 3, amino 1,2,4-triazole) augmented Pf-II-mediated cutaneous photosensitization. These data provide the first in vivo evidence for the involvement of superoxide anion in cutaneous porphyrin photosensitization.

Animals↗

PubMed1981

An experimental study of the flow-induced mass transfer distribution in the vicinity of prosthetic heart valves.

An experimental study of the flow-induced mass transfer distribution in the vicinity of a model disk valve and a ball valve was conducted using electrochemical techniques. Reynolds numbers ranged from 1000 to 6000, which are characteristic of physiologic conditions. Local instantaneous and time average data are presented. It was found that the flow-induced mass transfer distribution was high in regions of both low and high shear. It was also demonstrated that the fluctuations in the mass transfer to the wall of the test section around the valve are significantly affected by valve design. The regions of high mass transfer measured in this study were found to correlate very closely to regions where thrombus formations have been documented in-vivo studies.

Aorta↗

PubMed1981

Experimental measurements of the flow-induced shear stress distribution in the vicinity of prosthetic heart valves.

The present study examines the local shear stress distribution occurring during flow through prosthetic valves. The electrochemical technique is a powerful tool for the study of mass transfer related phenomena and was selected for this investigation. The present investigation attempts to establish the viability of the particular application of the technique. Three test section geometries were analyzed: a straight tube, a ball-in-cage valve, and a model disk-in-cage valve, and the tests were conducted at six Reynolds numbers range from 1000 to 6000 under steady-state conditions. The model disk valve provided a base-case check on the validity of the technique since it has been employed in several previous studies and the flow through it is well documented. High shear and low shear regions are clearly evident and their locations can be pinpointed. The ball-in-cage valve was tested over the full range of Reynolds numbers. The shear profiles demonstrate a double peak in the region of the ball, a result which was unexpected. Careful study revealed that this was a result of the test section geometry. The frequency of the fluctuations in wall shear for the ball valve were found to be different than those for the disk valve indicating that the environment at the aortic wall is definitely affected by valve design. This study showed the electrochemical technique to be a valuable tool for the study of the flow through prosthetic heart valves.

Biomechanical Phenomena↗

PubMed1980

The design, fabrication and evaluation of a trileaflet prosthetic heart valve.

Although prosthetic heart valves have been in existence for many years, the need for new improved designs and in-vitro evaluation techniques are apparent. This paper presents details on the design considerations, fabrication techniques and heart valve evaluation equipment. A valve performance index is discussed in light of various valve and mock circulatory test section designs. The need for national and indeed international valve evaluation techniques is made apparent.

Aortic Valve↗

PubMed1979

Inflicted burns in children. Recognition and treatment.

Inflicted burns are an essential part of the battered child syndrome. One hundred forty-two nonaccidental burns (16%) were found in 872 children admitted to the burn center at the Children's Hospital of Michigan during the six-year period (1972 to 1977). Of the 1,518 cases of child abuse treated during this period, 9% were caused by intentional burns. Family instability and an inability to deal with stress in crisis were important factors in the cause of these injuries.

Battered Child Syndrome↗

PubMed1978

Early laminar excision: improved control of burn wound sepsis by partial dermatome debridement.

The large mass of devitalized tissue that comprises the burn eschar is gradually becoming recognized as the principal source of complications in the burn patient. Clinical observations suggest that the topical agent silver sulfadiazine does not penetrate the eschar sufficiently to prevent bacterial infection from becoming established in the deeper levels of the wound but does penetrate to a depth of approximately 1.5 mm in bactericidal concentrations. A new technique that takes advantage of this fact, early laminar excision, has been developed at the Children's Hospital of Michigan Burn Center. The eschar is excised layer by layer with the electric dermatome under general anesthesia within the first 72 hr post burn, and the thickness of the devitalized tissue is reduced to a remnant of less than 1 mm. This is less than the depth to which silver sulfadiazine is capable of penetrating in bactericidal concentrations, and greatly enhanced control of burn wound sepsis is achieved. Early laminar excision of the eschar, combined with silver sulfadiazine dressings, aggressive resurfacing of the wound, and increased emphasis on nutrition, is an approach to management of the victims of thermal trauma that should significantly improve survival in patients with burn injuries greater than 60% body surface area.

Adolescent↗

PubMed1977