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Biomedical subjects

J A Davidson

Publications and source records attributed to J A Davidson.

At least 37 records · Page 2Linked to original sources
PubMed1997

Lack of effect of granulocyte-macrophage colony-stimulating factor on secretion of interferon-tau, other proteins, and prostaglandin E2 by the bovine and ovine conceptus.

Three experiments tested the effects of recombinant bovine granulocyte-macrophage colony-stimulating factor (rbGM-CSF) on the preimplantation bovine and ovine conceptus. There was no effect of rbGM-CSF on the secretion of total radiolabeled protein in conditioned medium, immunoreactive interferon-tau (IFN tau), antiviral activity, or prostaglandin E2 from Day 16-18 bovine conceptuses cultured for 24 hr with, [3H]leucine and +/- 10 ng/ml rbGM-CSF. Similarly, there was no effect of 1 ng/ml rbGM-CSF on the secretion of total radiolabeled protein. IFN tau, or antiviral activity from Day 17 ovine conceptuses. There was also no beneficial effect of 1 or 10 ng/ml rbGM-CSF on the presence of immunoreactive IFN tau in conditioned medium from in vitro-produced bovine blastocysts at Day 7-8 after fertilization. Results indicate that IFN tau secretion from bovine and ovine conceptuses are unresponsive to rbGM-CSF at the concentrations tested.

Animals↗
PubMed1997

Successful retrieval of a knotted pulmonary artery catheter trapped in the right ventricle using a dormier basket.

We report the case of a 71 year old patient in whom a pulmonary artery catheter (Swan Ganz) formed a knot which was fixed within the right ventricle in the region of the tricuspid valve annulus. The catheter was successfully dislodged to the right atrium, subsequently snared by a dormier basket advanced from the right femoral vein and retrieved by localised cut down of the femoral vein.

Aged↗
PubMed1997

The treatment of type II diabetes in Texas. Current issues for managed care and employers.

In 1995, a forum was held in Dallas, Texas, to discuss the current state of treatment for type II diabetes and the issues facing managed care organizations (MCOs) and employers. Attendees included representatives from the American Diabetes Association (ADA), diabetologists, medical directors from leading MCOs in the area, benefits managers and employee representatives from large corporations in the region, diabetes educators, and a range of health care personnel directly involved in the care and treatment of patients with type II diabetes. The objectives of the forum were to discuss the state of diabetes treatment from the perspectives of MCOs and employers, to create a better understanding of the issues in treating diabetic patients, and to reach a consensus on the standards of care and the treatment guidelines for managed care patients with diabetes. Several needs were agreed on and identified by the attendees, including the need to develop minimum standards of care for the management of diabetes care, to improve patient and physician education programs and the communication between MCOs and employers, to acquire more sophisticated outcomes data, to pursue aggressive treatment of hyperglycemia, to increase emphasis on managing care to achieve long-term cost savings, and to stress greater patient responsibility for their own care.

Algorithms↗
PubMed1996

Effect of induced pyometra on luteal lifespan and uterine fluid concentrations of prostaglandins and interferons in cows.

The objective was to determine whether occurrence of persistent corpora lutea in cows with pyometra could be explained by accumulation of prostaglandins and interferons in the uterus. Pyometra was induced by treatment with hCG, followed by intrauterine infusions of iodine and Actinomyces pyogenes . Five of the seven treated cows developed pyometra as indicated by extended estrous cycles (30-37 + d) and presence of purulent uterine exudate at slaughter (Day 37 after estrus). Mean (+/- standard error) concentrations of prostaglandins E(2) and F(2alpha) for the cows with pyometra were 34.7 +/- 14.4 and 96.3 +/- 28 ng/ml, while the concentrations in uterine flushings in the remaining 2 cows averaged 1.85 +/- 0.7 and 0.9 +/- 0.2 ng/ml, respectively. Based on Western blotting, none of the cows had detectable concentrations of either interferon-alpha or interferon-tau in uterine secretions. In conclusion, pyometra results in increased uterine prostaglandin secretion. While increased secretion of cytokines associated with bacterial infection may be contribute to this effect, there was no evidence in this study to suggest that interferons are involved in the mechanism which causes persistence of the corpus luteum in bovine pyometra.

Journal Article↗
PubMed1996

Initial hemocompatibility studies of titanium and zirconium alloys: prekallikrein activation, fibrinogen adsorption, and their correlation with surface electrochemical properties.

Two novel metal alloys, Ti-13Nb-13Zr and Zr-2.5Nb, have been engineered for applications in orthopedic implants because of their favorable mechanical properties, corrosion resistance, and compatibility with bone and tissue. These alloys also have the ability to form a hard, abrasion-resistant, ceramic surface layer upon oxidative heat treatment (diffusion hardening, DH). Previous studies have indicated that these and other ceramics cause limited hemolysis and exhibit remarkable structural integrity after extended exposure to physiological environments. Such observations suggest that DH Ti-13Nb-13Zr and ZrO2/Zr-2.5Nb could be used successfully as components in blood-contacting devices. Materials intended for such applications must possess properties that do not elicit adverse physiological responses, such as the initiation of the coagulation cascade or thrombus formation. In the present study measurements of prekallikrein activation, fibrinogen adsorption from diluted human plasma, and the strength of fibrinogen attachment as judged by residence-time experiments were performed to evaluate the potential hemocompatibility of these materials. The results of the prekallikrein activation and fibrinogen-retention studies correlated well with two electrochemical properties of the alloys, the open circuit potential and reciprocal polarization resistance. The results indicate that both the original and treated Ti and Zr alloys activate prekallikrein and adsorb as well as retain fibrinogen in amounts similar to other materials used as components of blood-contacting devices. On the basis of these studies, these alloys appear to be promising candidates for cardiovascular applications and merit further investigation.

Biocompatible Materials↗
PubMed1996

Histomorphological reaction of bone to different concentrations of phagocytosable particles of high-density polyethylene and Ti-6Al-4V alloy in vivo.

Wear debris has been implicated in the pathogenesis of loosening and osteolysis of total joint replacements by stimulating a foreign body and chronic inflammatory reaction capable of bone resorption. Whether increasing concentrations of wear particles have an adverse biological effect on bone has not been elucidated. We performed a histomorphological and semi-quantitative morphometric analysis of the reaction of bone to different concentrations of phagocytosable particles of high-density polyethylene (HDPE) and titanium 6-aluminium 4-vanadium alloy (Ti-6Al-4V) implanted in the rabbit tibia. The Ti-6Al-4V particles had a diameter of 4.0 +/- 4.4 microns (mean +/- SD); the HDPE particles averaged 4.7 +/- 2.1 microns. Suspensions of 10(6)-10(9) particles per ml were mixed in saline, sterilized, and introduced through a drill hole into the proximal tibia of 30 mature female rabbits. Controls included drilled, but non-implantable limbs. The animals were killed at 16 weeks and histological sections were made of the implant area. Histomorphological assessment was carried out using an interactive image analysis system. The parameters assessed included the presence of histiocytes, foreign body giant cells and inflammatory cells, the location and number of particles, the presence of haematopoeitic elements, fat or necrosis of the marrow, whether healing of the cortical window had taken place, and whether there was evidence of formation or resorption of bone by the periosteum, cortex and marrow. A semi-quantitative rating system was employed. Phagocytosable particles of Ti-6Al-4V and HDPE, in concentrations of 10(6)-10(9) particles per ml, evoked a histiocytic reaction without extensive fibrosis, necrosis or granuloma formation. This reaction occurred without disturbing the normal repair processes of bone formation and resorption to the surgical insult. A clear dose-response effect on the histological parameters assessed in this study was not noted. Using the present model, by 16 weeks, a similar "one time' particle load could be accommodated. The ongoing generation of particulate debris over a more extended period of time might be necessary before the remodelling processes of bone would be disturbed.

Alloys↗
PubMed1996

The effect of temperature upon pain during injection of propofol.

Propofol has been shown to cause pain on injection. This study investigated the effect of warming propofol to 37 degrees C on the pain of intravenous injection. One hundred and one women on outpatient gynaecology lists were allocated to receive propofol either at room temperature or at 37 degrees C. Warming propofol decreased the incidence of pain on injection by 37% (p < 0.001), and also decreased the severity of pain reported by patients (p < 0.001). We conclude that warming propofol to 37 degrees C provides a simple and safe method of reducing the incidence of pain on injection without the addition of other agents.

Adolescent↗
PubMed1996

Gestational diabetes: ensuring a successful outcome.

When gestational diabetes is diagnosed, the physician has an opportunity to help the patient deliver a healthy baby by encouraging optimal glycemic control. In this article, the authors describe risk factors, methods of diagnosis, and a plan of management that includes a nutritional program based on ADA guidelines, use of insulin if needed, home monitoring of glucose levels, and appropriate exercise.

Diabetes, Gestational↗
PubMed1996

Wear-resistant, hemocompatible Ti-Nb-Zr and Zr-Nb alloys to improve blood pump design and performance.

Over the past several years, we have developed novel titanium-niobium-zirconium (Ti-Nb-Zr) alloys to address the long-term performance needs of orthopedic implants. The unique properties of these alloys also render them promising candidates for blood pumps. These properties include excellent biocompatibility in combination with high strength and toughness, and low elastic modulus (low stiffness). Additionally, these metal alloys are readily hot or cold worked into complex shapes including wire, foil, tubing and bar. They are readily machined and polished, and they can be surface oxidized to form a hard, wear-resistant, low-friction ceramic surface layer. In this diffusion-hardened condition, oxygen also hardens the underlying metal to optimize the bone between the ceramic oxide surface and the tough metal substrate. Unlike metal surfaces, oxidative wear, which can alter surface energy, friction, and hemocompatibility, does not occur. Consequently, the combined benefits of a stable, wear-resistant, low-friction ceramic surface layer with the toughness, strength, formability, and thermal conductivity of metal may provide improvements in the design and performance of blood pumps and peripheral graft and percutaneous (power) components of the pump.

Alloys↗
PubMed1995

DNA synthesis and prostaglandin secretion by bovine endometrial cells as regulated by interleukin-1.

Interleukin-1 (IL-1) is a pleiotropic cytokine which has been implicated in the regulation of endometrial function through alterations in proliferation, protein synthesis, and prostaglandin secretion. The objectives of this study were to determine if recombinant bovine interleukin-1 beta (rbIL-1 beta) stimulated prostaglandin secretion and altered the proliferation of bovine endometrial epithelial and stromal cells. Uterine flushes were also evaluated by enzyme-linked immunosorbent assay (ELISA) to determine if IL-1 beta was present in the bovine uterus. Effects of rbIL-1 beta (1-1000 ng mL-1) on DNA synthesis by endometrial epithelial and stromal cells prepared from cows at Days 11, 14 and 17 after oestrus were determined by monitoring uptake of [3H]thymidine into DNA. Incorporation of [3H]thymidine by epithelial cells was not affected by IL-1, but rbIL-1 beta inhibited [3H]thymidine incorporation by stromal cells. Secretion of prostaglandin E2 (PGE2), PGF2 alpha, and 13,14-dihydro 15-keto PGF2 alpha (PGFM) by epithelial and stromal cells was increased by rbIL-1 beta. Uterine flushes collected on Days 11, 14 and 17 after oestrus were positive for IL-1 regardless of pregnancy status, whereas flushes from pregnant cows on Day 25 and Day 30 did not have any detectable IL-1. In conclusion, IL-1 can be considered as a local regulatory factor of the bovine endometrium because of its presence within the uterus and its ability to alter DNA synthesis and prostaglandin secretion of endometrial cells.

Animals↗
PubMed1995

Comparison of the effects of four i.v. anaesthetic agents on polymorphonuclear leucocyte function.

Initial resistance of bacterial infection is mediated primarily by polymorphonuclear leucocytes (PMN). Anaesthetic agents have been reported to impair various aspects of PMN function. It is possible that the use of these agents to sedate critically ill patients may further compromise an already depressed host defence mechanism. A flow cytometric technique with fresh whole blood from 10 healthy volunteers was used. Phagocytic and respiratory burst activity of PMN incubated for 1 h with either propofol, thiopentone, midazolam or ketamine at both clinical plasma concentrations and 100 times this concentration were determined. Thiopentone at the higher concentration reduced both respiratory burst activity (mean peak channel 50.7 compared with control value of 77.6 (P < 0.0001)) and phagocytosis (mean peak channel 47.5 compared with 79.9 (P < 0.0001)). Ketamine at 100 times the clinical plasma concentration also reduced respiratory burst and phagocytosis, but this failed to reach statistical significance (P = 0.10 and P = 0.053, respectively). No significant depression occurred in the other groups. The results suggest that these i.v. anaesthetic agents, at clinically relevant concentrations, have minimal effects on PMN phagocytosis and oxygen free radical production. At higher concentrations thiopentone and ketamine may affect phagocytic function and thiopentone may impair intracellular cytolysis.

Anesthetics, Dissociative↗
PubMed1995

Attitudes to the Association of Anaesthetists recommendations for standards of monitoring during anaesthesia and recovery.

A questionnaire was sent to 293 anaesthetists in the West of Scotland to assess their attitudes to the recommendations for standards of monitoring during anaesthesia and recovery published by the Association of Anaesthetists of Great Britain and Ireland. Such standards are considered achievable and affordable in terms of costs and allow the early detection of events occurring during anaesthesia, which might lead to injury to the patient. The survey shows that there is wide acceptance of the recommendations by anaesthetists of all grades, with resultant improvements in the quality of patients care.

Anesthesia↗
PubMed1994

Effects of interferon-tau and interferon-alpha on proliferation of bovine endometrial cells.

The ruminant conceptus secretes a unique interferon, interferon-tau, that regulates endometrial prostaglandin secretion during early pregnancy. Because one of the pleiotropic effects of interferons is to inhibit cellular proliferation, a series of experiments was conducted to determine whether or not the bovine endometrium is sensitive to the antiproliferative effect of interferon-tau and the related interferon, interferon-alpha. Endometrial epithelial and stromal cells were prepared from the endometrium of cows from Days 11-17 after estrus and incubated with recombinant bovine interferon-tau (rbIFN tau; 1-1000 ng/ml), recombinant bovine interferon-alpha 1 (rbIFN alpha; 1-1000 ng/ml), recombinant human interferon-alpha 2b (rhIFN alpha; 100 ng/ml), or ovine interferon-tau (oIFN tau; 100 ng/ml). Proliferation was determined by monitoring uptake of [3H]thymidine into DNA. Generally, interferons did not inhibit proliferation of endometrial epithelial cells. Exceptions were for 1000 ng/ml rbIFN tau, which inhibited proliferation by 23%; 100 ng/ml rbIFN alpha, which inhibited proliferation by 28% in one of two experiments only; and 100 ng/ml oIFN tau, which inhibited proliferation by 17%. Proliferation of endometrial stromal cells was not inhibited by any concentration of any interferon in two separate experiments. Therefore, unlike other bovine cells tested previously (lymphocytes and oviductal cells), bovine endometrial cells were not consistently inhibited by IFN tau or IFN alpha. Such reduced responsiveness of endometrial cells to the antiproliferative effects of type I interferons could allow for growth of the endometrium during the period of pregnancy when the conceptus produces IFN tau.

Animals↗
PubMed1994

Abrasive wear of ceramic, metal, and UHMWPE bearing surfaces from third-body bone, PMMA bone cement, and titanium debris.

The debris generated by the progressive wear of total joint replacement (TJR) devices is considered a primary cause of osteolysis, bone resorption, and premature failure of artificial hips and knees. The vast majority of this debris originates from the UHMWPE articulating surfaces caused by tribological interaction with the opposing metal or ceramic surface and hard particulates contained in the sinovial fluid. Entrapment of third body debris, such as cortical bone, PMMA cement, and titanium debris, between the articulating surfaces can cause abrasion of both the hard bearing surface and the UHMWPE. The propensity for abrasive wear is dependent on the relationship between the hardness of the third-body debris and the hardness of the bearing surfaces. To gain a better understanding of this relationship and its effect on wear, the abrasive wear behavior of several metal and ceramic bearing surfaces was characterized in terms of the hardness of both the third-body debris and the metal or ceramic substrate. The effects of abrasion and increased surface roughness of the metal or ceramic surfaces on wear of the UHMWPE was also determined. In addition, the amount of UHMWPE wear was quantified in terms of the amount (particles/ml) of titanium fretting-type debris contained in solution. The results of this investigation showed the resistance to abrasive wear of the metal and ceramic bearing surfaces to increase with increasing surface hardness. Bone debris, PMMA cement, and titanium debris produced visible abrasion of all metal surfaces including nitrogen ion implanted Ti-6Al-4V. The ceramic bearing surfaces showed no evidence of abrasion and produced the least amount of UHMWPE wear. The wear of UHMWPE sliding against Co-Cr-Mo was found to increase with increasing levels of 1.48 microns titanium debris added to the wear test solution. The rate of UHMWPE wear increased rapidly for concentrations of titanium debris in the test solution exceeding about 10(5) particles/ml. These test results suggest that third-body particles, both large and small, are capable of causing increased abrasive wear of UHMWPE, and that abrasion of the hard bearing surfaces will occur if the hardness of the third-body debris exceeds the hardness of the metal or ceramic bearing surface.

Biocompatible Materials↗
PubMed1994

New surface-hardened, low-modulus, corrosion-resistant Ti-13Nb-13Zr alloy for total hip arthroplasty.

To optimize the performance of total hip replacement, scientists and clinicians are seeking new materials and noncemented, press-fit designs that can improve load transfer to the bone and reduce the incidence of loosening and thigh pain. Currently used Co-Cr-Mo alloy has a relatively high elastic modulus (E = 227 GPa), which limits its ability to transfer load to the surrounding bone in the proximal calcar region. Thus to improve load transfer, designs are considered with less cross-sectional area to increase flexibility, but at the expense of fit and fill, and thus stability of the implant within the bone. Should stem loosening occur, the stem stresses may exceed the relatively low fatigue strength of the Co-Cr-Mo alloy and lead to stem breakage. To improve these conditions, lower modulus Ti-6Al-4V alloy (E = 115 GPa) is being used. More recently, a new lower-modulus (E = 79 GPa) Ti-13Nb-13Zr alloy has been developed which does not contain any elemental constituents associated with adverse cell response (i.e., Co, Cr, Mo, Ni, Fe, Al, V), and which possesses comparable or superior strength and toughness to existing Ti-6Al-4V alloy. The carefully selected Nb and Zr constituents improve bone biocompatibility and corrosion resistance compared to that of currently used implant metals. Additionally, a unique diffusion hardening (DH) treatment can be conducted during the age-hardening process of this near-beta alloy to produce a hardened surface with abrasion resistance superior to that of Co-Cr-Mo alloy. This also provides an improvement in the micro-fretting tendencies that may occur within femoral head-neck taper regions and modular interfaces of other implant designs. The present study describes the metallurgy and mechanical properties of this unique low modulus Ti-13Nb-13Zr alloy, and the heat treatments used to obtain the high strength, corrosion resistance, and surface hardening that renders this biocompatible alloy well-suited for press fit hip replacement applications. Because of the relatively lower beta transus (735 degrees C), this alloy is also much easier to net shape forge into more complex stem designs.

Alloys↗